Search Publications
Physical parameters and wind properties of galactic early B supergiants
Crowther, P. A.; Lennon, D. J.; Walborn, N. R.
We present optical studies of the physical and wind properties, plus CNO chemical abundances, of 25 O9.5-B3 Galactic supergiants. We employ non-LTE, line blanketed, extended model atmospheres, which provide a modest downward revision in the effective temperature scale of early B supergiants of up to 1-2 kK relative to previous non-blanketed result…
The Expansion Asymmetry and Age of the Cassiopeia A Supernova Remnant
Chevalier, Roger A.; Raymond, John C.; Dopita, Michael A. +7 more
HST images of the young supernova remnant Cas A are used to explore the expansion and spatial distribution of its highest velocity debris. ACS WFC images taken in 2004 March and December with Sloan F625W, F775W, and F850LP filters were used to identify 1825 high-velocity, outlying ejecta knots through measured proper motions of 0.35"-0.90" yr…
The Evolution of the Star Formation Activity in Galaxies and Its Dependence on Environment
Aragón-Salamanca, Alfonso; White, Simon D. M.; Milvang-Jensen, Bo +16 more
We study how the proportion of star-forming galaxies evolves between z=0.8 and 0 as a function of galaxy environment, using the O II line in emission as a signature of ongoing star formation. Our high-z data set comprises 16 clusters, 10 groups, and another 250 galaxies in poorer groups and the field at z=0.4-0.8 from the ESO Distant Cluster Surve…
A New Cepheid Distance to the Maser-Host Galaxy NGC 4258 and Its Implications for the Hubble Constant
Stanek, K. Z.; Bersier, D.; Reid, M. J. +2 more
We present initial results from a time series BVI survey of two fields in NGC 4258 using the HST ACS. This galaxy was selected because of its accurate maser-based distance, which is anticipated to have a total uncertainty of ~3%. The goal of the HST observations is to provide an absolute calibration of the Cepheid distance scale and to measure its…
XMM-Newton observations of the brightest ultraluminous X-ray sources
Wilms, J.; Roberts, T. P.; Stobbart, A. -M.
We present an analysis of 13 of the best quality ultraluminous X-ray source (ULX) data sets available from XMM-Newton European Photon Imaging Camera (EPIC) observations. We utilize the high signal-to-noise in these ULX spectra to investigate the best descriptions of their spectral shape in the 0.3-10keV range. Simple models of an absorbed power la…
[Si II], [Fe II], [C II], and H2 Emission from Massive Star-forming Regions
Kaufman, Michael J.; Wolfire, Mark. G.; Hollenbach, David J.
We calculate the [Si II] 34.8 µm, [Fe II] 26.0 µm, and [C II] 158 µm infrared fine-structure emission that may arise from ionized gas (H II regions) and/or associated neutral gas (photodissociation regions [PDRs]) in massive star-forming regions. Assuming thermal pressure balance between an H II region and a PDR, the relative amo…
What Is the Total Deuterium Abundance in the Local Galactic Disk?
Jenkins, Edward B.; Moos, H. W.; Blair, William P. +14 more
Analyses of spectra obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, together with spectra from the Copernicus and interstellar medium absorption profile spectrograph (IMAPS) instruments, reveal an unexplained, very wide range in the observed deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk beyond…
A magnetic reconnection X-line extending more than 390 Earth radii in the solar wind
Balogh, A.; McComas, D. J.; Reme, H. +8 more
Magnetic reconnection in a current sheet converts magnetic energy into particle energy, a process that is important in many laboratory, space and astrophysical contexts. It is not known at present whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Fre…
Cassini Dust Measurements at Enceladus and Implications for the Origin of the E Ring
Schmidt, Jürgen; Sremčević, Miodrag; Albers, Nicole +13 more
During Cassini's close flyby of Enceladus on 14 July 2005, the High Rate Detector of the Cosmic Dust Analyzer registered micron-sized dust particles enveloping this satellite. The dust impact rate peaked about 1 minute before the closest approach of the spacecraft to the moon. This asymmetric signature is consistent with a locally enhanced dust pr…
The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) for the Mars Express Mission
Coates, A. J.; Kallio, E.; Fedorov, A. +39 more
The general scientific objective of the ASPERA-3 experiment is to study the solar wind - atmosphere interaction and to characterize the plasma and neutral gas environment with within the space near Mars through the use of energetic neutral atom (ENA) imaging and measuring local ion and electron plasma. The ASPERA-3 instrument comprises four sensor…