Search Publications
The Lensed Arc Production Efficiency of Galaxy Clusters: A Comparison of Matched Observed and Simulated Samples
Maoz, Dan; Rix, Hans-Walter; Bartelmann, Matthias +3 more
We compare the statistical properties of giant gravitationally lensed arcs produced in matched simulated and observed cluster samples. The observed sample consists of 10 X-ray-selected clusters at redshifts zc~0.2 imaged with HST by Smith et al. The simulated data set is produced by lensing the Hubble Deep Field, which serves as a backg…
Boron Depletion in F and G Dwarf Stars and the Beryllium-Boron Correlation
Deliyannis, Constantine P.; Steinhauer, Aaron; Boesgaard, Ann Merchant
Boron provides a special probe below the stellar surface since it survives to greater depths than do Li and Be. To search for B depletions we have observed B in 13 F and G dwarfs with large Be depletions; for comparison we have also obtained spectra of five stars that are undepleted in Li and Be. We have used HST with STIS to obtain spectra of the…
Active Galactic Nucleus Feedback and Gas Mixing in the Core of NGC 4636
O'Sullivan, E.; Vrtilek, J. M.; Kempner, J. C.
Chandra observations of NGC 4636 show disturbances in the galaxy X-ray halo, including armlike high surface brightness features (tentatively identified as active galactic nucleus-driven shocks) and a possible cavity on the west side of the galaxy core. We present Chandra and XMM-Newton spectral maps of NGC 4636 that confirm the presence of the cav…
The Role of Magnetic Helicity in Coronal Mass Ejections
MacNeice, P. J.; Antiochos, S. K.; Phillips, A. D.
We investigate the factors responsible for initiating coronal mass ejections (CMEs), specifically, the role of magnetic helicity. Using numerical simulations of the breakout model for CMEs, we show that eruption occurs at a fixed magnitude of free energy in the corona, independent of the value of helicity. Almost identical eruptions are obtained f…
Detection and Diagnostics of a Coronal Shock Wave Driven by a Partial-Halo Coronal Mass Ejection on 2000 June 28
Raymond, J. C.; Ciaravella, A.; Li, J. +2 more
A fast partial-halo coronal mass ejection (CME) was observed on 2000 June 28 by instruments on the SOHO spacecraft. The CME leading edge and filamentary cold core were detected over the northwest limb at 2.32 Rsolar by the SOHO UV Coronagraph Spectrometer (UVCS). The broad profile of the O VI λ1032 line gives evidence of a shock front a…
Feedback and Brightest Cluster Galaxy Formation: ACS Observations of the Radio Galaxy TN J1338-1942 at z = 4.1
Ford, H. C.; Demarco, R.; Infante, L. +43 more
We present deep optical imaging of the z=4.1 radio galaxy TN J1338-1942, obtained using the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope, as well as ground-based near-infrared imaging data from the European Southern Observatory (ESO) Very Large Telescope (VLT). The radio galaxy is known to reside within a large galaxy over…
A Spectroscopic Analysis of Blue Stragglers, Horizontal Branch Stars, and Turnoff Stars in Four Globular Clusters
Saffer, Rex A.; De Marco, Orsola; Shara, Michael M. +4 more
We present a spectroscopic analysis of HST STIS and FOS low- and intermediate-resolution spectroscopy of 55 stars in four globular clusters (47 Tucanae, M3, NGC 6752, and NGC 6397). Stars hotter than Teff=5750 K and with a signal-to-noise ratio larger than 15 were analyzed with non-local thermodynamic equilibrium model atmospheres, and …
Two Pulsar Wind Nebulae: Chandra/XMM-Newton Imaging of GeV J1417-6100
Ng, C. -Y.; Romani, Roger W.; Roberts, Mallory S. E.
We report on Chandra ACIS and XMM-Newton MOS/pn imaging observations of two pulsar wind nebulae (K3/PSR J1420-6048 and G313.3+0.1, the ``Rabbit'') associated with the Galactic unidentified γ-ray source GeV J1417-6100. With excellent ACIS imaging the very energetic pulsar PSR J1420-6048 is separated from its surrounding nebula. This nebula has surp…
Abundance of Elements beyond the Iron Group in Cool DO White Dwarfs
Kruk, J. W.; Chayer, P.; Dupuis, J. +1 more
We report the presence of elements beyond the iron group in the atmospheres of the cool DO white dwarfs HD 149499 B and HZ 21. Photospheric lines of germanium (Z=32), arsenic (33), selenium (34), tin (50), tellurium (52), iodine (53), and perhaps bromine (35) are observed in ultraviolet spectra of HD 149499 B obtained with the Far Ultraviolet Spec…
Probing the Intergalactic Medium-Galaxy Connection toward PKS 0405-123. II. A Cross-Correlation Study of Lyα Absorbers and Galaxies at z<0.5
Weiner, Benjamin J.; Chen, Hsiao-Wen; Mulchaey, John S. +2 more
We present a pilot study of the clustering properties of Lyα absorbers with respect to known galaxies based on 112 Lyα absorbers and 482 galaxies identified at z<0.5 along the sight line toward PKS 0405-123. The principal goal is to determine the origin of Lyα absorbers based on their cross-correlation amplitude with known galaxies and to inves…