Search Publications
A Comparative Study of the Atmospheric Composition of the DA White Dwarfs Feige 24 and G191-B2B
Vennes, Stéphane; Lanz, Thierry
We analyze Hubble Space Telescope Imaging Spectrograph spectra of two white dwarfs, Feige 24 and G191-B2B, and we compare the measured abundance patterns. Except for carbon, which appears overabundant in G191-B2B by 0.3-0.5 dex relative to Feige 24, the average heavy-element abundance in Feige 24 is 0.17 dex larger than in the cooler, hence older,…
Hubble Space Telescope Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Imaging Polarimetry and Evidence for Microlensing of a Scattering Region
Turnshek, David A.; Rao, Sandhya M.; Schulte-Ladbeck, Regina E. +2 more
We report the results of Hubble Space Telescope Wide Field and Planetary Camera 2 broadband F555W and F702W photometric and F555W polarimetric observations of the ``Cloverleaf'' QSO H1413+1143. This is a four-component gravitationally-lensed broad absorption line (BAL) QSO. Observations were obtained at two epochs in 1999 March and 1999 June separ…
Dynamical Cycles in Charge and Energy for Iron Ions Accelerated in a Hot Plasma
Torsti, J.; Kocharov, L.; Kovaltsov, G. A.
We consider a unified model of Fe ion acceleration in the solar corona. The model comprises charge-changing processes, Coulomb energy losses, and both regular and stochastic acceleration. At a given acceleration scenario, the type of acceleration is found to have a minor effect on the mean charge states, but the shapes of the charge-state distribu…
LB 8827: A Variable, Magnetic DBA White Dwarf
Fontaine, G.; Bergeron, P.; Wesemael, F. +3 more
We present accurate CCD spectropolarimetry and spectra that show that the hot DB star LB 8827 (PG 0853+164) is a weakly magnetic, variable DBA white dwarf. We confirm Putney's detection of circular dichroism in the He I lines, but on three occasions we measure a weaker field strength and opposite sign of circular polarization, Be<~10…
Electron Densities, Radial and Terminal Wind Velocities for the Planetary Nebula NGC 6302 and Its O VI-Type Binary Nucleus
Feibelman, Walter A.
Archival high- and low-dispersion IUE spectra of NGC 6302 and its nucleus have been analyzed. The spectra in the NEWSIPS format reveal many high-excitation emission features, including stellar O V, O VI, O VII, and O VIII that identify the nucleus as a new member of the ``O VI sequence.'' Fe II features that are resonantly excited by O VI λ1032 ar…
The Formation of Broad-Line Clouds in the Accretion Shocks of Active Galactic Nuclei
Fromerth, Michael J.; Melia, Fulvio
Recent work on the gas dynamics in the Galactic center has improved our understanding of the accretion processes in galactic nuclei, particularly with regard to properties such as the specific angular momentum distribution, density, and temperature of the inflowing plasma. With the appropriate extrapolation of the physical conditions, this informa…
Hubble Space Telescope STIS Observations of GRB 000301C: CCD Imaging and Near-Ultraviolet MAMA Spectroscopy
Fruchter, Andrew S.; Hogg, David W.; Livio, Mario +24 more
We present Space Telescope Imaging Spectrograph observations of the optical transient (OT) counterpart of the γ-ray burster GRB 000301C obtained 5 days after the burst, on 2000 March 6. CCD clear-aperture imaging reveals a R~=21.50+/-0.15 source with no apparent host galaxy. An 8000 s, 1150 Å<λ<3300 Å near-ultraviolet MAMA prism spectrum sho…
Far-Ultraviolet Intensities and Center-to-Limb Variations of Active Regions and Quiet Sun Using UARS SOLSTICE Irradiance Measurements and Ground-based Spectroheliograms
Woods, Thomas N.; Worden, John R.; Bowman, Kevin W.
The average intensity and center-to-limb variation of active regions, enhanced network (large-scale active region fragments), and quiet Sun are estimated by minimizing the variance between time series of the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) far-ultraviolet (FUV) irradiance measurements and a model of the solar irradiance t…
Rapid Temporal Variations of Interstellar Absorption Lines in the Carina Nebula
Walborn, Nolan R.; Danks, Anthony C.; Landsman, Wayne B. +3 more
Two observations of the complex interstellar absorption-line profiles in the UV spectrum of CPD -59°2603, obtained 22 months apart in the R~110,000 mode of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, reveal substantial variations in the intensities of several high-velocity components, including the virtual disappearance…
The Inner Nebula and Central Binary of the Symbiotic Star HM Sagittae
Davis, R. J.; Eyres, S. P. S.; Bode, M. F. +2 more
We present contemporaneous Hubble Space Telescope Wide Field Planetary Camera 2 and Very Large Array observations of the symbiotic nova HM Sge. We identify a number of discreet features at spatial scales smaller than ~0.1" embedded in the extended nebula, with radio and optical emission well correlated in the inner 1". For the first time we measur…