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Issue A&A
Volume 365, Number 3, January III 2001
Page(s) 424 - 430
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20000140



A&A 365, 424-430 (2001)
DOI: 10.1051/0004-6361:20000140

Constraints on thick disc and halo parameters from HST photometry of field stars in the Galaxy

L. O. Kerber, S. C. Javiel and B. X. Santiago

Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501-970, RS, Brazil

(Received 11 July 2000 / Accepted 19 October 2000)

Abstract
We analyse a sample of over 1000 stars from 32 fields imaged in the V and I bands with the Wide Field and Planetary Camera , on board of the Hubble Space Telescope. The fields are located at Galactic latitudes $\vert b \vert \geq 15^{\circ}$ and in various directions on the sky. We consider models for the structure of the Galaxy with different choices for the main parameters governing the shape and luminosity function of the thick disk and stellar halo. Comparing model predictions with the observed colour-magnitude diagram we are able to rule out an increasing or flat stellar luminosity function at the low-luminosity end. We also rule out large values of the vertical scale height of the thick disc, z0, finding it to be in the range $800 \leq z_0 \leq 1200$ pc. As for the local density normalization, values within the range $4 \% \leq n_0 \leq 8 \%$ seem to better reproduce the data. Our data essentially rule out a flattened stellar halo ( $c/a \la 0.5$) or models with both large local normalization and effective radii.


Key words: Galaxy: structure -- stars: statistics

Offprint request: L. O. Kerber, kerber@if.ufrgs.br




© ESO 2001


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