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astro-ph/9812278 | Carraro Giovanni | Near IR photometry of the old open clusters Berkeley 17 and Berkeley 18.
Probing the age of the galactic disc | astro-ph | We report on near IR ($J$ and $K$ bands) observations of two $8 \times 8
\~(arcmin)^{2}$ regions centered on the old open clusters Berkeley~17 and
Berkeley~18, for which only optical photometry (in $B$,$V$ and $I$ bands)
exists. $J$ and $K$ photometry allows us to obtain an independent estimate of
cluster metallicity by means of the relationship between the spectroscopic
metallicity and the Red Giant Branch (RGB) slope calibrated by Tiede et al
(1997). From the analysis of the colour magnitude diagram (CMD) and luminosity
function (LF), Berkeley~17 turns out to have a metal content
$[Fe/H]~\sim~-0.35$. It is $9~Gyr$ old, suffers from a reddening $E(B-V) = 0.58
mag$ and has an heliocentric distance of $2.5 kpc$. Berkeley~17 comes out to be
substantially younger than in previous work (age $\approx 13~Gyr$). On the
other hand Berkeley~18 is found to have solar metal abundance, and to be
younger than Berkeley~17, with an age of about $4~Gyr$. While we confirm
Kaluzny (1997) reddening estimate, we significantly revise the distance of the
cluster, which lies $4.5 kpc$ from the Sun. These results on two open clusters
believed to be between the oldest put constraints on the age and the evolution
of the Galactic Disc. The absence of clusters older than $8-9~Gyr$ suggests the
possibility that the Galaxy underwent a star formation minimum between 13 and
$10~Gyr$ ago.
| No Label | No Label |
astro-ph/0207076 | Margarita Valdez-Gutierrez | Unveiling the Behavior of the Ionized Gas in Irregular Galaxies | astro-ph | We present the results of a detailed kinematical and dynamical analysis
performed in two highly interesting gas-rich Irregular galaxies (Irrs): IC 1613
and NGC 4449. The analysis has been accomplished by means of optical
Fabry-Perot interferometry mapping the Halpha and [SII] lines. The question we
addressed in this study is: how does the ionized gas behave -kinematically and
dynamically speaking- on global and local scales in gas-rich Irr galaxies?
| No Label | No Label |
astro-ph/0606029 | M\'ario Monteiro | On the effect of overshooting as predicted by the modelling of the
pre-main sequence evolution of a 2 solar-mass star | astro-ph | We discuss the effects of convective overshooting in the PMS evolution of
intermediate mass stars, by analysing in detail the early evolution towards the
main sequence of a 2 M_sun stellar model. These effects can be extremely
important in the end of the PMS, when the abundances in CNO elements approach
the equilibrium in the centre. We provide a possible physical explanation on
why a moderate amount of overshooting produces, as the star approaches the
ZAMS, an extra loop in the evolutionary tracks on the HR diagram.
An interesting feature is that there is a very well defined amount of
overshooting (for a given stellar mass and chemical composition) beyond which a
loop is produced. For smaller amounts of overshooting such a loop does not take
place and the evolutionary tracks are similar to the ones obtained by Iben
(1965). The amount of overshooting needed to produce the loop decreases with
stellar mass.
We discuss the underlining physical reasons for the behaviour predicted by
the evolution models and argue that it provides a crucial observational test
for convective overshooting in the core of intermediate mass stars.
| No Label | No Label |
0704.3637 | Han Uitenbroek | The discrepancy in G-band contrast: Where is the quiet Sun? | astro-ph | We compare the rms contrast in observed speckle reconstructed G-band images
with synthetic filtergrams computed from two magneto-hydrodynamic simulation
snapshots. The observations consist of 103 bursts of 80 frames each taken at
the Dunn Solar Telescope (DST), sampled at twice the diffraction limit of the
telescope. The speckle reconstructions account for the performance of the
Adaptive Optics (AO) system at the DST to supply reliable photometry. We find a
considerable discrepancy in the observed rms contrast of 14.1% for the best
reconstructed images, and the synthetic rms contrast of 21.5% in a simulation
snapshot thought to be representative of the quiet Sun. The areas of features
in the synthetic filtergrams that have positive or negative contrast beyond the
minimum and maximum values in the reconstructed images have spatial scales that
should be resolved. This leads us to conclude that there are fundamental
differences in the rms G-band contrast between observed and computed
filtergrams. On the basis of the substantially reduced granular contrast of
16.3% in the synthetic plage filtergram we speculate that the quiet-Sun may
contain more weak magnetic field than previously thought.
| No Label | No Label |
astro-ph/0409078 | Leon Brian Lucy | Similarity solutions for radiation in time-dependent relativistic flows | astro-ph | Exact analytic solutions are derived for radiation in time-dependent
relativistic flows. The flows are spherically-symmetric homologous explosions
or implosions of matter with a grey extinction coefficient. The solutions are
suitable for testing numerical transfer codes, and this is illustrated for a
fully relativistic Monte Carlo code.
| No Label | No Label |
astro-ph/9805193 | Claudia Vilega Rodrigues | Polarimetry and spectroscopy of the polar RX J1141.3-6410 | astro-ph | We present the first optical polarimetric measurements of RX J1141.3-6410
which confirm that star as a polar. The circular polarization varies between 0
and 13% with the orbital period. Halpha spectroscopy shows that this line is
formed by, at least, two components: a broad and a narrow one. The phase of
maximum redshift of the broad component is shifted by 0.5 with the phase of
maximum circular polarization which is not usual for this class of stars. We
suggest a geometrical configuration for the system which could explain the main
features of the polarimetric and spectroscopic data.
| No Label | No Label |
astro-ph/0412043 | Shuang Nan Zhang | A Single Intrinsic Luminosity Function for Both Type-I and Type-II
Active Galactic Nuclei | astro-ph | The luminous electromagnetic emission from distant active galactic nuclei
(AGNs) including quasars is believed to be powered by accretion onto
super-massive black holes (SMBHs). In the standard unification model for AGNs a
dusty torus covers a significant portion of the viewing angles to the accretion
disk and the BH. The system is classified as a type-I AGN if the accretion disk
is viewed through the opening part; otherwise it is called a type-II AGN.
Therefore the ratio of type-II to type-I AGNs serves as a sensitive probe to
the unification model. A surprising discovery made from several large sky
coverage and/or deep AGN surveys has found a significant anti-correlation
between the type-II fraction and the observed X-ray luminosity between 2-10
keV. This suggests two different luminosity functions for the two types of
AGNs, thus challenging the AGN unification model. However this observed
anti-correlation is a natural consequence of the AGN unification model with
only one intrinsic luminosity function if the inclination angle effects of the
X-ray emitting accretion disk are taken into account. Thus the AGN unification
model survived another critical test.
| No Label | No Label |
astro-ph/0606182 | Matthew Muterspaugh | Interferometric Observations of Explosive Variables: V838 Mon, Nova Aql
2005, and RS Oph | astro-ph | During the last two years we have used the Palomar Testbed Interferometer to
observe several explosive variable stars, including V838 Monocerotis, V1663
Aquilae and recently RS Ophiuchi. We observed V838 Monocerotis approximately 34
months after its eruption, and were able to resolve the ejecta. Observations of
V1663 Aql were obtained starting 9 days after peak brightness and continued for
10 days. We were able to resolve the milliarcsecond-scale emission and follow
the expansion of the nova photosphere. When combined with radial-velocity
information, these observations can be used to infer the distance to the nova.
Finally we have resolved the recurrent nova RS Oph and can draw some
preliminary conclusions regarding the emission morphology.
| No Label | No Label |
astro-ph/0610926 | Kaspar von Braun | The Astrobiology Primer: An Outline of General Knowledge - Version 1,
2006 | astro-ph | Astrobiology, the study of life as a planetary phenomenon, aims to understand
the fundamental nature of life on earth and the possibility of life elsewhere.
To achieve this goal, astrobiologists have initiated unprecedented
communication between the disciplines of astronomy, biology, chemistry, and
geology. The Astrobiology Primer has been created as a reference tool for those
who are interested in the interdisciplinary field of astrobiology. The field
incorporates many diverse research endeavors, but it is our hope that this slim
volume will present the reader with all he or she needs to know to become
involved and to understand, at least at a fundamental level, the state of the
art. Because of the great diversity of material, each section was written by a
different author with a different expertise. The Primer was constructed
collaboratively. Ninety researchers from around the world contributed
information with regard to what they expected from other astrobiologists and
what they would like to know themselves but still had difficulty understanding
(see Contributors). Those submissions were read and considered by the Editors
who produced a list of seven general categories of knowledge, represented by
the seven chapters in the Primer: 1) Stellar Formation and Evolution, 2)
Planetary Formation and Evolution, 3) Astrobiogeochemistry and the Origin of
Life, 4) Evolution of Life through Time, 5) Planet Detection &
Characterization, 6) Diversity of Life, and 7) Science in Space. No one volume,
of course, can contain the vast amount of information brought to play in
astrobiology, but we believe that the Primer will provide a forum and a
language around which the community will have the opportunity to develop a
consensus about central issues.
| No Label | No Label |
astro-ph/9501022 | Andrzej Udalski | THE OPTICAL GRAVITATIONAL LENSING EXPERIMENT. THE CATALOG OF PERIODIC
VARIABLE STARS IN THE GALACTIC BULGE. I. PERIODIC VARIABLES IN THE CENTER OF
THE BAADE'S WINDOW. | astro-ph | This paper is the first part of the Catalog of Periodic Variable Stars in the
Galactic bulge. The Catalog is based on observations collected during the OGLE
microlensing search. 213 periodic variable stars brighter than I=18 mag: 31
pulsating, 116 eclipsing and 66 miscellaneous type variables from the Baade's
Window BWC field are presented. Periodic variable stars from remaining 20
fields will be presented in similar form in the next parts of the Catalog. The
Catalog as well as observations of all periodic variable objects are available
to astronomical community over the Internet network.
| No Label | No Label |
astro-ph/0112241 | Patrick B. Hall | 2MASSI J1315309-264951: An L Dwarf with Strong and Variable H-alpha
Emission | astro-ph | 2MASSI J1315309-264951 is an L3 dwarf with strong H-alpha emission discovered
in the course of a color-selected survey for active galactic nuclei using the
Two-Micron All-Sky Survey (2MASS). The strength of its H-alpha emission
decreased by about a factor of two between two epochs separated by 137 days.
This is the first time that variable H-alpha emission has been reported in an L
dwarf, and is probably the first observation of an H-alpha flare in an L dwarf.
The value of log(L_Halpha/L_bol)>-4.17 observed at the discovery epoch is
larger than that of any other L dwarf but comparable to that of 2MASSI
J1237392+652615, the only reported T dwarf with H-alpha emission. The observed
variability indicates that the H-alpha emission of 2MASSI J1315309-264951 is
powered either by magnetic fields or by accretion in a binary system.
