Search Publications
Deviations from the Flux-Recurrence Time Relationship in GS 1826-238: Potential Transient Spectral Changes
Rothschild, Richard E.; Galloway, Duncan K.; Homer, Lee +1 more
The low-mass X-ray binary GS 1826-238 is presently unique for its consistently regular bursting behavior. In previous Rossi X-Ray Timing Explorer (RXTE) measurements between 1997 November and 2002 July, this source exhibited (nearly) limit-cycle bursts with recurrence times that decreased proportionately as the persistent flux increased. Here we r…
Non-Local Thermodynamic Equilibrium Model of NGC 6543's Central Star and Its Relation to the Surrounding Planetary Nebula
Hillier, D. J.; Richer, M. G.; Peimbert, M. +3 more
We analyze the chemical composition of the central star of the planetary nebula NGC 6543 based on a detailed NLTE model of its stellar wind. The logarithmic abundances by number are H = 12.00, He = 11.00, C = 9.03, N = 8.36, O = 9.02, Si = 8.19, P = 5.53, S = 7.57, and Fe = 7.24. Compared with the solar abundances, most of the elements have solar …
XMM-Newton Discovery of 217 s Pulsations in the Brightest Persistent Supersoft X-Ray Source in M31
Trudolyubov, Sergey P.; Priedhorsky, William C.
We report on the discovery of a periodic modulation in the bright supersoft X-ray source XMMU J004252.5+411540 detected in the 2000-2004 XMM-Newton observations of M31. The source exhibits X-ray pulsations with a period P ~ 217.7 s and a quasi-sinusoidal pulse shape and pulsed fraction ~7%-11%. We did not detect statistically significant changes i…
Intergalactic He II Absorption in the Spectra of Quasars at Redshifts 3.5 and 3.8, Observed with the HST ACS Prism
Anderson, Scott F.; Schneider, Donald P.; York, Donald G. +8 more
We present the UV spectra of two quasars obtained with the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) prism (R ~ 100). One quasar, at redshift z = 3.5, shows an absorption edge consistent either with nearly fully ionized helium with an intergalactic He II Lyα optical depth at 304 Å of τ304 > 3.1 (90% confidence), or…
The Role of Transient Brightenings in Heating the Solar Corona
Warren, Harry P.; Ugarte-Urra, Ignacio; Brooks, David H.
Nanoflare reconnection events have been proposed as a mechanism for heating the corona. Parker's original suggestion was that frequent reconnection events occur in coronal loops due to the braiding of the magnetic field. Many observational studies, however, have focused on the properties of isolated transient brightenings unassociated with loops, …
Polar Plume Brightening During the 2006 March 29 Total Eclipse
Rušin, V.; Druckmüller, M.; Minarovjech, M. +8 more
We discuss a remarkable brightening in a polar plume, as inferred from unique coordinated observations of the white-light corona during the total eclipse of the Sun of 2006 March 29. The polar plume (also known as a polar ray, with distinctions that we discuss) was observed at the positional angle of 9° the velocity at which the brightening propag…
Hubble Space Telescope Search for M Subdwarf Binaries
Gizis, John E.; Riaz, Basmah; Samaddar, Debasmita
We present HST ACS observations of 19 nearby M subdwarfs in a search for binary systems. Other than the wide common proper-motion pair LHS 2140/2139, none of our sdM and esdM targets are found to be binaries. Our survey is sensitive to equal-luminosity companions at close (2-8 AU) separations, while substellar secondaries could have been detected …
A Simulation of a Coronal Mass Ejection Propagation and Shock Evolution in the Lower Solar Corona
Gombosi, T. I.; Cohen, O.; Opher, M. +2 more
We present a detailed simulation of the evolution of a moderately slow coronal mass ejection (CME; 800 km s-1 at 5 R⊙, where R⊙ is solar radii) in the lower solar corona (2-5 R⊙). The configuration of the Sun's magnetic field is based on the MDI data for the solar surface during Carrington rotation 1922.…
The X-Ray Properties of Moderate-Redshift Galaxy Groups Selected by Association with Gravitational Lenses
McKean, J. P.; Auger, M. W.; Mulchaey, J. S. +5 more
We present results from a systematic investigation of the X-ray properties of a sample of moderate-redshift (0.3 < z < 0.6) galaxy groups. These groups were selected not by traditional X-ray or optical search methods, but rather by an association, either physical or along the line of sight, with a strong gravitational lens. We calculate the …
A Transient Black Hole Low-Mass X-Ray Binary Candidate in Centaurus A
Hardcastle, M. J.; Croston, J. H.; Birkinshaw, M. +14 more
We report the discovery of a bright transient X-ray source, CXOU J132518.2-430304, toward Centaurus A (Cen A) using six new Chandra X-Ray Observatory observations in 2007 March-May. Between 2003 and 2007, its flux has increased by a factor of >770. The source is likely a low-mass X-ray binary in Cen A with unabsorbed 0.3-10 keV band luminositie…