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The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| The unusual pre-main-sequence star VY Tauri
VY Tau is a pre-main-sequence star in the Taurus-Auriga clouds whichdiffers from conventional T Tauri stars in two respects: (1) its lightcurve, featuring sporadic outbursts from about B = 14 to 11-12interspersed with many years of inactivity; (2) its remarkable emissionspectrum, dominated by low-level lines of Fe I, Si I, Mg I with anexcitation temperature of about 2700 K. Higher excitation species suchas Fe II and the Balmer lines are relatively weak. An MO V absorptionspectrum is present when the star is inactive. Some very tentativemodels that might account for the unusual spectrum and photometricbehavior are offered. Since there is no significant infrared excess, aninterpretation in terms of an accretion or passive reprocessing disk isnot called for. The discussion is based on old spectroscopic material,largely collected prior to 1972, when the star was last active. There isneed for a modern reinvestigation at all wavelengths, particularly whenthe activity resumes.
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