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The Chandra Variable Guide Star Catalog
Variable stars have been identified among the optical-wavelength lightcurves of guide stars used for pointing control of the Chandra X-rayObservatory. We present a catalog of these variable stars along withtheir light curves and ancillary data. Variability was detected to alower limit of 0.02 mag amplitude in the 4000-10000 Å range usingthe photometrically stable Aspect Camera on board the Chandraspacecraft. The Chandra Variable Guide Star Catalog (VGUIDE) contains827 stars, of which 586 are classified as definitely variable and 241are identified as possibly variable. Of the 586 definite variable stars,we believe 319 are new variable star identifications. Types of variablesin the catalog include eclipsing binaries, pulsating stars, and rotatingstars. The variability was detected during the course of normalverification of each Chandra pointing and results from analysis of over75,000 guide star light curves from the Chandra mission. The VGUIDEcatalog represents data from only about 9 years of the Chandra mission.Future releases of VGUIDE will include newly identified variable guidestars as the mission proceeds. An important advantage of the use ofspace data to identify and analyze variable stars is the relatively longobservations that are available. The Chandra orbit allows forobservations up to 2 days in length. Also, guide stars were often usedmultiple times for Chandra observations, so many of the stars in theVGUIDE catalog have multiple light curves available from various timesin the mission. The catalog is presented as both online data associatedwith this paper and as a public Web interface. Light curves with data atthe instrumental time resolution of about 2 s, overplotted with the databinned at 1 ks, can be viewed on the public Web interface and downloadedfor further analysis. VGUIDE is a unique project using data collectedduring the mission that would otherwise be ignored. The stars availablefor use as Chandra guide stars are generally 6-11 mag and are commonlyspectral types A and later. Due to the selection of guide stars entirelyfor positional convenience, this catalog avoids the possible bias ofsearching for variability in objects where it is to be expected.Statistics of variability compared to spectral type indicate theexpected dominance of A-F stars as pulsators. Eclipsing binaries areconsistently 20%-30% of the detected variables across all spectraltypes.
| A catalogue of chromospherically active binary stars (third edition)
The catalogue of chromospherically active binaries (CABs) has beenrevised and updated. With 203 new identifications, the number of CABstars is increased to 409. The catalogue is available in electronicformat where each system has a number of lines (suborders) with a uniqueorder number. The columns contain data of limited numbers of selectedcross references, comments to explain peculiarities and the position ofthe binarity in case it belongs to a multiple system, classicalidentifications (RS Canum Venaticorum, BY Draconis), brightness andcolours, photometric and spectroscopic data, a description of emissionfeatures (CaII H and K, Hα, ultraviolet, infrared),X-ray luminosity, radio flux, physical quantities and orbitalinformation, where each basic entry is referenced so users can go to theoriginal sources.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| New Elements for 80 Eclipsing Binaries
This research presents new elements for 80 eclipsing binaries found withthe help of the ASAS-3, Hipparcos and TASS databases.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| HIPPARCOS distances of X-ray selected stars: implications on their nature as stellar population.
We present the parallaxes, measured by Hipparcos, for a sample of X-rayselected stars. The stars belong to the stellar sample of the EinsteinExtended Medium Sensitivity Survey. They are all at galactic latitude|b|>20deg, and are generally far away from known star formingregions. Several of these stars show lithium abundance and activitylevel typical of very young stars with ages comparable to that of thePleiades. We show that the majority of our sample stars are on the mainsequence, with only =~20% being giants. We do not find a significantpresence of pre-main sequence stars in our sample, notwithstanding thefact that some of our stars have a considerable lithium abundance,showing that the stars observed are most likely young and activemain-sequence objects.
| Photometry and spectroscopy of serendipitous X-ray sources detected by the Einstein satellite.
Three serendipitous X-ray sources detected by the Einstein satellitewere photometrically and spectroscopically observed during the course ofa systematic study of known or suspected chromospherically active starscarried out at the European Southern Observatory (La Silla, Chile).Clear optical variability of the source 1E0315.7-1955 and 1E0505.0-0527was discovered and their photometric periods computed. The data obtainedfor a third serendipitous source, 1E1127.9-1502, are also discussed.Spectral types, distances and X-ray fluxes have been estimated for allof the sources.
| The Einstein Extended Medium-Sensitivity Survey Second Epoch: Results for the Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..701F&db_key=AST
| The space density of active binaries from X-ray surveys.
