Search Publications
An X-Ray Jet from a White Dwarf: Detection of the Collimated Outflow from CH Cygni with Chandra
Sokoloski, J. L.; Galloway, Duncan K.
Most symbiotic stars consist of a white dwarf accreting material from the wind of a red giant. An increasing number of these objects have been found to produce jets. Analysis of archival Chandra data of the symbiotic system CH Cygni reveals faint extended emission to the south, aligned with the optical and radio jets seen in earlier Hubble Space T…
Helicity Patterns of Coronal Mass Ejection-associated Active Regions
Zhang, Jun; Wang, Jingxiu; Zhou, Guiping
Coronal mass ejections (CMEs) are thought to originate from the overaccumulation of magnetic helicity. While recent studies have revealed the inability of active region (AR) fields to create enough helicity for CMEs, we have tried, on the other hand, to examine whether particular helicity patterns are retained by CME-associated ARs. Nine ARs, whos…
Unveiling the Central Parsec Region of an Active Galactic Nucleus: The Circinus Nucleus in the Near-Infrared with the Very Large Telescope
Lutz, D.; Rouan, D.; Meisenheimer, K. +12 more
VLT J- to M'-band adaptive optics observations of the Circinus galaxy on parsec scales resolve a central bright Ks-band source with a FWHM size of 1.9+/-0.6 pc. This source is only visible at wavelengths longward of 1.6 µm and coincides in position with the peak of the [Si VII] 2.48 µm coronal line emission. With respect to …
Green Bank Telescope Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30
Ransom, Scott M.; Kaspi, Victoria M.; Hessels, Jason W. T. +4 more
We report the discovery of two binary millisecond pulsars in the core-collapsed globular cluster M30 using the Green Bank Telescope (GBT) at 20 cm. PSR J2140-2310A (M30A) is an eclipsing 11 ms pulsar in a 4 hr circular orbit, and PSR J2140-23B (M30B) is a 13 ms pulsar in an as yet undetermined but most likely highly eccentric (e>0.5) and relati…
Location of the Optical Reverse Shock in the Cassiopeia A Supernova Remnant
Chevalier, Roger A.; Borkowski, Kazimierz J.; van den Bergh, Sidney +4 more
We use two epochs of Hubble Space Telescope WFPC2 images separated by 2 yr to determine the location and propagation of the reverse shock (RS) in the young supernova remnant Cassiopeia A (Cas A). The images trace optical line emission from fast-moving knots and filaments of highly processed ejecta as they cross the RS, become heated and compressed…
RHESSI e+-e- Annihilation Radiation Observations: Implications for Conditions in the Flaring Solar Chromosphere
Smith, David M.; Lin, Robert P.; Share, Gerald H. +2 more
RHESSI has measured the positron-electron annihilation line and continuum in three solar flares: 2002 July 23, 2003 October 28, and 2003 November 2. The 511 keV line was broad (~4-8 keV) in all three flares, consistent with annihilations in an ambient ionized medium at temperatures above 105 K. The measured continuum from positronium an…
XMM-Newton Observations of PSR B1706-44
Cropper, M.; McGowan, K. E.; Kennea, J. A. +5 more
We report on the XMM-Newton observations of the young 102 ms pulsar PSR B1706-44. We have found that both a blackbody plus power law and a magnetized atmospheric model plus power law provide an excellent fit to the European Photon Imaging Camera (EPIC) spectra. The two scenarios are therefore indistinguishable on a statistical basis, although we a…
The Dynamical Distance to M15: Estimates of the Cluster's Age and Mass and of the Absolute Magnitude of Its RR Lyrae Stars
Baumgardt, H.; Harrison, T. E.; McNamara, B. J.
Newly determined high-precision relative proper motions determined from the Hubble Space Telescope Wide Field Planetary Camera 2 are used along with radial velocity measurements to determine the dynamical distance to the globular cluster M15. A comparison of the proper motion and radial velocity dispersions from a sample of 237 stars, located at a…
Non-LTE Radiative Transfer in Model Prominences. I. Integrated Intensities of He I Triplet Lines
Labrosse, N.; Gouttebroze, P.
In this work we use new results of radiative transfer calculations out of local thermodynamical equilibrium to study the triplet lines emitted by neutral helium in solar quiescent prominences. We compare two types of prominence atmospheres: isothermal and isobaric models versus nonisothermal and nonisobaric ones. We can thus investigate the effect…
Age Constraints for an M31 Globular Cluster from Main-Sequence Photometry
Ferguson, Henry C.; Brown, Thomas M.; Rich, R. Michael +5 more
We present a color-magnitude diagram (CMD) of the globular cluster SKHB 312 in the Andromeda galaxy (M31), obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. The cluster was included in deep observations taken to measure the star formation history of the M31 halo. Overcoming a very crowded field, our photometry of SKHB 31…