Search Publications
The Color-Magnitude Diagram in Baade's Window Revisited
Kiraga, Marcin; Paczyński, Bohdan; Stanek, Krzysztof Z.
We have reanalyzed the OGLE V and I photometry of ~500,000 stars in Baade's Window, and we confirm the extinction map published by Stanek. However, we find that the interpretation of the OGLE color-magnitude diagram for the disk stars proposed by Paczyński et al. was incorrect: the dominant disk population in Baade's Window is old, and we find no …
Final Astro-1 Calibration of the Hopkins Ultraviolet Telescope: A Test of White Dwarf Model Atmospheres as Far-Ultraviolet Calibration Standards
Kriss, Gerard A.; Holberg, J. B.; Kimble, Randy A. +5 more
We present the final calibration of the Hopkins Ultraviolet Telescope (HUT) for its flight during the Astro-1 space shuttle mission in 1990 December. The calibration is defined by a comparison between an observation obtained in flight of the hot DA white dwarf G191-B2B and the model atmosphere for this star calculated by P. Bergeron. We also prese…
The Mass and Radius of 40 Eridani B from HIPPARCOS: An Accurate Test of Stellar Interior Theory
Provencal, J. L.; Shipman, H. L.; Thejll, P. +1 more
The astrometric satellite HIPPARCOS has determined the distance to the important white dwarf 40 Eridani B with an accuracy surpassing 1%. We use this datum to redetermine the mass and radius of this star and find that M = 0.501 +/- 0.011 Msolar and R = 0.0136 +/- 0.00024 Rsolar. These values, the most accurately determined ma…
High-Resolution X-Ray Image of the Hydrogen-deficient Planetary Nebula Abell 30
Chu, You-Hua; Chang, Thomas H.; Conway, Gail M.
Abell 30 is the brighter of only two planetary nebulae that show extended X-ray emission. Our recent ROSAT high-resolution imager observation of A30 reveals a central source at a 4 σ level and emission knots at a 2 σ level. These emission features are within the same region as the H-deficient knots and filaments resolved in a previous HST WFPC2 [O…
Hubble Space Telescope Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Imaging
Turnshek, David A.; Rao, Sandhya M.; Espey, Brian R. +2 more
An analysis of Hubble Space Telescope (HST) Wide Field Planetary Camera (WFPC) and Wide Field Planetary Camera 2 (WFPC2) images of the gravitationally lensed Cloverleaf broad absorption line quasi-stellar object (QSO) H1413+1143 is presented. Astrometric and photometric measurements are derived for the four components of the lensed QSO for five di…
On the Relationship between the Periodic and Aperiodic Variability of Accreting X-Ray Pulsars
Stella, Luigi; Lazzati, Davide
Besides the narrow peaks originating from the periodic signal, the power spectra of accreting X-ray pulsars display continuum components usually increasing toward low frequencies; these arise from the source aperiodic variability. Most studies up to the present have adopted the view that the periodic and aperiodic variations are independent. Howev…
The Spectrum of the Large Magellanic Cloud Pulsar B0540-69
Boyd, Patricia T.; van Citters, G. W.; Taylor, M. J. +4 more
A prism spectrum of PSR B0540-69, the 50 ms pulsar in the Large Magellanic Cloud, was obtained with the Faint Object Spectrograph on the Hubble Space Telescope. This is only the second pulsar spectrum that has been observed in the optical. The 2500-5500 Å spectrum shows a smooth continuum with several broad emission lines. The lines are emitted by…
Hubble Space Telescope WFPC Images of Emission Nebulosity near XZ Tauri
Ballester, Gilda E.; Krist, John E.; Crisp, David +14 more
XZ Tauri is a M3 V T Tauri star with a pre-main-sequence binary companion detected by infrared speckle interferometry at a projected separation of 0.3" (about 40 AU). Previous ground-based observations of the system have shown bipolar emission nebulosity, including a possible jet knot. Images obtained with the Wide Field and Planetary Camera 2 on …
Galactic Cosmic-Ray Manganese: Ulysses High Energy Telescope Results
DuVernois, M. A.
The Ulysses High Energy Telescope (HET) allows for a study of Galactic cosmic-ray manganese because of the telescope's excellent mass resolution and large collecting area. The manganese isotopes in the cosmic rays provide a means of studying the parameters of the cosmic-ray propagation in the Galaxy. Each of the isotopes probes a separate aspect o…
Velocity Fields in the Solar Corona during Mass Ejections as Observed with UVCS-SOHO
Romoli, M.; Naletto, G.; Modigliani, A. +20 more
This Letter presents the observations of the first two coronal mass ejections (CMEs) obtained with the Ultraviolet Coronagraph Spectrometer of SOHO. Both CMEs were observed at high spectral resolution in the ultraviolet domain. The first event on 1996 June 6-7 was observed in H I Lyα λ1216 and Lyβ λ1026, O VI λλ1032 and 1037, Si XII λλ499 and 521 …