Search Publications
FUSE Observations of DB White Dwarfs
Kruk, J. W.; Chayer, P.; Petitclerc, N. +2 more
We present a comprehensive analysis of the far-ultraviolet spectra of three DB white dwarfs secured with the FUSE observatory. Transitions associated with various carbon ions are detected in all three objects. Atmospheric parameters are first redetermined on the basis of an analysis of archival data available, and the abundance of carbon, together…
The Chemical Composition and Equation of State of the Sun Inferred from Seismic Models through an Inversion Procedure
Lin, Chia-Hsien; Däppen, Werner
The remarkable quality of present helioseismic data provides the possibility to investigate the microscopic physics of the solar interior. An inversion procedure to reveal the equation of state and chemical composition in the Sun has been developed. The method is based on using the discrepancy in the adiabatic gradient γ1≡(∂lnP/∂lnρ)
Detection of Silicon Nitride Particles in Extreme Carbon Stars
Sturm, E.; Mutschke, H.; Henning, Th. +4 more
On the basis of spectra taken by the Infrared Space Observatory and laboratory measurements, we present the first spectroscopic evidence for the presence of silicon nitride (Si3N4) grains in the circumstellar shells of a number of extreme carbon stars. Laboratory measurements of α, β, and amorphous Si3N4…
First Ultraviolet Spectrum of a Brown Dwarf: Evidence for H2 Fluorescence and Accretion
Gizis, John E.; Shipman, Harry L.; Harvin, James A.
We analyze an HST STIS ultraviolet spectrum of the young brown dwarf 2MASSW J1207334-393254, a member of the 10 million year old TW Hya association that has a planetary-mass companion. We detect and identify numerous emission lines. C IV and other ions are seen that arise in hot gas. We identify a series of lines with Lyman-pumped H2 mo…
Why Optically Faint AGNs Are Optically Faint: The Spitzer Perspective
Rigby, J. R.; Barmby, P.; Fazio, G. G. +5 more
Optically faint X-ray sources (those with fX/fR>10) constitute about 20% of X-ray sources in deep surveys and are potentially highly obscured and/or at high redshift. Their faint optical fluxes are generally beyond the reach of spectroscopy. For a sample of 20 optically faint sources in CDFS, we compile 0.4-24 µm pho…
Host Galaxy Evolution in Radio-Loud Active Galactic Nuclei
Urry, C. Megan; O'Dowd, Matthew
We investigate the luminosity evolution of the host galaxies of radio-loud active galactic nuclei (AGNs) through Hubble Space Telescope imaging of 72 BL Lac objects, including new Space Telescope Imaging Spectrograph (STIS) imaging of nine z>0.6 BL Lacs. With their intrinsically low accretion rates and their strongly beamed jets, BL Lac objects…
Comparison of GONG and MDI: Sound-Speed Anomalies beneath Two Active Regions
Thompson, M. J.; Rajaguru, S. P.; Hughes, S. J.
Travel times of acoustic waves are calculated from Dopplergrams of solar oscillations obtained using the Global Oscillation Network Group (GONG) ground-based network and the Michelson Doppler Imager (MDI) instrument on board the SOHO satellite. These travel times are inverted using a standard ray approximation to ascertain the sound-speed anomalie…
Modeling the Energy Budget of Solar Wind Minor Ions: Implications for Temperatures and Abundances
Lie-Svendsen, Øystein; Esser, Ruth
The outflow of oxygen and silicon ions in the solar wind has been studied using a model that extends from the chromosphere into interplanetary space, with emphasis on understanding the energy budget of the minor ions. The model solves coupled gyrotropic transport equations, which account for temperature anisotropies and heat conduction, for all ch…
Mass Flows in a Disappearing Sunspot Plume
Brosius, Jeffrey W.
We observed a large sunspot in NOAA Active Region 9535 on 2001 July 12, 15, 17, and 19 with three instruments (CDS, EIT, and MDI) on board SOHO. EUV emission lines of O IV (formed at logarithmic temperature of 5.2), O V (5.4), Ne IV (5.2), Ne V (5.5), Ne VI (5.6), Ne VII (5.7), and Ca X (5.9) revealed a large bright plume within the sunspot penumb…
The Ultraluminous X-Ray Source X-37 Is a Background Quasar in the Antennae Galaxies
Hayward, T. L.; Brandl, B. R.; Eikenberry, S. S. +8 more
In this Letter we report that a bright, X-ray source in the Antennae galaxies (NGC 4038/9), previously identified as an ultraluminous X-ray source (ULX), is in fact a background quasar. We identify an isolated infrared and optical counterpart within 0.3" +/- 0.5" of the X-ray source X-37. After acquiring an optical spectrum of its counterpart, we …