Search Publications
The Galaxy Octopole Moment as a Probe of Weak-Lensing Shear Fields
Natarajan, Priyamvada; Goldberg, David M.
In this paper, we introduce the octopole moment of the light distribution in galaxies as a probe of the weak-lensing shear field. While traditional ellipticity estimates of the local shear derived from the quadrupole moment are limited by the width of the intrinsic ellipticity distribution of background galaxies, the dispersion in the intrinsic oc…
Nuclear Stellar Disks in Spiral Galaxies
Scarlata, C.; Stiavelli, M.; Morelli, L. +4 more
We report evidence for nuclear stellar disks in three early-type spirals, namely, NGC 1425, NGC 3898, and NGC 4698, revealed by Wide Field Planetary Camera 2 F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope data archive. Adopting the photometric method introduced by Scorza & Bender, we derived their …
The Detection of Pure Dark Matter Objects with Bent Multiply Imaged Radio Jets
Metcalf, R. Benton
When a gravitational lens produces two or more images of a quasar's radio jet the images can be compared to reveal the presence of small structures along one or more of the lines of sight. If mass is distributed smoothly on scales of <~107 Msolar, independent bends in the jet images on milliarcsecond scales will not be pro…
Afterglow Upper Limits for Four Short-Duration, Hard Spectrum Gamma-Ray Bursts
Frontera, F.; Price, P. A.; Berger, E. +22 more
We present interplanetary network localization, spectral, and time history information for four short-duration, hard spectrum gamma-ray bursts, GRB 000607, GRB 001025B, GRB 001204, and GRB 010119. All of these events were followed up with sensitive radio and optical observations (the first and only such bursts to be followed up in the radio to dat…
Statistical Investigation and Modeling of Sungrazing Comets Discovered with the Solar and Heliospheric Observatory
Sekanina, Zdenek
More than 300 sungrazing comets, most of them discovered with the Solar and Heliospheric Observatory (SOHO) coronagraphs since the beginning of 1996, are known to belong to the Kreutz group or system. Moving about the Sun in similar orbits, they are of indisputably common parentage and represent by far the most extensive data set in the history of…
The Likely Near-Infrared Counterpart to the Anomalous X-Ray Pulsar 1E 1048.1-5937
Chakrabarty, Deepto; Wang, Zhongxiang
We report our discovery of the likely near-infrared counterpart to the anomalous X-ray pulsar (AXP) 1E 1048.1-5937, using observations from the 6.5 m Baade (Magellan I) telescope in Chile. We derived a precise position for the X-ray source using archival data from the Chandra X-Ray Observatory. This position is inconsistent with a position reporte…
Variable Ultraviolet Absorption in the Seyfert 1 Galaxy NGC 3516: The Case for Associated Ultraviolet and X-Ray Absorption
Turner, T. J.; Kraemer, S. B.; Crenshaw, D. M. +3 more
We present observations of the UV absorption lines in the Seyfert 1 galaxy NGC 3516, obtained at a resolution of λ/Δλ~40,000 with the Space Telescope Imaging Spectrograph (STIS) on 2000 October 1. The UV continuum was ~4 times lower than that observed during 1995 with the Goddard High Resolution Spectrograph (GHRS), and the X-ray flux from a conte…
Non-LTE Calculation of the Ni I 676.8 Nanometer Line in a Flaring Atmosphere
Qiu, Jiong; Wang, Haimin; Ding, M. D.
The Ni I 676.8 nm line is used by the Solar and Heliospheric Observatory Michelson Doppler Imager to measure the magnetic field and velocity field in the solar atmosphere. We make non-LTE calculations of this line in an atmosphere that is bombarded by an energetic electron beam. This case is associated with the occurrence of solar flares. The elec…
Velocity-resolved [Fe II] Line Spectroscopy of L1551 IRS 5: A Partially Ionized Wind under Collimation around an Ionized Fast Jet
Kobayashi, Naoto; Tokunaga, Alan T.; Terada, Hiroshi +5 more
We present a new [Fe II] λ1.644 µm emission-line image of the L1551 IRS 5 jets and a velocity-resolved spectrum obtained with the Subaru Telescope. In the [Fe II] line image showing two separate jetlike features, a strong and spatially wide [Fe II] emission feature was found elongated along the northern jet at its base. The echelle spectrum …
X-Ray and Optical Variations in the Classical Be Star γ Cassiopeia: The Discovery of a Possible Magnetic Dynamo
Smith, Myron A.; Henry, Gregory W.; Robinson, Richard D.
The classical B0.5e star γ Cassiopeia is known to be a unique X-ray source by virtue of its moderate LX (1033 ergs s-1), hard X-ray spectrum, and light curve punctuated by ubiquitous flares and slow undulations. The peculiarities of this star have led to a controversy concerning the origin of these emissions: wheth…