Sally D. Hunsberger

Photometric calibration of the Swift ultraviolet/optical telescope

We present the photometric calibration of the Swift Ultraviolet/Optical Telescope (UVOT) which includes: optimum photometric and background apertures, effective area curves, colour transformations, conversion factors for count rates to flux and the photometric zero-points (which are accurate to better than 4 per cent) for each of the seven UVOT broad-band filters. The calibration was performed with observations of standard stars and standard star fields that represent a wide range of spectral star types. The calibration results include the position-dependent uniformity, and instrument response over the 1600‐8000 A operational range. Because the UVOT is a photon-counting instrument, we also discuss the effect of coincidence loss on the calibration results. We provide practical guidelines for using the calibration in UVOT data analysis. The results presented here supersede previous calibration results.

The formation of dwarf galaxies in tidal debris: A study of the compact group environment

From R-band images of 42 Hickson compact groups, we present a sample of 47 candidate dwarf galaxies that are associated with the tidal tails and arms in the groups. The candidates, found in 15 tidal features, have R magnitudes and masses (for M/L = 1) in the ranges -16.5 < M_R - 5 log h_{75} < -11.5 and 2x10^6 M_{\odot} < M < 2x10^8 M_{\odot}, respectively. Their masses and locations are compared to the predictions of theoretical/N-body tidal dwarf formation scenarios. Considering the longevity of tidal debris in the compact group environment and the results of this survey, we estimate the contribution of the tidal dwarf formation mechanism to the population of dwarf galaxies observed at large in compact groups. If the majority of our dwarf galaxy candidates are confirmed as being gravitationally bound stellar systems, then a significant fraction, perhaps as much as one-half, of the dwarf population in compact groups is the product of interactions among giant parent galaxies.

From globular clusters to tidal dwarfs: Structure formation in the tidal tails of merging galaxies

Using V and I images obtained with the Wide Field Planetary Camera 2 (WFPC2) of the Hubble Space Telescope, we investigate compact stellar structures within tidal tails. Six regions of tidal debris in the four classic Toomre sequence mergers: NGC 4038/39 (Antennae), NGC 3256, NGC 3921, and NGC 7252 (Atoms for Peace) have been studied in order to explore how the star formation depends on the local and global physical conditions. These mergers sample a range of stages in the evolutionary sequence and tails with and without embedded tidal dwarf galaxies. The six tails are found to contain a variety of stellar structures, with sizes ranging from those of globular clusters up to those of dwarf galaxies. From V and I WFPC2 images, we measure the luminosities and colors of the star clusters. NGC 3256 is found to have a large population of blue clusters (0.2 V-I 0.9), particularly in its western tail, similar to those found in the inner region of the merger. In contrast, NGC 4038/39 has no clusters in the observed region of the tail, only less luminous point sources likely to be individual stars. NGC 3921 and NGC 7252 have small populations of clusters along their tails. A significant cluster population is clearly associated with the prominent tidal dwarf candidates in the eastern and western tails of NGC 7252. The cluster-rich western tail of NGC 3256 is not distinguished from the others by its dynamical age or by its total H I mass. However, the mergers that have few clusters in the tail all have tidal dwarf galaxies, while NGC 3256 does not have prominent tidal dwarfs. We speculate that star formation in tidal tails may manifest itself either in small structures like clusters along the tail or in large structures such as dwarf galaxies, but not in both. Also, NGC 3256 has the highest star formation rate of the four mergers studied, which may contribute to the high number of star clusters in its tidal tails.

Hubble Space Telescope Images of Stephan’s Quintet: Star Cluster Formation in a Compact Group Environment* **

Analysis of Hubble Space Telescope Wide Field Planetary Camera 2 images of Stephans Quintet, Hickson Compact Group 92, yielded 115 candidate star clusters (with V (I \ 1.5). Unlike in merger remnants, the cluster candidates in Stephans Quintet are not clustered in the inner regions of the gal- axies; they are spread over the debris and surrounding area. Speci—cally, these sources are located in the long sweeping tail and spiral arms of NGC 7319, in the tidal debris of NGC 7318B/A, and in the intrag- roup starburst region north of these galaxies. Analysis of the colors of the clusters indicate several dis- tinct epochs of star formation that appear to trace the complex history of dynamical interactions in this compact group.

Extreme properties of GRB 061007: a highly energetic or a highly collimated burst?

%auto-ignore This paper has been withdrawn by the authors due to dublicate submission. To download the paper please go to astro-ph/0611081

The Luminosity Function of Galaxies in Compact Groups

From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts to determine a luminosity function extending to MR = -14.0+5 log h75, approximately 2 mag deeper than previous compact group luminosity functions. We find that a single Schechter function is a poor fit (χ

GRB 081203A: Swift UVOT captures the earliest ultraviolet spectrum of a gamma-ray burst

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ULTRAVIOLET, OPTICAL, AND X-RAY OBSERVATIONS OF THE TYPE Ia SUPERNOVA 2005am WITH SWIFT

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The Swift ultra-violet/optical telescope

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Swift UVOT Detection of GRB 050318

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