Issue |
Astron. Astrophys. Suppl. Ser.
Volume 131, Number 2, August 1998
|
|
---|---|---|
Page(s) | 345 - 354 | |
DOI | https://doi.org/10.1051/aas:1998429 | |
Published online | 15 August 1998 |
Metal–poor turnoff and subgiant field stars in the Galaxy
I. RGU photometry in a high–latitude field near M101
1
Department of Astronomy and Space Sciences, Istanbul University Observatory, Istanbul, Turkey
2
Astronomisches Institut der Universität Basel, Venusstr. 7, CH–4102 Binningen, Switzerland
Send offprint request to: R. Buser
Received:
29
October
1998
Accepted:
2
January
1998
Photographic RGU photometry for about 1800 stars down to a limiting G-magnitude
of 19.5 in a high-latitude field (() = (101°,
+60
) near the galaxy M101 is investigated.
We use an improved variant of the classical three-color method which is based
on recent UBV–RGU–photometric transforms and calibrations (Buser 1988; Buser & Fenkart 1990) and on models of the stellar density distributions of the
Galactic population components.
In particular, predictions from the Galactic models of Gilmore & Wyse (1985)
are employed as guides in determining the density functions from the present
data, which are then used in turn to derive consistent local luminosity
functions. We
find that a significant fraction of the intermediate and extreme Population II
stars must be (mildly) evolved (rather than main–sequence) stars whose
higher–luminosity nature cannot be inferred from their two–color positions
only. This conclusion is also consistent with results obtained from combined
RGU–photometric and proper motion data in two other Basel fields by Buser & Chiu (1981a,b) as well as from detailed model–calculations for the larger
survey of RGU–data in seven high–latitude fields by
Buser & Rong (1995) and Buser et al. (1998a).
Key words: Galaxy: structure of / Galaxy: stellar content of / Galaxy: solar neighborhood / stars: population II
© European Southern Observatory (ESO), 1998