Search Publications
Small Magellanic Cloud-Type Interstellar Dust in the Milky Way
Gordon, Karl D.; Clayton, Geoffrey C.; Valencic, Lynne A. +1 more
It is well known that the sight line toward HD 204827 in the cluster Trumpler 37 shows a UV extinction curve that does not follow the average Galactic extinction relation. However, when a dust component, foreground to the cluster, is removed, the residual extinction curve is identical to that found in the SMC within the uncertainties. The curve is…
Revealing New Physical Structures in the Supernova Remnant N63A through Chandra Imaging Spectroscopy
Hughes, John P.; Slane, Patrick O.; Warren, Jessica S.
We present Chandra X-ray observations of the supernova remnant (SNR) N63A in the Large Magellanic Cloud (LMC). N63A, one of the brightest LMC remnants, is embedded in an H II region and is probably associated with an OB association. The optical remnant consists of three lobes of emission contained within the approximately 3 times larger X-ray remn…
The Leo I Cloud: Secular Nuclear Evolution of NGC 3379, NGC 3384, and NGC 3368?
Moiseev, A. V.; Chavushyan, V. H.; Sil'chenko, O. K. +2 more
The central regions of the three brightest members of the Leo I galaxy group-NGC 3368, NGC 3379, and NGC 3384-are investigated by means of two-dimensional spectroscopy. In all three galaxies we have found separate circumnuclear stellar and gaseous subsystems-more probably, disks-whose spatial orientations and spins are connected to the spatial ori…
Molecular Gas and the Nuclear Star Cluster in IC 342: Sufficient Inflow for Recurring Star Formation Events?
Meier, David S.; Böker, Torsten; Schinnerer, Eva
We present high spatial resolution (1.2") millimeter-interferometric observations of the 12CO (2-1) line emission in the central 300 pc of the late-type spiral galaxy IC 342. The data, obtained with the Owens Valley Radio Observatory, allow first-time detection of a molecular gas disk that coincides with the luminous young stellar clust…
Some Constraints on the Effects of Age and Metallicity on the Low-Mass X-Ray Binary Formation Rate
Kundu, Arunav; Zepf, Stephen E.; Maccarone, Thomas J. +1 more
We have studied the low-mass X-ray binary (LMXB) populations within and outside globular clusters (GCs) in NGC 4365 and NGC 3115. Using published age and metallicity constraints from optical and IR observations of their GCs, we do not find any evidence for an increase in the LMXB formation rate in the intermediate-age cluster population of NGC 436…
A V-Band Survey for Variable Galactic Nuclei in the Hubble Deep Field
Gilliland, Ronald L.; Sarajedini, Vicki L.; Kasm, Christina
We present the results of a two-epoch variability survey in the Hubble Deep Field with the goal of investigating the population of active galactic nuclei (AGNs) to z~=1. The high resolution and stability of the Hubble Space Telescope allow accurate photometry to be obtained within subarcsecond apertures, resulting in the ability to probe much lowe…
An Intrinsic Absorption Complex toward RX J1230.8+0115: Geometry and Photoionization Conditions
Charlton, Jane C.; Sembach, Kenneth R.; Ganguly, Rajib +1 more
We present Hubble Space Telescope/Space Telescope Imaging Spectrograph and Far Ultraviolet Spectroscopic Explorer spectra of the quasar RX J1230.8+0115 (V=14.4,z=0.117). In addition to Galactic, Virgo, and intervening absorption, this quasar is host to a remarkable intrinsic absorption complex. Four narrow absorption line systems, strong in C IV, …
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…