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CHANVGUIDE - Chandra Variable Guide Star Catalog

HEASARC
Archive

Overview

Variable stars have been identified among the optical-wavelength light curves of guide stars used for pointing control of the Chandra X-ray Observatory. The authors present a catalog of these variable stars along with their light curves and ancillary data. Variability was detected to a lower limit of 0.02 mag amplitude in the 4000-10000 Angstroms range using the photometrically stable Aspect Camera on board the Chandra spacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains 827 stars, of which 586 are classified as definitely variable and 241 are identified as possibly variable. Of the 586 definite variable stars, the authors believe 319 are new variable star identifications. Types of variables in the catalog include eclipsing binaries, pulsating stars, and rotating stars. The variability was detected during the course of normal verification of each Chandra pointing and results from analysis of over 75,000 guide star light curves from the Chandra mission. The VGUIDE catalog represents data from only about 9 years of the Chandra mission. Future releases of VGUIDE will include newly identified variable guide stars as the mission proceeds. An important advantage of the use of space data to identify and analyze variable stars is the relatively long observations that are available. The Chandra orbit allows for observations up to 2 days in length. Also, guide stars were often used multiple times for Chandra observations, so many of the stars in the VGUIDE catalog have multiple light curves available from various times in the mission. The catalog is presented as both online data associated with this paper (from which this HEASARC representation was created) and as a public Web interface at http://cxc.harvard.edu/vguide/. Light curves with data at the instrumental time resolution of about 2 s, overplotted with the data binned at 1 ks, can be viewed on the above-mentioned public Web interface and downloaded for further analysis. (This HEASARC Browse table also contains links to these light curves). VGUIDE is a unique project using data collected during the mission that would otherwise be ignored. The stars available for use as Chandra guide stars are generally 6-11 magnitudes and are commonly spectral types A and later. Due to the selection of guide stars entirely for positional convenience, this catalog avoids the possible bias of searching for variability in objects where it is to be expected. Statistics of variability compared to spectral type indicate the expected dominance of A-F stars as pulsators. Eclipsing binaries are consistently 20%-30% of the detected var iables across all spectral types.

Catalog Bibcode

2010ApJS..188..473N

References

The Chandra Variable Star Catalog
    Nichols J.S., Henden A.A., Huenemoerder D.P., Lauer J.L., Martin, E.,
    Morgan D.L., Sundheim B.A.
   <Astrophys. J. Suppl. 188, 473 (2010)>
   =2010ApJS..188..473N

Provenance

This table was created by the HEASARC in July 2010 based on the electronic version of Table 4 from the paper which was obtained from the Astrophysical Journal web site.

Parameters

AGASCID
The AXAF (Chandra) Guide Star Catalog (AGASC) identification number for the star.

Name
The SIMBAD designation of the star, e.g., HD 21968, V* V429 Car, BD +12 2480, etc. Note that this field can contain a leading descriptor 'V*' or 'SV*' for variable star or suspected variable star, respectively, in front of the actual star name. In one case, we have removed the '**' descriptor (for double star) from the star with the original name '** COU 2386', thus rendering it as 'COU 2386' in this HEASARC representation.

RA
The Right Ascension of the star in the selected equinox based on the AGASC position. This was given in J2000.0 equatorial coordinates to a precision of 0.01 seconds of time in the original table.

Dec
The Declination of the star in the selected equinox based on the AGASC position. This was given in J2000.0 equatorial coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the star.

BII
The Galactic Latitude of the star.

SIMBAD_Class
The SIMBAD 'long type' of the star, being a self-explanatory text description of the stellar type, such as 'Star', 'Variable Star', 'High Proper-Motion Star', 'Spectroscopic Binary', etc.

Spect_Type
The spectral type of the star as listed in SIMBAD.

SIMBAD_Short_Type
The SIMBAD object type of the star. The definitions of these codes are available at http://simbad.u-strasbg.fr/simbad/sim-display?data=otypes. The HEASARC has made one change: solo values of '*' have been rendered as 'Star' in this representation, to avoid possible confusion with the use of the asterisk parameter as a wild card in Browse searches.

Var_Category
The general variability category of the star as listed in the Variable Star Index (VSX: Watson 2006, J. Am. Assoc. Var. Star Obs., 35, 318) and/or other sources, e.g., 'Eclipsing', 'Pulsating', 'Indeterminate', etc.

Var_Type
The GCVS variability classification of the star as listed in the Variable Star Index (VSX: Watson 2006, J. Am. Assoc. Var. Star Obs., 35, 318) and/or other sources. The full list of GCVS types is described at ftp://cdsarc.u-strasbg.fr/pub/cats/B/gcvs/vartype.txt. The HEASARC has made one change: solo values of '*' have been rendered as 'Star' in this representation, to avoid possible confusion with the use of the asterisk parameter as a wild card in Browse searches.

Var_Epoch
The epoch of maximum or minimum variability of the star, in Heliocentric Julian Date (HJD), as taken by the authors from the Variable Star Index (VSX: Watson 2006) table. This is available at CDS: ftp://cdsarc.u-strasbg.fr/pub/cats/B/vsx/. The HEASARC has corrected the epochs for two entries, RS Sgr, and GP Cep, where the values in the original VGUIDE tables where clearly incorrect (29.000 and 15.000, respectively), using the above-cited VSX table.

Var_Period
The period of variability of the star, in days, as taken by the authors from the Variable Star Index (VSX: Watson 2006) table. This is available at CDS: ftp://cdsarc.u-strasbg.fr/pub/cats/B/vsx/.

UV_Flag
This flag parameter is set to 'Y' or 'N', depending on whether or not the star is a known ultraviolet source according to SIMBAD..

Xray_Flag
This flag parameter is set to 'Y' or 'N', depending on whether or not the star is a known X-ray source according to SIMBAD.

IR_Flag
This flag parameter is set to 'Y' or 'N', depending on whether or not the star is a known infrared source according to SIMBAD.

Num_Chandra_Obs
The number of Chandra observations of the star.

Exposure
The total Chandra observational exposure time on this star, in seconds (converted by the HEASARC from the kiloseconds units used in the original table).

Known_Var_Flag
This flag parameter is set to 'Y' or 'N', depending on whether or not the star was a previously known variable star according to VSX.

Var_Status
THE VGUIDE status of the star as a variable star, being 'ACCEPTED' for confirmed variables, and 'SUSPECT' for suspected variables.

Class
The HEASARC Browse object classification, based on the spectral type (spect_type parameter value) of the star.


Contact Person

Questions regarding the CHANVGUIDE database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 26-Jul-2010