Search Publications

Old Faithful model for radiolytic gas-driven cryovolcanism at Enceladus

Rymer, Abigail M.; Sittler, Edward C.; Cooper, John F. +2 more

A new model is presented on how chemically driven cryovolcanism might contribute to episodic outgassing at the icy moon Enceladus and potentially elsewhere including Europa and Kuiper Belt Objects. Exposed water ices can become oxidized from radiolytic chemical alteration of near-surface water ice by space environment irradiation. In contact with …

Reconnection at High Latitudes: Antiparallel Merging

Escoubet, C. P.; Dunlop, M. W.; Fear, R. C. +5 more

New investigations have renewed the debate on the occurrence of magnetic reconnection of Earth’s dayside magnetopause. Here, we show for the first time strong evidence for a high-latitude reconnection site, located on initially closed field lines, where the magnetic field orientations inside and outside the magnetopause are close to antiparallel. …

Stellar Populations of Late-Type Bulges at z ≃ 1 in the Hubble Ultra Deep Field

Hathi, N. P.; Malhotra, S.; Rhoads, J. E. +5 more

We combine the exceptional depth of the Hubble Ultra Deep Field (HUDF) images and the deep GRism Advanced Camera for Surveys Program for Extragalactic Science (GRAPES) grism spectroscopy to explore the stellar populations of 34 bulges belonging to late-type galaxies at 0.8 <= z <= 1.3. The sample is selected based on the presence of a notice…

High-Energy Emission from a Solar Flare in Hard X-rays and Microwaves

Kundu, M. R.; White, S. M.; Grechnev, V. V. +3 more

We investigate accelerated electron energy spectra for different sources in a large flare using simultaneous observations obtained with two instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) at hard X-rays. This flare is one of the few in which emission up to en…

Titania's radius and an upper limit on its atmosphere from the September 8, 2001 stellar occultation

Sutherland, W.; Colas, F.; Lellouch, E. +150 more

On September 8, 2001 around 2 h UT, the largest uranian moon, Titania, occulted Hipparcos star 106829 (alias SAO 164538, a V=7.2, K0 III star). This was the first-ever observed occultation by this satellite, a rare event as Titania subtends only 0.11 arcsec on the sky. The star's unusual brightness allowed many observers, both amateurs or professi…

Identifications of Five INTEGRAL Sources via Optical Spectroscopy

Kaaret, Philip; Kalemci, Emrah; Walter, Roland +6 more

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is discovering hundreds of new hard X-ray sources, many of which remain unidentified. We report on optical spectroscopy of five such sources for which X-ray observations at lower energies (~0.5-10 keV) and higher angular resolutions than INTEGRAL have allowed for unique optical counter…

On the elusive hot oxygen corona of Venus

Lammer, H.; Shematovich, V. I.; Lichtenegger, H. I. M. +2 more

After more than two years in orbit still no Venus Express observations were published concerning the hot oxygen corona of Venus which could verify the corresponding controversial observations of Venera 11 and PVO, three decades ago. Based on recent energy and mass dependent collision cross sections, the energy distributions of hot atomic oxygen cr…

The structure and dynamics of Titan's middle atmosphere

Flasar, F. M.; Achterberg, R. K.

Compact Star Clusters in the M31 Disk

Narbutis, D.; Vansevičius, V.; Kodaira, K. +4 more

We have carried out a survey of compact star clusters (apparent size lsim3'') in the southwest part of the M31 galaxy, based on the high-resolution Suprime-Cam images (17farcm5 × 28farcm5), covering ~15% of the deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V lsim 20.5 mag) was performed using frames of the Local Gro…

Suzaku Wide Band Analysis of the X-Ray Variability of TeV Blazar Mrk 421 in 2006

Takahashi, Tadayuki; Tanaka, Takaaki; Kataoka, Jun +9 more

We present the results of X-ray observations of the well studied TeV blazar Mrk 421 with the Suzaku satellite in 2006 April 28. During the observation, Mrk 421 was undergoing a large flare and the X-ray flux was variable, decreasing by ~50%, from 7.8 × 10^-10 to 3.7 × 10^-10 erg s^-1 cm^-2 in about 6 hr, fol…