Search Publications
High- Speed Hubble Space Telescope Ultraviolet Photometry of Two DB White Dwarfs: NonRadial and Radial Pulsation
Bond, Howard E.; Kawaler, Steven D.; Sherbert, Lisa E. +1 more
We observed two DB white dwarf stars with the High Speed Photometer aboard the Hubble Space Telescope. The two targets, the nonradial pulsator GD 358, and PG 0112+104, a non-pulsating white dwarf with similar temperature, were each observed for 1800 s with a time resolution of 10 ms. We used the F140LP configuration, which gives a broadband respon…
Spectral Variations in the Low-Mass X-Ray Binary 4U 0614+09
Singh, K. P.; Apparao, K. M. V.
We report the X-ray spectra of a binary 4U 0614+09 observed with EXOSAT on five different occasions in 1984 and 1986. In four observations in 1984, the source intensity was 'low' compared to its intensity in the 1986 observation. The source was steady on timescales of 10 to 1000 s in each of the 1984 observations but highly variable during the 198…
Calibration of HST Wide Field Camera for Quantitative Analysis of Faint Galaxy Images
Casertano, Stefano; Griffiths, Richard E.; Ratnatunga, Kavan U. +2 more
We present the methods adopted to optimize the calibration of images obtained with the Hubble Space Telescope Wide Field Camera (1991-1993). Our main goal is to improve quantitative measurement of faint images, with special emphasis on the faint (I ~ 20-24 mag) stars and galaxies observed as a part of the Medium-Deep Survey. Several modifications …
Multifrequency monitoring of the Seyfert 1 galaxy NGC 4593 - I. Isolating the nuclear emission.
Glass, I. S.; Clavel, J.; Peterson, B. M. +4 more
We present data obtained within a Campaign to monitor spectral variations in the low-luminosity Seyfert 1 galaxy NGC 4593, at X-ray, ultraviolet, optical and near-IR (J, H, K and L) frequencies. The different `parasitic' contributions that contaminate the pure nuclear continuous emission have been isolated and modelled. The light from the composit…
The ultraviolet spectra of the symbiotic stars MWC 960, FN Sgr, SS 29 and Draco C-1.
Munari, Ulisse; Buson, Lucio M.
IUE observations of the symbiotic stars MWC 960, FN Sgr, SS 29 and C-1 in the Draco dwarf galaxy are presented. These systems were not formerly observed by the IUE. C-1 qualifies as the farthest symbiotic star detected by the satellite with the SWP camera. At least three of the four objects are found to contain very hot and luminous white dwarfs. …
Variable Stars with the HIPPARCOS Satellite
Eyer, L.; Mignard, F.; Grenon, M. +2 more
We present the photometric results of Hipparcos satellite for the first 1.5 year of the mission. For this period, the satellite gave numerous (20 to 120) photometric measurements of 120000 stars. More precisely, we describe: the precision, the capability to find periods with respect to the specific sampling of the satellite (based on simulated dat…
Far-Ultraviolet Imaging of the Globular Cluster NGC 6681 with WFPC2
Casertano, Stefano; Ballester, Gilda E.; Crisp, David +13 more
We have imagined the globular cluster NGC 6681 in the far-UV and visible with Wide Field/Planetary Camera-2 (WFPC2) on the Hubble Space Telescope (HST). Our far-UV images show a sparsely populated and fully resolved central region, and we detect 122 stars. The far-UV to visible color-magnitude diagram shows a well-defined horizontal branch with no…
Metal-Line Absorption at Z/abs - Z/em From Associated Galaxies
Bechtold, Jill; Yee, H. K. C.; Dobrzycki, Adam +1 more
For a preliminary study of whether C IV absorption at z_abs_~z_em_ is related to associated galaxy companions, we have collected data from a sample of 10 quasars with 0.15< z <0.65 for which high-resolution optical and UV spectroscopy is available from the literature, and for which we have deep optical images and limited spectroscopy. We als…
The origin of extended interstellar shells around Wolf-Rayet stars having bright optical ring nebulae.
Fesen, R. A.; Nichols, J. S.
Investigations of the interstellar environment around Wolf-Rayet (WR) stars have led to the discovery of extended shells of gas and dust 50-100pc in diameter in the lines of sight toward three WR stars. In this paper, several origins for these extended shells are discussed. While positional coincidences cannot be excluded, the locations of the WR …
Null fields in the outer Jovian magnetosphere: Ulysses observations
Dougherty, M. K.; Balogh, A.; Smith, E. J. +3 more
This paper reports on a magnetic field phenomenon, hereafter referred to as null fields, which were discovered during the inbound pass of the recent flyby of Jupiter by the Ulysses spacecraft. These null fields which were observed in the outer dayside magnetosphere are characterised by brief but sharp decreases of the field magnitude to values les…