Search Publications
A Lower Limit to the Distance of High-Velocity Cloud Complex H
Wakker, Bart; van Woerden, Hugo; de Boer, Klaas S. +1 more
We derive a lower limit for the distance of the high-velocity cloud (HVC) complex H, which is a structure covering 480 square degrees on the sky and is centered on l = 131°, b = 1°. Considering the uncertainties in the derivation of stellar distances, we find that the distance to the HVC is certainly larger than 3.4 kpc, probably larger than 5 kpc…
The Remarkable Boron-depleted, Lithium-normal Population II Star HD 160617
Primas, F.; Duncan, D. K.; Thorburn, J. A.
We present results of an analysis of the boron spectral region (2500 Å) in the metal-poor star HD 160617, observed with the Goddard High Resolution Spectrograph of the Hubble Space Telescope. HD 160617 has a metallicity of [Fe/H]~-1.8, a Teff~5900 K, and a log g ~ 3.5. Its Li abundance is the normal, primordial ``Spite plateau'' value l…
First Astronomical Images Sharpened with Adaptive Optics Using a Sodium Laser Guide Star
McLeod, B. A.; Hooper, E. J.; Angel, J. R. P. +7 more
Adaptive optics with a sodium resonance laser guide star was used at the Multiple Mirror Telescope (MMT) in 1996 April to image the core of the globular cluster M13 (NGC 6205). A 23" field was recorded in the Ks band with image resolution of 0.51", when the uncorrected resolution was 0.72". Global tilt, not sensed by the laser, was meas…
The Complete Spectral Energy Distribution and the Atmospheric Properties of the Helium-Rich White Dwarf MCT 0501-2858
Vennes, Stéphane; Polomski, Elisha F.; Chayer, Pierre +3 more
We analyze high-dispersion ultraviolet spectroscopic observations of the peculiar helium-rich white dwarf MCT 0501-2858. Ultraviolet spectra obtained during the 1996 November ORFEUS-SPAS II mission show the complete He II (n=2) line series as well as narrow heavy-element lines; the spectrum constrains the effective temperature (68,600 +/- 1800 K) …
An Absence of Gaps in the Main-Sequence Population of Field Stars
Yanny, Brian; Newberg, Heidi Jo
Using high-precision parallaxes from the Hipparcos catalog, we construct H-R diagrams for two samples of bright stars. The first is a magnitude-limited sample that is over 90% complete and uses uniform photometry from the Catalog of WBVR Magnitudes of Northern Sky Bright Stars (δ>-14deg). This sample shows a smooth distribution of st…
Far-Ultraviolet Continuum of G-Type Stars: A Signature of the Temperature Minimum Region
Morossi, C.; Malagnini, M. L.; Franchini, M.
The main results of a program of systematic comparison between observed and computed UV spectral energy distributions of field G-type stars are illustrated. We constructed the UV observed energy distributions for 53 G stars, starting from the IUE Uniform Low Dispersion Archive (ULDA) and computed the corresponding theoretical fluxes by using the a…
Spatiotemporal Correlations and Turbulent Photospheric Flows from SOHO/MDI Velocity Data
Tarbell, T.; Lawrence, J. K.; Cadavid, A. C. +2 more
Time series of high-resolution and full-disk velocity images obtained with the Michelson Doppler Imager (MDI) instrument on board SOHO have been used to calculate the spacetime spectrum of photospheric velocity flow. The effects of different methods for filtering acoustic oscillations have been carefully studied. It is found that the spectra show …
Large Variations in the Winds of Single Cool Giants: λ Velorum and γ Crucis
Carpenter, K. G.; Mullan, D. J.; Robinson, R. D.
UV spectra of the ``noncoronal'' single K supergiant λ Vel and of the single M giant γ Cru obtained with IUE and the Hubble Space Telescope at various epochs indicate that the profiles of many lines formed in the wind exhibit striking alterations in shape with time. We parameterize the wind profiles in terms of an empirical optical depth τemp…
Discovery of a Luminous White Dwarf in a Young Star Cluster in the Large Magellanic Cloud
Elson, Rebecca A. W.; Sigurdsson, Steinn; Hurley, Jarrod +2 more
We have identified a candidate ~1-2×105 yr old luminous white dwarf in NGC 1818, a young star cluster in the Large Magellanic Cloud. This discovery strongly constrains the boundary mass Mc at which stars stop forming neutron stars and start forming white dwarfs, to Mc>~7.6 Msolar.
Abundance and Isotopic Composition of Platinum in χ Lupi and HR 7775 Derived with the Help of New Laboratory Spectra of Pt II
Johansson, Sveneric; Wahlgren, Glenn M.; Leckrone, David S. +3 more
The platinum isotope anomaly observed in the chemically peculiar HgMn star χ Lupi has been confirmed by analysis with new high-resolution laboratory spectra recorded with the VUV Fourier transform spectrometer at Lund University. The χ Lupi platinum composition is shown to be a mixture of isotopes 196 and 198. Recent observations made with the Hub…