Search Publications
HST/GHRS Observations of the Velocity Structure of Interplanetary Hydrogen
Bertaux, Jean-Loup; Clarke, John T.; Lallement, Rosine +3 more
We present high-resolution spectra of the emission-line profile of inflowing interplanetary hydrogen atoms along lines of sight with the Earth orbital motion upwind (into the flow), downwind, and across the flow to Doppler-shift the line from the geocoronal emission. The line-center positions, in comparison with hot-model profiles, confirm that th…
Hubble Space Telescope WFPC2 Imaging of FS Tauri and Haro 6-5B
Ballester, Gilda E.; Krist, John E.; Crisp, David +14 more
We have observed the field of FS Tauri (Haro 6-5) with the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Centered on Haro 6-5B and adjacent to the nebulous binary system of FS Tauri A there is an extended complex of reflection nebulosity that includes a diffuse, hourglass-shaped structure. H6-5B, the source of a bipolar jet, is not …
On the accuracy of helioseismic determination of solar helium abundance
Dziembowski, W. A.; Goode, Philip R.; Richard, O. +1 more
The Helium abundance in the solar envelope is one of the most important seismic observables. We investigate the accuracy of its determination taking into account uncertainties in the data and in the inversion procedure. Our best value for the helium abundance in the photosphere is Ysun=0.248. The estimated uncertainty of 0.002 is domina…
Long-term monitoring of active stars. VIII. UBV(RI)_(c) photometry collected in February 1992
Cutispoto, G.
As a part of an extensive program focusing on the global properties and evolution of active stars, high-precision UBV(RI)_c photometry of 31 selected stars, collected at the European Southern Observatory over the 14-29 February 1992 interval, is presented. Significant evolution of the light curves, period variations and evidence for long-term vari…
An Infrared Search for Star-forming Galaxies at Z > 2
Teplitz, Harry I.; Malkan, M.; McLean, I. S.
We report the cumulative results of an ongoing near-infrared search for redshifted Hα emission from normal galaxies at z > 2. An infrared search reduces the bias due to reddening. Using narrowband imaging with the Near Infrared Camera on the Keck I 10 m telescope, a survey area of almost 12 arcmin2 has been covered. Target regions we…
Ionization Structure in the 30 Doradus Nebula as seen with Hubble Space Telescope Wide Field Planetary Camera 2
Watson, A. M.; Holtzman, J. A.; Stapelfeldt, K. R. +15 more
Using the Hubble Space Telescope (HST) and Wide Field Planetary Camera 2, we have imaged the central 20 pc of the giant H ii region 30 Doradus Nebula in three different emission lines. The images allow us to study the nebula with a physical resolution that is within a factor of 2 of that of typical ground-based observations of Galactic H ii region…
Temperature and density diagnostics of quiet Sun and active regions observed with CDS NIS
Landini, M.; Landi, E.
We study the Differential Emission Measure distribution of two pairs of active and quiet regions of the solar atmosphere, observed by CDS Normal Incidence Spectrometer (NIS) on SOHO, and investigate their temperature and density structure . Use is made of the Arcetri Method (Landi & Landini 1997) for DEM and density diagnostics. An iterative m…
Isotopic Composition of Solar Wind Nitrogen: First In Situ Determination with the CELIAS/MTOF Spectrometer on board SOHO
Bochsler, P.; Geiss, J.; Ipavich, F. M. +6 more
Using the high-resolution Mass Time-of-Flight (MTOF) spectrometer of the Charge, Element, and Isotope Analysis System (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO), we have determined the solar wind isotope abundance ratio 14N/15N = 200+/-55 (1 σ error), suggesting that the relative abundance of <…
Solar Wind at 6.8 Solar Radii from UVCS Observation of Comet C/1996Y1
Raymond, John C.; Ciaravella, A.; Fineschi, S. +10 more
The comet C/1996Y1, a member of the Kreutz family of Sun-grazing comets, was observed with the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) satellite. The Lyα line profile and spatial distribution are interpreted in terms of the theory of bow shocks driven by mass-loading. At the time of the obse…
Is There a Difference in Luminosity between Field and Cluster RR Lyrae Variables?
Catelan, Marcio
Recent Hipparcos results have lent support to the idea that RR Lyrae variables in the halo field and in globular clusters differ in luminosity by ~0.2 mag. In this Letter, we study the pulsation properties of RR Lyrae variables in clusters with distances determined via main-sequence fitting to Hipparcos parallaxes for field subdwarfs and compare t…