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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.
| Coronal X-ray sources in the Hyades: A 40 kilosecond ROSAT pointing
We present results of a 40 ks ROSAT pointed observation of the Hyadescluster. The limiting Lx is approximately = 2 x1027 ergs/sec at field center, increasing to approximately =2 x 1028 ergs/sec at 40 min off-axis. This represents themost sensitive X-ray observation to date in the Hyades region. More than30 sources have been detected in the Position Sensitive ProportionalCounter (PSPC) standard processing, of which 15 are Hyades members, fiveare cluster candidates that are likely non-members, four are foregroundor background stars, and the remainder are unidentified. One Hyad, VB173 (= VA 276), lies in a confused region, but is detected as a distinctsource in the soft band only (E approximately less than 0.5 keV). Wereport upper limits for four other Hyades members in our field, all Mdwarfs. Of the 16 Hyades detections, two represent the opticallyfaintest members seen to date in X-rays; VA 260 (V = 16.68) and VA 368(V = 16.25). These are both M dwarfs of mass approximately = 0.15-0.2solar mass and are fully convective stars according to current theory.Analysis of X-ray light curves using 1 ks bins indicates somevariability in the strongest sources and a possible flare in VA 383. TwoHyades stars, VB 141 and VB 71, were also detected with the co-alignedWide Field Camera (WFC) EUV instrument. VB 141, the second brightestX-ray source in the Hyades, remains an enigma: a rapidly rotating FOstar with a fainter, long-period companion, this object has an X-rayspectrum indicative of strong coronal activity. X-ray pulse-heightanalysis demonstrates that coronal models with at least two temperaturesare required for most of the stronger X-ray sources. The ROSAT X-rayspectra generally require higher temperatures for the hotter componentin the M dwarfs compared to the F-G dwarfs.
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