Search Publications
Difficulties with Recovering the Masses of Supermassive Black Holes from Stellar Kinematical Data
Emsellem, Eric; Merritt, David; Valluri, Monica
We investigate the ability of three-integral, axisymmetric, orbit-based modeling algorithms to recover the parameters defining the gravitational potential (mass-to-light ratio Υ and black hole mass M•) in spheroidal stellar systems using stellar kinematical data. We show that the potential estimation problem is generically underdetermin…
Galaxies at z~7-8: z850-Dropouts in the Hubble Ultra Deep Field
Bouwens, R. J.; Illingworth, G. D.; Thompson, R. I. +6 more
We have detected likely z~7-8 galaxies in the 144''×144'' Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) observations of the Hubble Ultra Deep Field. Objects are required to be >=3 σ detections in both NICMOS bands, J110 and H160. The selection criteria for this sample are (z850
The Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution
Jogee, S.; Dickinson, M.; Ferguson, H. C. +14 more
We examine the evolution of the sizes and number densities of disk galaxies using the high-resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys on the Hubble Space Telescope. The multiwavelength images are used to classify galaxies based on their rest-frame B-band morphologies out t…
X-ray emission from a metal depleted accretion shock onto the classical T Tauri star TW Hya
Schmitt, J. H. M. M.; Stelzer, B.
We present the X-ray spectrum of TW Hya observed at high and intermediate spectral resolution with the Reflection Grating Spectrometer (RGS) and the European Photon Imaging Camera (EPIC) onboard the XMM-Newton satellite. TW Hya is the first classical T Tauri star for which simultaneous X-ray data with both high spectral resolution and high sensiti…
A long hard look at MCG-6-30-15 with XMM-Newton- II. Detailed EPIC analysis and modelling
Vaughan, S.; Fabian, A. C.
The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best evidence to date for the existence of supermassive black holes in active galactic nuclei. Observations with ASCA revealed an X-ray iron line profile shaped by strong Doppler and gravitational effects. In this paper the shape of the iron line, its variability characteristics and …
Ultraviolet Extinction Properties in the Milky Way
Gordon, Karl D.; Clayton, Geoffrey C.; Valencic, Lynne A.
We have assembled a homogeneous database of 417 ultraviolet (UV) extinction curves for reddened sight lines having International Ultraviolet Explorer spectra. We have combined these with optical and Two Micron All Sky Survey photometry, allowing estimates of the ratio of total-to-selective extinction, RV, for the entire sample. Fitzpatr…
Rotation of Jets from Young Stars: New Clues from the Hubble Space Telescope Imaging Spectrograph
Bacciotti, Francesca; Coffey, Deirdre; Eislöffel, Jochen +2 more
We report findings from the first set of data in a current survey to establish conclusively whether jets from young stars rotate. We observed the bipolar jets from the T Tauri stars TH 28 and RW Aur and the blueshifted jet from T Tauri star LkHα 321, using the Hubble Space Telescope Imaging Spectrograph. Forbidden emission lines show distinct and …
Four-point discontinuity observations using Cluster magnetic field data: A statistical survey
Balogh, A.; Neubauer, F. M.; Horbury, T. +1 more
Using magnetic field data from the four Cluster spacecraft between February and May 2001, a detailed statistical analysis of interplanetary discontinuities is accomplished. In order to find the surface normals, we apply three different methods: (1) minimum variance analysis (MVA), (2) cross-product method, and (3) triangulation, the latter being t…
Three-dimensional MHD simulation of a flux rope driven CME
Gombosi, Tamas I.; Sokolov, I. V.; Opher, Merav +5 more
We present a three-dimensional (3-D) numerical ideal magnetohydrodynamics (MHD) model, describing the time-dependent expulsion of plasma and magnetic flux from the solar corona that resembles a coronal mass ejection (CME). We begin by developing a global steady-state model of the corona and solar wind that gives a reasonable description of the sol…
Relative Frequencies of Blue Stragglers in Galactic Globular Clusters: Constraints for the Formation Mechanisms
Djorgovski, S. G.; Rich, R. M.; Recio-Blanco, Alejandra +7 more
We discuss the main properties of the Galactic globular cluster (GC) blue straggler stars (BSSs), as inferred from our new catalog containing nearly 3000 BSSs. The catalog has been extracted from the photometrically homogeneous V versus (B-V) color-magnitude diagrams (CMDs) of 56 GCs, based on Wide Field Planetary Camera 2 images of their central …