Search Publications
The ASCA X-Ray Spectrum of η Carinae
Koyama, K.; Davidson, K.; Corcoran, M. F. +9 more
We have obtained high signal-to-noise ratio 0.5-10 keV band X-ray spectra of the peculiar, extremely luminous star η Carinae with the Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray observatory during Cycle 4 observations in mid-1996. These data comprise the best X-ray spectra to date of the cool source (kT ~ 0.3 keV) surrounding th…
Boron in Lithium- and Beryllium-deficient F Stars
Deliyannis, Constantine P.; Lambert, David L.; Boesgaard, Ann Merchant +1 more
The Goddard High Resolution Spectrograph (GHRS) has been used with the Hubble Space Telescope (HST) to observe the B I region at 2497 Å in nine F and G dwarfs of approximately solar metallicity. The stars were selected because they have a variety of Li and Be deficiencies. Most of the nine stars were newly observed at high spectral resolution and …
Galactic planetary nebulae with Wolf-Rayet nuclei. I. Objects with [WC]-early type stars
Koesterke, L.; Esteban, C.; Pena, M. +3 more
Spatially resolved long-slit spectrophotometric data for the planetary nebulae PB 6, NGC 2452, NGC 2867, NGC 6905 and He 2-55 are presented. Different knots were observed in each nebula. All the nebulae are ionized by [WC 2-3] type nuclei. For the five objects, we calculated photoionization models using the ionizing radiation field from models of …
HIPPARCOS Parallaxes of Eclipsing Binaries and the Radiative Flux Scale
Popper, Daniel M.
Eclipsing binaries with Hipparcos parallaxes are found to define a radiative flux relation for main-sequence stars in the B6-F0 range about as well as stars with angular diameters and to extend the range to F8. The fluxes of components of binaries showing large intrinsic variations fall well below the curve for other stars and its extension to low…
Heating Events in the Quiet Solar Corona
Krucker, Säm; Benz, Arnold O.
Sensitive observations of the quiet Sun observed by EIT on the SOHO satellite in high-temperature iron-line emission originating in the corona are presented. The thermal radiation of the quiet corona is found to fluctutate significantly, even on the shortest time scale of 2 min and in the faintest pixels. The power spectrum of the emission measure…
The helium isotopic ratio in the solar wind and ion fractionation in the corona by inefficient Coulomb drag
Bochsler, Peter; Bodmer, Roland
Using data obtained between 1991 and 1996 with the SWICS instrument (Solar Wind Ion Composition Spectrometer) aboard the Ulysses spacecraft, a long time average of the ((4) He / (3) He ) isotopic ratio of 2450 +/- 460 in coronal hole dominated solar wind is derived. To assess the influence of inefficient Coulomb friction in the inner corona and to…
The Optical Spectrum of the Geminga Pulsar
Halpern, Jules P.; Schiminovich, David; Martin, Christopher
We obtained an optical spectrum of the isolated pulsar Geminga at the Keck Observatory. The optical object is at the limit of spectroscopic capability of any telescope, with a continuum flux that is ~0.5% of the dark sky on Mauna Kea. With particular attention paid to the dominant systematics of sky subtraction in our observing and analysis method…
X-ray activity and evolutionary status of late-type giants
Schmitt, J. H. M. M.; Schroeder, K. -P.; Huensch, M.
We study the evolution of stellar activity in a volume-limited sample of single giants within 35 pc distance from the Sun as measured by the amount of soft X-ray emission. This sample of 36 stars is assumed to be complete for absolute magnitude M_V la 3.0 and for X-ray luminosities L_x ga 1.5 x 10(28) erg s(-1) . We use ROSAT data to determine ste…
The Cepheid period-luminosity zero-point from radial velocities and HIPPARCOS proper motions
Pont, Frederic; Feast, Michael; Whitelock, Patricia
A value for the zero-point (rho) of the Cepheid period-luminosity relation, <M_V>=2.81log P+rho, is deduced by comparing the value of the Oort constant, A, derived from radial velocities with that derived from Hipparcos proper motions. We find in this way that rho=-1.47+/-0.13, in excellent agreement with the value derived from Hipparcos tri…
Lyman-alpha observations of comet Hyakutake with SWAN on SOHO
Schmidt, W.; Bertaux, J. L.; Lallement, R. +7 more
The SWAN instrument on board SOHO is a Lyman-α (Lα) photometer able to map the sky intensity with a resolution of 1°, and a capability of microstepping (0.1°). SWAN is primarily devoted to the study of the large scale distribution of solar wind from its imprints on the interplanetary sky background, but was in addition extensively used to map the …