Spectroscopic or narrow-band H-alpha monitoring of L and T dwarfs on timescales
of hours to days would be the most useful step toward a better understanding of
their H-alpha emission mechanism(s).
| No Label | No Label |
astro-ph/0609272 | J. E. Horvath | What do exotic equations of state have to offer? | astro-ph | We present a short general overview of the main features of exotic models of
neutron stars, focusing on the structural and dynamical predictions derived
from them. In particular, we discuss the presence of ``normal'' quark matter
and Color-Flavor Locked (CFL) states, including their possible self-bound
versions, and mention some different proposals emerging from the study of QCD
microphysics. A connection with actual observed data is the main goal to be
addressed at this talk and along the meeting. It is demonstrated that exotic
equations of state are {\it not} soft if the vacuum contributions are large
enough, and argued that recent measurements of high pulsar masses ($M \geq 2
M_{\odot}$) create problems for {\it hadronic} models in which hyperons should
be present.
| No Label | No Label |
0712.1540 | Ganna Ivashchenko | Initial Magnetization of Galaxies by Exploding, Magnetized Stars | astro-ph | We conduct a series of magnetohydrodynamical (MHD) simulations of magnetized
interstellar medium (ISM) disturbed by exploding stars. Each star deposits a
randomly oriented, dipolar magnetic field into ISM. The simulations are
performed in a Cartesian box, in a reference frame that is corotating with the
galactic disk. The medium is stratified by vertical galactic gravity. The
resulting turbulent state of ISM magnetized by the stellar explosions is
processed with the aid of Fourier analysis. The results leads to the conclusion
that the input of magnetic energy from exploding stars is additionally
multiplied by differential rotation. The resulting magnetic field appears to
grow up in small-scale component, while the total magnetic flux remains
limited. Our results indicate that magnetic field originating from exploding
stars can be a source of initial magnetic fields for a subsequent dynamo
process.
| No Label | No Label |
astro-ph/0608549 | Arthur Kosowsky | The Atacama Cosmology Telescope Project: A Progress Report | astro-ph | The Atacama Cosmology Telescope is a project to map the microwave background
radiation at arcminute angular resolution and high sensitivity in three
frequency bands over substantial sky areas. Cosmological signals driving such
an experiment are reviewed, and current progress in hardware construction is
summarized. Complementary astronomical observations in other wavebands are also
discussed.
| No Label | No Label |
astro-ph/0606484 | Fabien Malbet | First astrophysical results from AMBER/VLTI | astro-ph | The AMBER instrument installed at the Very Large Telescope (VLT) combines
three beams from as many telescopes to produce spectrally dispersed fringes
from milli-arcsecond angular scale in the near infrared. Two years after
installation, first scientific observations have been carried out during the
Science Demonstration Time and the Guaranteed Time mostly on bright sources due
to some VLTI limitations. In this paper, we review these first astrophysical
results and we show which types of completely new information is brought by
AMBER. The first astrophysical results have been mainly focusing on stellar
wind structure, kinematics, and its interaction with dust usually concentrated
in a disk. Because AMBER has dramatically increased the number of measures per
baseline, this instrument brings strong constraints on morphology and models
despite a relatively poor (u, v) coverage for each object.
| No Label | No Label |
astro-ph/0605611 | Richard Lieu | The outermost gravitationally bound orbit around a mass clump in an
expanding Universe: implication on rotation curves and dark matter halo sizes | astro-ph | Conventional treatment of cold dark matter halos employs the
Navarro-Frenk-White (NFW) profile with a maximum radius set at $r=r_{200}$,
where the enclosed matter has an overdensity of 200 times the critical density.
The choice of $r=r_{200}$ is somewhat arbitrary. It is not the collapsed
(virial) radius, but does give $r \sim$ 1 Mpc for rich clusters, which is a
typical X-ray size. Weak lensing measurements, however, reveal halo radii well
in excess of $r_{200}$. Is there a surface that places an absolute limit on the
extension of a halo? To answer the question, we derived analytically the
solution for circular orbits around a mass concentration in an expanding flat
Universe, to show that an outermost orbit exists at $v/r = H$, where $v$ is the
orbital speed and $H$ is the Hubble constant. The solution, parametrized as
$r_2$, is independent of model assumptions on structure formation, and {\it is
the radius at which the furthest particle can be regarded as part of the bound
system}. We present observational evidence in support of dark matter halos
reaching at least as far out as $r=r_2$. An interesting consequence that
emerges concerns the behavior of rotation curves. Near $r=r_2$ velocities will
be biased low. As a result, the mass of many galaxy groups may have been
underestimated. At $r=r_2$ there is an abrupt cutoff in the curve, irrespective
of the halo profile. An important cosmological test can therefore be performed
if velocity disperion data are available out to 10 Mpc radii for nearby
clusters (less at higher redshifts). For Virgo it appears that there is no such
cutoff.
| No Label | No Label |
astro-ph/0607122 | Patrick McDonald | Dark energy and curvature from a future baryonic acoustic oscillation
survey using the Lyman-alpha forest | astro-ph | We explore the requirements for a Lyman-alpha forest (LyaF) survey designed
to measure the angular diameter distance and Hubble parameter at 2~<z~<4 using
the standard ruler provided by baryonic acoustic oscillations (BAO). The goal
would be to obtain a high enough density of sources to probe the
three-dimensional density field on the scale of the BAO feature. A
percent-level measurement in this redshift range can almost double the Dark
Energy Task Force Figure of Merit, relative to the case with only a similar
precision measurement at z~1, if the Universe is not assumed to be flat. This
improvement is greater than the one obtained by doubling the size of the z~1
survey, with Planck and a weak SDSS-like z=0.3 BAO measurement assumed in each
case. Galaxy BAO surveys at z~1 may be able to make an effective LyaF
measurement simultaneously at minimal added cost, because the required number
density of quasars is relatively small. We discuss the constraining power as a
function of area, magnitude limit (density of quasars), resolution, and
signal-to-noise of the spectra. For example, a survey covering 2000 sq. deg.
and achieving S/N=1.8 per Ang. at g=23 (~40 quasars per sq. deg.) with an
R~>250 spectrograph is sufficient to measure both the radial and transverse
oscillation scales to 1.4% from the LyaF (or better, if fainter magnitudes and
possibly Lyman-break galaxies can be used). At fixed integration time and in
the sky-noise-dominated limit, a wider, noisier survey is generally more
efficient; the only fundamental upper limit on noise being the need to identify
a quasar and find a redshift. Because the LyaF is much closer to linear and
generally better understood than galaxies, systematic errors are even less
likely to be a problem.
| No Label | No Label |
astro-ph/9611021 | Tomek Bulik | Spectral Effects of the Vacuum Resonance in Soft Gamma-Ray Repeaters | astro-ph | The association of all three soft gamma-ray repeaters (SGRs) with supernova
remnants has established that SGRs are young neutron stars, and has given us a
starting point for detailed modeling. One of the most popular classes of models
involves strongly magnetised neutron stars, with surface dipole fields B~
10^{14}-10^{15} Gauss. In such strong magnetic fields, many otherwise
negligible processes can play an important role. Here we consider the effects
of vacuum polarisation on Compton scattering. Vacuum polarisation introduces a
characteristic density-dependent photon frequency at which the normal modes of
polarisation become nonorthogonal and the mean free path of photons decreases
sharply. Our analytic results and Monte Carlo simulations of photon propagation
through a magnetised plasma show that this effect leads, under a wide range of
physical conditions, to a broad absorption-like feature in the energy range ~5
keV---40 keV. We discuss this effect in light of the spectra from SGR 1806-20.
| No Label | No Label |
astro-ph/0611897 | Paul Rajaguru | Radiative transfer effects on Doppler measurements as sources of surface
effects in sunspot seismology | astro-ph | We show that the use of Doppler shifts of Zeeman sensitive spectral lines to
observe wavesn in sunspots is subject to measurement specific phase shifts
arising from, (i) altered height range of spectral line formation and the
propagating character of p mode waves in penumbrae, and (ii) Zeeman broadening
and splitting. We also show that these phase shifts depend on wave frequencies,
strengths and line of sight inclination of magnetic field, and the polarization
state used for Doppler measurements. We discuss how these phase shifts could
contribute to local helioseismic measurements of 'surface effects' in sunspot
seismology.
| No Label | No Label |
astro-ph/9905219 | Christian Theis | Global Spiral Modes in Star-Forming Gravitating Disks | astro-ph | Using 2D nonlinear simulations, we study the generation and nonlinear
evolution of spiral structure in a star-forming multi-component gravitating
disk. We confirm in agreement with previous studies the destabilizing role of a
cold gaseous component and extend this conclusion for multi-component
star-forming disks exchanging mass and momentum between its components. We show
that the spiral structure growing on a non-stationary multi-phase background
reaches its saturation in a similar manner like the one-component disks. The
spiral structure survives even if most of the gas is transformed into stellar
remnants of larger velocity dispersion.
| No Label | No Label |
astro-ph/0309009 | Pilar Ruiz-Lapuente | Tycho Brahe's supernova: light from centuries past | astro-ph | The light curve of SN 1572 is described in the terms used nowadays to
characterize SNeIa. By assembling the records of the observations done in
1572--74 and evaluating their uncertainties, it is possible to recover the
light curve and the color evolution of this supernova. It is found that, within
the SNe Ia family, the event should have been a SNIa with a normal rate of
decline, its stretch factor being {\it s} $\sim$ 0.9. Visual light curve near
maximum, late--time decline and the color evolution sustain this conclusion.
After correcting for extinction, the luminosity of this supernova is found to
be M$_{V}$ $=$ --19.58 --5 log (D/3.5 kpc) $\pm$ 0.42.
| No Label | No Label |
0803.4298 | Gary Glatzmaier | A note on "Constraints on deep-seated zonal winds inside Jupiter and
Saturn" | astro-ph | Liu et al. 2008 discuss an important consideration for models of zonal winds
deep within giant planets. However, the constraints they propose for the depth
of the winds are based on their prescriptions for the internal structures of
the magnetic field and zonal winds. The same kinematic analysis applied to
other plausible configurations would produce no constraint on the depth to
which the winds extend.
| No Label | No Label |
astro-ph/9910308 | Pablo Fosalba | Gravitational Evolution of the Large-Scale Density Distribution: The
Edgeworth & Gamma Expansions | astro-ph | The gravitational evolution of the cosmic one-point Probability Distribution
Function (PDF) can be estimated using an analytic approximation that combines
gravitational Perturbation Theory (PT) with the Edgeworth expansion around a
Gaussian PDF. We present an alternative to the Edgeworth series based on an
expansion around the Gamma PDF, which is more appropriate to describe a
realistic PDF. The Gamma expansion converges when the PDF exhibits exponential
tails, which are predicted by PT and N-body simulations in the weakly
non-linear regime (i.e, when the variance, $\sigma^2$, is small). We compare
both expansions to N-body simulations and find that the Gamma expansion yields
a better overall match to the numerical results.
| No Label | No Label |
astro-ph/0002281 | Kaiki Taro Inoue | Geometric Gaussianity and Non-Gaussianity in the Cosmic Microwave
Background | astro-ph | In this paper, Gaussianity of eigenmodes and non-Gaussianity in the Cosmic
Microwave Background (CMB) temperature fluctuations in two smallest compact
hyperbolic (CH) models are investigated. First, it is numerically found that
the expansion coefficients of low-lying eigenmodes on the two CH manifolds
behave as if they are Gaussian random numbers at almost all the places. Next,
non-Gaussianity of the temperature fluctuations in the (l,m) space in these
models is studied. Assuming that the initial fluctuations are Gaussian, the
real expansion coefficients b_{l m} of the temperature fluctuations in the sky
are found to be distinctively non-Gaussian. In particular, the cosmic variances
are found to be much larger than that for Gaussian models. On the other hand,
the anisotropic structure is vastly erased if one averages the fluctuations at
a number of different observing points because of the Gaussian
pseudo-randomness of the eigenmodes. Thus the dominant contribution to the
two-point correlation functions comes from the isotropic terms described by the
angular power spectra C_l. Finally, topological quantities: the total length
and the genus of isotemperature contours are investigated. The variances of
total length and genus at high and low threshold levels are found to be
considerably larger than that of Gaussian models while the means almost agree
with them.
| No Label | No Label |
astro-ph/0411235 | Jaan Einasto | Toward Understanding Environmental Effects in SDSS Clusters | astro-ph | We find clusters and superclusters of galaxies using the Data Release 1 of
the Sloan Digital Sky Survey. We determine the luminosity function of clusters
and find that clusters in a high-density environment have a luminosity a factor
of ~5 higher than in a low-density environment. We also study clusters and
superclusters in numerical simulations. Simulated clusters in a high-density
environment are also more massive than those in a low-density environment.
