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Astron. Astrophys. 329, 81-86 (1998)

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Halo stars in the immediate solar neighbourhood *

B. Fuchs and H. Jahreiß

Astronomisches Rechen-Institut Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg, Germany

Received 15 July 1997 / Accepted 19 August 1997

Abstract

We have searched the Fourth Catalogue of Nearby Stars for halo stars and identified 15 subdwarfs and a high velocity white dwarf in the solar neighbourhood. This search was motivated mainly by the recent determinations of MACHO masses of about 0.5 [FORMULA], which are typical for halo dwarfs. The local mass density of these stars is 1.5 [FORMULA] 10-4 [FORMULA] pc-3, which is only 3% of the current estimate of the local mass density of the MACHO population. We compare the local density of subdwarfs with constraints set by HST observations of distant red dwarfs. Using models of the stellar halo with density laws that fall off like [FORMULA], [FORMULA] = 3.5 to 4, we find that the HST constraints can only be matched, if we assume that the stellar halo is flattened with an axial ratio of about 0.6. The non-detection of the analogues of MACHOs in the solar neighbourhood allows to set an upper limit to the luminosity of MACHOs of [FORMULA] 21 magnitudes.

Key words: Galaxy: halo – Galaxy: solar neighbourhood – Galaxy: structure – cosmology: dark matter

* Based in part on observations made with the ESA Hipparcos astrometry satellite

Send offprint requests to: B. Fuchs

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© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997
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