Search Publications
Classical Cepheids with Terminal Age Main-Sequence Companions: Constraints on Evolution
Evans, Nancy Remage
Eight binaries containing a Cepheid and a hot companion evolved beyond the ZAMS are studied using IUE spectra. The spectral types of these TAMS (terminal age main-sequence) companions are determined from the spectra and absolute magnitudes are determined from the magnitude difference between the two stars and the absolute magnitude of the Cepheid.…
A Thermal Pulse in Progress in the Nucleus of the Large Magellanic Cloud Planetary Nebula N66
Pena, M.; Torres-Peimbert, S.; Ruiz, M. T. +2 more
Optical and UV spectrophotometric data, gathered in the 1987-1994 interval, are presented for the planetary nebula N66 (WS 35 or SMP 83) in the Large Magellanic Cloud. These data show that the central star has suffered dramatic changes. Before 1987 it showed a featureless continuum while its present spectrum shows intense W-R features and P-Cygni …
A Spectrum Synthesis Program for Binary Stars
Linnell, Albert P.; Hubeny, Ivan
A new program produces synthetic spectra of binary stars at arbitrary values of orbital longitude, including longitudes of partial or complete eclipse. The stellar components may be distorted, either tidally or rotationally, or both. Either or both components may be rotating nonsynchronously. We illustrate the program performance with two cases: E…
Observation by Ulysses of hot (∼270 keV) coronal particles at 32° south heliolatitude and 4.6 AU
Simnett, G. M.; Pick, M.; Anderson, K. A. +11 more
An unusual event of streaming 60 keV-2 MeV ions (with energy spectrum peaked ∼270 keV) and of 42-315 keV electrons occurred during the passage of a coronal mass ejection (CME) over the Ulysses spacecraft June 9-13, 1993, located at helioradius 4.6 AU and heliolatitude 32° south. The topology of the interplanetary magnetic field (IMF) within the CM…
The X-Ray Selected Cataclysmic Variables H0459+246 and H0857-242
Buckley, D. A. H.; Schwartz, D. A.; Tuohy, I. R. +5 more
We report the discovery of two cataclysmic variables located with the assistance of X-ray positions from the HEAO 1 Modulation Collimator and the Large-Area Sky Survey. Each case is distinguished by evidence of two periodic modulations that appear to represent the orbital period and the spin period of the white dwarf, respectively. The first case,…
The HST Quasar Absorption Line Key Project VIII. CCD Imaging of Hubble Space Telescope Quasar Fields
Maoz, Dan; Schneider, Donald P.; Sargent, W. L. W. +4 more
We present an analysis of CCD images of more than 100 quasars; many of the objects have been or will be observed in the HST Key Project Quasar Absorption Line Survey. The data set consists of B, g, and i photometry of 117 quasars and deeper g (limiting magnitude of ~22) images of 101 quasar fields. Positions accurate to ~1", measured with the Spac…
ROSAT/XRT-PSPC observations and the ionizing continuum of Seyfert 1 galaxy MKN 478
Gondhalekar, P. M.; Kellett, B. J.; Matthews, L. +2 more
The ROSAT/XRT-PSPC observations of the Seyfert 1 galaxy Mrk 478 are presented. Together with the optical and ultraviolet spectra of this galaxy, obtained within 8 months of the X-ray observations, these new data are used to determine the continuum energy distribution (CED) of Mrk 478, from 1 micron to about 2.0 keV with a small break between 11.3 …
Spectroscopy of Chromospheric Lines of Giants in the Globular Cluster NGC 6752
Smith, Graeme H.; Dupree, A. K.; Hartmann, Lee +3 more
Spectroscopic observations of chromospheric transitions (Mg II, H-alpha, and Ca II K) from two red giants (A31 and A59) in the globular cluster NGC 6572 were made with the Goddard High Resolution Spectrograph on the Hubble Space Telescope and the coude spectrograph of the 1.9 m telescope at the Mount Stromlo Observatory. These measurements give ev…
Identification of the 1600A feature in Lambda Bootis stars
Koester, D.; Allard, N. F.; Holweger, H.
The nature of the absoprtion feature near 1600A in λ Bootis stars, which is one of the strongest features in these objects, is a longstanding puzzle. In this study we demonstrate that it is caused by quasimolecular absorption leading to a satellite in the Lyman α profile due to perturbations by neutral hydrogen. This feature has also been observed…
Stellar Photometry Including Saturated Images: Results on M67 with WFPC2
Gilliland, Ronald L.
The Wide Field and Planetary Camera 2 (WFPC2) on Hubble Space Telescope (HST) is providing unsurpassed imaging capabilities and supporting accurate stellar photometry over large fields of view at high angular resolution. I discuss a feature of the WFPC2 CCD systems that nominally limits the dynamic range attainable with single exposures: a 12 bit …