CDROM/AJ/V110/P2166 Variables in Sextans (Mateo+ 1995) ================================================================================ Variable Stars in the Sextans Dwarf Spheroidal Galaxy Mario Mateo, Philippe Fischer, & Wojtek Krzeminski <1995, AJ, 110, 2166> =1995AJ....110.2166M ================================================================================ Abstract: We describe a survey for variable stars in the Sextans dwarf spheroidal (dSph) galaxy based on the analysis of 113 B and 48 V CCD images of four fields covering a total area of 18'x18'. We have identified 44 variables: 36 RR Lyr star, 6 anomalous Cepheids, one long-period red variable, all probable members of Sextans, and one foreground contact binary. We have used the pulsating stars to derive a true distance modulus of 19.67 +/- 0.15 for Sextans (or D = 86 +/- 6 kpc), where the error is primarily due to uncertainties in the luminosity-metallicity relation for RR Lyr stars. Based on our new data we conclude that [Fe/H]_Sex = -1.6 +/- 0.2, somewhat higher than the value from Suntzeff et al. [ApJ, 418, 208 (1993)] obtained from the analysis of fiber spectroscopy of the near-IR Calcium triplet. We present a new deep color-magnitude diagram for Sextans which reveals the presence of anomalous Cepheids in the galaxy. This young population may represent as much as 25% of the total stellar content of Sextans. We find a surprisingly strong correlation between the frequency of anomalous Cepheids in dSph galaxies and galaxian luminosity and speculate on the possible origin of this strange effect. The RR Lyr stars in Sextans do not exhibit the Oosterhoff dichotomy observed in globular clusters and in the Galactic halo field. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table2.dat 63 161 Log of Sextans observations table8.dat 36 1038 B-band photometry of the Sextans variables table9.dat 36 560 V-band photometry of the Sextans variables table10.dat 72 2852 Photometry of non-variable stars in the deep Sextans images -------------------------------------------------------------------------------- Byte-by-byte Description of files: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- Frame Frame number 4- 5 2X --- --- Blank 6-15 A10 --- Date UT Date of observation 16-25 A10 --- UT_mid Time of mid-exposure, hh mm ss 26-32 F7.1 s Exp Exposure time 33-39 F7.3 --- X Air-mass at mid-exposure 40-51 D12.6 --- HJD_mid HJD of mid exposure, epoch 2448000 52-56 F5.1 arcsec Seeing Seeing 57-58 2X --- --- Blank 59-60 A2 --- Field Field, NE, NW, SE, SW 61-62 2X --- --- Blank 63 A1 --- Filt Filter, V or B -------------------------------------------------------------------------------- Byte-by-byte Description of file: table8.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 A3 --- Star Variable star number, V1, V2, ... V46 4-16 D13.6 --- HJD Heliocentric Julian Date of observation 17-24 F8.3 mag B B magnitude 25-30 F6.3 mag e_B B magnitude error 31-36 F6.3 --- Phase *[]? Pulsation or orbital phase -------------------------------------------------------------------------------- Notes for file: table8.dat -------------------------------------------------------------------------------- Phase: Pulsation or orbital phase calculated with the ephemerides in Table 4 of the printed paper. The phasing is defined so that phase zero corresponds to minimum light. No phase information is given for V16, V23, V35, or V46 because reliable periods could not be determined for these stars. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table9.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 A3 --- Star Variable star number, V1, V2, ... V46 4-16 D13.6 --- HJD Heliocentric Julian Date of observation 17-24 F8.3 mag V V magnitude 25-30 F6.3 mag e_V V magnitude error 31-36 F6.3 --- Phase *[]? Pulsation or orbital phase -------------------------------------------------------------------------------- Notes for file: table9.dat -------------------------------------------------------------------------------- Phase: Pulsation or orbital phase calculated with the ephemerides in Table 4 of the printed paper. The phasing is defined so that phase zero corresponds to minimum light. No phase information is given for V16, V23, V35, or V46 because reliable periods could not be determined for these stars. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table10.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4 --- Star Star number 5- 9 I5 pix X X coordinate 10-14 I5 pix Y Y coordinate 15-16 2X --- --- Blank 17-18 A2 --- Field Field, NE, NW, SE, SW 19-20 2X --- --- Blank 21-22 I2 h RAh Right ascension 2000 23 1X --- --- Always ":" 24-25 I2 min RAm R.A. 26 1X --- --- Always ":" 27-31 F5.2 s RAs R.A. 32 1X --- --- Blank 33 A1 --- DE- Declination sign 34 I1 deg DEd Declination, 2000 (always "1") 35 1X --- --- Always ":" 36-37 I2 arcmin DEm Dec. 38 1X --- --- Always ":" 39-43 F5.2 arcsec DEs Dec. 44-51 F8.3 mag V V magnitude 52-58 F7.3 mag e_V V magnitude error 59-65 F7.3 mag B-V B-V color 66-72 F7.3 mag e_B-V B-V color error -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 03-Nov-1995