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Hubble Space Telescope Imaging of the Poststarburst Quasar UN J1025-0040: Evidence for Recent Star Formation
Filippenko, Alexei V.; Canalizo, Gabriela; Shanks, Tom +5 more
We present new Hubble Space Telescope (HST) Wide Field Planetary Camera images of the poststarburst quasar UN J1025-0040, which contains both an active galactic nucleus (AGN) and a 400 Myr old nuclear starburst of similar bolometric luminosity (~1011.6 Lsolar). The F450W and F814W images resolve the AGN from the starburst and…
A Precise Orbit Determination of χ1 Orionis from Astrometric and Radial Velocity Data
Han, Inwoo; Gatewood, George
We have derived an accurate orbit of χ1 Orionis (HD 39587, HIP 27913, HR 2047) by combining precise astrometric and radial velocity data. The combined orbital analysis yields P=5156.7+/-2.5 days, K1=1.885+/-0.004 km s-1, α1=94.8+/-1.6 mas, e=0.451+/-0.003, and mass ratio (M2/M1) q=0…
Characterizing the Adaptive Optics Off-Axis Point-Spread Function. I. A Semiempirical Method for Use in Natural Guide Star Observations
Lloyd, J. P.; Graham, James R.; Faber, S. M. +11 more
Even though the technology of adaptive optics (AO) is rapidly maturing, calibration of the resulting images remains a major challenge. The AO point-spread function (PSF) changes quickly in both time and position on the sky. In a typical observation, the star used for guiding will be separated from the scientific target by 10"-30". This is sufficie…
Astrophysics in 2001
Aschwanden, Markus J.; Trimble, Virginia
During the year, astronomers provided explanations for solar topics ranging from the multiple personality disorder of neutrinos to cannibalism of CMEs (coronal mass ejections) and extra-solar topics including quivering stars, out-of-phase gaseous media, black holes of all sizes (too large, too small, and too medium), and the existence of the unive…
The Ultraviolet Light Curve of LMC X-4: X-Ray Heating of the O Star and Accretion Disk
Boroson, Bram; Vrtilek, Saeqa Dil; Preciado, Michael E.
We present an archival study of ultraviolet spectra of the X-ray binary LMC X-4 obtained with the IUE satellite. We fit these spectra with models that incorporate the X-ray heating of the O star and accretion disk. A systematic analysis of the UV continuum confirms the general picture of an O star that fills its Roche lobe and is heated by X-rays …
Solving Olin Wilson's Mystery
Abt, Helmut A.
Wilson showed that G8-M1 dwarfs have a range of 0.30 mag in P-V color whereas the color range for earlier stars is 0.12 mag. He attributed the increased range for the later stars to differing hydrogen-to-metal ratios in the temperature region where most of the electrons come from the metals. I explored those stars using Hipparcos parallaxes and ph…
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 …