Comparison of the density distribution at various epochs in simulations shows
that in large low-density regions (voids) dynamical evolution is very slow and
stops at an early epoch. In contrast, in large regions of higher density
(superclusters) dynamical evolution starts early and continues until the
present; here particles cluster early, and by merging of smaller groups very
rich systems of galaxies form.
| No Label | No Label |
astro-ph/0306084 | Yael Naze | WR bubbles and HeII emission | astro-ph | We present the very first high quality images of the HeII 4686 emission in
three high excitation nebulae of the Magellanic Clouds. A fourth high
excitation nebula, situated around the WR star BAT99-2, was analysed in a
previous letter. Using VLT FORS data, we investigate the morphology of the ring
nebulae around the early-type WN stars BAT99-49 & AB7. We derive the total HeII
fluxes for each object and compare them with the most recent theoretical WR
models. Using Halpha, [OIII] and HeI 5876 images along with long-slit
spectroscopy, we investigate the physical properties of these ring nebulae and
find only moderate chemical enrichment. We also surveyed seven other LMC WR
stars but we failed to detect any HeII emission but note that the nebula around
BAT99-11 shows a N/O ratio and an oxygen abundance slightly lower than the LMC
values, while the nebula around BAT99-134 presents moderate chemical enrichment
similar to the one seen near BAT99-2, 49 and AB7. The third high excitation
nebula presented in this paper, N44C, does not harbor stars hotter than mid-O
main sequence stars. It was suggested to be a fossil X-ray nebula ionized but
our observations of N44C reveal no substantial changes in the excitation
compared to previous results reported in the literature.
| No Label | No Label |
astro-ph/0611773 | Gary C. Hill | Neutrino astronomy with IceCube and AMANDA | astro-ph | Since the early 1990s, the South Pole has been the site of the construction
of the world's first under-ice Cherenkov neutrino telescopes - AMANDA and
IceCube. The AMANDA detector was completed in 2000, and its successor IceCube,
a kilometre scale neutrino detector, began construction in 2005. Completion of
IceCube is scheduled for 2011. This paper will give an overview of the history,
construction, latest physics results and potential of these detectors.
| No Label | No Label |
astro-ph/0410214 | Martin Asplund | The solar chemical composition | astro-ph | We review our current knowledge of the solar chemical composition as
determined from photospheric absorption lines. In particular we describe the
recent significant revisions of the solar abundances as a result of the
application of a time-dependent, 3D hydrodynamical model of the solar
atmosphere instead of 1D hydrostatic models. This has decreased the metal
content in the solar convection zone by almost a factor of two compared with
the widely used compilation by Anders & Grevesse (1989). While resolving a
number of long-standings problems, the new 3D-based element abundances also
pose serious challenges, most notably for helioseismology.
| No Label | No Label |
0808.3013 | William T. Reach | Properties of protostars in the Elephant Trunk globule IC 1396A | astro-ph | Extremely red objects, identified in the early Spitzer Space Telescope
observations of the bright-rimmed globule IC 1396A and photometrically
classified as Class I protostars Class II T Tauri stars based on their
mid-infrared colors, were observed spectroscopically at 5.5 to 38 microns
(IRS), at the 22 GHz water maser frequency (GBT), and in the optical (Palomar).
The sources photometrically identified as Class I are confirmed as objects
dominated by accretion luminosity from dense envelopes, with accretion rates
1e-5 to 1e-6 Msun/yr. The ice/silicate absorption ratio in the envelope is
exceptionally low for the IC 1396A protostars, compared to those in nearby
star-forming regions, suggesting the envelope chemistry is altered by the
radiation field or globule pressure. Only one 22 GHz water maser was detected
in IC 1396A; its infrared counterpart has luminosity <0.1 Lsun, the first H2O
maser from such a low-luminosity object. The objects photometrically classified
as Class II are confirmed as classical T Tauri stars with warm, luminous disks.
The disk properties change significantly with source luminosity: low-mass (G-K)
stars have prominent 9-11 micron emission features due to amorphous silicates
while higher-mass (A-F) stars have weaker features requiring abundant
crystalline silicates. The distribution of Class I sources is concentrated
within the molecular globule, while the Class II sources are more widely
scattered. Combined with the spectral results, this suggests two phases of star
formation, the first (4 Myr ago) leading to the widespread Class II sources and
the central O star of IC 1396, and the second (<1 Myr ago) occurring within the
globule.
| No Label | No Label |
astro-ph/0011213 | Yael Fuchs | Mid-Infrared observations of GRS 1915+105 and SS433 | astro-ph | We have observed in the mid-infrared (4-18 micron) the counterpart of the
compact object GRS 1915+105, and the western jet of SS433. The images were
carried out with the ISOCAM infrared camera on board of the Infrared Space
Observatory (ISO). The mid-infrared photometry of GRS 1915+105 shows the
presence of an additional contribution besides the synchrotron emission. The 15
micron images of the large-scale western lobe of the SS433/W50 nebula are
compared to the radio and X-ray ones. They show infrared synchrotron emission
on the western edge of SS433/W50 lobe.
| No Label | No Label |
astro-ph/0104457 | F. H. Briggs | Cold Gas Kinematics in an L* Spiral Galaxy at z=0.437: The Nature of
Damped Lyman-alpha Absorbers | astro-ph | Westerbork Radio Synthesis Telescope observations of the redshifted 21cm line
absorber against the z_em = 0.871 double lobed quasar 3C196 show that the
intervening absorber is an L approximately equal L* spiral galaxy (3C196-G1)
and that the absorbing layer of cold gas extends to radii of at least 30
h_50^-1 kpc. The new data solve several long standing puzzles about this system
by (1) discovering a second 21cm absorption feature, corresponding to
absorption against the NE lobe of the background radio source and (2) spatially
``resolving'' the two absorption features to isolate the absorption along the
two lines of sight to the opposing radio lobes. These findings resolve the
disagreement in redshift between the UV metal and 21cm lines, and as well as
demonstrating that the neutral layer does absorb both lobes of the background
radio source. Simple kinematic models with an inclined, rotating gas disk match
the observed 21cm profile and are also compatible with both the redshift and
velocity spread of the absorption measured in UV resonance lines along a third,
independent line of sight to the quasar nucleus and with the lack of 21cm
absorption in as earlier VLBI experiment that was sensitive to opacity against
the hot spot in the northern lobe. The inferred rotation speed and luminosity
for the galaxy are compatible with the z approximately 0 Tully-Fisher Relation.
This system illustrates well how 21cm absorption against extended background
radio sources is a powerful tool in determining the nature of the damped
Lyman-alpha class of QSO absorption line system.
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astro-ph/0005520 | J. Christopher Howk | The Abundance of Interstellar Boron | astro-ph | We use new Space Telescope Imaging Spectrograph (STIS) and archival Goddard
High Resolution Spectrograph (GHRS) observations to study interstellar B II
1362 and O I 1355 absorption along seven sightlines. Our new column density
measurements, combined with measurements of four sightlines from the
literature, allow us to study the relative B/O abundances over a wide range of
interstellar environments. We measure sightline-integrated relative gas-phase
abundances in the range [B/O] = -1.00 to -0.17, and our data show the B/O
abundances are anticorrelated with average sightline densities over the range
log <n_H> ~ -1.3 to +0.7. Detailed comparisons of the B II and O I line shapes
show that the B/O ratio is significantly higher in warm interstellar clouds
than in cool clouds. These results are consistent with the incorporation of
boron into dust grains in the diffuse ISM. Since boron is likely incorporated
into grains, we derive a lower limit to the present-day total (gas+dust)
interstellar boron abundance of B/H > (2.5+/-0.9)x10^-10. The effects of dust
depletion and ionization differences from element to element will make it very
difficult to reliably determine 11B/10B along most interstellar sightlines.
| No Label | No Label |
astro-ph/9403059 | Simon Ellingsen | A Search for Extragalactic Methanol Masers | astro-ph | A sensitive search for 6.7--GHz methanol maser emission has been made towards
10 galaxies that have yielded detectable microwave molecular--line transitions.
These include several which show OH megamaser or superluminous \water\/ maser
emission. Within the Galaxy, \methanol\/ and OH masers often occur in the same
star formation regions and, in most cases, the \methanol\/ masers have a
greater peak flux density than their OH counterparts. Thus we might expect
\methanol\/ masers to be associated with extragalactic OH maser sources. We
failed to detect any emission or absorption above our 60--mJy detection limit.
We conclude that if the physical conditions exist to produce \methanol\/
megamaser emission, they are incompatible with the conditions which produce OH
megamaser emission.
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astro-ph/0402121 | Jan Staff E. | JETGET - An analysis and visualization tool for (magneto-)hydrodynamic
jet simulations | astro-ph | In simulations of (magnetized-)fluid dynamics in physics and astrophysics,
the visualization techniques are so frequently applied to analyse data that
they have become a fundamental part of the research. Data produced is often a
multi-dimensional set with several physical quantities, that are usually
complex to manage and analyse. JETGET is a visualization and analysis tool we
developed for accessing data stored in Hierarchical Data Format (HDF) and ASCII
files. Although JETGET has been optimized to handle data output from jet
simulations using the Zeus code from NCSA, it is also capable of analysing
other data output from simulations using other codes. JETGET can select
variables from the data files, render both two- and three-dimensional graphics
and analyse and plot important physical quantities. Graphics can be saved in
encapsulated Postscript, JPEG, VRML or saved into an MPEG for later
visualization and/or presentations. An example of use of JETGET in analysing a
3-dimensional simulation of jets emanating from accretion disks surrounding a
protostar is shown. The strength of JETGET in extracting the physics underlying
such phenomena is demonstrated as well as its capabilities in visualizing the
3-dimensional features of the simulated magneto-hydrodynamic jets. The JETGET
tool is written in Interactive Data Language (IDL) and uses a graphical user
interface to manipulate the data. The tool was developed on a LINUX platform
and can be run on any platform that supports IDL. JETGET can be downloaded
(including more information about its utilities) from
http://www.capca.ucalgary.ca/software.
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astro-ph/0309827 | Robert Zinn | Halo Substructure in the QUEST RR Lyrae Survey | astro-ph | A survey of 380 sq. deg. of the sky with the 1m Schmidt telescope at the
Observatorio Nacional de Llano del Halo and the QUEST camera has found 498 RR
Lyrae variables lying from 4 to 60 kpc from the Sun. We describe the halo
substructure revealed by these data and the results of measuring some of the
stars' radial velocities and metal abundances.
| No Label | No Label |
astro-ph/0501258 | Ian Bonnell | Competitive Accretion and the IMF | astro-ph | Competitive accretion occurs when stars in a cluster accrete from a shared
reservoir of gas. The competition arises due to the relative attraction of
stars as a function of their mass and location in the cluster.
The low relative motions of the stars and gas in young, gas dominated
clusters results in a tidal limit to the accretion whereas in the stellar
dominated cluster cores, the high relative velocities results in Bondi-Hoyle
accretion.
The combination of these two accretion processes produces a two power-law IMF
with $\gamma \approx -1.5$, for low-mass stars which accrue their mass in the
gas dominated regime, and a steeper, $\gamma\approx -2.5$, IMF for higher-mass
stars that form in the core of a cluster. Simulations of the fragmentation and
formation of a stellar cluster show that the final stellar masses, and IMF, are
due to competitive accretion. Competitive accretion also naturally results in a
mass segregated cluster and in a direct correlation between the richness of a
cluster and the mass of the most massive star therein. The {\sl knee} where the
IMF slope changes occurs near the Jeans mass of the system.
| No Label | No Label |
astro-ph/0405434 | Matthias Hoeft | Feedback in AGN heating of galaxy clusters | astro-ph | One of the challenges that models of AGN heating of the intracluster medium
(ICM) face, is the question how the mechanical luminosity of the AGN is tuned
to the radiative losses of the ICM. Here we implement a simple 1D model of a
feedback mechanism that links the luminosity of the AGN to the accretion rate.
We demonstrate how this simple feedback mechanism leads to a quasi-steady state
for a broad range of parameters. Moreover, within this feedback model, we
investigate the effect of thermal conduction and find that its relative
importance depends strongly on the cluster mass.
| No Label | No Label |
astro-ph/9710141 | Priscilla Chapman Frisch | The Local Bubble, Local Fluff, and Heliosphere | astro-ph | The properties of the Local Bubble, Local Fluff complex of nearby
interstellar clouds, and the heliosphere are mutually constrained by data and
theory. Observations and models of the diffuse radiation field, interstellar
ionization, pick-up ion and anomalous cosmic-ray populations, and interstellar
dust link the physics of these regions. The differences between the
one-asymmetric-superbubble and two-superbubble views of the Local Bubble are
discussed.
| No Label | No Label |
astro-ph/0401340 | Jochen Weller | Neutral hydrogen surveys for high redshift galaxy clusters and
proto-clusters | astro-ph | We discuss the possibility of performing blind surveys to detect large-scale
features of the universe using 21cm emission. Using instruments with approx.
5'-10' resolution currently in the planning stage, it should be possible to
detect virialized galaxy clusters at intermediate redshifts using the combined
emission from their constituent galaxies, as well as less overdense structures,
such as proto-clusters and the `cosmic web', at higher redshifts. Using
semi-analytic methods we compute the number of virialized objects and those at
turnaround which might be detected by such surveys. We find a surprisingly
large number of objects might be detected even using small (approx. 5%)
bandwidths and elaborate on some issues pertinent to optimising the design of
the instrument and the survey strategy. The main uncertainty is the fraction of
neutral gas relative to the total dark matter within the object. We discuss
this issue in the context of the observations which are currently available.
| No Label | No Label |
astro-ph/0212332 | Renato A. Dupke | Chandra Analysis of Abell 496 - No Chemical Gradients Across Cold Fronts | astro-ph | We present the results of a spatially-resolved spectroscopic analysis of the
galaxy cluster Abell 496 with the S3 chip on-board the Chandra satellite. We
confirm the presence of a central positive temperature gradient consistent with
a cooling flow, but with a minimum gas temperature of ~0.5-0.9 keV. The cluster
also exhibits sharp edges in gas density and temperature which are consistent
with "cold front" substructures. The iron abundance profile is not radially
symmetric relative to the cluster center. Towards the direction of the most
prominent (northerly) cold front, the iron abundance is roughly flat, with
nearly solar values. In the opposite (southerly) direction from the center, the
iron abundance distribution shows an "off-center" peak. Various abundance
ratios suggest that the heavy elements in the central regions of the cluster
are dominated by SN Ia ejecta. However, for radii greater than 100 kpc, the
abundance ratios vary in such a way that different abundance ratios provide
very different estimates of the proportion of SN Ia/II ejecta. Nonetheless,
observed abundances and abundance ratios are continuous across the cold fronts,
which suggests that the cold fronts are not likely to be the result of a
subcluster merger. We suggest instead that the cold fronts in A496 are caused
by "sloshing" of the central cooling flow gas, induced by the motion of the cD
about the cluster center.
