Support Capabilities for Large Telescopes Workshop

Science Programs


[ Workshop Summary ] [ Panel Memebers ] [ Table 1 ] [ Table 2 ] [ Table 3 ]

Group #1: Origins of Solar System objects
Program 1a

To carry out physical and population studies of Kuiper Belt objects (KBOs). These trans-Neptunian objects are the most primitive solar system material known, and their physical and dynamical characteristics have important implications for formation of planetary systems -- our own and perhaps others, if circumstellar disks around main sequence stars can be interpreted as Galactic analogs of the Kuiper Belt.

We propose to study the surface composition of KBOs (via optical color and near-IR spectroscopy), measure their sizes (via occultations and space-based infrared observations), shapes and rotational properties (via lightcurves), dynamical characteristics (via high precision astrometry), and, if possible, to resolve the largest KBOs via speckle interferometry. We also propose to search for faint (red magnitude m_R ~ 27) KBOs to constrain the small size end of the size distribution.

Group #2: Extrasolar planets/brown dwarfs/faint white dwarfs
Program 2a

Variations in the sub-stellar mass function

The goal of this project is to use surveys of young (50-100 Myr) and intermediate-age (600 Myr) open clusters to determine the mass function to mass limits significantly below the H-burning limit. Selecting young clusters maximises the chances of detecting brown dwarfs, since those objects are still relatively luminous and have not yet cooled substantially; dynamical evolution has not yet had sufficient time to produce substantial mass segregation and evaporation; and the objects have known age and abundance.

A related project, surveying old open clusters to determine the extent and evolution of dynamical effects, would require similar facilities for preparatory and complementary observations.

Program 2b

This project seeks to measure the disk white dwarf luminosity function (WDLF) below log(L/Lsun)~-3 from a magnitude limited sample, giving a measurement of the age of the galactic disk and constraining the physics of white dwarf cooling.

The chronology of star formation is recorded in the white dwarf luminosity function. White dwarf structure implies a relatively simple connection between luminosity and age. First attempts to exploit the white dwarfs as chronometers have come from Liebert and collaborators (Liebert, Dahn, and Monet 1987, ApJ, 332, 891 LDM, Winget et al. 1987, ApJ 315 L77). They showed that the white dwarf luminosity function was a map of the history of star formation in the disk, and that there was a significant shortfall of low-luminosity degenerates---the inevitable consequence of the finite age of the disk. The shortfall near log(L/Lsun)~-4.3 implies a disk age between 6-9 Gyrs (Wood 1992, ApJ 386, 539). More recently the white dwarf luminosity function from wide common proper motion binaries (Oswalt, Smith, Wood and Hintzen 1995, Nature 382, 692) does *not* show the shortfall seen by Liebert, Dahn, and Monet. The Oswalt et al. luminosity function suggests that the disk is at least ~9.5 Gyrs old and is consistent with arbitrarily old models at the 2 sigma level. Both the Liebert, Dahn, and Monet and Oswalt, et al. luminosity functions for white dwarfs were derived from proper motion catalogs, hence may be affected by significant kinematical bias as well as incompleteness in the parent sample. The simple fact is, the faintest, age dependent, end of the white dwarf luminosity function is not yet reliably determined.

Along with the shortfall from the finite age of the galactic disk, the WDLF should also exhibit structure related to the physics of white dwarf cooling. A well-defined observational WDLF will not only yield the age of the disk, but will also show whether phase transitions occur in high density white dwarf interiors. Theoretically proposed transitions include crystallization and chemical separation, both of which would release latent heat, prolong the cooling process, and create a local excess in the WDLF at the temperature where the phase transitions occurs. Measuring or constraining the size of this excess is important, both for learning about Coulomb interactions at high density, and for improving the precision of white dwarf age estimates.

Program 2c

Three Ages of The Mass-Luminosity Relation

The goal is to determine mass-luminosity relations (MLRs) for low mass stars and brown dwarfs in the Hyades and Pleiades. When combined with the MLR in the solar neighborhood, the cluster MLRs will be used to convert LFs to MFs over a range of ~100 in age (0.07 to 5 Gyr), thereby allowing astronomers to discover the effects of age on the MLR and, ultimately, to weigh the galaxy. Emphasis is on objects with masses less than 0.2 Msun, with special attention to determining brown dwarf masses.

