Title | The Leo II Dwarf Spheroidal - an Old Galaxy With a Large Intermediate-age Population |
Authors | Mighell, Kenneth J.; Rich, R. Michael |
Bibcode | 1996AJ....111..777M Search ADS ↗ |
Abstract | Deep F555W (broadband V) and F814W (broadband I) observations have been obtained of the Leo II dwarf spheroidal galaxy with the Hubble Space Telescope Wide Field Planetary Camera 2 instrument. The resulting color- magnitude diagrams reach V = 27.4 mag and I = 26.6 mag, and the fiducial sequence has a main-sequence turnoff at V = 25.1 mag. A metallicity of [Fe/H] = -1.60+/-0.25 dex and reddening E (V - I) = 0.035+/-0.019 were determined simultaneously using the technique of Sarajedini [AJ, 107,618 (1994)]. A well-defined horizontal branch is seen at V_HB_ = 22.18+/-0.08 mag and the true distance modulus is (m - M)_0_ = 21.55+/-0.18 mag. The apparent distance moduli in V and I are (m - M)_V_=21.63+/-0.18 mag and (m - M)_I__ = 21.60+/-0.18 mag, respectively. Using a variety of age indicators, we have determined that the main stellar population of Leo II has an age of 9+/-1 Gyr. By analyzing the distribution of stars near the base of the red giant branch, we have determined that half of the stars in Leo II probably formed during a period of star formation lasting about 4 Gyr. The Leo II dwarf spheroidal galaxy started forming stars about 14+/-1 Gyr ago and formed most of its stellar population during the succeeding 7 +/- 1 Gyr with the typical star having been formed about 9+/-1 Gyr ago. The rate of star formation has been negligibly small for the last ~7 Gyr. |
Objects | 1 Objects Search NED ↙ |