Abstract

We present integrated Washington CT1 photometry of 18 bright blue objects discovered in the dwarf galaxy UGC 7636 which is located 5'.5 southeast of the giant elliptical galaxy NGC 4472, the brightest galaxy in the Virgo cluster. Several lines of evidence indicate that UGC 7636 is interacting violently with NGC 4472. These objects are very blue with colors of -0.4(C-T-1) 0.6, and their magnitudes are in the range of 20.6 T-1 22.9 mag which corresponds to absolute magnitudes of -10.6(T?1) -8.3 mag for a distance modulus of (m - M)(0) = 31.2. These objects are grouped spatially in three regions: the central region of UGC 7636, the tidal tail region, and the H I cloud region. No such objects were found in the counter-tail region. It is concluded that these objects are probably young star clusters which formed 10(8) yr ago during the interaction between UGC 7636 and NGC 4472. Surface photometry of UGC 7636 (r83 '') shows that there is a significant excess of blue light along the tidal tail region compared with ether regions. The star clusters are bluer than the stellar light in the tidal tail region, indicating that these clusters might have formed later than most stars in the tidal tail region which were formed later than most stars in the main body of the galaxy. (C) 1997 American Astronomical Society.