Galactic structure studies with BATC star counts

Abstract

We report the first results of star counts carried out with the National Astronomical Observatories (NAOC) 60/90 cm Schmidt Telescope in 15 intermediate-band filters from 3000 to 10000 Ã in the BATC survey. We analyze a sample of over 1400 main sequence stars ($14\le$V$\le 21$), which lie in the field with central coordinates R.A.=$09^{h}53^{m}13^s.30$ and DEC=47${}^{\circ }49^{\prime }00^{\prime \prime }.0$ (J2000). The field of view is 0.95 deg${}^2$, and the spatial scale was $1\arcsec.67$. In our model, the distribution of stars perpendicular to the plane of the Galaxy is given by two exponential disks (thin disk plus thick disk) and a de Vaucouleurs halo. Based on star counts, we derive the scale heights of the thin disk to be $320_{-15}^{+14}$ pc and of the thick disk to be $640_{-32}^{+30}$ pc, respectively, with a local density of $7.0\pm 1$ of the thin disk. We find that the observed counts support an axial ratio of $c/a\le 0.6$ for a de Vaucouleurs $r^{1/4}$ law, implying a more flattened halo. We also derive the stellar luminosity function (SLF) for the thin disk, and it partly agrees with the Hipparcos luminosity function.

17pages,9 figures