Search Publications
Toward Unbiased Determination of the Redshift Evolution of Lyman-Alpha Forest Clouds
Lu, Limin; Zuo, Lin
The possibility of using D_A_, the mean depression of a quasar spectrum due to Lyα forest absorption, to study the number density evolution of the Lyα forest clouds is examined in some detail. Current D_A_ measurements are made against a continuum that is a power- law extrapolation from the continuum longward of Lyα emission. Compared to the line-…
The massive star content of the blue dwarf galaxy IZw 36 from Faint Object Camera observations
Boksenberg, A.; Barbieri, C.; Weigelt, G. +16 more
We have observed the blue dwarf galaxy IZw 36 with the f/96 relay of the Faint Object Camera and have for the first time resolved massive stars, using the broad band filters F175W, F342W, F430W and F480LP. We have measured the fluxes of 143 of these objects and studied their characteristics in color-magnitude diagrams. A few stars may be red super…
The Optical and X-Ray Content of the 1992 May 1 Gamma-Ray Burst Error Box
Cline, T.; Hurley, K.; Kouveliotou, C. +9 more
A gamma-ray burst which occurred on 1992 May 1 was observed by three spacecraft in the third interplanetary network, and rapidly localized to a small error box. The coordinates were promptly circulated to a wide astronomical community, and radio, optical, and X-ray counterpart searches were carried out. A weak X-ray source was found in the error b…
Ultraviolet flare activity on the eclipsing binary SZ Piscium.
Doyle, J. G.; Mathioudakis, M.; Mitrou, C. K. +1 more
The estimated total chromospheric, transition region and coronal losses for a flare observed on the eclipsing binary SZ Psc with the International Ultraviolet Explorer (IUE) satellite on 6 July 1990 is of the order of 4.5 1036 ergs. This estimate is similar to that derived by Doyle et al. (1989) for an ultraviolet flare on another RS CV…
Concurrent X-Ray and Optical Observations of Two Dwarf Novae during Eruption
Raymond, J. C.; Vrtilek, S. D.; Silber, A.
The dwarf novae SU UMa and RU Peg were each observed with the ROSAT Observatory during outburst. SU UMa was also observed twice between outbursts. The spectrum of SU UMa during quiescence is well fitted by a 2.1 keV thermal bremsstrahlung model with a Gaussian line at 0.97 keV absorbed by a column density of 1.4 x 1020/sq cm. During the…
A Hubble Space Telescope Study of Posteclipse Brightening and Albedo Changes on Io
Secosky, James J.; Potter, Michael
Images of Io taken by the Hubble Space Telescope Planetary Camera using filters at 7120 and 3577 Å in April and May 1992 shortly after Io emerged from Jupiter's shadow have been analyzed for the effect of posteclipse brightening first reported by Binder and Cruikshank (1964, Icarus 3,299-305). The classic effect displays a 10% increase in brighten…
X-ray Planetary Nebulae
Feibelman, Walter A.
A study of IUE archival low-dispersion spectra was conducted in an attempt to correlate the C IV/He II and C III]/C IV emission line ratios as indicators of x-ray emission in planetary nebulae. The presence of P Cygni lines revealed a strong correlation for planetaries known to exhibit x-ray emission. Of the twelve planetaries definitely known to …
The interior structure and evolution of blue straggler stars in open clusters.
Napiwotzki, R.; Schoenberner, D.
We present a detailed spectroscopic determination of effective temperatures and surface gravities of B- and A-type blue straggler stars in four open clusters by means of model atmospheres and new optical/UV spectrograms. By using a new method of analysis which also allows to separate objects not belonging to the cluster under investigation we show…
Markarian 315: A Test Case for the Active Galactic Nucleus--Merger Hypothesis?
MacKenty, John W.; Wilson, Andrew S.; Griffiths, Richard E. +2 more
Using the Hubble Space Telescope Wide Field/Planetary Camera, we have detected a diffuse continuum knot in the inner regions of the Seyfert galaxy Markarian 315. This knot may be a remnant nucleus. It is associated with a complex, ringlike structure in both the continuum and ionized gas emission. We have measured the kinematics of the ionized gas …
HST Imaging of the Large Magellanic Cloud: The Field Star Population near 30 Doradus
Forbes, Duncan A.; Elson, Rebecca A. W.; Gilmore, Gerard F.
We present deep color-magnitude diagrams for two fields in the Large Magellanic Cloud, located about 6 arcminutes from 30 Doradus. The data are from images taken with the Hubble Space Telescope's Wide Field Camera, as part of the Medium Deep Survey Key Project. We describe a procedure for measuring stellar magnitudes in relatively crowded HST imag…