*** This program can be used as critical step toward direct detection of ***
*** extrasolar planets given the low luminosity of brown dwarf companions. ***

*** This program is exceptional in that it utilizes the full diffraction ***
*** limit capability of 8m telescopes. (They're not just light buckets!) ***

Program Goals include:

1. 4 objects each in the Hyades and Pleiades with masses less than 0.08 Msun and determined to 10%, probably as companions in ...

2. 10 binaries each in the Hyades and Pleiades with masses less than 0.2 Msun and determined to 5%.

3. 10 binaries each in the Hyades and Pleiades with masses 0.2-1.0 Msun determined to 5%.

Group #3: High resolution studies of stars
Program 3a)

Physical Parameters of Luminous Stars in Extragalactic Environments

The new generation of large telescopes offers the means to study the individual brightest stars in nearby galaxies. A survey of high dispersion (R~30000) optical spectroscopy of several dozen targets in each galaxy (LMC, SMC, M31, M33, IC 1613, NGC 6822) will address three broad subjects:

a) Galactic abundance gradients. The luminous stars are young (<30 Myr), and measuring the abundances of key species of C, N, O, Mg, and Fe will show how chemical enrichment has progressed in different locations throughout the galaxy.

b) Fundamental physical parameters for each star (effective temperature, surface gravity, atmospheric turbulence, projected rotational velocity) in addition to detailed abundances. These parameters make the targets especially useful as standard candles. For example, the B and A supergiants shed matter in a stellar wind which follows a well-defined wind momentum - luminosity relation, and by modeling of the H-alpha emission profile, the wind strength can be determined and the true luminosity estimated. The survey will also include photometric and spectroscopic observations of a small sample of Cepheids for each galaxy, and their distance would be estimated individually using the Baade-Wesselink method, which is a direct single-step determination.

c) The interaction of the stars and the interstellar medium. The winds of the stars evacuate large bubbles in the local ISM, and the observations will help establish the current wind mass loss rates and velocities.

Group #3: High resolution studies of stars
Program 3b)

Gravitational Microlensing

This is a new technique for studying the surfaces of distant stars by gravitational microlensing, with the unique ability to provide center-to-limb variations of spectroscopic diagnostic lines. Such variation maps into a variation with depth in the stellar atmosphere; spectral lines provide a large choice of center-to-limb variations. One can measure the depth-dependence of temperature, pressure, and Doppler broadening in the lensed star's atmosphere; such information is ONLY available for the Sun. Red Giants' model atmospheres are constructed without such input. The dynamics and 3-D structure of their atmospheres are poorly known and affects the color-Teff calibrations, bolometric corrections, etc. (e.g. stellar ages, etc.)

Stellar microscopy on red giants in the bulge of the Galaxy is now feasible and a proof-of-concept was accomplished on MACHO event M95-30. The rate of such giant lensing events (a dark lens crossing a giant's disk) is ~ 4%*(Mlens/(0.1Msun))**-0.5, a large fraction given the current rate of ~100 bulge microlensings detected per year. The amplification brightens a typical giant to ~13th mag.

The lensed image sweeps through the solar system at a transverse velocity which will introduce a time delay between Cerro Pachon and Mauna Kea of ~ 2-5 minutes, called microlensing parallax.

Analysis of such observations will provide: (1) unique constraints for red giant atmosphere models; (2) the lens mass & distance, and its transverse velocity - valuable information for characterizing dark matter in our Galaxy

Group #3: High resolution studies of stars
Program 3c)

Planets and the Pleiades

Before a comprehensive theory of planet formation can be formulated we must first characterize a large number of planetary systems. Central to this problem is an understanding of how the characteristics of planetary systems (mass, orbital radius, eccentricity, etc.) correlate with the properties of the central star (i.e metallicity, age, rotation, level of activity,etc.) Field stars are ill-suited for such studies since they have a wide range of metalicities and their ages are uncertain. Stars in galactic clusters on the other hand, represent a homogeneous sample of stars with the same age and metallicity. This program will search for planetary companions to solar type stars in the Pleiades cluster using precise radial velocity measurements made using an iodine absorption cell. This should achieve an RV precision of 3-5 m/s on stars of V mag 10-14. A survey of 100 mid F through mid-K main sequence stars spanning 6 years should find all Jovian-mass planets with periods ranging from a few days to several years as well as Saturn- and Neptune-mass planets in "51 Peg-like" orbits. Subsequent studies will examine clusters with different ages and metallicities. The primary goals of this study include a) the mass distribution for the planetary companions, b) the distribution of eccentricity and orbital periods as a function of age, and c) the lithium-planet connection. Li can be a probe of the angular momentum history of the star and could be a diagnostic as to whether the star had a massive disk in its past. Such a massive disk may be a conducive environment for the formation of planetary companions. The Li abundance, however, is also a function of stellar age so it is difficult to explore the connection between lithium abundance and planetary companions using field stars. Cluster stars, because they have the same initial abundance and are coeval are an ideal laboratory for exploring this connection.

