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