Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. IV. The northern hemisphere sample
Abstract
We present high-precision photometry, high- and medium-resolution spectroscopy for a sample of 32 stars likely to be the optical counterparts of X-ray sources serendipitously detected by the EXOSAT satellite. Using also recent results from the Hipparcos satellite, we infer spectral types, compute X-ray luminosities and Li abundances and investigate the single or binary nature of the sample stars. We found eleven new variable stars, whose photometric periods fall in the 1.2-27.5 day range, for most of which the optical variability is consistent with the presence of photospheric cool spots. For our sample of X-ray selected stars we confirm the existence of a strong correlation between the stellar rotation rate and the level of activity, and also between the X-ray and bolometric luminosities. Two stars in our sample are likely to be pre-main sequence objects, one is likely to be a previously unknown M-type star within 25 pc. Based on data collected at Catania Astrophysical Observatory (Mt. Etna, Italy), at Observatorio Astronomico Nacional (UNAM, S. Pedro Martir, BC, Mexico) and at Kitt Peak National Observatory (Kitt Peak, AZ, USA) Table 1 is available in the on-line version; Table 3 and the complete data set are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr or via http://cdsweb.u-strasbg.fr/Abstract.html}
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2000
- Bibcode:
- 2000A&A...364..205C
- Keywords:
-
- TECHNIQUES: PHOTOMETRIC;
- TECHNIQUES: SPECTROSCOPIC;
- STARS: ABUNDANCES;
- STARS: LATE-TYPE;
- STARS: VARIABLES: GENERAL;
- X-RAYS: STARS