We review the currently available data on active binaries selected fromEinstein observatory based X-ray surveys, and compare the inferred spacedensity with the available estimates based on optically selectedsamples. It is shown that, in contrast to previous reports, nodisagreement is present between the optical and X-ray based estimates,and that the space density of active binaries is likely to be smallerthan previous estimates based on X-ray selected data. In particular, weshow that of the 18 systems in the δ>-20deg subsample of theEinstein Extended Medium Sensitivity Survey previously classified asactive binaries, 6 are not to be considered as such, while a further 5have a somewhat doubtful status. The total space density we derive is7.7x10^-5^pc^-3^ if the 5 doubtful systems are retained and3.7x10^-5^pc^-3^ if they are excluded. Both values are substantiallylower than the value of 4.5x10^-4^pc^-3^ originally derived from thesame subsample of Extended Medium Sensitivity Survey fields. Also, themedian X-ray luminosity of X-ray selected active binaries is found to behigher than previously reported, and again in contrast with previousreports, we find no disagreement between the X-ray luminosities of X-rayand optically selected samples. We briefly discuss the implication ofthe revised value of the space density on the contribution of activebinaries to the soft X-ray background.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| The ROSAT All-Sky Survey of active binary coronae. I - Quiescent fluxes for the RS Canum Venaticorum systems
One hundred and thirty-six RS CV(n) active binary systems were observedwith the ROSAT Position Sensitive Proportional Counter (PSPC) during theAll-Sky Survey component of the mission. The entire sky was surveyed,which represents the largest sample of RS CV(n) systems observed to dateat any wavelength, including X-rays. X-ray surface fluxes for the RSCV(n) systems are found to lie in the range 10 exp 4 to 10 exp 8 ergs/sqcm seconds. Surface flux as a function of (B - V) color is reported. Adecrease in surface flux with increasing rotation period for the entiresample is observed. The rotation period provides the best stellar ororbital parameter to predict the X-ray surface flux level. The absenceof correlation of F(x) or L(x) with Gamma is noted due to the fact thatthe coronal heating mechanism for these active stars must be magnetic incharacter, and the magnetic field depends on the interaction betweenconvection and differential rotation inside the star. X-ray propertiesof the RS CV(n) systems with 6 cm radio and C IV UV emission systems iscompared.
| The Einstein Observatory Extended Medium-Sensitivity Survey. II - The optical identifications
The optical identifications are presented of the Einstein ExtendedMedium-Sensitivity Survey (EMSS), including the methodology used tooptically identify the EMSS sources and the uncertainties involved withthat process. The optical properties of the classes of X-ray, optical,and radio data for each of the identified and, as yet, unidentifiedsources of the survey are described. A new class of X-ray emitters,cooling flow galaxies, is proposed. The criteria used to determinewhether the proposed optical counterpart to the X-ray source is aplausible identification are described. Plausibility is based on theoptical classification of the counterpart, e.g., AGN, cluster, G star,and the X-ray-to-optical flux ratios previously observed for theseclasses of X-ray emitters. Two independent schemes of opticalclassification of the counterparts are used to check the plausibility ofthese identifications; one is based on moderate-resolution opticalspectroscopy, and the other, on inferred X-ray luminosity and theoverall energy distribution.
| The Einstein Observatory Extended Medium-Sensitivity Survey. I - X-ray data and analysis
This paper presents the results of the analysis of the X-ray data andthe optical identification for the Einstein Observatory ExtendedMedium-Sensitivity Survey (EMSS). The survey consists of 835serendipitous sources detected at or above 4 times the rms level in 1435imaging proportional counter fields with centers located away from theGalactic plane. Their limiting sensitivities are about (5-300) x 10 tothe -14th ergs/sq cm sec in the 0.3-3.5-keV energy band. A total area of778 square deg of the high-Galactic-latitude sky has been covered. Thedata have been analyzed using the REV1 processing system, which takesinto account the nonuniformities of the detector. The resulting EMSScatalog of X-ray sources is a flux-limited and homogeneous sample ofastronomical objects that can be used for statistical studies.
| X-ray-selected candidates for the RS CVn and W UMa classes of binary stars
X-ray luminosity, spectral type, radial-velocity variation, rotationallybroadened line profile, and Ca II H and K line emission data are used toidentify 12 new candidates for the RS CVn class and seven new candidatesfor the W UMa class from spectroscopic binaries which are contained inthe Einstein Extended Medium Sensitivity Survey. Under the assumptionthat the candidates are genuine members of each class, local spacedensity estimates of 4.47 + or - 1.19 x 10 to the -4th/cu pc for RS CVnbinaries and 8.47 + or - 3.00 x 10 to the -5th/cu pc for W UMa binariesare found. Although the density estimate for the W UMa binaries is shownto be consistent with previous estimates obtained from opticallyselected samples, the estimate for the RS CVn binaries is more than anorder of magnitude greater than previously determined space densities.
| The relation between X-ray emission and rotation in late-type stars from the perspective of X-ray selection
An X-ray-selected sample of 128 late-type (F-M) stars analyzed. Thesestars were identified as optical counterparts to serendipitous X-raydetections made by the Einstein Observatory Extended Medium SensitivitySurvey. Once identified as X-ray sources, the sample was followed up byan extensive program of optical observations, including high-resolutionand low-resolution spectroscopy and photometry. Spectral types,luminosity classes, distances, X-ray luminosities, projected rotationrates (v sin i), radial velocities, and binary status have beendetermined for the sample.
| IUE observations of X-ray-selected stars
UV spectra for four X-ray-selected bright (V less than 10) late-type (Fand G) stars have been obtained in both the long- and short-wavelengthcameras of the IUE satellite. The stars were selected because they hadthe largest ratios of X-ray to optical luminosity for their spectraltype, with known binaries being eliminated from the sample in order todetermine if other mechanisms for extreme X-ray emission are present.Three of the four stars in the sample have since been observed to bebinaries with radial-velocity variations consistent with periods of afew days. The fourth star, HD 142361 is a pre-main-sequence star basedon the detection of Li I at a wavelength of 6707 A in absorption.
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