Search Publications
Impulsive Variations of the Magnetic Helicity Change Rate Associated with Eruptive Flares
Moon, Y. -J.; Wang, Haimin; Chae, Jongchul +2 more
In this paper, we investigate impulsive variations of the magnetic helicity change rate associated with eruptive solar flares (three X class flares and one M class flare) accompanying halo coronal mass ejections. By analyzing four sets of 1 minute cadence full-disk magnetograms taken by the Michelson Doppler Imager on board the Solar and Heliosphe…
The Optical Counterpart of an Ultraluminous X-Ray Object in M81
Bregman, Joel N.; Seitzer, Patrick; Liu, Ji-Feng
Ultraluminous X-ray objects (ULXs) are off-nucleus point sources with LX=1039-1041 ergs s-1 they are among the most poorly understood X-ray sources. To help understand their nature, we are trying to identify their optical counterparts by combining images from the Hubble Space Telescope and the Chandra X-…
The Variability of the Hg II λ3984 Line of the Mercury-Manganese Star α Andromedae
Adelman, Saul J.; Gulliver, Austin F.; Kochukhov, Oleg P. +1 more
The variability of the Hg II λ3984 line in the primary of the binary star α And was discovered through the examination of high-dispersion spectra with signal-to-noise ratios greater than 500. This first definitively identified spectrum variation in any mercury-manganese star is not due to the orbital motion of the companion. Rather, the variation …
The Luminosity Function of QSO Host Galaxies
Turnshek, David A.; Casertano, Stefano; Hamilton, Timothy S.
We present some results from our HST archival image study of 71 QSO host galaxies. The objects are selected to have z<=0.46 and total absolute magnitude MV<=-23 in our adopted cosmology (H0=50 km s-1 Mpc-1, q0=0.5, and Λ=0). The aim of this initial study is to investigate the composition…
X-Ray Evidence for Flare Density Variations and Continual Chromospheric Evaporation in Proxima Centauri
Skinner, Stephen L.; Güdel, Manuel; Audard, Marc +1 more
Using the XMM-Newton X-ray observatory to monitor the nearest star to the Sun, Proxima Centauri, we recorded the weakest X-ray flares on a magnetically active star ever observed. Correlated X-ray and optical variability provide strong support for coronal energy and mass supply by a nearly continuous sequence of rapid explosive energy releases. Var…
The Velocity Distribution of the Nearest Interstellar Gas
Welty, Daniel E.; Frisch, Priscilla C.; Grodnicki, Lauren
The bulk flow velocity for the cluster of interstellar cloudlets within ~30 pc of the Sun is determined from optical and ultraviolet absorption line data, after omitting from the sample stars with circumstellar disks or variable emission lines and the active variable HR 1099. A total of 96 velocity components toward the remaining 60 stars yield a …
A Chandra High Resolution Camera Observation of X-Ray Point Sources in M31
Kaaret, Philip
We present results from a 47 ks observation of the Andromeda galaxy, M31, using the High Resolution Camera of the Chandra X-Ray Observatory. We detect 142 point sources spanning 3 orders of magnitude in luminosity, from LX=2×1035 to 2×1038 ergs s-1 in the 0.1-10 keV band. The X-ray source location accura…
Hubble Space Telescope Space Telescope Imaging System Observations of the He II Gunn-Peterson Effect toward HE 2347-4342
Tripp, Todd M.; Jenkins, Edward B.; Heap, Sara R. +3 more
We present an HST Space Telescope Imaging System (STIS) spectrum of the He II Gunn-Peterson effect toward HE 2347-4342. Compared to the previous HST Goddard High Resolution Spectrograph data obtained by Reimers et al. the STIS spectrum has a much improved resolution. The two-dimensional detector also allows us to better characterize the sky and da…
An Enshrouded Active Galactic Nucleus in the Merging Starburst System Arp 299 Revealed by BeppoSAX
Maraschi, L.; Cappi, M.; Franceschini, A. +9 more
Using a long (~=150 ks) broadband (0.1-40 keV) BeppoSAX observation of the merging starburst system Arp 299 (=IC 694+NGC 3690), we found the first unambiguous evidence of the presence of a deeply buried (NH~=2.5×1024 cm-2) active galactic nucleus (AGN) having  an intrinsic luminosity of L0.5-100keV~=1.9…
Coronal White-Light Jets near Sunspot Maximum
Sheeley, N. R., Jr.; Wang, Y. -M.
During the 1996-1997 activity minimum, the Large Angle and Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) recorded numerous jetlike ejections above the Sun's polar regions. In a previous study, we showed that these white-light ejections were the outward extensions of extreme-ultraviolet (EUV) jets, which in turn…