1. Galactic structure and star counts Du cuihua 2005. 8. 11 BATC meeting, NAOC

2.  Basic components of the Galaxy  BATC observation data  object classification and photometric parallaxes  Space density distribution  conclusions

3. Dark halo Stellar halo Thick disk bulge Thin disk Basic components of the Galaxy

4. It is primary stellar component 1. The thin disk  a young thin disk, with mean [Fe/H] of 0.0 dex and an exponential scale height of 100 pc.  a old thin disk, with mean [Fe/H] of –0.3 dex and an exponential scale height of 300 pc

5. 2. the thick disk  its exponential scale height is about 500-1400 pc, with local normalization 2%-14%.  its velocity dispersion is much higher than that of the thin disk  more metal poor than the thin disk ( - 2.2  [Fe/H]  - 0.5 ) our Galaxy have a second thicker disk component

6. 3. The stellar halo is metal-poor : a very old and diffuse population of stars and globular clusters extending far beyond the disk [Fe/H]<-1.0 Only about 1/50 of the mass of the disk but very significant because it contains the oldest (>12 Ga) stars in the Galaxy

7. 4. The dark halo Almost all galaxies have a dark halo.... in other spirals We would like to know more about the properties and history of the galactic dark halo - but it is difficult to study Most of our insights into the growth and structure of the dark halo come from numerical simulations. Contribute at least 90% of galactic mass, is spheroid rather than disklike.

8. 5. central bulge Our galactic bulge is really a small bar Age=6 ~ 12 Gyr, [Fe/H]=-1.0 ~ +0.5

9. BATC observation data  At first, try three fields to study the structure  T329: (l=170, b=50)  TA01: (l=134,b=-62)  T516: (l=124,b=-62 )

10.  Recently, use 20 fields to continue the previous work.

11. Object classification and photometric parallaxes  These fields have been observed by the Sloan Digital Space Survey (SDSS) and each object type (stars- galaxies-QSO) has been given.  For stars, use the stellar spectra library to obtain the stellar type. (Pickles 1998 stellar library )

12. According to the stellar type ， the absolute magnitude Mv can be obtained. (Lang K.R., 1992, Astrophysical Data I, Plantes and stars)

13.  According to the absolute magnitude from the stellar type, the stellar photometric parallaxes can be derived.

14. Space density distribution  Vertical density distribution for the disk:  The density law of the halo:

16.  Using two exponential disks, we determined that the scale height of thin disk is pc, and thick disk scale height is pc, with 7.0% of the thin disk.  Adopting a law halo, the observed counts yield a axial ratio of c/a<0.6, implying a more flatted halo.  The stellar luminosity function of thin disk is also derived. (Du cuihua, Zhou xu, Ma jun, Alfred-B-C Chen, et al. 2003, A&A, 407,541) Conclusion 1

18. Recent observation data: As an example,we list several fields as follows: U085, T521, T359, T534, T491,T193

26. Conclusions 2 (3) Our results suggest that the disk itself may be irregular with a scale height and density that are variable with direction. (1)Using 20 fields, we found that the scale height of the thin disk is 210-320 pc, And thick disk scale height is 600-840 pc, with a corresponding density normalization 2~10% of the thin disk. (2)The axial ratio of the stellar halo approximate from 0.4 –0.6. and the parameters for the halo are most applicable to the inner halo.

27. Thank you !