Search Publications
The Oort Constants Measured from Proper Motions
Olling, Rob P.; Dehnen, Walter
The Oort constants describe the local spatial variations of the stellar streaming field. The classic way for their determination employs their effect on stellar proper motions. We discuss various problems arising in this procedure. A large, hitherto apparently overlooked, source of potential systematic error arises from longitudinal variations of …
Density-Transition Scale at Quasiperpendicular Collisionless Shocks
Bale, S. D.; Horbury, T. S.; Mozer, F. S.
Measurements of a spacecraft floating potential, on the four Cluster spacecraft, are used as a proxy for electron plasma density to study, for the first time, the macroscopic density transition scale at 98crossings of the quasiperpendicular terrestrial bow shock. A timing analysis gives shock speeds and normals; the shock speed is used to convert …
Radial Velocity Studies of Close Binary Stars. VIII.
Rucinski, Slavek M.; Capobianco, Christopher C.; Lu, Wenxian +7 more
Radial velocity measurements and sine-curve fits to the orbital velocity variations are presented for the seventh set of 10 close binary systems: V410 Aur, V523 Cas, QW Gem, V921 Her, V2357 Oph, V1130 Tau, HN UMa, HX UMa, HD 93917, and NSV 223. All systems but three (V523 Cas, HD 93917, NSV 223) were discovered photometrically by the Hipparcos mis…
Heavy-element abundance patterns in hot DA white dwarfs
Barstow, M. A.; Bruhweiler, F. C.; Holberg, J. B. +5 more
We present a series of systematic abundance measurements for 25 hot DA white dwarfs in the temperature range ~20 000-110 000 K, based on far-ultraviolet spectroscopy with the Space Telescope Imaging Spectrograph (STIS)/Goddard High Resolution Spectrograph (GHRS) on-board Hubble Space Telescope, IUE and FUSE. Using our latest heavy-element blankete…
Nascent Starbursts in Synchrotron-deficient Galaxies with Hot Dust
Helou, G.; Roussel, H.; Beck, R. +4 more
Three nearby galaxies that have abnormally high infrared-to-radio continuum ratios, NGC 1377, IC 1953, and NGC 4491, are investigated with a view to understanding the physical origin of their peculiarity. We review the existing data and present new radio continuum measurements along with near-infrared integral-field spectroscopy and molecular gas …
VLBI astrometry of circumstellar OH masers: Proper motions and parallaxes of four AGB stars
Schilizzi, R. T.; Habing, H. J.; Vlemmings, W. H. T. +2 more
The main-line OH masers around 4 AGB stars have been observed with the NRAO Very Long Baseline Array (VLBA) at 8 epochs over a period of 2.5 yrs. Using a phase referencing technique, the position of the most compact maser spot of each star was monitored with respect to two extragalactic reference sources. For U Her and W Hya, we observe the most b…
The radiative response of solar loop plasma subject to transient heating
Mason, H. E.; Bradshaw, S. J.
In Bradshaw & Mason (\cite{Bradshaw2003}) we carried out a hydrodynamic simulation of a cooling solar loop and investigated the nonequilibrium response of the population of C VII ions to the changing conditions in the plasma. We also compared equilibrium and nonequilibrium calculations of the total plasma emissivity. In this paper we present t…
Hubble Space Telescope Astrometry of m4 and the Galactic Constant V0/R0
Anderson, Jay; Bedin, Luigi R.; Piotto, Giampaolo +1 more
From multiepoch WFPC2/HST observations we present astrometric measurements of stars in the Galactic globular cluster M4 (NGC 6121) and in the foreground and background. The presence of an extragalactic point source allows us to determine the absolute proper motion of the cluster and, through use of the field stars in this region only 18° from the …
Deep Hubble Space Telescope Imaging of Sextans A. III. The Star Formation History
Dolphin, Andrew E.; Skillman, Evan D.; Saha, A. +6 more
We present a measurement of the star formation history of Sextans A, based on WFPC2 photometry that is 50% complete to V=27.5 (MV~+1.9) and I=27.0. The star formation history and chemical enrichment history have been measured through modeling of the color-magnitude diagram (CMD). We find evidence for increased reddening in the youngest …
Gemini observations of Wolf-Rayet stars in the Local Group starburst galaxy IC 10
Smartt, S. J.; Crowther, P. A.; Royer, P. +2 more
We present Gemini-N GMOS and CFHT MOS spectroscopy of Wolf-Rayet candidates in the Local Group dwarf galaxy IC 10 that were previously identified by Massey et al. and Royer et al. From the present spectroscopic survey, the WC/WN ratio for IC 10 remains unusually high, given its low metallicity, although none of the WC9 stars suspected from narrow-…