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PROBING THE INTERMEDIATE-AGE GLOBULAR CLUSTERS IN NGC 5128 FROM ULTRAVIOLET OBSERVATIONS
Rey, Soo-Chang,Sohn, Sangmo T.,Beasley, Michael A.,Lee, Young-Wook,Rich, R. Michael,Yoon, Suk-Jin,Yi, Sukyoung K.,Bianch, Luciana,Kang, Yongbeom,Lee, Kyeongsook,Chung, Chul,Lee, Sang-Yoon,Barlow, Tom IOP Publishing 2009 ASTROPHYSICAL JOURNAL LETTERS - Vol.700 No.1
<P>We explore the age distribution of the globular cluster ( GC) system of the nearby elliptical galaxy NGC 5128 using ultraviolet (UV) photometry from GALEX observations, with UV-optical colors used as the age indicator. Most GCs in NGC 5128 follow the general trends of GCs in M31 and the Milky Way in the UV-optical color color diagram, which indicates that the majority of GCs in NGC 5128 are old similar to the age range of old GCs in M31 and the Milky Way. A large fraction of spectroscopically identified intermediate-age GC (IAGC) candidates with similar to 3-8 Gyr are not detected in the far-UV (FUV) passband. Considering the nature of intermediate-age populations being faint in the FUV passband, we suggest that many of the spectroscopically identified IAGCs may be truly intermediate in age. This is in contrast to the case of M31 where a large fraction of spectroscopically suggested IAGCs are detected in FUV and therefore may not be genuine IAGCs but rather older GCs with developed blue horizontal branch stars. Our UV photometry strengthens the results previously suggesting the presence of GC and stellar subpopulation with intermediate age in NGC 5128. The existence of IAGCs strongly indicates the occurrence of at least one more major star formation episode after a starburst at high redshift.</P>
BLUE STRAGGLER STARS IN THE GLOBULAR CLUSTER M53
REY SOO-CHANG,LEE YOUNG-WOOK,CHUN MUN-SUK,BYUN YONG-IK The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
The first large-format CCD color-magnitude diagram (CMD) in the B and V passbands is presented for the Galactic globular cluster M53 (NGC 5024). We have discovered 117 new blue straggler (BS) candidates in the field of M53. The analysis of bright BS stars (V <19.0) clearly shows a bimodal radial distribution, with a high frequency in the inner and outer regions. The distribution is similar to that found in M3, a globular cluster with similar central density and concentration.