| |
 |
| Paper: |
The Leo II Dwarf Spheroidal --- an Old Galaxy With A Large Intermediate-Age Population |
| Volume: |
92, Formation of the Galactic Halo. . . . Inside and Out |
| Page: |
528 |
| Authors: |
Mighell, Kenneth J.; Rich, R. Michael |
| Abstract: |
Deep F555W (broad-band V) and F814W (broad-band 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. The fiducial sequence has a main-sequence turnoff at V=25.1 mag. A metallicity of [Fe/H]=-1.6+/-0.25 dex and reddening E(V-I) = 0.035+/-0.019 were determined simultaneously using the technique of Sarajedini (1994, AJ, 107, 618). 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+/-0.19 mag and (m-M)_I=21.60+/-0.19 mag, respectively. Using a variety of age indicators, we have determined that the the main stellar population of Leo II is probably 8--10 Gyr old. 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 13--15 Gyr ago and formed most of its stellar population during the succeeding 6--8 Gyr with the typical star having been formed about 8--10 Gyr ago. The rate of star formation has been negligibly small for the last 6--7 Gyr. Full details of this research project will be published in the Astronomical Journal in 1996. |
|
|
|
|
|