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astro-ph/0111375 | Boris T. Gaensicke | Properties of a spectroscopically selected CV sample | astro-ph | We have initiated a dedicated search for new CVs, selecting candidates on the
base of their spectroscopic properties in the Hamburg Quasar Survey (HQS),
which lead up to now to the identification of 50 new CVs and a dozen good
candidates. Using the HQS data of the previously known CVs for extensive tests
of our selection scheme, we demonstrate that our survey should be very
efficient in finding short period systems as long as they have emission lines
with equivalent widths >=10 A. So far, orbital periods have been measured for
15 of the new CVs, with the surprising result that only two systems lie at or
below the lower boundary of the period gap. This - somewhat preliminary -
result is in uncomfortable disagreement with the predictions of the standard
scenario of CV evolution.
| No Label | No Label |
astro-ph/0610179 | John Johnson | A Long-Period Jupiter-Mass Planet Orbiting the Nearby M Dwarf GJ849 | astro-ph | We report precise Doppler measurements of GJ849 (M3.5V) that reveal the
presence of a planet with a minimum mass of 0.82 Mjup in a 5.16 year orbit. At
a = 2.35 AU, GJ849b is the first Doppler-detected planet discovered around an M
dwarf to orbit beyond 0.21 AU, and is only the second Jupiter mass planet
discovered around a star less massive than 0.5 Msun. This detection brings to 4
the number of M stars known to harbor planets. Based on the results of our
survey of 1300 FGKM main--sequence stars we find that giant planets within 2.5
AU are ~3 times more common around GK stars than around M stars. Due to the
GJ849's proximity of 8.8 pc, the planet's angular separation is 0."27, making
this system a prime target for high--resolution imaging using adaptive optics
and future space--borne missions such as the Space Interferometry Mission. We
also find evidence of a linear trend in the velocity time series, which may be
indicative of an additional planetary companion.
| No Label | No Label |
astro-ph/9511085 | Somnath Bharadwaj | Perturbative Growth of Cosmological Clustering II: The Two Point
Correlation | astro-ph | We use the BBGKY hierarchy equations to calculate, perturbatively, the lowest
order nonlinear correction to the two point correlation and the pair velocity
for Gaussian initial conditions in a critical density matter dominated
cosmological model. We compare our results with the results obtained using the
hydrodynamic equations which neglect pressure and we find that the two match,
indicating that thare are no effects of multistreaming at this order of
perturbation. We analytically study the effect of small scales on the large
scales by calculating the nonlinear correction for a Dirac delta function
initial two point correlation. We find that the induced two point correlation
has a $x^{-6}$ behaviour at large separations. We have considered a class of
initial conditions where the initial power spectrum at small $k$ has the form
$k^n$ with $0 < n \le 3$ and have numerically calculated the nonlinear
correction to the two point correlation, its average over a sphere and the pair
velocity over a large dynamical range. We find that at small separations the
effect of the nonlinear term is to enhance the clustering whereas at
intermediate scales it can act to either increase or decrease the clustering.
At large scales we find a simple formula which gives a very good fit for the
nonlinear correction in terms of the initial function. This formula explicitly
exhibits the influence of small scales on large scales and because of this
coupling the perturbative treatment breaks down at large scales much before one
would expect it to if the nonlinearity were local in real space. We physically
interpret this formula in terms of a simple diffusion process. We have also
investigated the case $n=0$ and we find that it differs from the other cases in
certain respects. We investigate a recently proposed scaling property of
| No Label | No Label |
astro-ph/0602072 | Paolo Tozzi | Cosmological parameters from Galaxy Clusters: an Introduction | astro-ph | This lecture is an introduction to cosmological tests with clusters of
galaxies. Here I do not intend to provide a complete review of the subject, but
rather to describe the basic procedures to set up the fitting machinery to
constrain cosmological parameters from clusters, and to show how to handle data
with a critical insight. I will focus mainly on the properties of X-ray
clusters of galaxies, showing their success as cosmological tools, to end up
discussing the complex thermodynamics of the diffuse intracluster medium and
its impact on the cosmological tests.
| No Label | No Label |
astro-ph/0002501 | Schuyler D. Van Dyk | Radio Supernovae and GRB 980425 | astro-ph | Study of radio supernovae (RSNe) over the past 20 years includes two dozen
detected objects and more than 100 upper limits. From this work we are able to
identify classes of radio properties, demonstrate conformance to and deviations
from existing models, estimate the density and structure of the circumstellar
material and, by inference, the evolution of the presupernova stellar wind, and
reveal the last stages of stellar evolution before explosion. It is also
possible to detect ionized hydrogen along the line of sight, to demonstrate
binary properties of the stellar system, and to show clumpiness of the
circumstellar material. More speculatively, it may be possible to provide
distance estimates to radio supernovae.
The interesting and unusual radio supernova SN 1998bw, which is thought to be
related to the gamma-ray burst GRB 980425, is discussed in particular detail.
Its radio properties are compared and contrasted with those of other known
RSNe.
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astro-ph/0112540 | Richard Ellis | Conference Summary | astro-ph | Concluding remarks at the international workshop ``Tracing Cosmic Evolution
with Galaxy Clusters", held at Sesto Pusteria, Italy, July 3-6, 2001.
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astro-ph/0304456 | Vladimir Zhu | A new hypothesis of sunspot formation | astro-ph | The process of sunspot formation is considered with the account of heat
effects. According to the Le Chatelier principle, a local overheating must
precede to the cooling of solar surface in the places of sunspot formation. The
sunspot dynamics is a process close to the surface nucleate-free boiling in a
thin layer with formation of bubbles (or craters), so we focus on the analogy
between these two processes. Solar spots and surface nucleate-free boiling in a
thin layer have similarities in formation conditions, results of impact on the
surface were they have been formed, periodicity, and their place in the
hierarchy of self-organization in complex systems. The difference is in the
working medium and method of channelling of extra energy from the overheated
surface -for boiling process, the energy is forwarded to generation of vapor,
and in sunspots the solar energy is consumed to formation of a strong magnetic
field. This analogy explains the problem of a steady brightness (temperature)
of a spot that is independent of the spot size and other characteristics.
| No Label | No Label |
astro-ph/0503569 | Aigen Li | Interstellar Grains -- The 75th Anniversary | astro-ph | The year of 2005 marks the 75th anniversary since Trumpler (1930) provided
the first definitive proof of interstellar grains by demonstrating the
existence of general absorption and reddening of starlight in the galactic
plane. This article reviews our progressive understanding of the nature of
interstellar dust.
| No Label | No Label |
astro-ph/9911227 | David Crampton | Searching for z = 6.5 Galaxies with Multislit Windows | astro-ph | A method for searching for emission-line objects in "windows" between
atmospheric emission lines using multislits is described. A search for Ly alpha
emitters at z = 6.5 in the 9130A window using this technique is being carried
out with the multi-object spectrograph on CFHT. This technique could be
extended to similar windows at longer wavelengths, aided by the (1 + z) factor
in observed equivalent widths. In the J band there are windows corresponding to
Ly alpha at z = 7.7, 8.7 and 9.3; in the H band, there are two at z = 11.9 and
13.4. Multislit window observations in these bands coupled with photometric
redshift information offer perhaps the best method of the detecting extremely
high redshift galaxies.
| No Label | No Label |
astro-ph/0112296 | Brian E. Wood | Deuterium Toward WD1634-573: Results from the Far Ultraviolet
Spectroscopic Explorer (FUSE) Mission | astro-ph | We use Far Ultraviolet Spectrocopic Explorer (FUSE) observations to study
interstellar absorption along the line of sight to the white dwarf WD1634-573
(d=37.1+/-2.6 pc). Combining our measurement of D I with a measurement of H I
from Extreme Ultraviolet Explorer data, we find a D/H ratio toward WD1634-573
of D/H=(1.6+/-0.5)e-5. In contrast, multiplying our measurements of D I/O
I=0.035+/-0.006 and D I/N I=0.27+/-0.05 with published mean Galactic ISM gas
phase O/H and N/H ratios yields D/H(O)=(1.2+/-0.2)e-5 and
D/H(N)=(2.0+/-0.4)e-5, respectively. Note that all uncertainties quoted above
are 2 sigma. The inconsistency between D/H(O) and D/H(N) suggests that either
the O I/H I and/or the N I/H I ratio toward WD1634-573 must be different from
the previously measured average ISM O/H and N/H values. The computation of
D/H(N) from D I/N I is more suspect, since the relative N and H ionization
states could conceivably vary within the LISM, while the O and H ionization
states will be more tightly coupled by charge exchange.
| No Label | No Label |
astro-ph/0608184 | Andrew R. Liddle | Cosmological model selection | astro-ph | Model selection aims to determine which theoretical models are most plausible
given some data, without necessarily asking about the preferred values of the
model parameters. A common model selection question is to ask when new data
require introduction of an additional parameter, describing a newly-discovered
physical effect. We review several model selection statistics, and then focus
on use of the Bayesian evidence, which implements the usual Bayesian analysis
framework at the level of models rather than parameters. We describe our
CosmoNest code, which is the first computationally-efficient implementation of
Bayesian model selection in a cosmological context. We apply it to recent WMAP
satellite data, examining the need for a perturbation spectral index differing
from the scale-invariant (Harrison-Zel'dovich) case.
| No Label | No Label |
astro-ph/9609087 | Marcella Marconi | Second Overtone Pulsators Among Delta Scuti Stars | astro-ph | We investigate the modal stability of stellar models at masses and luminosity
levels corresponding to post main sequence luminous delta scuti pulsators. The
envelope models have been computed at fixed mass value, luminosity level and
chemical composition (Y=0.28, Z=0.02). According to a nonlinear approach to
radial oscillations the present investigation predicts the occurrence of stable
second overtone pulsators for the first time. The shape of both light and
velocity curves are presented and discussed, providing a useful tool for the
identification of second overtone pulsators among the known groups of radially
pulsating stars. The period ratios of mixed mode pulsators obtained by
perturbing the first and the second overtone radial eigenfunctions are in
agreement with observative values. Finally, the physical structure and the
dynamical properties of second overtone pulsators are discussed in detail. The
role played by the nodal lines in the destabilization of second overtone
pulsators is also pointed out.
| No Label | No Label |
astro-ph/0003390 | Georges Meylan | Mass Segregation in Star Clusters | astro-ph | Star clusters - open and globulars - experience dynamical evolution on time
scales shorter than their age. Consequently, open and globular clusters provide
us with unique dynamical laboratories for learning about two-body relaxation,
mass segregation from equipartition of energy, and core collapse. We review
briefly, in the framework of star clusters, some elements related to the
theoretical expectation of mass segregation, the results from N-body and other
computer simulations, as well as the now substantial clear observational
evidence.
| No Label | No Label |
astro-ph/0601685 | Xi Kang | Massive and Red Objects predicted by a semianalytical model of galaxy
formation | astro-ph | We study whether hierarchical galaxy formation in a concordance $\Lambda$CDM
universe can produce enough massive and red galaxies compared to the
observations. We implement a semi-analytical model in which the central black
holes gain their mass during major mergers of galaxies and the energy feedback
from active galaxy nuclei (AGN) suppresses the gas cooling in their host halos.
