Statistics
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295..655n&link_type=abstract
Astronomy and Astrophysics, v.295, p.655
Statistics
36
Methods: Data Analysis, Numerical, Stars: General, Hr Diagram, Statistics, Galaxy: General, Stellar Content, Structure
Scientific paper
In this paper we address the analysis of the structure of the Galaxy towards the Centre. For this purpose we developed the so-called HRD-GST, the Hertzsprung-Russell Diagram Galactic Software Telescope, which simulates the stellar distribution in the line of sight. With the aid of the HRD-GST we analyze the stellar content in field #3 of the Palomar-Groningen Survey (PG3), located at the periphery of the Galactic Bulge. The observations are well described by a two component model with a disc and spheroid. There is no need to include a population from the so-called thick disc in the direction of field #3. The majority of the stars (B_J_<18mag) in this field are located in the disc. The main stellar population is well described with the following structural parameters for the scale height and scale length: (z_0_=250pc; h_0_=4.5kpc) or (z_0_=230pc; h_0_=3.5kpc). For the metallicity and age we obtained: Z=0.008-0.015 and t=7.0-4.5Gyr for an exponentially decreasing star formation rate with a characteristic time scale equal to 2.5Gyr. At brighter magnitudes there is a significant contribution from a younger disc population. This population is described with the following structural and evolutionary parameters: (z_0_=100pc; h_0_=4.5kpc), Z=0.015-0.020, and t=5.0-2.0Gyr for a constant star formation rate. A peak at B_J_=16.4mag and B_J_-R_F_=~1.5mag in the Colour-Magnitude Diagram is identified with stars on the Horizontal Branch from a stellar population within the spheroid. Two stellar populations are the main contributors to the spheroidal component. The analysis is restricted to a maximum metallicity Z=0.020. For the older and metal poorer halo population we use a R^1/4^-law with flattening q=0.60, Z=0.0004-0.0050, and t=16-10Gyr for an exponentially increasing star formation rate with a characteristic time scale equal to 3.0Gyr. For the younger and metal richer bulge population we used a power-law with index n=4.0 and flattening q=0.8, Z=0.005-0.020, and t=10-5.0Gyr for an exponentially decreasing star formation rate with a characteristic time scale equal to 2.5Gyr.
Bertelli Giampaolo
Bressan Alberto
Chiosi Cesare
Lub Jan
Ng Yiu-Kai
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