Search Publications
Photometric Confirmation of MACHO Large Magellanic Cloud Microlensing Events
Bennett, David P.; Becker, Andrew C.; Tomaney, Austin
We present previously unpublished photometry of three Large Magellanic Cloud (LMC) microlensing events and show that the new photometry confirms the microlensing interpretation of these events. These events were discovered by the MACHO Project alert system and were also recovered by the analysis of the 5.7 yr MACHO data set. This new photometry pr…
Ultraviolet Hubble Space Telescope Observations of the Jet in M87
Zepf, Stephen E.; Waters, Christopher Z.
We present new ultraviolet photometry of the jet in M87 obtained from Hubble Space Telescope (HST) WFPC2 imaging. We combine these ultraviolet data with previously published photometry for the knots of the jet in radio, optical, and X-ray and fit three theoretical synchrotron models to the full data set. The synchrotron models consistently overpre…
Helium Abundance in High-Temperature Solar Flare Plasmas
Landi, E.; Feldman, U.; Laming, J. M.
In the present work we use emission from dense plasmas late in the decay phase of flares, while the plasmas are still hot [(2-4)×106 K], to determine the absolute helium abundance in flaring solar corona. To achieve this, we make use of intensity ratios of H I and He II lines and of intensity ratios between the He II lines and the brems…
Three Criteria to Discriminate between Elementary and Composite Coronal Loops
Aschwanden, Markus J.
In this Letter, we establish three simple criteria to discriminate between elementary and composite loop structures, based on observations from high-resolution (TRACE) and low-resolution (EIT) imagers. Both data sets contain triple-filter data with a temperature diagnostic in the range of T~0.7-2.8 MK, which we use for forward-fitting of a differe…
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…