Search Publications
HST Eclipse Mapping of Dwarf Nova OY Carinae in Quiescence: an ``Fe II Curtain'' with Mach 6 Velocity Dispersion Veils the White Dwarf
Horne, Keith; Marsh, T. R.; Hubeny, Ivan +2 more
Hubble Space Telescope (HST) observations of the eclipsing dwarf nova OY Car in its quiescent state are used to isolate the ultraviolet spectrum (1150-2500 A at 9.2 A Full Width at Half Maximum (FWHM) resolution) of the white dwarf, the accretion disk, and the bright spot. The white dwarf spectrum has a Stark-broadened photospheric L(alpha) absorp…
The whistler heat flux instability: Threshold conditions in the solar wind
Gary, S. Peter; Scime, Earl E.; Phillips, John L. +1 more
Solar wind electrons are observed often to consist of two components: a core and a halo. The anisotropies and relative average speed of these two components correspond to a heat flux that has the potential to excite several different electromagnetic instabilities; wave-particle scattering by the resulting enhanced fluctuations can limit this heat …
Ulysses at 50° south: constant immersion in the high-speed solar wind
Balogh, A.; Hoeksema, J. T.; McComas, D. J. +7 more
We present speed observations from the Ulysses solar wind plasma experiment through 50° south latitude. The pronounced speed modulation arising from solar rotation and the tilt of the heliomagnetic current sheet has nearly disappeared. Ulysses is now observing wind speeds in the 700 to 800 km s-1 range, with a magnetic polarity indicati…
Charged-Particle Motion in Multidimensional Magnetic Field Turbulence
Giacalone, J.; Jokipii, J. R.
We present a new analysis of the fundamental physics of charged-particle motion in a turbulent magnetic field using a numerical simulation. The magnetic field fluctuations are taken to be static and to have a power spectrum which is Kolmogorov. The charged particles are treated as test particles. It is shown that when the field turbulence is indep…
A new class of forward-reverse shock pairs in the solar wind
McComas, D. J.; Forsyth, R. J.; Goldstein, B. E. +4 more
A new class of forward-reverse shock pairs in the solar wind has been discovered using Ulysses observations at high heliographic latitudes. These shock pairs are produced by expansion of coronal mass ejections, CMEs, that have internal pressures that are higher than, and speeds that are comparable to, that of the surrounding solar wind plasma. Of …
The Cepheid Distance to NGC 5253: Calibration of M(max) for the Type I Supernovae SN 1972E and SN 1895B
Panagia, N.; Saha, A.; Labhardt, Lukas +4 more
The apparent V distance modulus of NGC 5253, parent galaxy to the Type Ia supernovae SN 1972E and SN 1895B, is (m - M)_AV_ = 28.06+/-0.06 mag (internal error) determined from 11 Cepheid variables discovered with the Hubble Space Telescope. The internal differential absorption between the Cepheids and the two SNs is taken to be zero based on four i…
Terminal velocities of Wolf-Rayet winds from infrared He I lines.
Williams, P. M.; Eenens, P. R. J.
We have observed 1- and 2- im spectra covering the He i 2s-2p triplet and singlet lines in a sample of Wolf-Rayet stars. Most of the He ilines have P Cygni profiles, which are fitted using the SEI (Sobolev with exact integration) method to derive terminal velocities. From our observations of 41 stars, the He i velocities are only about 70 per cent…
Interstellar Carbon Monoxide toward zeta Ophiuchi
Gilliland, Ronald L.; Federman, S. R.; Lambert, David L. +1 more
Interstellar CO A-X bands in the spectrum of zeta Oph were recorded at high Sound-to-Noise (S/N) with grating G160M of the Goddard High Resolution Spectrograph on the Hubble Space Telescope. Isotopic fractionation of CO is severe: CO-12/CO-13 = 167, C(16)O/C(18)O approximately equal to 1550 and C(16)O/C(17)O is greater than 5900 are found where C-…
Regulation of the solar wind electron heat flux from 1 to 5 AU: Ulysses observations
Gary, S. Peter; Scime, Earl E.; Bame, Samuel J. +3 more
In this study we use observations from the three-dimensional electron spectrometer and magnetometer aboard the Ulysses spacecraft to examine the solar wind electron heat flux from 1.2 to 5.4 AU in the ecliptic plane. Throughout Ulysses' transit to 5.4 AU, the electron heat flux decreases more rapidly (~R-3.0) than simple collisionless e…
GHRS observations of Sirius-A I. Interstellar clouds toward Sirius and Local Cloud ionization
Bertaux, J. L.; Ferlet, R.; Vidal-Madjar, A. +2 more
Echelle spectra of Sirius-A have been obtained with the Goddard High-Resolution Spectrograph (GHRS) on board the Hubble Space Telescope (HST). Interstellar absorption lines of iron and magnesium clearly show for the first time the presence of two distinct interstellar clouds between the Sun and Sirius at 2.7pc. Their projected heliocentric velocit…