The Hubble Deep Field (HDF) is a Director's Discretionary program on HST in Cycle 5 to image an undistinguished field at high Galactic latitude in four passbands as deeply as reasonably possible. These images provide the most detailed view to date of distant field galaxies and are likely to be important for a wide range of studies in galaxy evolution and cosmology. In order to optimize observing in the time available, a field in the northern continuous viewing zone was selected and images were taken for ten consecutive days, or approximately 150 orbits. Shorter 1-2 orbit images were obtained of the fields immediately adjacent to the primary HDF in order to facilitate spectroscopic follow-up by ground-based telescopes. The observations were made from 18 to 30 December 1995, and both raw and reduced data have been put in the public domain as a community service. We present a summary of the criteria for selecting the field, the rationale behind the filter selection and observing times in each band, and the strategies for planning the observations to maximize the exposure time while avoiding earth-scattered light. Data reduction procedures are outlined, and images of the combined frames in each band are presented. Objects detected in these images are listed in a catalog with their basic photometric parameters.

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One third of present-day spirals host optically visible strong bars that drive their dynamical evolution. However, the fundamental question of how bars evolve over cosmological times has yet to be resolved, and even the frequency of bars at intermediate redshifts remains controversial. We investigate the frequency of bars out to z ∼ 1 drawing on a sample of 1590 galaxies from the Galaxy Evolution from Morphology and SEDs survey, which provides morphologies from Hubble Space Telescope Advanced Camera for Surveys (ACS) two-band images and accurate redshifts from the COMBO-17 survey. We identify spiral galaxies using three independent techniques based on the Sersic index, concentration parameter, and rest-frame color. We characterize bar and disk features by fitting ellipses to F606W and F850LP images, using the two bands to minimize shifts in the rest-frame bandpass. We exclude highly inclined (i > 60 • ) galaxies to ensure reliable morphological classifications and apply different completeness cuts of M V ≤ −19.3 and −20.6. More than 40% of the bars that we detect have semi major axes a < 0. ′′ 5 and would be easily missed in earlier surveys without the small point spread function of ACS. The bars that we can reliably detect are fairly strong (with ellipticities e ≥ 0.4) and have a in the range ∼1.2-13 kpc. We find that the optical fraction of such strong bars remains at ∼30% ± 6% from the present-day out to look-back times of 2-6 Gyr (z ∼ 0.2-0.7) and 6-8 Gyr (z ∼ 0.7-1.0); it certainly shows no sign of a drastic decline at z > 0.7. Our findings of a large and similar bar fraction at these three epochs favor scenarios in which cold gravitationally unstable disks are already in place by z ∼ 1 and where on average bars have a long lifetime (well in excess of 2 Gyr). The distributions of structural bar properties in the two slices are, however, not statistically identical and therefore allow for the possibility that the bar strengths and sizes may evolve over time.

Observations of u Centauri have been used to characterize the charge-transfer efficiency (CTE) of the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space T elescope. A set of formulae has been developed to correct aperture photometry for CTE loss with dependencies on the X-and Y -positions, the background counts, the brightness of the star, and the time of the observation. The observations indicate that for very faint stars on a very faint background, the CTE loss from the top to the bottom of a chip has increased from about 3% shortly after the cooldown of WFPC2 (1994 April 23) to roughly 40% in 1999 February. In general, typical WFPC2 exposures are much longer than these shortcalibration images, resulting in higher background which signiÐcantly reduces the CTE loss and minimizes the CTE problem for most science exposures.

We present WFPC2 images in the F450W, F606W and F814W filters of the interacting pair of galaxies NGC 454. Our data indicate that the system is in the early stages of interaction. A population of young star-clusters has formed around the late component, and substantial amounts of gas have sunk into the center of the earlier component, where it has not yet produced significant visible star formation or nuclear activity. We have photometric evidence that the star-clusters have strong line emission, which indicate the presence of a substantial component of hot, massive stars which formed less than 5-10Myrs ago.