The energy feedback from AGN acts effectively only in massive galaxies when
supermassive black holes have been formed in the central bulges. Compared with
previous models without black hole formation, our model predicts more massive
and luminous galaxies at high redshift, agreeing with the observations of K20
up to $z\sim 3$. Also the predicted stellar mass density from massive galaxies
agrees with the observations of GDDS. Because of the energy feedback from AGN,
the formation of new stars is stopped in massive galaxies with the termination
of gas cooling and these galaxies soon become red with color $R-K>$5 (Vega
magnitude), comparable to the Extremely Red Objects (EROs) observed at redshift
$z\sim$1-2. Still the predicted number density of very EROs is lower than
observed at $z\sim 2$, and it may be related to inadequate descriptions of dust
extinction, star formation history and AGN feedback in those luminous galaxies.
| No Label | No Label |
astro-ph/9610126 | James G. Bartlett | Cross Wavelength Comparison of Images and Catalogs | astro-ph | We discuss some aspects of data management important to cross-wavelength
comparison of images and catalogs. We then consider the application of
statistics to the general problem of object cross-identification. Finally, two
software systems developed as tools to aid the comparison of catalogs and
images are briefly presented.
| No Label | No Label |
astro-ph/0210506 | Peter Jonker | The mass of the neutron star in the low-mass X-ray binary 2A 1822-371 | astro-ph | Using phase resolved spectroscopic observations obtained with the Ultraviolet
and Visual Echelle Spectrograph on ESO's Kueyen Very Large Telescope
supplemented by spectroscopic observations obtained with the Boller and Chivens
Spectrograph on the Walter Baade Magellan telescope, we found sinusoidal
radial-velocity variations with a semi-amplitude 327+-17 km/s. From previous
observations and from the fact that the epoch of minimum velocity arrived early
with respect to the epoch calculated from pulse timing we know that the
companion star is suffering from irradiation. Since we most likely observed
primarily the side of the companion star facing the observer at phase ~0.75 the
velocity quoted above is not the true radial velocity semi-amplitude of the
companion star. Assuming a uniform contribution to the line profile from this
hemisphere yields a radial velocity semi-amplitude of 280+-26 km/s for a
systemic velocity of 54+-24 km/s; if the contribution is instead weighted
somewhat more towards the side of the companion facing the X-ray source then
the true semi-amplitude is larger than this value. Together with the well
constrained inclination (81<i<84 degrees) and the mass-function determined from
pulse-timing analysis (2.03+-0.03 x 10^-2 Msun), we derive a lower limit to the
mass of the neutron star and to that of the companion star of 0.97+-0.24 Msun
and 0.33+-0.05 Msun, respectively (1 sigma; including uncertainties in the
inclination). We briefly discuss other aspects of the spectrum and the
implications of our findings.
| No Label | No Label |
0706.2351 | Neelima Sehgal | Probing the Relation Between X-ray-Derived and Weak-Lensing-Derived
Masses for Shear-Selected Galaxy Clusters: I. A781 | astro-ph | We compare X-ray and weak-lensing masses for four galaxy clusters that
comprise the top-ranked shear-selected cluster system in the Deep Lens Survey.
The weak-lensing observations of this system, which is associated with A781,
are from the Kitt Peak Mayall 4-m telescope, and the X-ray observations are
from both Chandra and XMM-Newton. For a faithful comparison of masses, we adopt
the same matter density profile for each method, which we choose to be an NFW
profile. Since neither the X-ray nor weak-lensing data are deep enough to well
constrain both the NFW scale radius and central density, we estimate the scale
radius using a fitting function for the concentration derived from cosmological
hydrodynamic simulations and an X-ray estimate of the mass assuming
isothermality. We keep this scale radius in common for both X-ray and
weak-lensing profiles, and fit for the central density, which scales linearly
with mass. We find that for three of these clusters, there is agreement between
X-ray and weak-lensing NFW central densities, and thus masses. For the other
cluster, the X-ray central density is higher than that from weak-lensing by 2
sigma. X-ray images suggest that this cluster may be undergoing a merger with a
smaller cluster. This work serves as an additional step towards understanding
the possible biases in X-ray and weak-lensing cluster mass estimation methods.
Such understanding is vital to efforts to constrain cosmology using X-ray or
weak-lensing cluster surveys to trace the growth of structure over cosmic time.
| No Label | No Label |
astro-ph/0611785 | Ognev Igor | Neutrino heating of a shock wave within magnetorotational model | astro-ph | Based on the magnetorotational model of a supernova explosion with core
collapse, we investigate the significant processes of neutrino heating of the
supernova shock. These processes should be taken into account in
self-consistent modeling, since the neutrino heating mechanism is capable of
increasing the explosion efficiency. We show that, even in the presence of a
strong magnetic field in the shock formation region, the heating rate is
determined with good accuracy by the absorption and emission of neutrinos in
direct URCA processes. Moreover, the influence on them of a magnetic field is
reduced to insignificant corrections.
| No Label | No Label |
astro-ph/0601392 | Witold Maciejewski | Can gas dynamics in centres of galaxies reveal orbiting massive black
holes? | astro-ph | If supermassive black holes in centres of galaxies form by merging of
black-hole remnants of massive Population III stars, then there should be a few
black holes of mass one or two orders of magnitude smaller than that of the
central ones, orbiting around the centre of a typical galaxy. These black holes
constitute a weak perturbation in the gravitational potential, which can
generate wave phenomena in gas within a disc close to the centre of the galaxy.
Here we show that a single orbiting black hole generates a three-arm spiral
pattern in the central gaseous disc. The density excess in the spiral arms in
the disc reaches values of 3-12% when the orbiting black hole is about ten
times less massive than the central black hole. Therefore the observed density
pattern in gas can be used as a signature in detecting the most massive
orbiting black holes.
| No Label | No Label |
astro-ph/0301343 | Andrea Biviano | Clues on the Evolution of Cluster Galaxies From The Analysis of Their
Orbital Anisotropies | astro-ph | We study the evolution of galaxies in clusters by the analysis of a sample of
about 3000 galaxies, members of 59 clusters from the ESO Nearby Abell Cluster
Survey (ENACS). We distinguish four cluster galaxy populations, based on their
radial and velocity distributions within the clusters. Using the class of
ellipticals and S0's (excluding the very bright ellipticals), we determine the
average cluster mass profile, that we compare with mass models available from
numerical simulations. We then use this cluster mass profile to solve for the
anisotropy profiles of the three other cluster galaxy populations, viz. the
very bright ellipticals, the early spirals, and the late spirals with the
emission-line galaxies. We discuss the implications of our findings for the
evolution of cluster galaxies.
| No Label | No Label |
astro-ph/9706004 | C. Popescu | Results of a search for emission-line galaxies towards nearby voids. The
spatial distribution | astro-ph | We present the results of a search for emission-line galaxies (ELGs) towards
nearby voids, based on a sample selected on the HQS (Hamburg Quasar Survey) -
III-aJ objective-prism plates. The survey was based on the presence of
emission-lines and therefore has the advantage to detect very faint objects
(with all the flux in the emission-lines and almost no continuum), that would
be missed by an apparent magnitude limited survey. We found objects as faint as
B=20.5 and M(B)=(-15.0,-12.0).
The observational data are given in Popescu et al. (1996) and in the present
paper we consider a complete subsample from these data. We analyse the spatial
distribution of our sample of ELGs in comparison with the distribution of
normal galaxies. Overall both distributions trace the same structures.
Nevertheless we also found a few ELGs in voids, from which at least 8 lie in
the very well defined nearby voids. The isolated galaxies seem to form fainter
structures that devide the larger voids into smaller ones. {}From our estimates
of the expected number of void galaxies we conclude that we did not find an
underlying homogenous void population.
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0801.2694 | Fabien Malbet | Milli-arcsecond astrophysics with VSI, the VLTI spectro-imager in the
ELT era | astro-ph | Nowadays, compact sources like surfaces of nearby stars, circumstellar
environments of stars from early stages to the most evolved ones and
surroundings of active galactic nuclei can be investigated at milli-arcsecond
scales only with the VLT in its interferometric mode. We propose a
spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe
these sources both over spatial and spectral scales in the near-infrared
domain. This instrument will provide information complementary to what is
obtained at the same time with ALMA at different wavelengths and the extreme
large telescopes.
| No Label | No Label |
astro-ph/9508082 | Sergio Campana | Strong gravitational field light deflection in binary systems containing
a collapsed star | astro-ph | Large light deflection angles are produced in the strong gravitational field
regions around neutron stars and black holes. In the case of binary systems,
part of the photons emitted from the companion star towards the collapsed
object are expected to be deflected in the direction of the earth. Based on a
semi-classical approach we calculate the characteristic time delays and
frequency shifts of these photons as a function of the binary orbital phase.
The intensity of the strongly deflected light rays is reduced by many orders of
magnitude, therefore making the observations of this phenomenon extremely
difficult. Relativistic binary systems containing a radio pulsar and a
collapsed object are the best available candidates for the detection of the
strongly deflected photons. Based on the accurate knowledge of their orbital
parameters, these systems allow to predict accurately the delays of the pulses
along the highly deflected path, such that the sensitivity to very weak signals
can be substantially improved through coherent summation over long time
intervals. We discuss in detail the cases of PSR 1913+16 and PSR 1534+12 and
find that the system geometry is far more promising for the latter. The
observation of the highly deflected photons can provide a test of general
relativity in an unprecedented strong field regime as well as a tight
constraint on the radius of the collapsed object.
| No Label | No Label |
0712.3585 | Eran O. Ofek | GRB 070201: A possible Soft Gamma Ray Repeater in M31 | astro-ph | The gamma-ray burst (GRB) 070201 was a bright short-duration hard-spectrum
GRB detected by the Inter-Planetary Network (IPN). Its error quadrilateral,
which has an area of 0.124 sq. deg, intersects some prominent spiral arms of
the nearby M31 (Andromeda) galaxy. Given the properties of this GRB, along with
the fact that LIGO data argues against a compact binary merger origin in M31,
this GRB is an excellent candidate for an extragalactic Soft Gamma-ray Repeater
(SGR) giant flare, with energy of 1.4x10^45 erg. Analysis of ROTSE-IIIb visible
light observations of M31, taken 10.6 hours after the burst and covering 42% of
the GRB error region, did not reveal any optical transient down to a limiting
magnitude of 17.1. We inspected archival and proprietary XMM-Newton X-ray
observations of the intersection of the GRB error quadrilateral and M31,
obtained about four weeks prior to the outburst, in order to look for periodic
variable X-ray sources. No SGR or Anomalous X-ray Pulsar (AXP) candidates
(periods in range 1 to 20 s) were detected. We discuss the possibility of
detecting extragalactic SGRs/AXPs by identifying their periodic X-ray light
curves. Our simulations suggest that the probability of detecting the periodic
X-ray signal of one of the known Galactic SGRs/AXPs, if placed in M31, is about
10% (50%), using 50 ks (2 Ms) XMM-Newton exposures.
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astro-ph/0008435 | Soeren S. Larsen | HST observations of star clusters in NGC 1023: Evidence for three
cluster populations? | astro-ph | Using HST images we have carried out a study of cluster populations in the
nearby S0 galaxy NGC 1023. In two WFPC2 pointings we have identified 221
cluster candidates. The small distance (~9 Mpc) combined with deep F555W and
F814W images allows us to reach about two magnitudes below the expected
turn-over of the globular cluster luminosity function. NGC 1023 appears to
contain at least three identifiable cluster populations: the brighter clusters
show a clearly bimodal color distribution with peaks at V-I = 0.92 and at V-I =
1.15 and in addition there are a number of fainter, more extended objects with
predominantly red colors. Among the brighter clusters, we find that the blue
clusters have somewhat larger sizes than the red ones with mean effective radii
of R(eff) ~ 2 and R(eff) ~ 1.7 pc, respectively. These clusters have luminosity
functions (LFs) and sizes consistent with what is observed for globular
clusters in other galaxies. Fitting Gaussians to the LFs of the blue and red
compact clusters we find turn-over magnitudes of M(TO,blue)=-7.58 and
M(TO,red)=-7.37 in V and dispersions of sigma(V,blue)=1.12 and
sigma(V,red)=0.97. The fainter, more extended clusters have effective radii up
to R(eff) ~ 10-15 pc and their LF appears to rise at least down to M(V) ~ -6,
few of them being brighter than M(V) = -7. We suggest that these fainter
objects may have a formation history distinct from that of the brighter GCs.
| No Label | No Label |
astro-ph/0012327 | null | A Balloon-borne Large Aperture Submillimeter Telescope | astro-ph | A new generation of sub-orbital platforms will be operational in the next few
years. These new telescopes will operate from airborne and balloon-borne
platforms where the atmosphere is transparent enough to allow sensitive
measurements to be made in the submillimeter bands. The telescopes will take
advantage of state-of-the-art instrumentation including large format bolometer
arrays and spectrometers. Other papers in this volume will deal specifically
with the potential of these bands. In this paper will review the capabilities
the BLAST balloon-borne telescope.
