Search Publications
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…
A Strategy for Identifying the Grid Stars for the Space Interferometry Mission
Quirrenbach, Andreas; Röser, Siegfried; Schilbach, Elena +2 more
We present a strategy to identify several thousand stars that are astrometrically stable at the microarcsecond level for use in the Space Interferometry Mission (SIM) astrometric grid. The requirements on the grid stars make this a rather challenging task. Taking a variety of considerations into account, we argue for K giants as the best type of s…
The 1993-1994 Activity of EX Lupi
Herbig, G. H.; Aspin, C.; Gilmore, Alan C. +2 more
EX Lupi is a classical T Tauri star (and the EXor prototype) subject to sporadic outbursts. The historic record shows that it remains at about V=13.2 (or mpg=14.7:) for extended periods, from which it has been observed to brighten to as much as V=8.4 (on one occasion in 1955-1956). During 1993-1994 the star remained slightly above norma…
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…
Spectroscopic Observation of the Planetary Nebula IC 4846
Hyung, Siek; Aller, Lawrence H.; Lee, Woo-baik
A high-dispersion optical (3700-10100 Å) spectrum was secured with the Hamilton echelle spectrograph at the coudé focus of the 120 inch (3 m) Shane telescope at Lick Observatory, with the goal of deriving chemical abundances for the compact planetary nebula IC 4846. We also remeasured the UV spectra from the IUE archive. Diagnostics indicate that …
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,…
Markarian 478: A Second Seyfert Galaxy with 1 Micron Fe II Emission Lines
Hamann, F.; Rudy, Richard J.; Puetter, R. C. +3 more
We present infrared spectroscopy of the narrow-line Seyfert 1 galaxy Mrk 478 that shows the 1 µm Fe II lines λ9997, λ10501, λ10863, and λ11126. This is the second active galaxy, after I Zw 1, in which these features have been observed. Like I Zw 1, the 1 µm Fe II lines of Mrk 478 appear to arise from collisional excitation of their com…
Astrophysics in 2000
Aschwanden, Markus J.; Trimble, Virginia
It was a year in which some topics selected themselves as important through the sheer numbers of papers published. These include the connection(s) between galaxies with active central engines and galaxies with starbursts, the transition from asymptotic giant branch stars to white dwarfs, gamma-ray bursters, solar data from three major satellite mi…
The Accretion Disk and White Dwarf in the Short-Period Dwarf Novae TY Piscium and V436 Centauri during Quiescence
Sion, Edward M.; Nadalin, Ira
The short-period dwarf novae TY Psc and V436 Cen are SU UMa systems with very similar orbital periods, similar recurrence times for normal outbursts (~23 days) and superoutbursts (~340 days), and nearly identical outburst amplitudes. We have carried out high-gravity model atmosphere and accretion disk synthetic spectra from the grid of Wade & …