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The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Variable HST guide stars (I)
We have performed time series analyses on more than 4500 sets of HubbleSpace Telescope (HST) Fine Guidance Sensor (FGS) data, obtained fromabout 3600 guide stars in the period from August 1992 to December 1995.We discuss here a subset of 20 stars that were found to be variable at ahigh confidence level. This subset contains all definite variables inour sample for which at least spectral type, B-V, or Strömgrencolors, respectively, are available. Our variability survey ischaracterized by comparably high photometric accuracy and high timeresolution. The time base of a data set for a given guide star can rangefrom half an hour to several days and even up to years in some cases.The elimination of scintillation noise in a space-borne experiment andthe usage of the identical instrument throughout the survey results invery homogeneous data with a typical photometric precision of about 500ppm, and with a best case of 50 ppm. Half of the cases discussed hereare probably delta Sct variables, and two are eclipsing binaries. Wehave also found four K-type stars with a photometric period of a fewhours, which is difficult to interpret as rotation. Currently, severalspace missions are in preparation, dedicated to high precisionphotometry with the goal of applying asteroseismic techniques to asignificant sample of stars. The HST-FGS data provide an excellenttesting ground for modelling the photometric characteristics of suchspace experiments and for gaining experience in handling the issuesrelated to the respective data and algorithms. Based on observationsmade with the NASA/ESA Hubble Space Telescope, obtained from the dataarchive at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555.
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