Search Publications
On the Use of [Na/Fe] and [alpha/Fe] Ratios and Hipparcos-based (U, V, W) Velocities as Age Indicators among Low-Metallicity Halo Field Giants
Sneden, Christopher; Hanson, Robert B.; Kraft, Robert P. +1 more
We have examined the [Na/Fe] and [Mg/Fe] ratios in a sample of 68 field halo giants with -3 <~ [Fe/H] <~ -1. We recalculated the Galactic (U, V, W) velocity components for these stars, using Hipparcos proper motions and a new Hipparcos-based distance scale. We used these data to see how the abundance ratios may relate to kinematical substruc…
The Optical Gravitational Lensing Experiment. The Distance Scale: Galactic Bulge -- LMC -- SMC.
Udalski, A.
We analyze the mean luminosity of three samples of field RRab Lyr stars observed in the course of the OGLE microlensing experiment: 73 stars from the Galactic bulge and 110 and 128 stars from selected fields in the LMC and SMC, respectively. The fields are the same as in the recent distance determination to the Magellanic Clouds with the red clump…
A Study of Nine High-Redshift Clusters of Galaxies. I. The Survey
Postman, Marc; Lubin, Lori M.; Oke, J. B.
We present a description of the observations and data reduction procedures for an extensive spectroscopic and multiband photometric study of nine high-redshift, optically selected cluster candidates. The primary goal of the survey is to establish new constraints on cluster and galaxy evolution, with specific emphasis on the evolution of galaxy mor…
Variable sub-arcsecond structure in the circumstellar envelope of IRC+10216
Haniff, C. A.; Buscher, D. F.
We present new diffraction-limited interferometric images of the carbon star IRC+10216 at wavelengths of 2.2 mu m and 3.4 mu m. These show that the distribution of the near-infrared emission from the star departs significantly from a spherical geometry on 0.1 arcsecond scales. At 3.4 mu m, i.e. close to the peak of the star/dust-shell spectral ene…
Hubble Space Telescope Imaging of IRAS 17441-2411: A Case Study of a Bipolar Nebula with a Circumstellar Disk
Volk, Kevin; Kwok, Sun; Hrivnak, Bruce J. +1 more
The bipolar proto-planetary nebula IRAS 17441-2411 (the ``Silkworm Nebula'') was observed with the Hubble Space Telescope. By fitting the observed spectral energy distribution and the V-band image by a two-dimensional radiation transfer model, we derive the properties of the circumstellar wind and a proposed circumstellar ``disk.'' We suggest that…
2.12 Micron Molecular Hydrogen Emission from Circumstellar Disks Embedded in the Orion Nebula
Schneider, Glenn; Young, Erick T.; Rieke, Marcia +5 more
We present narrowband images of two externally illuminated circumstellar disks embedded in the Orion Nebula. The images were taken with camera 2 of the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) as part of the Hubble Space Telescope Early Release Observations program. Molecular hydrogen emission is confined to the silhouettes embed…
Ultraviolet Imaging Telescope Observations of the Magellanic Clouds
Parker, Joel Wm.; O'Connell, Robert W.; Bohlin, Ralph C. +8 more
We present wide-field far-ultraviolet (FUV; 1300-1800 Å) images of the Large and Small Magellanic Clouds (LMC, SMC). These data were obtained by the Ultraviolet Imaging Telescope (UIT) during the Astro-1 (1990 December 1-10) and Astro-2 (1995 March 2-18) missions; the images provide an extensive FUV mosaic of the SMC and contain numerous regions i…
The Adiabatic Exponent in the Solar Core
Kosovichev, A. G.; Elliott, J. R.
We present helioseismic inversions of solar p-mode frequencies obtained by the Michelson Doppler Imager instrument of the Solar Oscillation Investigation project on board SOHO, which indicate a lower central value for the adiabatic exponent Γ1 in the Sun than in current models. We show how the inclusion of relativistic effects in the eq…
Fundamental stellar parameters for nearby visual binary stars: eta Cas, XI Boo, 70 OPH and 85 Peg. Helium abundance, age and mixing length parameter for low mass stars
Morel, P.; Baglin, A.; Lebreton, Y. +1 more
The calibration of nearby visual binary stars on the HR diagram is used to determine the helium abundance, age and mixing length parameter for stars other than the Sun. Four Population I low mass systems with high-quality data are analysed by means of standard evolutionary stellar models: eta Cas, 70 Oph, xi Boo and 85 Peg. Complementing these res…
Physical Structure of a Coronal Streamer in the Closed-Field Region as Observed from UVCS/SOHO and SXT/Yohkoh
Romoli, M.; Raymond, J. C.; Naletto, G. +4 more
We analyze a coronal helmet streamer observed on 1996 July 25 using instruments aboard two solar spacecraft, the Ultraviolet Coronagraph Spectrometer (UVCS) on board Solar and Heliospheric Observatory (SOHO) and the Soft X-Ray Telescope (SXT) on board Yohkoh. We derive temperatures and electron densities at 1.15 R⊙ from SXT/Yohkoh obser…