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Astron. Astrophys. 351, 925-936 (1999)


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Kinematics and age of stellar populations in the solar neighbourhood from Hipparcos data *

V. Caloi 1, D. Cardini 1, F. D'Antona 2, M. Badiali 1, A. Emanuele 1 and I. Mazzitelli 1

1 Istituto di Astrofisica Spaziale C.N.R., Via Fosso del Cavaliere, 00133 Roma, Italy
2 Osservatorio Astronomico di Roma, 00040 Monte Porzio, Italy

Received 23 December 1998 / Accepted 21 September 1999

Abstract

The large sample of main sequence stars with Hipparcos parallaxes and estimates of the radial velocity has been used to study the relations among kinematics, age and heavy element content for the solar neighbourhood. The samples with V [FORMULA] -30 km s-1, although including stars as old as [FORMULA] yr, have a very young component (age [FORMULA] [FORMULA] yr), and have a metallicity close to the solar one. Most of the stars with space velocity component V [FORMULA] -40 km s-1 have a minimum age of about 2 [FORMULA] yr. Stars with V [FORMULA] -80 km s-1 share a common age [FORMULA] [FORMULA] yr. The distribution in [Fe/H] of these latter objects suggests a decrease in metal content with increasing [FORMULA] till [Fe/H] [FORMULA] -2. For V [FORMULA] -180 km s-1 only the metal poor component ([Fe/H] [FORMULA] -0.7) is found. The common age for large space velocity suggests that no substantial age spread exists in the inner halo, at least in the local sample.

Key words: Galaxy: solar neighbourhood – Galaxy: kinematics and dynamics – Galaxy: stellar content

* Based on data collected by the Hipparcos ESA consortium

Send offprint requests to: V. Caloi

Correspondence to: caloi@saturn.ias.rm.cnr.it

© European Southern Observatory (ESO) 1999

Online publication: November 16, 1999

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