Search Publications
Effects of errors in the solar radius on helioseismic inferences
Basu, Sarbani
Frequencies of intermediate-degree f modes of the Sun seem to indicate that the solar radius is smaller than what is normally used in constructing solar models. We investigate the possible consequences of an error in radius on results for solar structure obtained using helioseismic inversions. It is shown that solar sound speed will be overestimat…
Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
van der Hucht, K. A.; Moffat, A. F. J.; van den Heuvel, E. P. J. +9 more
Reliable systemic radial velocities are almost impossible to secure for Wolf-Rayet stars, difficult for O stars. Therefore, to study the motions - both systematic in the Galaxy and peculiar - of these two related types of hot, luminous star, we have examined the Hipparcos proper motions of some 70 stars of each type. We find that (a) both groups f…
Systematics of RR Lyrae Statistical Parallax. III. Apparent Magnitudes and Extinctions
Gould, Andrew; Popowski, Piotr
We sing the praises of the central limit theorem. Having previously removed all other possible causes of significant systematic error in the statistical-parallax determination of RR Lyrae absolute magnitudes, we investigate systematic errors from two final sources of input data: apparent magnitudes and extinctions. We find corrections due to each …
Modeling the Brightness Profiles of the Orion Proplyds
Henney, W. J.; Arthur, S. J.
We investigate whether simple models of a photoevaporated flow from an externally ionized neutral clump or wind can reproduce the observed Hα intensity profiles of the proplyds in the inner Orion Nebula. We find that models fitted to the bright ``cusp'' at the head of each proplyd successfully predict the brightness distribution of the extended di…
Photoionization of Disk Winds
Chiang, J.; Murray, N.
The disk-wind model suggests that the broad emission lines of a quasar are emitted from the surface of the accretion disk feeding the central black hole. In this paper, we assume that a line-driven wind emerges from the illuminated face of the disk and calculate the line emission produced by this wind. The location and mass-loss rate of the wind a…
The nucleus and inner coma of Comet 46P/Wirtanen
Jorda, L.; Lamy, P. L.; Toth, I. +2 more
We report the detection of the nucleus of comet 46P/Wirtanen from analysis of images taken with the Planetary Camera (WFPC2) of the Hubble Space Telescope (HST) on 28 August 1996. The high spatial resolution (a WFPC2 pixel projects to 50 km at the distance of the comet) allowed us to separate the signal of the nucleus from that of the coma and to …
Keck HIRES Spectroscopy of M92 Subgiants: Surprising Abundances near the Turnoff
King, Jeremy R.; Boesgaard, Ann M.; Stephens, Alex +1 more
Using high-resolution, moderate signal-to-noise ratio spectroscopy obtained with the 10 m Keck I Telescope and efficient HIRES echelle spectrograph, we derive abundances of several elements in subgiants near the M92 turnoff. As a consistency check, we also analyze the metal-poor field star HD 140283 and find an Fe abundance in fine agreement with …
Early Evolution of the Galactic Halo Revealed from Hipparcos Observations of Metal-poor Stars
Yoshii, Yuzuru; Chiba, Masashi
The kinematics of 122 red giant and 124 RR Lyrae stars in the solar neighborhood are studied using accurate measurements of their proper motions obtained by the Hipparcos astrometry satellite, combined with their published photometric distances, metal abundances, and radial velocities. A majority of these sample stars have metal abundances of [Fe/…
Solar Active Region and Quiet-Sun Extreme-Ultraviolet Spectra from SERTS-95
Brosius, Jeffrey W.; Thomas, Roger J.; Davila, Joseph M.
Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph was flown on 1995 May 15 (SERTS-95), carrying a multilayer-coated toroidal diffraction grating that enhanced the instrumental sensitivity in its second-order wave band (171-225 Å). Spectra and spectroheliograms of NOAA active region 7870 (N09 W22) were obtained in this wave …
Spatially Resolved STIS Spectroscopy of SN 1987A: Evidence for Shock Interaction with Circumstellar Gas
Lundqvist, P.; Gull, T. R.; McCray, R. +15 more
Visual and ultraviolet spatially resolved (~0.1") spectra of SN 1987A obtained on days 3715 and 3743 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope show that the high-velocity supernova debris is colliding with circumstellar gas. Very broad Lyα emission with velocities extending to ~+/-20,000 km s-1 originat…