The BATC Multicolor Photometric Study of M 31
The BATC Multicolor Photometric Study of M 31 Globular Clusters Fan Zhou Profs Jun Ma and Xu Zhou BATC Group, NAOC
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. Size FOV Pixel Scale BQE(~400 nm) RON New E 2 V 4 K × 4 K 90’× 90’ 12 um/pixel 1. 3"/pixel 92. 2% <4 e Old Thick 2 K × 2 K 58’× 58’ 15 um/pixel 1. 7"/pixel <5% >12 e
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 M 31 • The central 1 o× 1 o field in 15 intermediate bands • 1995 Sep. 1999 Dec. • Total EXP: 37 hr 20 mi n
The ages of M 31 GCs • Jiang & Ma (2003) use the Battistini et al. (1987) to obtain BATC SEDs of 172 GCs • Using the BC 96 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) + 2 MASS(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.
BC 03 SSP model • • Age: 0. 1 Myr ~ 20 Gyr Wavelength: 91 Å-160 μm Track: Padova 1994 (Z=0. 0001 -0. 10) IMF: Salpeter 1955
The SED fitting with BC 03 model
The age distribution of our sample GCs in M 31
The metallicity ~age relationship in M 31 • Old metal-poor • Young metal-rich
Future Work 9 o× 9 o field with >1000 GCs and candidates Green boxes : Observed already White boxes: to be observed in the future 15 intermediateband
Thanks very much! http: //batc. bao. ac. cn/~fanzhou
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