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Astron. Astrophys. 326, 221-227

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Hipparcos distances of X-ray selected stars: implications
on their nature as stellar population*

G. Micela1, F. Favata2, and S. Sciortino1

1Istituto e Osservatorio Astronomico di Palermo, Palazzo dei Normanni, I-90134 Palermo, Italy
(gmicela@oapa.astropa.unipa.it, ssciortino@oapa.astropa.unipa.it)
2Astrophysics Division, European Space Agency - Postbus 299, 2200 AG Noordwijk, The Netherlands

Received 14 January 1997 / Accepted 1 April 1997


We present the parallaxes, measured by Hipparcos, for a sample of X-ray selected stars. The stars belong to the stellar sample of the Einstein Extended Medium Sensitivity Survey. They are all at galactic latitude |b| > 20 deg, and are generally far away from known star forming regions. Several of these stars show lithium abundance and activity level typical of very young stars with ages comparable to that of the Pleiades. We show that the majority of our sample stars are on the main sequence, with only FORMULA % being giants. We do not find a significant presence of pre-main sequence stars in our sample, notwithstanding the fact that some of our stars have a considerable lithium abundance, showing that the stars observed are most likely young and active main-sequence objects.

Key words: astrometry - stars: activity - stars: late-type

*Based on data from the ESA Hipparcos astrometry satellite

Send offprint requests to: G. Micela

© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 20, 1998