RV measurements can also arise from rotational modulation by surface features as well as stellar oscillations. As apart of this program we will verify the presence of planetary companions by characterizing the effect of stellar activity (spots, plage) on the apparent radial velocity and line shapes. Ca II H and K measurements will establish periods for both rotation and stellar activity. These are important not only for ensuring that the planet RV signal is not due to rotation but also for getting estimates of the stellar inclination which is important for deriving the true mass of the companion (RV studies only yield m sin i). The high resolution spectra for the RV survey will also yield spectral line bisector information that will provide valuable information on surface granulation and possibly stellar pulsations.


Group #4: Young stellar objects and physics of star formation
Program 4a)

The Nature of Protostars

Investigate in detail the earliest phase of the star formation process, i.e., the physical properties of protostellar objects and their circumstellar environments.

High resolution spectroscopy (R=5000-100,000) will be used to (1) determine the effective temperatures, surface gravities, masses, luminosities, rotation rates, veilings, etc. of protostars from studies of their photospheres, (2) provide unique constraints on the physical, chemical, and dynamical properties of their surrounding accretion disks, associated winds and jets, and infalling envelopes.

High resolution spectroscopy in the near- to mid-IR takes advantage of the large aperture, IR optimization, and excellent angular resolution (smaller slits mean more compact instrument design) offered by the new generation of large telescopes.

Group #4: Young stellar objects and physics of star formation
Program 4b)

Determining the Initial Mass Function in Nearby Star Forming Regions

Goal: Determine the IMF in multiple star-forming regions to learn whether it is universal, and if not, it depends on initial or environmental conditions.

Approach: Establish the shape of the IMF in all molecular clouds (~10) within ~1 kpc with sensitivity sufficient to detect objects well below the hydrogen-burning limit. Requires a complete photometric and spectroscopic inventory of PMS star population in each cloud.

Group #5: Star formation and other activity in nearby galaxies
Program 5a)

With the advent of two major space infrared missions in the next 4 years, WIRE and SIRTF, it will be possible to directly study the cosmological evolution of starburst galaxies, and the corresponding evolution of the cosmic star formation rate based on infrared-selected samples of galaxies.

The WIRE mission will perform moderate and deep surveys at 12 and 25um over 100's and 10's of square degrees respectively to levels 500-1000 times deeper than the IRAS all sky survey. This will permit the detection via the infrared emission of starburst galaxies to redshifts in excess of 1 with the mean redshift of the WIRE deep survey targets expected to be ~.5.

The goal of this project is to perform a comprehensive optical and near-infrared follow-up survey to the WIRE mission, and address the following issues:

i) Determine the evolution of the starburst galaxy population over the redshift range 0.2 - 1. The WIRE sample will allow us to probe this evolution as a function of bolometric luminosity, and will constrain the role of galaxy interaction in triggering starbursts.

ii) Derive the star formation rate for the WIRE sources, and determine from that comparison the star formation rate in IR luminous starbursts for z< 0.2. Compare these rates with those determined from UV/Optical selected surveys spanning the same range in redshift.

iii) Clarify the nature of the AGN's detected in the sample. Determine the fraction of BAL AGN's selected from WIRE, compare with opt/UV selected samples.

The observational stategy to reach these goals will be to

i) perform optical/radio identifications of WIRE detected targets with positional accuracies adequate to perform followup redshift surveys with multiobject spectrographs

ii) perform a redshift survey of the identified targets

iii) Classify the identified targets as AGNs/starbursts

iv) explore the oddballs, find dusty protogalaxies in the WIRE sample for z up to 3.

Group #6: Stellar populations in nearby galaxies
Program 6a)

We propose a spectroscopic and imaging survey of halo populations in the Local Group. Specifically, we want to investigate the metallicity and velocity distributions of stars in the outer halos of M31, M33, NGC 205, NGC 147, and NGC 185. We also want to investigate the shapes of these stellar halos as a function of metallicity, and the shape of the dark halos as well.

