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New absolute magnitude calibrations for W Ursa Majoris type binaries
Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed.31 W UMa stars, which have the most accurate parallaxes(σπ/π<0.15) which are neither associated with aphotometric tertiary nor with evidence of a visual companion, wereselected for re-calibrating the Period-Luminosity-Color (PLC) relationof W UMa stars. Using the Lutz-Kelker (LK) bias corrected (mostprobable) parallaxes, periods ({0.26< P< 0.87}, P in days), andcolors ({0.04<(B-V)0<1.28}) of the 31 selected W UMa,the PLC relation have been revised and re-calibrated. The differencebetween the old (revised but not bias corrected) and the new (LK biascorrected) relations are almost negligible in predicting the distancesof W UMa stars up to about 100 pc. But, it increases and may becomeintolerable as distances of stars increase. Additionally, using(J-H)0 and (H-K_s)0 colors from 2MASS (Two MicronAll Sky Survey) data, a PLC relation working with infrared data wasderived. It can be used with infrared colors in the range-0.01<(J-H)0<0.58, and{-0.10<(H-K_s)0<0.18}. Despite of the fact that the2MASS data refer to single epoch observations which are not guaranteedto be taken at maximum brightness of the W UMa stars, the establishedrelation has been found surprisingly consistent and reliable inpredicting LK corrected distances of W UMa stars.
| Search for associations containing young stars (SACY). I. Sample and searching method
We report results from a high-resolution optical spectroscopic surveyaimed to search for nearby young associations and young stars amongoptical counterparts of ROSAT All-Sky Survey X-ray sources in theSouthern Hemisphere. We selected 1953 late-type (B-V~≥~0.6),potentially young, optical counterparts out of a total of 9574 1RXSsources for follow-up observations. At least one high-resolutionspectrum was obtained for each of 1511 targets. This paper is the firstin a series presenting the results of the SACY survey. Here we describeour sample and our observations. We describe a convergence method in the(UVW) velocity space to find associations. As an example, we discuss thevalidity of this method in the framework of the β Pic Association.
| Contact Binaries with Additional Components. I. The Extant Data
We have attempted to establish observational evidence for the presenceof distant companions that may have acquired and/or absorbed angularmomentum during the evolution of multiple systems, thus facilitating orenabling the formation of contact binaries. In this preliminaryinvestigation we use several techniques (some of themdistance-independent) and mostly disregard the detection biases ofindividual techniques in an attempt to establish a lower limit to thefrequency of triple systems. While the whole sample of 151 contactbinary stars brighter than Vmax=10 mag gives a firm lowerlimit of 42%+/-5%, the corresponding number for the much better observednorthern-sky subsample is 59%+/-8%. These estimates indicate that mostcontact binary stars exist in multiple systems.
| 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.
| Key parameters of W UMa-type contact binaries discovered by HIPPARCOS
A sample of W UMa-type binaries which were discovered by the HIPPARCOSsatellite was constructed with the aid of well defined selectioncriteria described in this work. The selection process showed up thatseveral systems of which the variability types have been assigned as EBin HIPPARCOS catalogue are genuine contact binaries of W UMa-type. Thelight curves of the 64 selected systems based on HIPPARCOS photometrywere analyzed with the aid of light curve synthesis method by Rucinskiand their geometric elements (namely mass ratio q, degree of contact f,and orbital inclination i) were determined. The solutions were obtainedfor the first time for many of the systems in the sample and would be agood source for their future light curve analyses based on more precisefollow-up observations.Based on observations made with the ESA HIPPARCOSastrometry satellite.
| A systematic study of X-ray variability in the ROSAT all-sky survey
We present a systematic search for variability among the ROSAT All-SkySurvey (RASS) X-ray sources. We generated lightcurves for about 30 000X-ray point sources detected sufficiently high above background. For ourvariability study different search algorithms were developed in order torecognize flares, periods and trends, respectively. The variable X-raysources were optically identified with counterparts in the SIMBAD, theUSNO-A2.0 and NED data bases, but a significant part of the X-raysources remains without cataloged optical counterparts. Out of the 1207sources classified as variable 767 (63.5%) were identified with stars,118 (9.8%) are of extragalactic origin, 10 (0.8%) are identified withother sources and 312 (25.8%) could not uniquely be identified withentries in optical catalogs. We give a statistical analysis of thevariable X-ray population and present some outstanding examples of X-rayvariability detected in the ROSAT all-sky survey. Most prominent amongthese sources are white dwarfs, apparently single, yet neverthelessshowing periodic variability. Many flares from hitherto unrecognisedflare stars have been detected as well as long term variability in theBL Lac 1E1757.7+7034.The complete version of Table 7 is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/247
| Catalogue of the field contact binary stars
A catalogue of 361 galactic contact binaries is presented. Listedcontact binaries are divided into five groups according to the type andquality of the available observations and parameters. For all systemsthe ephemeris for the primary minimum, minimum and maximum visualbrightness and equatorial coordinates are given. If available,photometric elements, (m1+m2)sin3i,spectral type, parallax and magnitude of the O'Connell effect are alsogiven. Photometric data for several systems are augmented by newobservations. The quality of the available data is assessed and systemsrequiring modern light-curve solutions are selected. Selectedstatistical properties of the collected data are discussed.
| Star Modeling with a Laptop
The author has written a Windows program that writes and reads files tointerface with the Wilson-Devinney (star modeling) program. Somesolutions to systems recently studied at the Mt. John Observatory in NewZealand (WY Hor, TU Mus) will be presented
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| True and Possible Contact Binaries in the Hipparcos Catalogue
A comprehensive list of contact binaries included in the HIPPARCOScatalogue is given.
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