Detalles de publicación
PP 06061
The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Whitout Previous HST Photometry.
(1) Univ. of Florida (2) ESO-Garching (3) Dartmouth College (4) Univ. of Texas (5) Rice Univ. (6) IAC (7) Univ. of Washington (8) Univ. of Virginia (9) Univ. of Padova (10) Space Telescope Science Institute.
We present the first results of a large ACS Survey of Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N~10 for main sequence stars with masses ~0.2 M_odot
in a sample of globulars using the Advanced Camera for Surveys (ACS) Wide Field Channel. Here we focus on clusters without previous HST imaging data. These include NGC 5466, 6779, 5053, 6144, Palomar 2, E3, Lynga 7, Palomar 1, and
NGC 6366. Our CMDs extend reliably from the horizontal branch to as much as seven magnitudes fainter than the main sequence turnoff and represent the deepest CMDs published to-date for these clusters. Using fiducial sequences for three standard clusters (M92, NGC 6752, and 47 Tuc) with well-known metallicities and distances, we perform main sequence fitting on the target clusters in order to obtain estimates of their distances and reddenings. These comparisons along with fitting the cluster main sequences to theoretical
isochrones yield ages for the target clusters. We find that the majority
of the clusters have ages that are consistent with the standard clusters
at their metallicities. The exceptions are E3 which appears ~2 Gyr younger
than 47 Tuc, and Pal 1, which could be as much as 8 Gyr younger than 47 Tuc.
in a sample of globulars using the Advanced Camera for Surveys (ACS) Wide Field Channel. Here we focus on clusters without previous HST imaging data. These include NGC 5466, 6779, 5053, 6144, Palomar 2, E3, Lynga 7, Palomar 1, and
NGC 6366. Our CMDs extend reliably from the horizontal branch to as much as seven magnitudes fainter than the main sequence turnoff and represent the deepest CMDs published to-date for these clusters. Using fiducial sequences for three standard clusters (M92, NGC 6752, and 47 Tuc) with well-known metallicities and distances, we perform main sequence fitting on the target clusters in order to obtain estimates of their distances and reddenings. These comparisons along with fitting the cluster main sequences to theoretical
isochrones yield ages for the target clusters. We find that the majority
of the clusters have ages that are consistent with the standard clusters
at their metallicities. The exceptions are E3 which appears ~2 Gyr younger
than 47 Tuc, and Pal 1, which could be as much as 8 Gyr younger than 47 Tuc.