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The nature of isolated T Tauri stars
We present the results of a search for young stellar objects around thetwo isolated T Tauri stars (TTSs) TW Hya and CoD-29degr 8887. From thespectroscopic properties of these two objects, it is obvious that theyare T Tauri stars, although they are not associated with a star-formingregion as it is the case for most of the known TTSs. Especially TW Hyais the only classical TTS that is not located in a dark cloud with starformation activity. The same is true for the weak-line T Tauri starCoD-29degr 8887. We searched for pre-main sequence stars using ROSATPSPC observations pointing at our two main targets. With a sophisticatedsearch strategy we could identify 107 X-ray sources in our fields. Forthe 37 stellar-like optical counterparts we did spectroscopic follow-upobservations. These show that within the viewing field of ROSAT thereare no other X-ray emitting young stellar objects around TW Hya andCoD-29degr 8887. For the isolated TTSs TW Hya and HD 98800 Hipparcosparallax measurements are available locating them at distances of 56 and46pc, respectively. This means that they are the closest TTSs withcircumstellar dusty disks known today. The space velocities of these twoobjects are 3-5km/sec. From their position in the HR diagram, weobtained an age of about 10(7) years. Hence, we conclude that these twoobjects travelled not far away from their original birthplace and theirparental molecular cloud dispersed meanwhile. This is the solution whythese T Tauri stars appear to be isolated. Based on observationsobtained at the European Southern Observatory, La Silla, Chile
| Hyades and Sirius supercluster members brighter than magnitude (V) 7.1. II - Right ascension six to twelve hours
The present star sample is contained in the Bright Star Catalogue andits Supplement, augmented with a further supplement of 788 stars foundduring various observing programs over the past 40 years. Accurate,four-color and H-beta, or (RI), photometry is available for most of thesupercluster members. The criteria for membership are the comparisons ofthe proper motion, radial velocity, and luminosity obtained from thesupercluster parameters with the observed motions and the luminosityderived from the photometric parameters. New proper motions, based onall available catalogs, have been derived for the additional 788 starsdiscussed here, as well as all supercluster members.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נחש מים |
| התרוממות ימנית: | 11h09m58.74s |
| סירוב: | -29°47'39.0" |
| גודל גלוי: | 6.814 |
| מרחק: | 308.642 פארסק |
| תנועה נכונה: | -51 |
| תנועה נכונה: | -12 |
| B-T magnitude: | 8.558 |
| V-T magnitude: | 6.958 |
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