The scientific aims are:

(1) to quantify the fraction of halo stars that may have been contributed by the disintegration of dwarf spheroidal galaxies, which may vary as a function of parent galaxy mass, Hubble Type, or environment; In particular, M31 has 3 dwarf spheroidal companions of its own (And I-III) which have lower metallicities than the surrounding halo field stars, and which also may have their own population substructures.

(2) To measure the abundance distribution function and compare that to chemical evolution models. Using new techniques that have been developed for abundance analysis of low S/N spectra, we aim to measure [alpha/Fe] for target, small subsamples of stars.

(3) To use the kinematics to investigate abundance/kinematics correlations, and to constrain measurements of the dynamical mass. On the major axes of M31 and M33, the potential gradient is given by the HI rotation curve. On the minor axis, these new data will give an estimate of the vertical potential gradient and hence of the shape of the dark halo.

(4) Radial velocities with a 10 km/sec precision could be used to discover ghost dwarf spheroidals (i.e. Sgr dwarf-like systems) in the course of this survey.

(5) Variable star populations are a useful diagnostic of characteristics such as age and metallicity, and are related to issues of importance in stellar populations e.g. the second parameter problem. We propose to use imaging on 4m telescopes to discover these stars.

Group #6: Stellar populations in nearby galaxies
Program 6b)

We seek to understand galaxy formation and evolution in the simplest systems that have had multiple generations of star formation: dwarf spheroidal galaxies (dSph). Examples of the fundamental questions that we plan to investigate are: What are the star formation, chemical enrichment, and kinematical histories of dSph galaxies? For example, what are the age-metallicity relations and kinematics-age relations for dwarf spheroidals. How are these different between different parts of the same dSph galaxy? How are these different between a dSph such as Carina, which has had episodic star formation, and Fornax, which has had more continuous star formation? These are the simplest systems with extended star formation and chemical enrichment histories, and thus provide a crucial test of galaxy formation models.

How do we address these questions? With the new generation of large telescopes, for the first time we can measure spectroscopic abundances and radial velocities for stars with unambiguous age information. Recent results have shown multiple generations of star formation in several dwarf spheroidals. We plan to survey the entire population of Milky Way dwarf spheroidal galaxies, and determine the star formation histories of each of these. Follow-up spectroscopy of selected populations will yield information on the evolution of abundance and kinematics with age.

Group #6: Stellar populations in nearby galaxies
Program 6c)

What did galactic disks look like 10 Gyrs ago? One solution is to measure ages, velocities, and chemistry for samples of stars across the disks of the Milky Way, M31, and M33. All three require study since their differing bulge/bar-to-disk rations may imply different histories. Further, they offer differing orientations of their disks and different levels of detail.

For the Milky Way, the goal is to identify relatively large numbers of old stars with measurable ages using Stromgren photometry (i.e., subgiants). The stars should also be selected over a large range of galactocentric distance, with most of them at about 3 disk scale heights from the plane to compensate the increasing incremental volumes by the declining star densities. Proper motions will provide two velocity components, to be supplemented by radial velocity measures of all the age-dated subgiants. Finally, detailed element-to-iron ratios will measure the nucleosynthesis history across the disk and will enable more direct comparisons with metal absorption lines in QSO damped Lyman-alpha systems.

For M31 and M33, average age measurements can be made via very deep HST imaging down to the turnoff in selected outer disk fields. Velocity-metallicity relations for single stars can be obtained for the older populations from 8m moderate-resolution (R=3000) spectroscopy.

Group #7: Galaxy formation and evolution
Program 7a)

The overall goal is to study the formation and growth of galaxies by following the evolution of their gas, stellar, and dark matter content from 1<z<3. This includes:

1) Determination of the luminosity function (LF) and galaxy-galaxy correlation function on < few Mpc scales down to present M*+2 as a function of environment, galaxy type, mass, and redshift.

2) Detailed evolution of stellar populations, morphology, star-formation rate, chemical abundance, and dust content.

To achieve these goals, the sample will be selected (for the usual reasons) in the near-infrared based on wide-field imaging surveys using 4m-class telescopes, and followed up with high resolution spatial imaging and spectroscopy with 8m-class telescopes using multi-object and integral field optical/near-IR spectrographs.

The survey will have the following structure:

1. An imaging survey on 4m-class telescopes covering 5x1 deg^2 for selection of 200,000 targets to K<21 (imaging to K<23 at 5 sigma and commensurate depth in UBRIJH). Fields will be chosen to correspond to deep fields surveyed at x-ray, mid-infrared, and radio wavelengths at high galactic latitude and low extinction.

