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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
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Lithium in Rs-Canum Binaries and Related Chromospherically Active Stars - Part Two - Spectrum Synthesis Analysis
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...273..194R&db_key=AST
| Lithium in RS CVn binaries and related chromospherically active stars. I - Observational results
The present survey of the Li I 6708 A line in a sample of spectral typeG and K stars with luminosity classes III, IV, and V shows that manyK-type stars in the sample, including a large number of RS CVn binaries,show an anomalously high Li abundance relative to typical inactive starsof the same spectral type. Only a few stars in the sample are likely tobe premain sequence objects of stars which have recently arrived on themain sequence. Mechanisms that could lead to the enhanced Li absorptionin chromospherically active stars are discussed; these encompass largecool spots on the stellar surface, the production of Li in stellarflares by spallation reactions, and the evolution from main-sequenceprogenitors without, or with very shallow, outer convective zones.
| A microwave survey of southern active stars
The results of a survey of 153 active-chromosphere stars made with theParkes 64-m telescope at 5.0/8.4 GHz from 1981 to 1987 are reported.Microwave emission was detected from 70 stars on at least one occasion,with the highest detection rate of 68 percent from the RS CVn group. TheCa II stars and Algol-type binaries yielded detection rates of 44 and 30percent, respectively. The maximum powers emitted by the stars at5.0/8.4 GHz ranged over five orders of magnitude, with a median of 2.5 x10 to the 10th W/Hz. The maximum brightness temperatures had a smallerrange of three orders of magnitude, with a median of 3.6 x 10 to the 9thK.
| Observations of active stars at 843 MHz
The Molonglo Observatory Synthesis Telescope is being used in ancontinuing program of observation of known Southern active stars. By May1987, a total of 41 stars had been observed, and 843-MHz quiescentemission, presumably associated with the star, had been detected in nineinstances. The emission from five of these stars has shown markedvariation on a time scale over 1 day.
| Near infrared photometry of some RS CVn systems and candidates
Infrared observations in the J, H, and K bands were made on eleven RSCVn systems. IR excess greater than about 0.3 mag in the J, H, and Kbands was observed from the three systems UX Ari, HR 1099 and sigma CrB.Similar observations were also made on the RS CVn candidates HD 26354,39937, 42449, 51268, and 86005. The IR excess in the RS CVn systems forwhich near-infrared photometric data are available is found to becorrelated with the maximum optical wave amplitude of these systems. Theobserved excess cannot be explained on the basis of a single processsuch as emission from cool spots on the photosphere; free-free emissionfrom an optically thin circumstellar plasma; or dust-grain emission fromcircumstellar material.
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