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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…
The Hubble Constant: A Summary of the Hubble Space Telescope Program for the Luminosity Calibration of Type Ia Supernovae by Means of Cepheids
Panagia, N.; Saha, A.; Macchetto, F. D. +3 more
This is the final summary paper of our 15 yr program using the Hubble Space Telescope (HST) to determine the Hubble constant from the Cepheid-calibrated luminosity of Type Ia supernovae. Several recent developments have made it necessary to put the summary on H0 on a broader basis than we originally thought (see the four papers cited in…
Is the SMC Bound to the LMC? The Hubble Space Telescope Proper Motion of the SMC
van der Marel, Roeland P.; Kallivayalil, Nitya; Alcock, Charles
We present a measurement of the systemic proper motion of the Small Magellanic Cloud (SMC) made using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). We tracked the SMC's motion relative to four background QSOs over a baseline of approximately 2 yr. The measured proper motion is µW=-1.16+/-0.18 mas yr
A Statistical Study of Main and Residual Accelerations of Coronal Mass Ejections
Zhang, J.; Dere, K. P.
In this paper we present the results of a statistical study of the accelerations of coronal mass ejections (CMEs). A CME usually undergoes a multiphased kinematic evolution, with a main acceleration phase characterized by a rapid increase of CME velocity in the inner corona, followed by a relatively smooth propagation phase characterized by a cons…