Search Publications
The Homogeneity of Interstellar Oxygen in the Galactic Disk
Meyer, David M.; Cartledge, Stefan I. B.; Lauroesch, J. T. +1 more
We present an analysis of high-resolution Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) observations of O I λ1356 and H I Lyα absorption in 36 sight lines that probe a variety of Galactic disk environments and include paths that range over nearly 4 orders of magnitude in f(H2), over 2 orders of magnitude in &l…
The ACS Virgo Cluster Survey. III. Chandra and Hubble Space Telescope Observations of Low-Mass X-Ray Binaries and Globular Clusters in M87
Jordán, Andrés; Tonry, John L.; Côté, Patrick +7 more
The ACIS instrument on board the Chandra X-Ray Observatory has been used to carry out the first systematic study of low-mass X-ray binaries (LMXBs) in M87, the giant elliptical galaxy near the dynamical center of the Virgo Cluster. These images-with a total exposure time of 154 ks-are the deepest X-ray observations yet obtained of M87. We identify…
Metallicity in the Galactic Center: The Arches Cluster
Hillier, D. John; Figer, Donald F.; Kudritzki, Rolf P. +1 more
We present a quantitative spectral analysis of five very massive stars in the Arches cluster, located near the Galactic center, to determine stellar parameters, stellar wind properties, and, most importantly, metallicity content. The analysis uses a new technique, presented here for the first time, and uses line-blanketed non-LTE wind/atmosphere m…
Average Ultraviolet Quasar Spectra in the Context of Eigenvector 1: A Baldwin Effect Governed by the Eddington Ratio?
Marziani, P.; Zamanov, R.; Bachev, R. +3 more
We present composite UV spectra for low-redshift type 1 active galactic nuclei binned to exploit the information content of the eigenvector 1 (E1) parameter space. Composite spectra show high enough S/N and spectral resolution to permit a decomposition of the C IV λ1549 line profile: one of the strongest high-ionization lines (HILs), and fundament…
The Coronal Heating Mechanism as Identified by Full-Sun Visualizations
Aschwanden, Markus J.; Schrijver, Carolus J.; De Rosa, Marc L. +1 more
We constrain the properties of the mechanism(s) responsible for the bulk of the heating of the corona of the Sun by simulating, for the first time, the appearance of the entire solar corona. Starting from full-sphere magnetic field maps for 2000 December 1 and 8, when the Sun was moderately active, we populate nearly 50,000 coronal field lines wit…
Deep Hubble Space Telescope ACS Observations of I Zw 18: a Young Galaxy in Formation
Thuan, Trinh X.; Izotov, Yuri I.
We present V and I photometry of the resolved stars in the most metal-deficient blue compact dwarf galaxy known, I Zw 18 (Zsolar/50), using Hubble Space Telescope/ACS images, the deepest ones ever obtained for this galaxy. The resulting I versus V-I color-magnitude diagram (CMD) reaches limiting magnitudes V=I=29 mag. It reveals a young…
Revealing a Cool Accretion Disk in the Ultraluminous X-Ray Source M81 X-9 (Holmberg IX X-1): Evidence for an Intermediate-Mass Black Hole
Fabian, A. C.; Miller, J. M.; Miller, M. C.
We report the results of an analysis of two XMM-Newton EPIC-pn spectra of the bright ultraluminous X-ray source M81 X-9 (Holmberg IX X-1) obtained in snapshot observations. Soft thermal emission is clearly revealed in spectra dominated by hard power-law components. Depending on the model used, M81 X-9 was observed at a luminosity of LX=…
The Abundance of Low-Luminosity Lyα Emitters at High Redshift
Richard, Johan; Ellis, Richard S.; Kneib, Jean-Paul +2 more
We derive the luminosity function of high-redshift Lyα-emitting sources from a deep, blind, spectroscopic survey that utilized strong-lensing magnification by intermediate-redshift clusters of galaxies. We observed carefully selected regions near nine clusters, consistent with magnification factors generally greater than 10 for the redshift range …
The Contribution of Primordial Binaries to the Blue Straggler Population in 47 Tucanae
Ferraro, Francesco R.; Sills, Alison; Beccari, Giacomo +5 more
Recent observations of the blue straggler population in 47 Tucanae give the first detailed characterization of their spatial distribution in the cluster over its entire volume. Relative to the light distribution, blue stragglers appear to be overabundant in the core and at large radii. The observed surface density profile shows a central peak, a z…
Dust and Diffuse Interstellar Bands in the za = 0.524 Absorption System toward AO 0235+164
Cohen, Ross D.; Burbidge, E. M.; Lyons, R. W. +3 more
We present new Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) NUV-MAMA and STIS CCD observations of the BL Lac object AO 0235+164 and the intervening damped Lyα (DLA) line at za=0.524. The line profile gives N(HI)=(5+/-1)×1021 cm-2 and, combined with the H I 21 cm absorption data, leads to…