Search Publications
The Discovery of Oxygen-rich Chromospheres in Two Massive DQ White Dwarfs
Provencal, J. L.; Shipman, H. L.; MacDonald, James
We present HST observations of the massive DQ white dwarfs G227-5 and G35-26 in which we find the first clear evidence of chromospheric activity in cool field white dwarfs. The chromospheric spectra, obtained over a very narrow wavelength range, show lines of the usually expected species O I, N I, C II, and possibly Si III and Mg II. The O I/C II …
The Disk Atmospheres of Three Herbig Ae/Be Stars
Woodward, Charles E.; Temi, Pasquale; Wooden, Diane H. +1 more
We present infrared (IR) spectrophotometry (R~=180) of three Herbig Ae/Be stars surrounded by possible protoplanetary disks: HD 150193, HD 100546, and HD 179218. We construct a mid-IR spectral energy distributions (SEDs) for each object by using 7.6-13.2 µm HIFOGS spectra, 2.4-45 µm spectrophotometry from the Infrared Space Observatory…
Optical Constraints on an X-ray Transient Source in M31
Williams, Benjamin F.; McClintock, Jeffrey E.; Murray, Stephen S. +2 more
We have detected a transient X-ray source in the M31 bulge through a continuing monitoring campaign with the Chandra ACIS-I camera. The source was detected at R.A.=00h42m33.428s+/-0.11", decl.=+41deg17'03.37"+/-0.11" in only a single observation taken 2004 May 23. Fortuitous optical HST ACS imaging of th…
The Impact of Sunspots on the Interpretation of Coronal Observations of the O VI Doublet
Morgan, H.; Habbal, S. Rifai
Due to their high intensity of emission in the O VI λλ1031.9 and 1037.6 lines, even small sunspots on the solar disk can strongly influence the intensity of the radiative scattering component of O VI lines in the corona. Observations of O VI disk spectra show a λ1032/λ1038 line intensity ratio of >2.6 in a sunspot, compared to quiet-disk values…
Hubble Space Telescope STIS Spectroscopy of the Lyα Emission Line in the Central Dominant Galaxies in A426, A1795, and A2597: Constraints on Clouds in the Intracluster Medium
Koekemoer, Anton M.; Baum, Stefi A.; Mack, Jennifer +2 more
We report on HST STIS spectra of the Lyα emission in the central dominant galaxies in three rich clusters of galaxies. We find evidence for a population of clouds in the intracluster medium. We detect 10 Lyα absorption systems toward the nucleus of NGC 1275 with columns of N(HI)~1012-1014 cm-2. These columns would …
A Chandra Observation of the Diffuse Emission Centered on the Low-Mass X-Ray Binary 4U 1755-33
McClintock, Jeffrey E.; Miller, Jon M.; Murray, Stephen S. +1 more
We present an analysis of a Chandra observation of the field surrounding the low-mass X-ray binary 4U 1755-33, which has been in quiescence since 1996. In 2003, Angelini & White reported the appearance of a narrow 7'-long jetlike feature centered on the position of 4U 1755-33 using the XMM-Newton telescope. Although the source and jet are not …
HST Imaging of MEGA Microlensing Candidates in M31
Crotts, Arlin P. S.; Kuijken, Konrad; Widrow, Lawrence M. +5 more
We investigate HST/ACS and WFPC2 images at the positions of five candidate microlensing events from a large survey of variability in M31 (MEGA). Three closely match unresolved sources, and two produce only flux upper limits. All are confined to regions of the color-magnitude diagram where stellar variability is unlikely to be easily confused with …
Far-Ultraviolet and Optical Observations of BW Vulpeculae
Smith, Myron A.; Fullerton, Alex W.; Sterken, Christiaan
We have compared the behavior of 39 Far-Ultraviolet Spectroscopic Explorer spectra through the pulsation cycle of the very large amplitude β Cephei star BW Vul with optical and UV (IUE) spectra, as well as optical photometry. The FUSE light curve suggests a temperature amplitude of about 4000 K, while the radial velocity curve is similar to corres…
Stream-Field Interactions in the Magnetic Accretor AO Piscium
Hellier, Coel; van Zyl, Liza
UV spectra of the magnetic accretor AO Psc show absorption features for half the binary orbit. The absorption is unlike the wind-formed features often seen in similar stars. Instead, we attribute it to a fraction of the stream that overflows the impact with the accretion disk. Rapid velocity variations can be explained by changes in the trajectory…
A MERLIN Observation of PSR B1951+32 and Its Associated Plerion
Muxlow, T. W. B.; Golden, A.; Shearer, A. +4 more
In an investigative 16 hr L-band observation using the MERLIN radio interferometric array, we have resolved both the pulsar PSR B1951+32 and the structure within the flat spectral radio continuum region, believed to be the synchrotron nebula associated with the interaction of the pulsar and its ``host'' supernova remnant CTB 80. The extended struc…