Search Publications

Lithium abundance and mass

Mallik, Sushma V.

Observations of cool giants have shown that there exists a large range in their lithium abundances even for apparently similar stars. The depletions are large in a majority of them, far in excess of the predictions of the standard stellar evolution models. In order to explore whether the large spread in Li abundances observed in giants can be inte…

The EXOSAT medium-energy slew survey catalog

Parmar, A. N.; Pollock, A. M. T.; Taylor, B. G. +4 more

We present a catalog of X-ray sources observed during slew maneuvers by the Medium Energy Detector Array onboard the EXOSAT Observatory. The EXOSAT Medium Energy slew-survey catalog (EXMS) provides a unique record of the 1-8 keV X-ray sky between 1983 and 1986. 98% of the sky was observed, with 85% receiving an exposure of >60 s. 1210 sources w…

The D/H Ratio in Interstellar Gas toward G191-B2B

Gull, T. R.; Barstow, M. A.; Bruhweiler, F. C. +7 more

Recent analysis of Goddard High-Resolution Spectrograph (GHRS) echelle spectra suggests ~30% variations in the D/H abundance ratio along the line of sight to the nearby (69 pc) hot white dwarf (WD) G191-B2B (Vidal-Madjar et al.). Variations in the D/H ratio on such short length scales imply nonuniform production/destruction of deuterium and an ine…

Observational Constraints on Models of the Solar Background Spectrum

Fleck, B.; Jefferies, S. M.; Tarbell, T. +3 more

We discuss the properties of the solar background signal as observed in high-quality, l-ν power and phase difference spectra of the continuum (C), velocity (V), and line intensity (I) fluctuations of the Ni I 6768 Å line. These spectra were generated from high-resolution images acquired by the Michelson Doppler Imager on board SOHO.

We confir…

Direct calibration of the Cepheid period-luminosity relation

Paturel, G.; Garnier, R.; Lanoix, P.

After the first release of Hipparcos data, Feast & Catchpole gave a new value for the zero-point of the visual Cepheid period-luminosity relation, based on trigonometric parallaxes. Because of the large uncertainties on these parallaxes, the way in which individual measurements are weighted is of crucial importance. We therefore conclude that …

Doppler imaging of stellar surface structure. X. The FK Comae-type star HD 199178 = V 1794 Cygni

Strassmeier, K. G.; Lupinek, S.; Dempsey, R. C. +1 more

Doppler imaging is used to derive the surface temperature distribution of the FK Comae star HD 199178 for five observing epochs between 1988 and 1997. Our maps are mainly based on Ca i 6439-Ä line profiles and simultaneous and contemporary BV and VI photometry. All images of HD 199178 are characterized by a large polar spot and several low-latitud…

Transient events in the EUV transition region and chromosphere

Baudin, F.; Keenan, F. P.; Phillips, K. J. H. +2 more

Rapid time cadence observations of the quiet Sun extreme ultraviolet emission, observed by the cds instrument on soho, are discussed. Numerous transient brightenings are observed in network features in both a transition region line (O V 629.73 Ä) and a chromospheric line (He I 584.33 Ä), indicating a dynamic coupling between the chromospheric and …

Discovery of solid HDO in grain mantles

Emerson, J. P.; Teixeira, T. C.; Devlin, J. P. +1 more

The observation of deuterium fractionation in the molecular gas in hot cores is currently interpreted as evaporation of deuterium-rich molecules from the icy grain mantles where they accumulated during the cold, dense cloud core stage. The predicted enrichment in deuterium of the ices has never been observed. This work provides the first detection…

Physical Properties of the X-Ray-Luminous SN 1978K in NGC 1313 from Multiwavelength Observations

Staveley-Smith, L.; Schlegel, Eric M.; Dopita, M. +4 more

We update the light curves from the X-ray, optical, and radio bandpasses which we have assembled over the past decade and present two observations in the ultraviolet using the Hubble Space Telescope Faint Object Spectrograph. The HRI X-ray light curve is constant within the errors over the entire observation period. This behavior is confirmed in t…

The H⁺₃ Latitudinal Profile of Saturn

Ballester, Gilda E.; Miller, Steve; Stallard, Tom +3 more

We present an H⁺₃ latitudinal profile of Saturn, obtained in 1998 October using the CSHELL spectrometer on the NASA Infrared Telescope Facility. The profile, measured at 3.953 µm, shows that the majority of the emission is concentrated in the auroral ovals, making Saturn similar to Jupiter and different from Uranus. The…