---
abstract: 'The preliminary results of a three-site CCD photometric campaign are reported. The $\delta$ Scuti variable V650 Tauri belonging to the Pleiades cluster was observed photometrically for 14 days on three continents during 2008 November. An overall run of 164 hr of data was collected. At least five significant frequencies for V650 Tauri have been detected.'
author:
- 'L. Fox Machado'
- 'R. Michel'
- 'M. Alvarez'
- 'C. Zurita'
- 'J.N. Fu'
title: CCD Photometry of the Pleiades Delta Scuti Star V650 Tauri
---

[ address=[Observatorio Astronómico Nacional, Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 877, Ensenada, BC 22860, Mexico]{} ]{}

[ address=[Observatorio Astronómico Nacional, Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 877, Ensenada, BC 22860, Mexico]{} ]{}

[ address=[Observatorio Astronómico Nacional, Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 877, Ensenada, BC 22860, Mexico]{} ]{}

[ address=[Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, E-38205, La Laguna, Tenerife, Spain]{} ]{}

[ address=[Department of Astronomy, Beijing Normal University, Beijing 100875, China]{} ]{}

Introduction
============

$\delta$ Scuti variables are stars with masses between 1.5 and 2.5 $M_{\odot}$ located at the intersection of the classical Cepheid instability strip with the main sequence. These variables are thought to be excellent laboratories for probing the internal structure of intermediate mass stars. Intents of modelling $\delta$ Scuti stars belonging to open clusters have been performed recently (e.g. \[1\], \[2\], \[3\]). Although the constraints imposed by the cluster parameters have proved to be very useful when modelling an ensemble of $\delta$ Scuti stars, more detected frequencies in individual stars would improve current seismic studies.

The target star V650 Tau (HD 23643, $V=7^{\rm m}.79$, A7) was identified as a short-period pulsating variable by Breger (1972). Intensive observations performed by the STEPHI network in November 1990, revealed four frequency peaks in V650 Tau \[4\]. One-site CCD photometric observations carried out by \[5\] in November-December 1993, confirmed the results obtained by the STEPHI campaign. Since then, no new observations of V650 Tauri have been performed.

The present paper provides preliminary observational results of a three-site campaign on V650 Tauri in 2008.

Observations and data reduction
===============================

Three observatories were involved in the observational campaign. They are listed in Table \[tab:tel\] together with the telescopes and instruments used. Table \[tab:log\] gives the log of observations. A total amount of 164 hours of useful data were obtained from the three sites.

The observations were obtained through a Johnson $V$ filter except at the SPM observatory where a Strömgren $y$ filter was used. Table \[tab:stars\] shows the main observational parameters corresponding to the target and comparison stars as taken from the SIMBAD database operated by CDS (Centre de Données astronomique de Strasbourg). Two comparison stars have been used during the observations depending on the constraints set by the field of view of the CCD’s and sizes of the telescopes. The first one, HD 23605 ($V=6^{\rm m}.99$, F5), is a suitable comparison star considering its brightness and spectral type. However, this star could not be observed neither at Teide nor at San Pedro Martir observatory because it is so bright that at these telescopes the CCD detectors saturated in a few seconds of exposure time. Rather at these sites we observed the comparison star, HD 23653 ($V=7^{\rm m}.71$, K0), since its magnitude is similar to that of the target star. Figure \[fig:field\] shows a typical image of the CCD’s field of view ($20' \times 20'$) at the 0.50m telescope of the Xing Long observatory.

Sky flats, dark and bias exposures were taken every night at all sites. All data were calibrated and reduced using standard IRAF routines. Aperture photometry was implemented to extract the instrumental magnitudes of the stars. The differential magnitudes were normalized by subtracting the mean of differential magnitudes for each night. In Figure \[fig:curves\] the entire light curves V650 Tau - Comp 2 are presented.

  Observatory                                    Telescope    Instrument      Observers
  --------------------------------------------- ----------- --------------- -------------
  Observatorio del Teide (OT, Spain)               0.80m     2048x2048 CCD       CZ
  Observatorio San Pedro Mártir (SPM, Mexico)      0.84m     1024x1024 CCD   LFM, RM, MA
  Xing Long Station (XL, China)                    0.50m     1024x1024 CCD       JNF

  : List of instruments and telescopes involved in the campaign. Observer’s abbreviations correspond to initial of the co-authors.[]{data-label="tab:tel"}