2. Optical/NIR MOS on 8m-class telescopes of 1000 galaxies to calibrate photometric redshifts for subsequent target selection and for LF studies.

3. Selection of subsamples of roughly 1000 galaxies (each) for detailed spectroscopic follow-up to address the following issues:

a) H-alpha rotation curves for disk galaxies for internal velocity - luminosity relation study (NIR);

b) Stellar populations in red-envelope galaxies (OP/NIR);

c) QSO absorption line-selected samples to study abundances, dust and kinematics;

d) Radio, x-ray, and mid-infrared selected samples to correlate with dust, activity, star formation, etc.;

e) Variability selected targets (extended sources) to study the evolution of the faint end of the AGN LF and its relation to the global galaxy LF.

Group #8: Large scale structure/Cosmology
Program 8a)

We wish to study large-scale structure at high redshifts. The redshift range 1-5 is quite feasible to study with wide-field imaging surveys and spectroscopic follow-up on the 8-m class telescopes, while beyond remains quite speculative at this time. We are interested in the evolution of large-scale structure. On large scales, the evolution of clustering is strongly Omega-dependent; clustering evolves rapidly in a flat universe, while it is frozen in at a high redshifts in a low Omega universe. On small scales (100 kpc-10 Mpc), the study of LSS is intimately tied to the formation of galaxies, and galaxies in formation are likely to exhibit a strong bias. Hence, an imaging survey that defines samples for studying the evolution of structure beyond z = 1, must be defined broadly enough to explore the variation in clustering properties with galaxy type, luminosity, and environment.

For scales $>>10Mpc,$ the galaxy-galaxy correlation, itself, falls to low amplitudes, making less it effective as a diagnostic of power on large-scales. Constraining both the form and amplitude of the mass-spectrum on large scales is important, however; this can be provided by the {\it cluster-cluster} correlation function, the void-probability function, as well as topological measures such as the genus-number of the 3D distribution of galaxies in redshift and the two transverse spatial dimensions. The scale length of the cluster-cluster correlation function is $\sim20Mpc$ at $z=0,$ and voids, ``great walls,'' and so on, are observed to have $\sim100Mpc$ scales, thus observing the evolution of large scale structure at $z>1$ on the very largest scales important at this epoch requires that the parent image survey cover several contiguous square degrees. For example, $100Mpc$ subtends $\sim 1^\circ$ at $z=1-4$ (almost independent of z!) thus the imaging survey must cover this angular scale in one-dimension at least to provide a fair sample of the ancient universe. Furthermore, the geometry of the survey cannot be too anisotropic lest improper sampling of the structure in the short dimension alias measurement of structure sampled by the long dimension.

Galaxy clusters are of particular interest as tracers of large scale structure; however, the surface density of rich clusters is relatively low --- typically $\sim10$ abell-like clusters of richness 1 are seen per square degree for $0<z<1,$ with the richest clusters (such as Coma), at least an order of magnitude rarer still. Clusters at $z>>1$ have been seen in only a few special cases and can only be detected in general with deep IR-imaging --- again a large area is required.

We only have upper limits at present on the number density of $z > 5$ galaxies, from the photometric surveys that have been done (HDF, etc.). Yet, for the mission of NGST, a large-scale exploratory survey is of utmost importance.

The deep imaging survey proposed below can address a large number of other cosmological questions:

1. Surveys for $z \approx 2 $ supernovae, for determination of $\Omega$ and $\Lambda$ separately;

2. Gravitational lensing studies, both weak and strong;

3. QSO absorption line studies, the power spectrum of absorption from the IGM, and the correlation between the IGM and the galaxy distribution.

In order to meet these goals, we propose two photometric surveys with 4-meter class telescopes:

1. 10 square degree multicolor (UBVRIJHK) survey to 5\% precision at $K_AB = 23.5$ (comparable limits in the other bands);

2. 0.5 square degree multicolor survey to $K_AB = 25.0$.

We will do a complete spectroscopic survey of $z > 2$ galaxies selected from the first photometric survey, covering roughly 1 square degree, and containing 20,000 galaxies.

These surveys will provide:

-- photometric redshift estimates (\sigma_z = 0.07)

-- a measure of the luminosity functions for galaxies of different types at different redshifts

-- a basis for "galaxy-type" selection of samples

-- a sample of galaxy clusters for followup

-- samples of rare objects (QSOs, low luminosity AGNs, LENSING)

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Last updated: 30Jan1998
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