We present V and I photometry of the resolved stars in the cometary blue compact dwarf galaxy UGC 4483 using Hubble Space Telescope Wide Field Planetary Camera 2 ( WFPC2 ) images .
The resulting I vs . ( V - I ) color-magnitude diagram ( CMD ) reaches limiting magnitudes V = 27.5 mag and I = 26.5 mag for photometric errors less than 0.2 mag .
It reveals not only a young stellar population of blue main-sequence stars and blue and red supergiants , but also an older evolved population of red giant and asymptotic giant branch stars .
The measured magnitude I = 23.65 \pm 0.10 mag of the red giant branch tip results in a distance modulus ( m - M ) = 27.63 \pm 0.12 , corresponding to a distance of 3.4 \pm 0.2 Mpc .
The youngest stars are associated with the bright H ii region at the northern tip of the galaxy .
The population of older stars is found throughout the low-surface-brightness body of the galaxy and is considerably more spread out than the young stellar population , suggesting stellar diffusion .
The most striking characteristics of the CMD of UGC 4483 are the very blue colors of the red giant stars and the high luminosity of the asymptotic giant branch stars .
Both of these characteristics are consistent with either : 1 ) a very low metallicity ( [ Fe/H ] = –2.4 like the most metal-deficient globular clusters ) and an old age of 10 Gyr , or 2 ) a higher metallicity ( [ Fe/H ] = –1.4 as derived from the ionized gas emission lines ) and a relatively young age of the oldest stellar population in UGC 4483 , not exceeding \sim 2 Gyr .
Thus our data do not exclude the possibility that UGC 4483 is a relatively young galaxy having formed its first stars only \sim 2 Gyr ago .