Joel D. Offenberg

THE ULTRAVIOLET IMAGING TELESCOPE: INSTRUMENT AND DATA CHARACTERISTICS

The Ultraviolet Imaging Telescope (\UIT) was flown as part of the \AstroMiss\ observatory on the Space Shuttle Columbia in December 1990 and again on the Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300A) images of a variety of astronomical objects, with a 40\arcmin\ field of view and a resolution of about 3\arcsec, were recorded on photographic film. The data recorded during the first flight is available to the astronomical community through the National Space Science Data Center (NSSDC); the data recorded during the second flight will soon be available as well. This paper discusses in detail the design, operation, data reduction, and calibration of \UIT, providing the user of the data with information for understanding and using the data. It also provides guidelines for analyzing other astronomical imagery made with image intensifiers and photographic film.

The Ultraviolet Imaging Telescope - Design and performance

The instrumental configuration, calibration, and operations during the first flight of the Ultraviolet Imaging Telescope on the Astro-1 mission, December 2-10, 1990, are described. The UV images of a wide variety of astronomical objects were recorded with a 40-arcmin diameter field of view. Images of targets as faint as magnitude 21 (UV) were secured with a resolution of about 3 arcsec. The optics, light baffling, and image motion compensation system are summarized, and detectors and electronic subsystems are described.

Validation of Up-the-Ramp Sampling with Cosmic-Ray Rejection on Infrared Detectors

We examine cosmic-ray rejection methodology on data collected from InSb and Si:As detectors. The application of an up-the-ramp sampling technique with cosmic-ray identification and mitigation is the focus of this study. This technique is valuable for space-based observatories which are exposed to high-radiation environments. We validate the up-the-ramp approach on radiation-test data sets with InSb and Si:As detectors which were generated for SIRTF. The up-the-ramp sampling method studied in this paper is over 99.9% effective at removing cosmic rays and preserves the structure and photometric quality of the image to well within the measurement error.

Correcting the distortion of images taken with the ultraviolet imaging telescope

The Ultraviolet Imaging Telescope cameras include two-stage magnetically focussed image intensifiers that introduce small but significant geometrical distortions to the data. These distortions, which create positional offsets as large as 25 arcseconds at the field edges, are corrected by the procedure described here to 2-3 arcseconds, approximately the resolution of the images. The distortion is measured by comparing and correcting UIT images to digitized Guidestar survey plates of the same fields. Two-dimensional third-order polynomials are used to model the distortion. The models assume that the distortion is an instrumental effect, independent of mission elapsed time and target, and that the effect of distortion in the center of each field is minimal. The models are used to improve computed astrometric plate solutions and to remove the geometric distortion while transforming the image to a standard north-up, east-left orientation.

HgCdTe Detectors for the Hubble Space Telescope Wide Field Camera 3 IR Channel

Detector performance has been characterized for the HST WFC3 IR channel. This will be the first TEC cooled IR instrument on the Hubble Space Telescope (HST), which is made possible because of recent progress in HgCdTe technology. The original detector requirements are compared with the performance of the delivered devices. Achievements in quantum efficiency and dark current are described, as well as difficulties in meeting requirements for noise and dark stability. A special technique developed to illuminate a single pixel, which has demonstrated the excellent spatial resolution of the detectors is described.

Ultraviolet morphologies of nearby barred and unbarred spiral galaxies

Deep high-resolution imaging of galaxies at high-redshift has revealed a remarkable diversity of emission structures in the restframe ultraviolet. To better understand these remote and primeval realms, it is important to compare them with UV-emitting counterparts in the local universe. As part of two Spacelab/Astro missions, the Ultraviolet Imaging Telescope (UIT) has obtained wide-field (40-arcmin), well-resolved (3 arcsec) images of ∼50 nearby galaxies in the vacuum ultraviolet. Followup groundbased imaging at UBVRI and Hα bands has been completed for most of the well-resolved galaxies. Analysis of a small subset of these galaxies has revealed strong variations in the emission morphologies as a function of restframe wavelength. In the present study, we compare the UV morphologies of barred and unbarred spiral galaxies as a function of Hubble type and absolute luminosity. Radial extents are measured relative to their visible counterparts, and characteristic UV emission structures are identified (e.g. rin...

The Hubble Space Telescope Wide Field Camera 3 Instrument Charge-Coupled Device Detectors

The Hubble Space Telescope Wide Field Camera 3 (WFC3) is a new instrument planned for deployment during Servicing Mission 4 in 2004. One of its key scientific goals is to provide panchromatic coverage from the near-UV through the near-IR. This is accomplished using two detector technologies, Marconi Applied Technologies back-thinned CCDs and Rockwell Scientific Mercury-Cadmium-Telluride (HgCdTe) IR focal planes. The Marconi CCDs have been delivered and characterized. The performance of these devices is exceptionally good, and will provide a new wide-field, near-UV capability for the observatory. Several notable advances are described.