Deep HST V- and I-Band Observations of Two Globular Clusters in the Halo of M31.
Abstract
We present deep (V∼=27) V- and I-band stellar photometry of G302 and G312, two globular star clusters in the halo of M31. These data were obtained using the Hubble Space Telescope's Wide Field/Planetary Camera 2. We find iron abundances of [Fe/H]= -1.85±0.12 for G302 and [Fe/H]=-0.56±0.03 for G312, consistent with spectroscopic measurements. The color-magnitude diagrams for each cluster show no evidence for an intermediate-aged population of stars, or a second parameter effect in the morphology of the horizontal branch. G302 shows no evidence for a color gradient but the inner regions of G312 are bluer than the outer regions. G312 shows no evidence of ellipticity or an extended halo of stars. G302 has a projected ellipticity of ɛ=0.195± 0.012 with the projected major axis oriented towards the center of M31. G302 also shows evidence of an extended asymmetric stellar halo extending to at least twice the fitted Michie-King tidal radius. The amount of mass beyond the tidal radius of G302 is consistent with the stellar escape rates which have been predicted by N-body simulations of globular clusters in the Galactic tidal field.
- Publication:
-
The Astronomical Journal
- Pub Date:
- October 1997
- DOI:
- 10.1086/118579
- arXiv:
- arXiv:astro-ph/9708232
- Bibcode:
- 1997AJ....114.1488H
- Keywords:
-
- GALAXIES: M31;
- STARS: HORIZONTAL-BRANCH;
- GALAXIES: KINEMATICS AND DYNAMICS;
- Astrophysics
- E-Print:
- 29 pages, 21 Postscript figures, uses aaspp4.sty, to be published in the October 1997 AJ