Fan Zhou

Profs Jun Ma and Xu Zhou

BATC Group,NAOC

The BATC Multicolor Photometric Study of M31 Globular Clusters

The BATC Multicolor Photometry System

The Bejing-Arizona-Taiwan-Connecticut (BATC) group was created by Academician Chen J.-S. 15 years ago.

60/90 cm f/3 Schmidt Telescope at Xionglong.

>12e

<4e

RON

<5%15um/pixel 1.7"/pixel

58’×58’2K × 2KOld Thick

 92.2%12um/pixel 1.3"/pixel

90’×90’4K × 4KNew E2V

BQE(~400nm)Pixel ScaleFOVSize

The BATC intermediate band filters

• The BATC multicolor photometric system includes 15 intermediate band filters, covering the total optical wavelength range from ~3000 to ~10000Å.

• The filters are designed to avoid the brightest and most variable night sky emission lines.

The BATC multicolor photometry of M31

• The central 1o×1o field in 15 intermediate bands

• 1995 Sep.-1999 Dec.

• Total EXP:37hr20min

The ages of M31 GCs

• Jiang & Ma (2003) use the Battistini et al. (1987) to obtain BATC SEDs of 172 GCs

• Using the BC96 SSP model to derive the ages and metallicities

• Nearly all the GCs are older than 1 Gyr

• Metal-poor ->old• Metal-rich->young

Break the degeneracy!

• One big problem in the SSP model: age~metallcity degeneracy! Reddening also affects it!

• Idea: use the known metallicty and reddening to derive the age.

Our data for our sample GCs

• BATC(13) + Broadband(5) + 2MASS(3) JHKs photometry (Galleti et al. 2004).

• Spectroscopic [Fe/H] obtained: Perrett et al. (2002) and Barmby et al. (2000)

• The reddening data: Barmby priv. comm.

BC03 SSP model

• Age: 0.1Myr ~ 20 Gyr

• Wavelength: 91 Å-160 μm

• Track: Padova 1994 (Z=0.0001-0.10)

• IMF:Salpeter 1955

2.5log 48.6AB

dF R

md

R

The SED fitting with BC03 model

The age distribution of our sample GCs in M31

The metallicity ~age relationship in M31

• Old metal-poor

• Young metal-rich

Future Work

9o×9o field with >1000 GCs and candidates

Green boxes:Observed already

White boxes: to be observed in the future

15 intermediate-band

Thanks very much!

http://batc.bao.ac.cn/~fanzhou