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astro-ph/0005532 | Denis A. Leahy | EUVE Observations of Hercules X-1 During a Short High State Turn-On | astro-ph | Observations of Hercules X-1 by the Extreme Ultraviolet Explorer (EUVE)
covering low state and the early part of the Short High state are reported
here. This is the first EUV observation of this part of the 35-day cycle of Her
X-1. The low state portion of the EUV light curve (prior to the start of the
Short High state) has similar properties as that following the end of the Short
High state (Leahy and Marshall, 1999). This is evidence that the low state EUV
emission is primarily due to EUV reflection from the companion star HZ Her. The
EUV lightcurve during the Short High state is pulsed and closely resembles the
average 2-12 keV X-ray Short High state lightcurve indicating that the EUV
emission, like the X-ray emission, originates near the neutron star. The Short
High state EUV spectrum is consistent with a blackbody of temperature 0.13 keV
and radius 230 km. The Short High state EUV spectrum and pulse shape are
similar to that in the soft X-rays (0.1 - 1 keV). The most likely origin of the
EUV emission is reprocessed X-rays from the inner edge of the accretion disk,
and the radius of the inner edge of the accretion disk is likely to be small,
consistent with that determined from analysis of the X-ray pulse shape
evolution (Scott, Leahy and Wilson, 2000).
| No Label | No Label |
astro-ph/0003032 | Bryan Gaensler | Non-detection of a pulsar-powered nebula in Puppis A, and implications
for the nature of the radio-quiet neutron star RX J0822-4300 | astro-ph | We report on a deep radio search for a pulsar wind nebula associated with the
radio-quiet neutron star RX J0822-4300 in the supernova remnant Puppis A. The
well-determined properties of Puppis A allow us to constrain the size of any
nebula to less than 30 arcsec; however we find no evidence for such a source on
any spatial scale up to 30 arcmin. These non-detections result in an upper
limit on the radio luminosity of any pulsar-powered nebula which is three
orders of magnitude below what would be expected if RX J0822-4300 was an
energetic young radio pulsar beaming away from us, and cast doubt on a recent
claim of X-ray pulsations from this source. The lack of a radio nebula leads us
to conclude that RX J0822-4300 has properties very different from most young
radio pulsars, and that it represents a distinct population which may be as
numerous, or even more so, than radio pulsars.
| No Label | No Label |
astro-ph/0201333 | John C. Lattanzio | AGB Stars: Summary and Warning | astro-ph | The Asymptotic Giant Branch (AGB) phase is very short but its importance is
seen in its nucleosynthesis. A revolution in stellar modelling has taken place
in the last 20 years, inspired jointly by this rich nucleosynthesis and partly
by new data. For example, the isotopic data coming from pre-solar grains (see
this volume) forces theorists to include species that were previously ignored,
species which are energetically of no importance (i.e. they play no role in
determining the stellar structure) but which can be used to constrain the
models. Nucleosynthesis is now important as a tracer of temperature and mixing,
and not simply a by-product of energy generation. But along with these advances
come more quantitative demands. It is now increasingly important to know what
is known well and what is less sure. This is the goal of this paper.
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astro-ph/9508132 | Konrad Kuijken | Observational Evidence for a Bar in the Milky Way | astro-ph | Evidence from a variety of sources points towards the existence of a bar in
the central few kpc of the Galaxy. The measurements roughly agree on the
direction of the bar major axis, but other parameters (axis ratio, size,
pattern speed) are still poorly determined. Current dynamical models are
limited by the quality of hydro simulations, the degeneracy of stellar orbit
models, stellar-kinematic data and the significant lopsidedness of the central
kpc. Microlensing promises new constraints on the mass distribution in the
bulge/bar region.
| No Label | No Label |
0712.0839 | Jonathan Devor | Identification, Classifications, and Absolute Properties of 773
Eclipsing Binaries Found in the TrES Survey | astro-ph | In recent years we have witnessed an explosion of photometric time-series
data, collected for the purpose of finding a small number of rare sources, such
as transiting extrasolar planets and gravitational microlenses. Once combed,
these data are often set aside, and are not further searched for the many other
variable sources that they undoubtedly contain. To this end, we describe a
pipeline that is designed to systematically analyze such data, while requiring
minimal user interaction. We ran our pipeline on a subset of the Trans-Atlantic
Exoplanet Survey dataset, and used it to identify and model 773 eclipsing
binary systems. For each system we conducted a joint analysis of its light
curve, colors, and theoretical isochrones. This analysis provided us with
estimates of the binary's absolute physical properties, including the masses
and ages of their stellar components, as well as their physical separations and
distances. We identified three types of eclipsing binaries that are of
particular interest and merit further observations. The first category includes
11 low-mass candidates, which may assist current efforts to explain the
discrepancies between the observation and the models of stars at the bottom of
the main-sequence. The other two categories include 34 binaries with eccentric
orbits, and 20 binaries with abnormal light curves. Finally, this uniform
catalog enabled us to identify a number of relations that provide further
constraints on binary population models and tidal circularization theory.
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astro-ph/0302520 | Jason A. Stevens | The radio flaring behaviour of GRO J1655-40: an analogy with
extragalactic radio sources? | astro-ph | At radio frequencies, the current evidence for the microquasar-quasar
connection is based on imaging observations showing that relativistic
outflows/jets are found in both classes of objects. Some microquasars also
display superluminal motion, further strengthening the view that microquasars
are in fact Galactic miniatures of quasars. Here we demonstrate that this
connection can be extended to incorporate timing and spectral observations. Our
argument is based on the striking similarity found in the radio flaring
behaviour of the Galactic superluminal source GRO J1655-40 and of the
extragalactic sources, such as the blazar 3C 273. We find that the variability
of GRO J1655-40 can be explained within the framework of the successful
generalised shock model for compact radio sources in which the radio emission
arises from shocked plasma in relativistic jets. Specifically, the
multifrequency flare amplitudes, time delays and radio polarization position
angle measurements are consistent with the predictions of the growth stage of
this model.
| No Label | No Label |
astro-ph/0406138 | Dan Watson | The state of protoplanetary material 10 Myr after stellar formation:
circumstellar disks in the TW Hydrae association | astro-ph | We have used the Spitzer Infrared Spectrograph to observe seven members of
the TW Hya association, the nearest stellar association whose age ($\sim$ 10
Myr) is similar to the timescales thought to apply to planet formation and disk
dissipation. Only two of the seven targets display infrared excess emission,
indicating that substantial amounts of dust still exist closer to the stars
than is characteristic of debris disks; however, in both objects we confirm an
abrupt short-wavelength edge to the excess, as is seen in disks with
cleared-out central regions. The mid-infrared excesses in the spectra of Hen
3-600 and TW Hya include crystalline silicate emission features, indicating
that the grains have undergone significant thermal processing. We offer a
detailed comparison between the spectra of TW Hya and Hen 3-600, and a model
that corroborates the spectral shape and our previous understanding of the
radial structure of these protoplanetary disks.
| No Label | No Label |
0705.3776 | Silvia Giordano | The photospheric environment of a solar pore with light bridge | astro-ph | Pores are one of the various features forming in the photosphere by the
emergence of magnetic field onto the solar surface. They lie at the border
between tiny magnetic elements and larger sunspots. Light bridges, in such
structures, are bright features separating umbral areas in two or more
irregular regions. Commonly, light bridges indicate that a the merging of
magnetic regions or, conversely, the breakup of the area is underway. We
investigate the velocity structure of a solar pore (AR10812) with light bridge,
and of the quiet solar photosphere nearby, analyzing high spatial and spectral
resolution images. The pore area has been observed with the Interferometric
BI-dimensional Spectrometer (IBIS) at the Dunn Solar Telescope, acquiring
monochromatic images in the Ca II 854.2 nm line and in the Fe I 709.0 nm line
as well as G-band and broad-band images. We also computed the Line of Sight
(LoS) velocity field associated to the Fe I and Fe II photospheric lines. The
amplitude of the LoS velocity fluctuations, inside the pore, is smaller than
that observed in the quiet granulation near the active region. We computed the
azimuthal average LoS velocity and derived its radial profile. The whole pore
is characterized by a downward velocity -200 m/s and by an annular downflow
structure with an average velocity of -350 m/s with respect to the nearby quiet
sun. The light bridge inside the pore, when observed in the broad-band channel
of IBIS and in the red wing of Ca II 854.2 nm line, shows an elongated dark
structure running along its axis, that we explain with a semi-analytical model.
In the highest resolution LoS velocity images the light bridge shows a profile
consistent with a convective roll: a weak upflow, 50-100m/s, in correspondence
of the dark lane, flanked by a downflow, -(200-300) m/s.
| No Label | No Label |
astro-ph/0408397 | Cesar Esteban | Carbon and Oxygen Galactic Gradients: Observational Values from HII
Region Recombination Lines | astro-ph | We present results of deep echelle spectrophotometry of eight Galactic HII
regions located at Galactocentric distances between 6.3 and 10.4 kpc. The data
have been taken with the Very Large Telescope (VLT) Ultraviolet Echelle
Spectrograph (UVES) in the 3100 to 10360 A range. We have derived C++ and O++
abundances from recombination lines for all the objects, as well as O+
abundances from this kind of lines for three of the nebulae. The intensity of
recombination lines is almost independent of the assumed electron temperature
as well as of the possible presence of spatial temperature variations or
fluctuations inside the nebulae. These data allow the determination of the
gas-phase C and O abundance gradients of the Galactic disk, of paramount
importance for chemical evolution models. This is the first time the C gradient
is derived from such a large number of HII regions and for such a wide range of
Galactocentric distances. Abundance gradients are found of the form
$\Delta$log(O/H) = -0.044$\pm$0.010 dex kpc^-1, $\Delta$log(C/H) =
-0.103$\pm$0.018 dex kpc^-1, and $\Delta$log(C/O) = -0.058$\pm$0.018 dex
kpc^-1.
| No Label | No Label |
0801.1470 | Dorodnitsyn Anton | An axisymmetric, hydrodynamical model for the torus wind in AGN | astro-ph | We report on time-dependent axisymmetric simulations of an X-ray excited flow
from a parsec-scale, rotating, cold torus around an active galactic nucleus.
Our simulations account for radiative heating and cooling and radiation
pressure force. The simulations follow the development of a broad bi-conical
outflow induced mainly by X-ray heating. We compute synthetic spectra predicted
by our simulations. The wind characteristics and the spectra support the
hypothesis that a rotationally supported torus can serve as the source of a
wind which is responsible for the warm absorber gas observed in the X-ray
spectra of many Seyfert galaxies.
| No Label | No Label |
astro-ph/0112551 | Roman Scoccimarro | Large-Scale Structure of the Universe and Cosmological Perturbation
Theory | astro-ph | We review the formalism and applications of non-linear perturbation theory
(PT) to understanding the large-scale structure of the Universe. We first
discuss the dynamics of gravitational instability, from the linear to the
non-linear regime. This includes Eulerian and Lagrangian PT, non-linear
approximations, and a brief description of numerical simulation techniques. We
then cover the basic statistical tools used in cosmology to describe cosmic
fields, such as correlations functions in real and Fourier space, probability
distribution functions, cumulants and generating functions. In subsequent
sections we review the use of PT to make quantitative predictions about these
statistics according to initial conditions, including effects of possible non
Gaussianity of the primordial fields. Results are illustrated by detailed
comparisons of PT predictions with numerical simulations. The last sections
deal with applications to observations. First we review in detail practical
estimators of statistics in galaxy catalogs and related errors, including
traditional approaches and more recent developments. Then, we consider the
effects of the bias between the galaxy distribution and the matter
distribution, the treatment of redshift distortions in three-dimensional
surveys and of projection effects in angular catalogs, and some applications to
weak gravitational lensing. We finally review the current observational
situation regarding statistics in galaxy catalogs and what the future
generation of galaxy surveys promises to deliver.
| No Label | No Label |
astro-ph/0403585 | Elizabeth R. Stanway | Near-Infrared Properties of I-Drop Galaxies in the Hubble Ultra Deep
Field | astro-ph | We analyse near-infrared HST/NICMOS F110W (J) and F160W (H) band photometry
of a sample of 27 i'-drop candidate z~6 galaxies in the central region of the
HST/ACS Ultra Deep Field (HUDF). The infrared colours of the 20 objects not
affected by near neighbours are consistent with a high redshift interpretation.
