Inaccuracies in the spectral classification of stars from the Tycho-2 Spectral Type Catalogue
We compare the spectroscopic and trigonometric parallaxes of commonstars from the Tycho-2 Spectral Type and Hipparcos Catalogues. Thiscomparison has revealed that the distance estimations for theoverwhelming majority of stars by both methods yield very similarresults. However, there is a small fraction of stars for which thedistance estimates differ significantly. It is these stars that are thesubject of our study. We have been able to find the causes of thesedifferences.
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Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
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Searching for Faint Companions to Nearby Stars with the Hubble Space Telescope
A search for faint companions (FC's) to selected stars within 5 pc ofthe Sun using the Hubble Space Telescope's Planetary Camera (PC) hasbeen initiated. To assess the PC's ability to detect FC's, we haveconstructed both model and laboratory-simulated images and compared themto actual PC images. We find that the PC's point-spread function (PSF)is 3-4 times brighter over the angular range 2"-5" than the PSF expectedfor a perfect optical system. Azimuthal variations of the PC's PSF are10-20 times larger than expected for a perfect PSF. These variationssuggest that light is scattered nonuniformly from the surface of thedetector. Because the anomalies in the PC's PSF cannot be preciselysimulated, subtracting a reference PSF from the PC image is problematic.We have developed a computer algorithm that identifies local brightnessanomalies within the PSF as potential FC's. We find that this searchalgorithm will successfully locate FC's anywhere within thecircumstellar field provided that the average pixel signal from the FCis at least 10 sigma above the local background. This detection limitsuggests that a comprehensive search for extrasolar Jovian planets withthe PC is impractical. However, the PC is useful for detecting othertypes of substellar objects. With a stellar signal of 10^9 e-, forexample, we may readily detect brown dwarfs as faint as M_I = 16.7separated by 1" from alpha Cen A. (SECTION: AstronomicalInstrumentation)
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Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
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Old stellar populations. IV - Empirical functions for features in the spectra of G and K stars
Empirical fitting functions are derived for 11 atomic and molecularfeatures prominent in the spectra of G and K stars. The fitting behaviorclosely mimics that expected from the physics of stellar atmospheres,except for the index CN (4150 A), for which only minimal evidence isfound for traditional gravity effects but strong evidence forevolutionary mixing of CNO products to the stellar surface. This findingis important for modeling the integrated CN indices of external stellarpopulations.
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Determinations of the Parallaxes of Barnard's Star BD-70DEG68 and BD-4DEG4157
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An unsuccessful search for a planetary companion of Barnard's star (BD +4 3561).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973AJ.....78..769G&db_key=AST
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Absorption bands of titanium monoxide of alpha-system in stellar spectra of M class.
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