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The Discovery of Mg II λ4481 in the White Dwarf EG 102: Evidence for Ongoing Accretion
Barstow, M. A.; Holberg, J. B.; Green, Elizabeth M.
Recent optical spectra of the DA3 white dwarf EG 102 clearly show a feature due to Mg II λ4481. This is the first spectroscopic detection of Mg in a DA star at a temperature of 20,000 K. The presence of this ion in the stellar photosphere poses a severe dilemma for the theory of radiative levitation, which predicts a vanishingly small equilibrium …
The Pele Plume (Io): Observations with the Hubble Space Telescope
Ballester, Gilda E.; McGrath, Melissa A.; Spencer, John R. +3 more
In July 1996, with the Hubble Space Telescope (HST), we observed the Pele plume silhouetted against Jupiter at a wavelength of 0.27µm, the first definitive observation of an Io plume from Earth. The height, 420 ± 40 km, was greater than any plume observed by Voyager. The plume had significantly smaller optical depth at 0.34 and 0.41µm, where it wa…
Hubble Space Telescope Spectrum of SN 1987A at an Age of 8 Years: Radioactive Luminescence of Cool Gas
Challis, Peter M.; Chevalier, Roger A.; Kirshner, Robert P. +1 more
The Hubble Space Telescope 2000-8000 Å spectrum of SN 1987A observed on 1995 January 7 (7.87 yr after the explosion) is dominated by Hα and UV lines, including Mg II-Mg I λ2825 (equal to Hα in luminosity), Fe II UV 2 (two-thirds the intensity of Hα), Fe II UV 3 (one-half the intensity of Hα), and a 3730 Å emission feature identified with a blend o…
High Velocity Features in the Orion Nebula
Hartigan, Patrick; O'Dell, C. R.; Bally, John +1 more
We have surveyed the inner 7' of the Orion Nebula for high velocity outflows with Fabry-Perot images in [S II] and [O III]. The new survey recovers all known HH objects in the region, and also reveals a number of new high velocity flows. New flows include (1) jets over an arcminute in length that extend from the center of the nebula to HH 202 in t…
Spectroscopy of Close Companions to Quasi-Stellar Objects and the Ages of Interaction-Induced Starbursts
Stockton, Alan; Canalizo, Gabriela
We present low-resolution absorption-line spectra of three candidate close (<3") companions to the low-redshift QSOs 3CR 323.1, PG 1700+518, and PKS 2135-147. The spectra were obtained with the Low-Resolution Imaging Spectrometer (LRIS) on the Keck telescopes and with the Faint Object Spectrograph on the University of Hawaii 2.2 m telescope. Fo…
Identification of moving groups from a sample of B, A and F type stars.
Figueras, F.; Torra, J.; Chen, B. +1 more
An algorithm to find moving groups has been developed and applied to a sample of 1924 B, A, and F main sequence stars, basically extracted from the Hipparcos Input Catalogue. This algorithm uses a non-parametric kernel estimator to describe the stellar distribution in a 4-dimensional space of velocities and age, although it can be used to detect t…
The Dwarf Irregular Galaxy Sextans A. I. HST Photometry of the Resolved Stars
Skillman, Evan D.; Saha, A.; Gallagher, J. +6 more
We have used the Hubble Space Telescope to observe the resolved stars of the nearby (D = 1.4 Mpc) dwarf irregular galaxy Sextans A (DDO 75, A 1008-04). The data consist of dithered WFPC2 images in 3 bands: F439W (1 hour), F555W (30 minutes), and F814W (30 minutes). The stellar photometry was extracted using the DoPHOT program developed by Schechte…
Radial velocities and iron abundances of field RR Lyraes. I.
Barnes, T. G.; Fernley, J.
We present systemic velocities and iron abundances for 56 RR Lyraes, the majority of which have been observed by the HIPPARCOS satellite. Comparison between our systemic velocities and previous values identifies several binary candidates only one of which, TU UMa, was previously suspected of being a binary. However, spectra of the unusual RR Lyrae…
The Extragalactic Distance Scale Key Project. VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope
Illingworth, Garth D.; Huchra, John P.; Kennicutt, Robert C. +18 more
We report on the discovery of Cepheids in the field spiral galaxy NGC 3621, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as a part of the HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% accur…
On Calibrating Brightest Asymptotic Giant Branch Stars as Age Indicators: The Bulge Globular Cluster NGC 6553 and the Age of M32
Renzini, Alvio; Ortolani, Sergio; Guarnieri, Maria Donata
Bright asymptotic giant branch (AGB) stars can be used as an age indicator for stellar populations that are too far away for their main-sequence turnoffs to be reachable. However, the method requires an empirical calibration, as the brightness of the AGB termination depends on both age and metallicity in ways that cannot be predicted from first pr…