  -------- ----------- ---------- ------- ------- -------
    Day     Date 2008     HJD     SPM     XL      OT
                        2454774+                  
     01      Nov 11        07     0.70            5.70
     02      Nov 12        08     3.58            8.80
     03      Nov 13        09     4.76            -
     04      Nov 14        10     9.68            1.08
     05      Nov 15        11     9.42            -
     06      Nov 16        12     9.79    -       8.17
     07      Nov 17        13     7.64    -       -
     08      Nov 18        14     10.15   10.28   -
     09      Nov 19        15     10.26   10.19   -
     10      Nov 20        16     10.33   10.59   -
     11      Nov 21        17     7.22    10.36   -
     12      Nov 22        18     -       10.66   -
     13      Nov 23        19     -       -       -
     14      Nov 24        20     -       4.98    -
   Total    observing     time    SPM     XL      OT
   Nov 11    Nov 24      164.34   83.52   57.06   23.75
  -------- ----------- ---------- ------- ------- -------

  : Log of observations. Observing time is expressed in hours.

\[tab:log\]

![Image of the CCD field-of-view ($20' \times 20'$) of the Xing Long Observatory. The positions of the target and comparison stars are indicated in the figure. North is up and East is left.[]{data-label="fig:field"}](fox2_fig1.eps){width="7cm"}

  -------------- ------- ---- ------ --------- --------- -------------------------- ---------
  Star             HD     ST   $V$     $B-V$     $U-B$           $v \sin i$          $\beta$
                                                          $(\mathrm{km\, s}^{-1})$  
  V650 Tau        23643   A7   7.79   $+$0.25   $+$0.14             219               2.823
  Comparison 1    23605   F5   6.99   $+$0.50   $+$0.09              -                2.653
  Comparison 2    23653   K0   7.71   $+$1.27   $+$1.12              -                  -
  -------------- ------- ---- ------ --------- --------- -------------------------- ---------

  : Observational properties of the stars observed in the campaign.

\[tab:stars\]

Spectral analysis
=================

The period analysis has been performed by means of standard Fourier analysis and least-squares fitting. In particular, the amplitude spectra of the differential time series were obtained by means of Period04 package \[6\], which considers Fourier as well as multiple least-squares algorithms. This computer package allows to fit all the frequencies simultaneously in the magnitude domain.

The amplitude spectrum of the differential light curve V650 Tauri - Comparison 2 (see Fig \[fig:curves\]) is shown in Figure \[fig:spec\]. As can be seen, V650 Tauri presents high-amplitude peaks distributed between 17 c/d and 35 c/d.

The frequencies have been extracted by means of standard prewhitening method. In order to decide which of the detected peaks in the amplitude spectrum can be regarded as intrinsic to the star we follow Breger’s criterion given by \[7\], where it was shown that the signal-to-noise ratio (in amplitude) should be at least 4 in order to ensure that the extracted frequency is significant.

The frequencies, amplitudes and phases are listed in Table \[tab:frec\]. Five significant frequencies have been detected in V650 Tauri. Among these only the first two frequencies (35.66 c/d and 17.04 c/d) are similar to that found by Kim & Lee (1996). A detailed analysis of these observations will be given in a forthcoming paper \[8\].

![Differential light curve V650 Tau $-$ Comparison 2.[]{data-label="fig:curves"}](fox2_fig2.ps){width="7.3cm"}

  --------- -------- -------------------- -------
    Freq.      A      $\varphi$/($2\pi$)   $S/N$
    (c/d)    (mmag)                       
   32.6565    4.43           0.39          13.4
   17.0356    2.65           0.09          10.0
   35.5970    2.49           0.25           8.6
   31.6285    1.91           0.85           6.4
   34.6409    1.41           0.04           4.5
  --------- -------- -------------------- -------

  : Frequency peaks detected in the light curve V650 Tauri - Comparison 2. S/N is the signal-to-noise ratio in amplitude after the prewhitening process.[]{data-label="tab:frec"}

![Amplitude spectrum derived from the light curve V650 Tau - Comparison 2. The amplitude is in mag and the frequencies in c/d.[]{data-label="fig:spec"}](fox2_fig3.eps){width="7.7cm"}

This work has received financial support from the UNAM under grants PAPIIT IN108106 and IN114309. Special thanks are given to the technical staff and night assistants of the San Pedro Mártir, Teide and Xing Long Observatories. This research has made use of the SIMBAD database operated at CDS, Strasbourg (France).

[9]{}

L. Fox Machado, et al., 2006, A&A, 446, 611. M.M. Hernández, et al., 1998, A&A, 338, 511. E. Michel, et al., 1999, A&A, 342, 253. J.A. Belmonte, et al., in: Weiss W.W., Baglin, A. (eds.) IAU Coll. 137, Inside the stars, p. 347 S.-L. Kim, S.-W. Lee, A&A, 310, 831 P. Lenz, M. Breger, 2005, CoAst, 146, 53 M. Breger, et al., 1993, A&A, 271, 482. L. Fox Machado, 2009, et al., AJ, submitted.