This suggests that the low redshift contamination of this i'-drop sample is
smaller than that observed at brighter magnitudes where values of 10-40% have
been reported. The J-H colours are consistent with a slope flat in f_nu (f_lam
\propto lam^{-2}), as would be expected for an unreddened starburst. There is,
however, evidence for a marginally bluer spectral slope (f_lam propto
lam^{-2.2) which is perhaps indicative of an extremely young starburst (~10 Myr
old) or a top heavy initial mass function and little dust. The low levels of
contamination, median photometric redshift of z~6.0 and blue spectral slope,
inferred using the near-infrared data, supports the validity of the assumptions
in our earlier work in estimating the star formation rates and, that the
majority of the i-drop candidates galaxies lie at z~6.
| No Label | No Label |
astro-ph/0002398 | Crystal L. Brogan | OH Zeeman Magnetic Field Detections Toward Five Supernova Remnants Using
the VLA | astro-ph | We have observed the OH (1720 MHz) line in five galactic SNRs with the VLA to
measure their magnetic field strengths using the Zeeman effect. We detected all
12 of the bright ($S_{\nu} > 200$ mJy) OH (1720 MHz) masers previously detected
by Frail et al. (1996) and Green et al. (1997) and measured significant
magnetic fields (i.e. $ > 3\sigma$) in ten of them. Assuming that the
``thermal'' Zeeman equation can be used to estimate $\mid\vec{B}\mid$ for OH
masers, our estimated fields range from 0.2 to 2 mG. These magnetic field
strengths are consistent with the hypothesis that ambient molecular cloud
magnetic fields are compressed via the SNR shock to the observed values.
Magnetic fields of this magnitude exert a considerable influence on the
properties of the cloud with the magnetic pressures ($10^{-7} - 10^{-9}$ erg
cm$^{-3}$) exceeding the pressure in the ISM or even the thermal pressure of
the hot gas interior to the remnant. This study brings the number of galactic
SNRs with OH (1720 MHz) Zeeman detections to ten.
| No Label | No Label |
astro-ph/0010656 | Renyue Cen | Metal Enrichment and Temperature of the Intergalactic Medium | astro-ph | Hydrodynamic simulations of Lyman alpha clouds based on ab inito cosmological
models have produced results that are in broad agreement with observations.
However, further analyses have revealed that, with progressively higher
numerical resolution, the median or cutoff line width of the simulated Lyman
alpha clouds (i.e. the Doppler parameter) appears to converge to a value
significantly below what is observed at z~3 (by about a factor of 1.5). These
convergence test simulations do not include feedback from star formation. Given
the observed metallicity in the Lyman alpha clouds we suggest that supernovae,
which presumably polluted the IGM with metals, may have deposited a sufficient
amount of energy in the IGM to reconcile the theory with observations. Simple
arguments immediately narrow the redshift range of pollution down to
4<z_{dep}<9. It seems quite certain that dwarf and sub-dwarf galaxies with
total masses in the range 10^{6.5-9.0}Msun have to be largely responsible for
the pollution. Furthermore, it is implied that either star formation is very
efficient or metal yield is very high for these early dwarf galaxies, if the
mean metallicity in the universe at z=3 is as high as <Z>=0.01Zsun. Finally,
assuming the specific supernova heating energy is proportional to the
metallicity of a gas, we note that the picture proposed here would be
consistent with supernovae being the apparently needed heating source for the
intra-cluster gas, if the required heating of the intra-cluster gas is no
greater than 1 keV per particle.
| No Label | No Label |
astro-ph/9702113 | Biswajit Paul | Torque-luminosity correlation and possible evidence for core-crust
relaxation in the X-ray pulsar GX 1+4 | astro-ph | We present the detection of a positive correlation between spin-down rate
$\dot{P}$ and pulsed X-ray luminosity in the BATSE archival data of the bright
hard X-ray pulsar GX 1+4. We have also seen a delay of 5.6 $\pm$ 1.2 days
between the luminosity change and the corresponding change in the spin-down
rate. The observed correlation between $\dot{P}$ and L_X is used to reproduce
the period history of GX 1+4 based on the observed luminosity alone, and it is
found that the spin period can be predicted correct to 0.026% when the
luminosity is adequately sampled. The idea that at a higher luminosity more
matter is accreted and the accretion disk extends closer to the neutron star
thereby transferring more angular momentum to the system, seems not to be the
case with GX 1+4. The observed lag between the spin-down rate and the
luminosity is reported here for the first time in any such binary X-ray pulsar,
and is found to be consistent with the time scale for the core-crust relaxation
in a neutron star.
| No Label | No Label |
astro-ph/0503373 | Jean-Luc Starck | Weak Lensing Mass Reconstruction using Wavelets | astro-ph | This paper presents a new method for the reconstruction of weak lensing mass
maps. It uses the multiscale entropy concept, which is based on wavelets, and
the False Discovery Rate which allows us to derive robust detection levels in
wavelet space. We show that this new restoration approach outperforms several
standard techniques currently used for weak shear mass reconstruction. This
method can also be used to separate E and B modes in the shear field, and thus
test for the presence of residual systematic effects. We concentrate on large
blind cosmic shear surveys, and illustrate our results using simulated shear
maps derived from N-Body Lambda-CDM simulations with added noise corresponding
to both ground-based and space-based observations.
| No Label | No Label |
0810.1415 | Antonia Wilmot-Smith | Magnetic Braiding and Parallel Electric Fields | astro-ph | The braiding of the solar coronal magnetic field via photospheric motions -
with subsequent relaxation and magnetic reconnection -- is one of the most
widely debated ideas of solar physics. We readdress the theory in the light of
developments in three-dimensional magnetic reconnection theory. It is known
that the integrated parallel electric field along field lines is the key
quantity determining the rate of reconnection, in contrast with the
two-dimensional case where the electric field itself is the important quantity.
We demonstrate that this difference becomes crucial for sufficiently complex
magnetic field structures.
A numerical method is used to relax a braided magnetic field to an ideal
force-free equilibrium; that equilibrium is found to be smooth, with only
large- scale current structures. However, the equilibrium is shown to have a
highly filamentary integrated parallel current structure with extremely short
length- scales. An analytical model is developed to show that, in a coronal
situation, the length scales associated with the integrated parallel current
structures will rapidly decrease with increasing complexity, or degree of
braiding, of the magnetic field. Analysis shows the decrease in these length
scales will, for any finite resistivity, eventually become inconsistent with
the stability of a force- free field. Thus the inevitable consequence of the
magnetic braiding process is shown to be a loss of equilibrium of the coronal
field, probably via magnetic reconnection events.
| No Label | No Label |
astro-ph/0008264 | Carlos De Breuck | A Statistical Study of Emission Lines from High Redshift Radio Galaxies | astro-ph | We have compiled a sample of 165 radio galaxies from the literature to study
the properties of the extended emission line regions and their interaction with
the radio source over a large range of redshift 0<z<5.2. For each source, we
have collected radio (size, lobe distance ratio and power) and spectroscopic
parameters (luminosity, line width and equivalent width) for the four brightest
UV lines. We also introduce a parameter A_{Ly-alpha} measuring the asymmetry of
the Ly-alpha line. Using these 18 parameters, we examine the statistical
significance of all 153 mutual correlations, and find the following significant
correlations: (i) Ly-alpha asymmetry A_{Ly-alpha} with radio size and redshift,
(ii) line luminosity with radio power, (iii) line luminosities of UV lines with
each other, and (iv) equivalent widths of UV lines with each other. Using
line-ratio diagnostic diagrams, we examine the ionization mechanism of the
extended emission line regions in HzRGs. The high ionization lines seem to
confirm previous results showing that AGN photo-ionization provides the best
fit to the data, but are inconsitent with the CII/CIII ratio, which favour the
highest velocity shock ionization models. We note that the CII line is 5 times
more sensitive to shock ionization than the high ionization UV lines, and show
that a combination of shock and photo-ionization provides a better overall fit
to the integrated spectra of HzRGs. Because most HzRGs have radio sizes <~150
kpc, their integrated spectra might well contain a significant contribution
from shock ionized emission. [abridged]
| No Label | No Label |
0810.1511 | Matthew Walker | Systemic Proper Motions of Milky Way Satellites from Stellar Redshifts:
the Carina, Fornax, Sculptor and Sextans Dwarf Spheroidals | astro-ph | The transverse motions of nearby dwarf spheroidal (dSph) galaxies contribute
line-of-sight components that increase with angular distance from the dSph
centers, inducing detectable gradients in stellar redshift. In the absence of
an intrinsic velocity gradient (e.g., due to rotation or streaming), an
observed gradient in the heliocentric rest frame (HRF) relates simply to a
dSph's systemic proper motion (PM). Kinematic samples for the Milky Way's
brightest dSph satellites are now sufficiently large that we can use stellar
redshifts to constrain systemic PMs independently of astrometric data. Data
from our Michigan/MIKE Fiber System (MMFS) Survey reveal significant HRF
velocity gradients in Carina, Fornax and Sculptor, and no significant gradient
in Sextans. Assuming there are no intrinsic gradients, the data provide a
relatively tight constraint on the PM of Fornax,
(mu_{alpha}^{HRF},mu_{delta}^{HRF})=(+48 +/- 15,-25 +/- 14) mas/century, that
agrees with published HST astrometric measurements. Smaller data sets yield
weaker constraints in the remaining galaxies, but our Carina measurement,
(mu_{alpha}^{HRF},mu_{delta}^{HRF})=(+25 +/- 36,+16 +/- 43) mas/century, agrees
with the published astrometric value. The disagreement of our Sculptor
measurement, (mu_{alpha}^{HRF},mu_{delta}^{HRF})= (-40 +/- 29, -69 +/- 47)
mas/century, with astrometric measurements is expected if Sculptor has a
rotational component as reported by Battaglia et al. (2008). For Sextans, which
at present lacks an astrometric measurement, we measure
(mu_{alpha}^{HRF},mu_{delta}^{HRF})=(-26 +/- 41, +10 +/- 44) mas/century.
| No Label | No Label |
astro-ph/0111227 | Alberto Fernandez-Soto | Error analysis of the photometric redshift tecnique | astro-ph | We present a calculation of the systematic component of the error budget in
the photometric redshift technique. We make use of it to describe a simple
technique that allows for the assignation of confidence limits to redshift
measurements obtained through photometric methods. We show that our technique,
through the calculation of a redshift probability function, gives complete
information on the probable redshift of an object and its associated confidence
intervals. This information can and must be used in the calculation of any
observable quantity which makes use of the redshift.
| No Label | No Label |
astro-ph/0409647 | Sergei Zharikov | Time-resolved observations of the short period CV SDSS J123813.73-033933 | astro-ph | We present simultaneous spectral and photometric observations of SDSS
J123813.73-033933.0. From Ha radial velocity measurements we determined the
orbital period of the system to be 0.05592+/-0.00002 days (80.53 min). The
spectrum shows double Balmer emission lines flanked by strong, broad
absorption, indicating a dominant contribution from the white dwarf. The
photometric light curve shows complex variability. The system undergoes cyclic
brightening up to 0.4 mag which are semi-periodical on short time scales with
periods of the order of 7-12 hours. We also detect 40.25 min variability (~0.15
mag) in the light curve, that corresponds to half the orbital period. Its
amplitude increases with the cyclic brightening of the system.
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astro-ph/0404266 | Sylvie Vauclair | Asteroseismic Signatures of Helium gradients in Main-Sequence A Stars ;
Application to the roAp Star HD60435 | astro-ph | Asteroseismology is found to be a excellent tool for detecting
diffusion-induced helium gradients inside main-sequence A stars. Models have
been computed for 1.6 and 2.0 M$_{\odot}$ stars with pure helium diffusion, at
different ages, so that the helium gradient lies at different depths inside the
star. The adiabatic oscillation frequencies have been analysed and compared
with those of a model without diffusion. Clear signatures of the
diffusion-induced helium gradient are found in the so-called ``second
differences" : these frequency differences present modulations due to the
partial reflexion of the sound waves on the layer where the helium gradient
takes place. A tentative application to the roAp star HD60435, which presents
enough detected oscillation frequencies for the test to be possible, is very
encouraging. The results suggest the presence of a helium gradient inside the
star, which is consistent with the idea that the triggering of the oscillations
is due to the hydrogen $\kappa$-mechanism.
