有哪些信誉好的足球投注网站Constraints on thick disc and halo parameters from HST photometry of field stars in the Gal.pdf
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Constraints on thick disc and halo parameters from HST photometry of field stars in the Gal
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AA manuscript no.
(will be inserted by hand later)
Your thesaurus codes are:
10.19.3; 08.19.1
ASTRONOMY
AND
ASTROPHYSICS
Constraints on Thick Disc and Halo parameters from HST
photometry of field stars in the Galaxy
L. O. Kerber, S. C. Javiel, B. X. Santiago
Universidade Federal do Rio Grande do Sul, IF, CP15051, Porto Alegre 91501–970, RS, Brazil
Received 11 July 2000 / Accepted 19 October 2000
Abstract. We analyze 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 lati-
tudes |b| ≥ 15? and in various directions on the sky. We
consider models for the structure of the Galaxy with dif-
ferent 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 ≤ z0 ≤ 1200 pc. As for the local density normal-
ization, values within the range 4% ≤ n0 ≤ 8% seem to
better reproduce the data. Our data essentially rule out
a flattened stellar halo (c/a
～ 0.5) or models with both
large local normalization and effective radii.
Key words: Galaxy: Structure; Stars: Statistics
1. Introduction
Our Milky Way galaxy is known to have a large disk with
spiral structure, typical of luminous galaxies of Sb type.
It has also been known for a long time to contain a po-
pulation of old (τ
～ 10 Gyrs) stars distributed in an
spheroidal component. More recent models of its struc-
ture have included at least a third component, of inter-
mediate properties, often called the thick disc (Gilmore
Reid 1983). Our understanding of the spatial, kinemat-
ical and che
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