We present radial velocities and metallicities for a sample of 39 open clusters with ages greater than about 700 million years. For 24 clusters new moderate-resolution spectroscopic data obtained with multiobject spectrographs on the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory 4 m telescopes are used to determine radial velocities and mean cluster metallicities. These new results are combined with data published previously by Friel & Janes to provide a sample of 459 giants in 39 old open clusters, which are used to investigate radial abundance gradients in the Galactic disk. Based on an updated abundance calibration of spectroscopic indices measuring Fe and Fe-peak element blends, this larger sample yields an abundance gradient of À0.06 AE 0.01 dex kpc À1 over a range in Galactocentric radius of 7 to 16 kpc. There is a slight suggestion of a steepening of the abundance gradient with increasing cluster age in this sample, but the significance of the result is limited by the restricted distance range for the youngest clusters. The clusters show no correlation of metallicity with age in the solar neighborhood. Consistent with the evidence for a steepening of the gradient with age, the clusters in the outer disk beyond 10 kpc show a suggestion at the 1.5 level of a dependence of metallicity on age.

The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (D < 4 Mpc). The survey volume encompasses 69 galaxies in diverse environments, including close pairs, small & large groups, filaments, and truly isolated regions. The galaxies include a nearly complete range of morphological types spanning a factor of ∼ 10 4 in luminosity and star formation rate. The survey data consists of images taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST), supplemented with archival data and new Wide Field Planetary Camera (WFPC2) imaging taken after the failure of ACS. Survey images include wide field tilings covering the full radial extent of each galaxy, and single deep pointings in uncrowded regions of the most massive galaxies in the volume. The new wide field imaging in ANGST reaches median 50% completenesses of m F 475W = 28.0 mag, m F 606W = 27.3 mag, and m F 814W = 27.3 mag, several magnitudes below the tip of the red giant branch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the structure in the red clump (RC). The resulting photometric catalogs are publicly accessible and contain over 34 million photometric measurements of >14 million stars. In this paper we present the details of the sample selection, imaging, data reduction, and the resulting photometric catalogs, along with an analysis of the photometric uncertainties (systematic and random), for both the ACS and WFPC2 imaging. We also present uniformly derived relative distances measured from the apparent magnitude of the TRGB.

The rapid localization of GRB 021004 by the HETE-2 satellite allowed nearly continuous monitoring of its early optical afterglow decay, as well as high-quality optical spectra that determined a redshift of z 3 ¼ 2:328 for its host galaxy, an active starburst galaxy with strong Ly emission and several absorption lines. Spectral observations show multiple absorbers at z 3A ¼ 2:323, z 3B ¼ 2:317, and z 3C ¼ 2:293 blueshifted by $450, $990, and $3155 km s À1 , respectively, relative to the host galaxy Ly emission. We argue that these correspond to a fragmented shell nebula that has been radiatively accelerated by the gamma-ray burst (GRB) afterglow at a distance e0.3 pc from a Wolf-Rayet star GRB progenitor. The chemical abundance ratios indicate that the nebula is overabundant in carbon and silicon. The high level of carbon and silicon is consistent with a swept-up shell nebula gradually enriched by a carbon-rich late-type Wolf-Rayet progenitor wind over the lifetime of the nebula prior to the GRB onset. The detection of statistically significant fluctuations and color changes about the jetlike optical decay further supports this interpretation, since fluctuations must be present at some level as a result of irregularities in a clumpy stellar wind medium or if the progenitor has undergone massive ejection prior to the GRB onset. This evidence suggests that the mass-loss process in a Wolf-Rayet star might lead naturally to an iron core collapse with sufficient angular momentum that could serve as a suitable GRB progenitor. Even though we cannot rule out definitely the alternatives of a dormant QSO, large-scale superwinds, or a several hundred year old supernova remnant responsible for the blueshifted absorbers, these findings point to the likelihood of a signature for a massive-star GRB progenitor.

We have used archival ROSAT data to present X-ray images of 31 supernova remnants (SNRs) in the Large Magellanic Cloud (LMC). We have classiÐed these remnants according to their X-ray morphologies, into the categories of shell-type, di †use face, centrally brightened, point-sourceÈdominated, and irregular. We suggest possible causes of the X-ray emission for each category and for individual features of some of the SNRs.

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