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Cosmic-Ray Rejection by Laplacian Edge Detection
van Dokkum, Pieter G.
Conventional algorithms for rejecting cosmic rays in single CCD exposures rely on the contrast between cosmic rays and their surroundings and may produce erroneous results if the point-spread function is smaller than the largest cosmic rays. This paper describes a robust algorithm for cosmic-ray rejection, based on a variation of Laplacian edge de…
The Star Clusters in the Irregular Galaxy NGC 4449
Gallagher, J. S.; Hunter, Deidre A.; Gelatt, Andrea E.
We examine the star clusters in the luminous irregular galaxy NGC 4449. We use a near-infrared spectrum and broadband images taken with the Hubble Space Telescope to place a limit of 8-15 Myr on the age of the bright central object in NGC 4449. Its luminosity and size suggest that it is comparable to young super star clusters. However, there is a …
Measuring Sizes of Marginally Resolved Young Globular Clusters with the Hubble Space Telescope
Holtzman, Jon A.; Carlson, Matthew N.
We present a method for deriving sizes of marginally resolved star clusters from Hubble Space Telescope/WFPC2 observations by fitting King models to observations. We describe results both on simulated images and on observations of young compact clusters in NGC 3597 and NGC 1275. From the simulations, we find that we can measure King model concentr…
SPIRAL Phase A: A Prototype Integral Field Spectrograph for the Anglo-AustralianTelescope
Kenworthy, Matthew A.; Taylor, Keith; Parry, Ian R.
We present details of a prototype fiber feed for use on the Anglo-Australian Telescope (AAT) that uses a dedicated fiber-fed medium/high-resolution (R~=10,000) visible-band spectrograph to give integral field spectroscopy (IFS) of an extended object. A focal reducer couples light from the telescope to the close-packed lenslet array and fiber feed,…
Dying Pulse Trains in Cygnus XR-1: Evidence for an Event Horizon?
Dolan, Joseph F.
The X-ray-emitting component in the Cyg XR-1/HDE 226868 system is a leading candidate for identification as a stellar-mass-sized black hole. The detection of an event horizon surrounding the point singularity in such a system would constitute a positive identification of a black hole as predicted by general relativity. One signature of such an eve…
Spectroscopy of Massive Stars in NGC 6822 and M33
Bianchi, Luciana; Hutchings, John B.; Scuderi, Salvatore +1 more
We present blue spectra of massive stars in the Local Group galaxies NGC 6822 and M33. For all the targets, selected from our previous Hubble Space Telescope WFPC2 photometry, no previous spectroscopic studies exist, to our knowledge, except for a bright Wolf-Rayet star in NGC 6822. Photospheric parameters Teff and gravity are derived b…
Hubble Space Telescope Photometry of Clusters of Galaxies behind the Dwarf Irregular Galaxies DDO 216 and IC 1613 and the Small Magellanic Cloud
Hodge, Paul W.; Krienke, Karl
We have measured the integrated colors of galaxies in clusters located behind the dwarf irregular galaxies DDO 216 (Pegasus) and IC 1613 and a position in the Small Magellanic Cloud (SMC) near the cluster Lindsey 31. We examine limits on the accuracy of using these for studying the total extinction in galaxies. We show that the method is feasible …
Hubble Space Telescope Color-Magnitude Data for Globular Clusters. I. Transformations between STIS LP Magnitudes and WFPC2 F606W and F814W Magnitudes
Wyse, Rosemary F. G.; Gilmore, Gerard; Houdashelt, Mark L.
We present deep Hubble Space Telescope optical imaging observations of two Galactic globular clusters, 47 Tucanae and M15, using the Space Telescope Imaging Spectrograph (STIS) longpass (LP) filter and the Wide Field and Planetary Camera 2 (WFPC2) F606W and F814W filters. These globular clusters have very different metallicities ([Fe/H]~-0.7 dex f…
The Confusion Limit on Astrometry with the Space Interferometry Mission
Böker, Torsten; Allen, Ronald J.; Rajagopal, Jayadev
An important requirement for the Space Interferometry Mission (SIM) is to carry out precision astrometry in crowded fields. This capability is crucial, for example, to accurately measure proper motions of bright stars in nearby galaxies. From such measurements, one can obtain distance estimates, explore the dynamics of these systems, and measure t…
A Study of the Wavelength Calibration of NEWSIPS High-Dispersion Spectra
Smith, Myron A.
In this study we cross-correlate many IUE echellograms of a variety of well-observed stars to evaluate systematic error sources in the wavelength zero points (velocities) of all three cameras. We first evaluate differences between the final archived (``NEWSIPS'') and the originally processed (``IUESIPS'') echellograms. These show a marked time dep…