Search Publications
The Remarkable Alternating Spectra of the Of?p Star HD 191612
Walborn, Nolan R.; Howarth, Ian D.; Herrero, Artemio +1 more
The spectrum of HD 191612 has been found to display large, recurrent variations between two highly reproducible, peculiar states; at least four transformations have occurred since 1950. In one state, the spectral type is O6-O7, with C III λ4650 emission comparable to N III λ4640 (the definition of the Of?p category) and P Cygni profiles at He II λ…
INTEGRAL and XMM-Newton Observations of the Weak Gamma-Ray Burst GRB 030227
Tiengo, A.; Götz, D.; Mereghetti, S. +16 more
We present International Gamma-Ray Astrophysical Laboratory (INTEGRAL) and XMM-Newton observations of the prompt γ-ray emission and the X-ray afterglow of GRB 030227, the first gamma-ray burst for which the quick localization obtained with the INTEGRAL Burst Alert System has led to the discovery of X-ray and optical afterglows. GRB 030227 had a du…
Magnetoacoustic Waves in Sunspots
Bellot Rubio, L. R.; Collados, M.; Khomenko, E. V.
Observed variations of the magnetic field strength in sunspot umbrae consist of intrinsic oscillations and ``false'' oscillations due to time-dependent opacity effects. Here we present an approach intended for the separation of these components. We develop a mathematical formalism based on the analytical solution of the MHD equations including gra…
The First Two Host Galaxies of X-Ray Flashes: XRF 011030 and XRF 020427
Berger, E.; Bloom, J. S.; Djorgovski, S. G. +4 more
Given the paucity of empirical constraints, the nature of the newly recognized phenomena called X-ray flashes (XRFs) has been an open question. However, with the recent detections of radio and X-ray afterglow it is finally possible to study the large- and small-scale environments of XRFs. We present Chandra, Hubble Space Telescope (HST), and Keck …
The Multiphase Absorption Systems toward PG 1206+459
Charlton, Jane C.; Churchill, Christopher W.; Palma, Christopher +1 more
A high-resolution (R=30,000) ultraviolet spectrum is presented, which covers Lyα and many low-, intermediate-, and high-ionization transitions in the three Mg II-selected absorption systems toward the quasar PG 1206+459. Three systems (A, B, and C), which are clustered within 1500 km s-1 at z~0.93, were originally identified in a spectr…
On the Size Difference between Red and Blue Globular Clusters
Brodie, Jean P.; Larsen, Søren S.
Several recent studies have reported a mean size difference of about 20% between the metal-rich and metal-poor subpopulations of globular clusters (GCs) in a variety of galaxies. In this paper, we investigate the possibility that the size difference might be a projection effect, resulting from a correlation between cluster size and galactocentric …
The Stellar Content of Henize 2-10 from Space Telescope Imaging Spectrograph Ultraviolet Spectroscopy
Calzetti, Daniela; Leitherer, Claus; Chandar, Rupali +1 more
We use new Space Telescope Imaging Spectrograph long-slit ultraviolet spectroscopy of region A in the nearby starbursting galaxy He 2-10 to examine properties of both compact individual super-star clusters and diffuse intracluster regions. The four most luminous clusters in our slit formed coevally 4-5 Myr ago and have lower mass estimates of seve…
An XMM-Newton Observation of 4U 1755-33 in Quiescence: Evidence of a Fossil X-Ray Jet
White, Nicholas E.; Angelini, Lorella
We report an XMM-Newton observation of the low-mass X-ray binary and black hole candidate 4U 1755-33. This source had been a bright persistent source for at least 25 yr, but in 1995 it entered an extended quiescent phase. 4U 1755-33 was not detected with an upper limit to the 2-10 keV luminosity of 3.6×1031d24kpc e…
A Turbulent Origin for Flocculent Spiral Structure in Galaxies. II. Observations and Models of M33
Cuillandre, Jean-Charles; Elmegreen, Bruce G.; Elmegreen, Debra Meloy +1 more
Fourier transform power spectra of azimuthal scans of the optical structure of M33 are evaluated for B, V, and R passbands and fitted to fractal models of continuum emission with superposed star formation. Power spectra are also determined for Hα. The best models have intrinsic power spectra with one-dimensional slopes of around -0.7+/-0.7, signif…
Chandra and XMM Observations of the Accretion Disk Corona Source 2S 0921-63
Kallman, T. R.; Angelini, L.; Boroson, B. +1 more
We analyze observations of the low-mass X-ray binary (LMXB) 2S 0921-63 obtained with the gratings and CCDs on Chandra and XMM. This object is a high-inclination system showing evidence for an accretion disk corona (ADC). Such a corona has the potential to constrain the properties of the heated accretion disk in this system and other LMXBs by exten…