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astro-ph/9711144 | null | Stellar Populations in Three Outer Fields of the LMC | astro-ph | We present HST photometry for three fields in the outer disk of the LMC
extending approximately four magnitudes below the faintest main sequence
turnoff. We cannot detect any strongly significant differences in the stellar
populations of the three fields based on the morphologies of the
color-magnitude diagrams, the luminosity functions, and the relative numbers of
stars in different evolutionary stages. Our observations therefore suggest
similar star formation histories in these regions, although some variations are
certainly allowed. The fields are located in two regions of the LMC: one is in
the north-east field and two are located in the north-west. Under the
assumption of a common star formation history, we combine the three fields with
ground-based data at the same location as one of the fields to improve
statistics for the brightest stars. We compare this stellar population with
those predicted from several simple star formation histories suggested in the
literature, using a combination of the R-method of Bertelli et al (1992) and
comparisons with the observed luminosity function. The only model which we
consider that is not rejected by the observations is one in which the star
formation rate is roughly constant for most of the LMC's history and then
increases by a factor of three about 2 Gyr ago. Such a model has roughly equal
numbers of stars older and younger than 4 Gyr, and thus is not dominated by
young stars. This star formation history, combined with a closed box chemical
evolution model, is consistent with observations that the metallicity of the
LMC has doubled in the past 2 Gyr.
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0807.1913 | Claus Leitherer | Revision of Star-Formation Measures | astro-ph | Rotation plays a major role in the evolution of massive stars. A revised grid
of stellar evolutionary tracks accounting for rotation has recently been
released by the Geneva group and implemented into the Starburst99 evolutionary
synthesis code. Massive stars are predicted to be hotter and more luminous than
previously thought, and the spectral energy distributions of young populations
mirror this trend. The hydrogen ionizing continuum in particular increases by a
factor of up to 3 in the presence of rotating massive stars. The effects of
rotation generally increase towards shorter wavelengths and with decreasing
metallicity. Revised relations between star-formation rates and monochromatic
luminosities for the new stellar models are presented.
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0810.0275 | Niklas Karlsson | Hadronic Production of Gamma Rays and Starburst Galaxies | astro-ph | The Milky Way has been estabished to emit gamma rays. These gamma rays are
presumably dominated by decays of neutral pions, although inverse Compton
scatterings and bremsstrahlung also contribute. It is plausible that other
galaxies can be diffuse sources of gamma rays in a similar manner. Starburst
galaxies are particularly interesting to study as they are expected to have
much higher cosmic-ray fluxes and interstellar matter densities. The neutral
pions are created in cosmic-ray interactions with interstellar matter.
Presented here is an overview of the recent work by Karlsson and co-workers on
proton-proton interactions and the resulting secondary particle inclusive cross
sections and angular distributions. This model can be used to calculated the
$\pi^{0}$ component of the gamma-ray yield and spectrum from a starburst
galaxy. The yield is expected to increase significantly (30% to 50%) and the
spectrum to be harder than the incident proton spectrum.
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astro-ph/0112476 | Patrick McDonald | Large-scale Correlation of Mass and Galaxies with the Lyman-alpha Forest
Transmitted Flux | astro-ph | We present predictions of the correlation between the Lyman-alpha forest
absorption in quasar spectra and the mass within \sim 5 Mpc/h (comoving) of the
line of sight, using fully hydrodynamic and hydro-PM numerical simulations of
the cold dark matter model supported by present observations. The observed
correlation based on galaxies and the Lya forest can be directly compared to
our theoretical results, assuming that galaxies are linearly biased on large
scales. Specifically, we predict the average value of the mass fluctuation,
<delta_m>, conditioned to a fixed value of the Lya forest transmitted flux
delta_F, after they have been smoothed over a 10 Mpc/h cube and line of sight
interval, respectively. We find that <delta_m>/sigma_m as a function of
delta_F/sigma_F has a slope of 0.6 at this smoothing scale, where sigma_m and
sigma_F are the rms dispersions (this slope should decrease with the smoothing
scale). We show that this value is largely insensitive to the cosmological
model and other Lya forest parameters. Comparison of our predictions to
observations should provide a fundamental test of our ideas on the nature of
the Lya forest and the distribution of galaxies, and can yield a measurement of
the bias factor of any type of galaxies that are observed in the vicinity of
Lya forest lines of sight.
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astro-ph/0608318 | Dragan Huterer | Mysteries on Universe's Largest Observable Scales | astro-ph | We review recent findings that the universe on its largest scales shows hints
of the violation of statistical isotropy, in particular alignment with the
geometry and direction of motion of the solar system, and missing power at
scales greater than 60 degrees. We present the evidence, attempts to explain it
using astrophysical, cosmological or instrumental mechanisms, and prospects for
future understanding.
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0806.3276 | Avishay Gal-Yam | GALEX Spectroscopy of SN 2005ay suggests a UV spectral uniformity among
type II-P supernovae | astro-ph | We present the first results from our GALEX program designed to obtain
ultraviolet (UV) spectroscopy of nearby core-collapse supernovae (SNe). Our
first target, SN 2005ay in the nearby galaxy NGC 3938, is a typical member of
the II-P SN subclass. Our spectra show remarkable similarity to those of the
prototypical type II-P event SN 1999em, and resemble also Swift observations of
the recent type II-P event SN 2005cs. Taken together, the observations of these
three events trace the UV spectral evolution of SNe II-P during the first month
after explosion, as required in order to interpret optical observations of
high-redshift SNe II-P, and to derive cross-filter K-corrections. While still
highly preliminary, the apparent UV homogeneity of SNe II-P bodes well for the
use of these events as cosmological probes at high redshift.
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0708.1444 | Athina Meli | Efficiency limits of diffusive shock acceleration | astro-ph | It is well accepted today that diffusive acceleration in shocks results to
the cosmic ray spectrum formation. This is in principle true for
non-relativistic shocks, since there is a detailed theory covering a large
range of their properties and the resulting power-law spectrum, which is
nevertheless not as efficient to reach the very high energies observed in the
cosmic ray spectrum. On the other hand, the cosmic ray maximum energy and the
resulting spectra from relativistic shocks, are still under investigation and
debate concerning their contribution to the features of the cosmic ray spectrum
and the measured, or implied, cosmic ray radiation from candidate astrophysical
sources. Here, we discuss the efficiency of the first order Fermi (diffusive)
acceleration mechanism up to relativistic shock speeds, presenting Monte Carlo
simulations.
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astro-ph/0302568 | Henrik Spoon | Detection of strongly processed ice in the central starburst of NGC4945 | astro-ph | The composition of ice grains provides an important tool for the study of the
molecular environment of star forming regions. Using ISAAC at the VLT to obtain
spectra around 4.65 microns we have detected for the first time `XCN' and CO
ice in an extragalactic environment: the nuclear region of the nearby dusty
starburst/AGN galaxy NGC4945. The profile of the solid CO band reveals the
importance of thermal processing of the ice while the prominence of the XCN
band attests to the importance of energetic processing of the ice by FUV
radiation and/or energetic particles. In analogy to the processing of ices by
embedded protostars in our Galaxy, we attribute the processing of the ices in
the center of NGC4945 to ongoing massive star formation. Our M-band spectrum
also shows strong HI Pfund-beta and H2 0-0 S(9) line emission and gas phase CO
absorption lines. The HI, H2, PAH, gas phase CO and the ices seem to be
embedded in a rotating molecular disk which is undergoing vigorous star
formation. Recently, strong OCN- absorption has been detected in the spectrum
of the Galactic center star GC:IRS19. The most likely environment for the OCN-
absorption is the strongly UV-exposed GC molecular ring. The presence of
processed ice in the center of NGC4945 and our Galactic center leads us to
believe that processed ice may be a common characteristic of dense molecular
material in star forming galactic nuclei.
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astro-ph/0404299 | Wlodzimierz Godlowski | Brane Universes Tested by Supernovae Ia | astro-ph | We discuss observational constrains coming from supernovae Ia imposed on the
behaviour of the Randall-Sundrum models. In the case of dust matter on the
brane, the difference between the best-fit Perlmutter model with a
$\Lambda$-term and the best-fit brane models becomes detectable for redshifts
$z > 1.2$. It is interesting that brane models predict brighter galaxies for
such redshifts which is in agreement with the measurement of the $z = 1.7$
supernova. We also demonstrate that the fit to supernovae data can also be
obtained, if we admit the "super-negative" dark energy (phantom matter) $p= -
(4/3) \varrho$ on the brane, where the dark energy in a way mimics the
influence of the cosmological constant. It also appears that the dark energy
enlarges the age of the universe which is demanded in cosmology. Finally, we
propose to check for dark radiation and brane tension by the application of the
angular diameter of galaxies minimum value test. We point out the existence of
coincidence problem for the brane tension parameter.
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astro-ph/0611504 | Riccardo Scarpa | Using globular clusters to test gravity in the weak acceleration regime:
NGC 7099 | astro-ph | A test of Newton's law of gravity in the low acceleration regime using
globular clusters is presented. New results for the core collapsed globular
cluster NGC 7099 are given. The run of the gravitational potential as a
function of distance is probed studying the velocity dispersion profile of the
cluster, as derived from a set of 125 radial velocities with accuracy better
than 1 km/s. The velocity dispersion profile is traced up to ~18 pc from the
cluster center. The dispersion is found to be maximal at the center, then
decrease until 10+-2 pc from the center, well inside the cluster tidal radius
of 42 pc. After that the dispersion remains constant with average value
2.2+-0.3 km/s. Assuming for NGC 7099 a total V mag of M(V)=-7.43 mags and
mass-to-light ratio M/L=1, the acceleration at 10 pc from the center is 1.1e-8
cm/s/s. Thus, the flattening of the velocity dispersion profile occurs for a
value of the internal acceleration of gravity fully consistent with a_0=1.2e-8
cm/s/s observed in galaxies. This new result for NGC 7099 brings to 4 the
clusters with velocity dispersion profile probing acceleration below a_0. All
four have been found to have a flat dispersion profile at large radii where the
acceleration is below a_0, mimicking qualitatively and quantitatively
elliptical galaxies. Whether this indicates a failure of Newtonian dynamics in
the low acceleration limit or some more conventional dynamical effect (e.g.,
tidal heating) is still unclear. However, the similarities emerging between
very different globular clusters, as well as between globular clusters and
elliptical galaxies seem to favor the first of these two possibilities.
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astro-ph/0409389 | Sandy Leggett | Spectral Classification Beyond M | astro-ph | Significant populations of field L and T dwarfs are now known, and we
anticipate the discovery of even cooler dwarfs by Spitzer and ground-based
infrared surveys. However, as the number of known L and T dwarfs increases so
does the range in their observational properties, and difficulties have arisen
in interpreting the observations. Although modellers have made significant
advances, the complexity of the very low temperature, high pressure,
photospheres means that problems remain such as the treatment of grain
condensation as well as incomplete and non-equilibrium molecular chemistry.
Also, there are several parameters which control the observed spectral energy
distribution - effective temperature, grain sedimentation efficiency,
metallicity and gravity - and their effects are not well understood. In this
paper, based on a splinter session, we discuss classification schemes for L and
T dwarfs, their dependency on wavelength, and the effects of the parameters
T_eff, f_sed, [m/H] and log g on optical and infrared spectra. We will discuss
the various hypotheses that have been presented for the transition from the
dusty L types to the clear atmosphere T types. We conclude with a brief
discussion of the spectral class beyond T. Authors of each Section are
identified by their initials.
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0707.1754 | Beate Stelzer | Emission Line Variability of the Accreting Young Brown Dwarf 2MASSW
J1207334-393254: From Hours to Years | astro-ph | We have obtained a series of high-resolution optical spectra for the brown
dwarf 2MASSW J1207334-393254 (2M1207) using the ESO Very Large Telescope with
the UVES spectrograph during two consecutive observing nights (time resolution
of ~12 min) and the Magellan Clay telescope with the MIKE spectrograph.
Combined with previously published results, these data allow us to investigate
changes in the emission line spectrum of 2M1207 on timescales of hours to
years. Most of the emission line profiles of 2M1207 are broad, in particular
that of Halpha, indicating that the dominant fraction of the emission must be
attributed to disk accretion rather than to magnetic activity. From the Halpha
10% width we deduce a relatively stable accretion rate between
10^(-10.1...-9.8) Msun/yr for two nights of consecutive observations.
Therefore, either the accretion stream is nearly homogeneous over (sub-)stellar
longitude or the system is seen face-on. Small but significant variations are
evident throughout our near-continuous observation, and they reach a maximum
after ~8 h, roughly the timescale on which maximum variability is expected
across the rotation cycle. Together with past measurements, we confirm that the
accretion rate of 2M1207 varies by more than one order of magnitude on
timescales of months to years. Such variable mass accretion yields a plausible
explanation for the observed spread in the accretion rate vs. mass diagram. The
magnetic field required to drive the funnel flow is on the order of a few
hundred G. Despite the obvious presence of a magnetic field, no radio nor X-ray
emission has been reported for 2M1207. Possibly strong accretion suppresses
magnetic activity in brown dwarfs, similar to the findings for higher mass T
Tauri stars.
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