Identification of a complete sample of northern ROSAT All-Sky Survey X-ray sources

Free access article

Issue		A&A Volume 433, Number 1, April I 2005


Page(s)		151 - 171
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20041847

A&A 433, 151-171 (2005)
DOI: 10.1051/0004-6361:20041847

VIII. The late-type stellar component

F.-J. Zickgraf¹, J. Krautter², S. Reffert³, J. M. Alcalá⁴, R. Mujica⁵, E. Covino⁴ and M. F. Sterzik⁶

¹ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: st9b310@hs.uni-hamburg.de
² Landessternwarte Königstuhl, 69117 Heidelberg, Germany
³ Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
⁴ Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁵ Instituto Nacional de Astrofisica, Optica y Electronica, A. Postal 51 y 216 Z.P., 72000 Puebla, Mexico
⁶ European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile

(Received 16 August 2004 / Accepted 3 December 2004)

Abstract
We present results of an investigation of the X-ray properties, age distribution, and kinematical characteristics of a high-galactic latitude sample of late-type field stars selected from the ROSAT All-Sky Survey (RASS). The sample comprises 254 RASS sources with optical counterparts of spectral types F to M distributed over six study areas located at $\vert b\vert \ga 20\degr$ , and ${\rm Dec} \ge -9\degr$ . A detailed study was carried out for the subsample of ~200 G, K, and M stars. Lithium abundances were determined for 179 G-M stars. Radial velocities were measured for most of the 141 G and K type stars of the sample. Combined with proper motions these data were used to study the age distribution and the kinematical properties of the sample. Based on the lithium abundances half of the G-K stars were found to be younger than the Hyades (660 Myr). About 25% are comparable in age to the Pleiades (100 Myr). A small subsample of 10 stars is younger than the Pleiades. They are therefore most likely pre-main sequence stars. Kinematically the PMS and Pleiades-type stars appear to form a group with space velocities close to the Castor moving group but clearly distinct from the Local Association.

Key words: surveys -- X-rays: stars -- stars: late-type -- stars: pre-main sequence -- stars: kinematics -- solar neighbourhood

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