Search Publications
Forward Modeling of the Corona of the Sun and Solar-like Stars: From a Three-dimensional Magnetohydrodynamic Model to Synthetic Extreme-Ultraviolet Spectra
Peter, Hardi; Gudiksen, Boris V.; Nordlund, Åke
A forward model is described in which we synthesize spectra from an ab initio three-dimensional MHD simulation of an outer stellar atmosphere, where the coronal heating is based on braiding of magnetic flux due to photospheric footpoint motions. We discuss the validity of assumptions such as ionization equilibrium and investigate the applicability…
Dynamical Properties of Ultraluminous Infrared Galaxies. II. Traces of Dynamical Evolution and End Products of Local Ultraluminous Mergers
Lutz, D.; Genzel, R.; Sturm, E. +8 more
We present results from our Very Large Telescope large program to study the dynamical evolution of local ultraluminous infrared galaxies (ULIRGs) and QSOs. This paper is the second in a series presenting the stellar kinematics of 54 ULIRGs, derived from high-resolution, long-slit H- and K-band spectroscopy. The data presented here, including obser…
The Galaxy Environment of O VI Absorption Systems
Shull, J. Michael; Danforth, Charles W.; Stocke, John T. +3 more
We combine a FUSE sample of O VI absorbers (z<0.15) with a database of 1.07 million galaxy redshifts to explore the relationship between absorbers and galaxy environments. All 37 absorbers with NOVI>=1013.2 cm-2 lie within 800 h-170 kpc of the nearest galaxy, with no compelling evidence …
The Dynamical Mass-to-Light Ratio Profile and Distance of the Globular Cluster M15
Gebhardt, Karl; van de Ven, Glenn; van den Bosch, Remco +2 more
We construct orbit-based axisymmetric dynamical models for the globular cluster M15 that fit ground-based line-of-sight velocities and Hubble Space Telescope line-of-sight velocities and proper motions. This allows us to constrain the variation of the mass-to-light ratio M/L as a function of radius in the cluster and to measure the distance and in…
Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks around Sun-like Stars
Wolf, S.; Pascucci, I.; Carpenter, J. M. +17 more
We have carried out a sensitive search for gas emission lines at IR and millimeter wavelengths for a sample of 15 young Sun-like stars selected from our dust disk survey with Spitzer. We have used mid-IR lines to trace the warm (300-100 K) gas in the inner disk and millimeter transitions of 12CO to probe the cold (~20 K) outer disk. We …
A ``Combination Nova'' Outburst in Z Andromedae: Nuclear Shell Burning Triggered by a Disk Instability
Sokoloski, J. L.; Filippenko, A. V.; Charles, P. A. +11 more
We describe observational evidence for a new kind of interacting binary star outburst that involves both an accretion instability and an increase in thermonuclear shell burning on the surface of an accreting white dwarf. We refer to this new type of eruption as a combination nova. In late 2000, the prototypical symbiotic star Z Andromedae brighten…
Nonthermal Spectral Line Broadening and the Nanoflare Model
Klimchuk, J. A.; Patsourakos, S.
A number of theoretical and observational considerations suggest that coronal loops are bundles of unresolved, impulsively heated strands. This ``nanoflare'' model, as it is sometimes called, predicts high-speed evaporative upflows, which might be revealed as nonthermal broadening of spectral line profiles. We have therefore generated synthetic li…
Gamma-Ray Imaging of the 2003 October/November Solar Flares
Krucker, S.; Lin, R. P.; Smith, D. M. +3 more
We present RHESSI imaging of three flares (2003 October 28 and 29 and November 2) in the 2.223 MeV neutron-capture gamma-ray line with angular resolution as high as 35". Comparisons of imaged and spatially integrated fluences show that in all cases most, if not all, of the emission was confined to compact sources with size scales of tens of arcsec…
A Chandra Survey of Early-Type Galaxies. I. Metal Enrichment in the Interstellar Medium
Humphrey, Philip J.; Buote, David A.
We present a Chandra study of the emission-weighted metal abundances in 28 early-type galaxies, spanning ~3 orders of magnitude in X-ray luminosity (LX). We report constraints for Fe, O, Ne, Mg, Si, S, and Ni. We find no evidence of the very subsolar Fe abundance (ZFe) historically reported, confirming a trend in recent obser…
The Stellar Masses and Star Formation Histories of Galaxies at z ~ 6: Constraints from Spitzer Observations in the Great Observatories Origins Deep Survey
Dickinson, Mark; Ferguson, Henry C.; Giavalisco, Mauro +3 more
Using the deep Spitzer Infrared Array Camera (IRAC) observations of the Great Observatories Origins Deep Survey (GOODS), we study the stellar masses and star formation histories of galaxies at z~6 based on the i775-band dropout sample selected from the GOODS fields. In total, we derive stellar masses for 53 i775-band dropouts…