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Searching for Earth Analogs Around the Nearest Stars: The Disk Age-Metallicity Relation and the Age Distribution in the Solar Neighborhood
Valenti, Jeff A.; Reid, I. Neill; Turnbull, Margaret C. +2 more
The chemical composition of Earth's atmosphere has undergone substantial evolution over the course of its history. It is possible, even likely, that terrestrial planets in other planetary systems have undergone similar changes; consequently, the age distribution of nearby stars is an important consideration in designing surveys for Earth analogs. …
The Aptly Named Phoenix Dwarf Galaxy
Dolphin, Andrew E.; Skillman, Evan D.; Weisz, Daniel R. +1 more
The Local Group galaxy Phoenix has the properties of a dwarf spheroidal galaxy, but an adjacent H I cloud has been recently found to be at the same radial velocity as the stars. The proximity suggests that this cloud is associated with the most recent (<=100 Myr) star formation in Phoenix. We have obtained relatively high sensitivity and high r…
Joint Analysis of Cluster Observations. I. Mass Profile of Abell 478 from Combined X-Ray, Sunyaev-Zel'dovich, and Weak-Lensing Data
Hoekstra, Henk; Babul, Arif; Mahdavi, Andisheh +3 more
We provide a new framework for the joint analysis of cluster observations (JACO) using simultaneous fits to X-ray, Sunyaev-Zel'dovich (SZ), and weak-lensing data. Our method fits the mass models simultaneously to all data, provides explicit separation of the gaseous, dark, and stellar components, and-for the first time-allows joint constraints on …
A Statistical Study of Accretion Disk Model Spectra for Cataclysmic Variables
Hubeny, Ivan; Puebla, Raúl E.; Diaz, Marcos P.
We have performed a statistical test of the currently used accretion disk models for cataclysmic variables (CVs) using a set of 33 CVs with steady disks (10 old novae and 23 nova-like systems). The mass transfer rate () for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization meth…
XMM-Newton and Chandra Spectroscopy of the Variable High-Energy Absorption of PG 1115+080: Refined Outflow Constraints
Brandt, W. N.; Chartas, G.; Gallagher, S. C. +1 more
We present results from multi-epoch spectral analysis of XMM-Newton and Chandra observations of the mini-broad absorption line (BAL) quasar PG 1115+080. This is one of the few X-ray-detected mini-BAL quasars to date that is bright enough in the X-ray band, mostly due to large gravitational-lensing magnifications, to allow in-depth spectral analysi…
Magnetic Helicity Injection in Active Regions
Chae, Jongchul; Jeong, Hyewon
Magnetic helicity is now regarded as an important physical quantity in understanding solar magnetic activities. We have studied the injection of magnetic helicity through the photosphere of four active regions during the long periods of their lifetimes. The rate of helicity injection was determined as a function of time in each active region by ap…
The Galaxy Evolution Explorer UV emission in shell galaxies: tracing galaxy `rejuvenation' episodes
Rich, R. M.; Buson, L. M.; Marino, A. +6 more
We present the Galaxy Evolution Explorer (GALEX) far-ultraviolet (FUV) and near-ultraviolet (NUV) imaging of three nearby shell galaxies, namely NGC 2865, NGC 5018 and NGC 7135 located in low-density environments.
The system of shells and fine structures visible in the optical is detected in the NUV image of NGC 2865 and in both NUV and FUV i…Preferential Perpendicular Heating of Coronal Hole Minor Ions by the Fermi Mechanism
Isenberg, Philip A.; Vasquez, Bernard J.
We present a kinetic mechanism for the preferential perpendicular heating of minor ions in coronal holes, which may be responsible for the consistent observation in fast solar wind that the heavy ions are hotter and flow faster than the proton population. The basis of this mechanism is the familiar resonant cyclotron interaction between ions and p…
Venus atmospheric circulation: Known and unknown
Limaye, Sanjay S.
After a pause of more than two decades, Venus' atmosphere is being explored again. Since April 2006, European Space Agency's Venus Express has been acquiring data, exploiting the near-infrared windows that allow us to peer into the deep night-side atmosphere. In June 2007, NASA's MESSENGER mission will fly past Venus on its way to Mercury, collect…
On the Absence of Wind Signatures in GRB Afterglow Spectra: Constraints on the Wolf-Rayet Winds of GRB Progenitors
Foley, Ryan J.; Ramirez-Ruiz, Enrico; Chen, Hsiao-Wen +3 more
We investigate available constraints on the circumstellar medium (CSM) around long-duration γ-ray burst (GRB) progenitors from afterglow spectra. We first establish a statistical sample of five GRB afterglow spectra that have been collected and analyzed with no prior knowledge of the line-of-sight properties. This sample is then adopted for a unif…