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WFPC2 Stellar Photometry with HSTPHOT
Dolphin, Andrew E.
HSTphot, a photometry package designed to handle the undersampled point-spread functions (PSFs) found in WFPC2 images, is introduced and described, as well as some of the considerations that have to be made in order to obtain accurate PSF-fitting stellar photometry with WFPC2 data. Tests of HSTphot's internal reliability are made using multiple ob…
Toward High-Precision Astrometry with WFPC2. I. Deriving an Accurate Point-Spread Function
Anderson, Jay; King, Ivan R.
The first step toward doing high-precision astrometry is the measurement of individual stars in individual images, a step that is fraught with dangers when the images are undersampled. The key to avoiding systematic positional error in undersampled images is to determine an extremely accurate point-spread function (PSF). We apply the concept of th…
SN 1997bs in M66: Another Extragalactic η Carinae Analog?
Van Dyk, Schuyler D.; Filippenko, Alexei V.; Li, Weidong +4 more
We report on SN 1997bs in NGC 3627 (M66), the first supernova discovered by the Lick Observatory Supernova Search using the 0.75 m Katzman Automatic Imaging Telescope (KAIT). Based on its early-time optical spectrum, SN 1997bs was classified as Type IIn. However, from the BVRI light curves obtained by KAIT early in the supernova's evolution, and F…
The Hipparcos and Tycho Photometric System Passbands
Bessell, Michael S.
Hipparcos and Tycho magnitudes have been extracted for many of the E-region standard stars. Differences between B, V, and the Hipparcos and Tycho magnitudes have been derived and regressed against color. Fiducial lines and polynomial fits have been derived and compared with values in the Hipparcos and Tycho Catalogues. Synthetic photometry has bee…
The Ultraviolet and Optical Spectra of Metal-deficient O Stars in the Small Magellanic Cloud
Walborn, Nolan R.; Parker, Joel Wm.; Smith, Linda J. +4 more
An ultraviolet and optical spectral atlas of 15 O stars in the Small Magellanic Cloud (SMC) is presented and described. The echelle data have resolving powers of order 104; they were obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph in the UV, and at the Anglo-Australian Telescope or the European Southern Obs…
LINER/HII ``Transition'' Nuclei and the Nature of NGC 4569
Shields, Joseph C.; Barth, Aaron J.
Motivated by the discovery of young, massive stars in the nuclei of some LINER/H II ``transition'' nuclei such as NGC 4569, we have computed photoionization models to determine whether some of these objects may be powered solely by young star clusters rather than by accretion-powered active nuclei. The models were calculated with the photoionizati…
Resolving the Controversy over the Core Radius of 47 Tucanae (NGC 104)
Gilliland, Ronald L.; Guhathakurta, Puragra; Howell, Justin H.
This paper investigates the discrepancy between recent measurements of the density profile of the globular cluster 47 Tuc that have used Hubble Space Telescope data sets. A large core radius would support the long-held view that 47 Tuc is a relaxed cluster, while a small core radius may indicate that it is in a post-core-collapse phase or possibly…
Photometric Recovery of Crowded Stellar Fields Observed with HST/WFPC2 and the Effects of Confusion Noise on the Extragalactic Distance Scale
Freedman, Wendy L.; Stetson, Peter B.; Ferrarese, Laura +4 more
We explore the limits of photometric reductions of crowded stellar fields observed with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. Two photometric procedures, based on the DoPHOT and DAOPHOT/ALLFRAME programs, are tested, and the effects of crowding, complex sky background, and cosmic-ray contamination are discussed…
Analysis of Polarized Light with NICMOS
Schneider, Glenn; Hines, Dean C.; Schmidt, Gary D.
The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) aboard the Hubble Space Telescope (HST) contains optics in Cameras 1 and 2 (NIC1 and NIC2) that enable imaging polarimetry at ~1 and 2 µm, respectively, with unprecedented spatial detail. Preflight thermal vacuum tests revealed that the three polarizers in each camera have uniqu…
Hubble Space Telescope Observations of the Hubble Clusters in NGC 6822: Ages and Structure
Zucker, Daniel B.; Hodge, Paul W.; Wyder, Ted K.
We present Hubble Space Telescope observations of four cluster candidates in NGC 6822 originally identified by Hubble. One of them, Hubble IV, is an H II region while Hubble VI, VII, and VIII are confirmed as rich star clusters. Based upon cluster color-magnitude diagrams from which the field star contamination has been subtracted, we derive ages …