Search Publications
On the Helium Content of Galactic Globular Clusters via the R-Parameter
Djorgovski, S. G.; Zoccali, M.; Rich, R. M. +3 more
We estimate the empirical R-parameter in 26 Galactic globular clusters covering a wide metallicity range, imaged by Wide Field Planetary Camera 2 on board the Hubble Space Telescope. The improved spatial resolution permits a large fraction of evolved stars to be measured and permits accurate assessment of radial population gradients and completene…
Multi-component structure of solar and stellar transition regions
Peter, H.
Emission lines from the solar transition region between the chromosphere and the corona often show a two Gaussian component profile with a core and a broad second component contributing up to 25% to the total intensity. For the first time a systematic study of the broadening and Doppler shift of the second weaker components is performed using SUME…
ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur and HD 163296
Waters, L. B. F. M.; van Dishoeck, E. F.; van den Ancker, M. E. +3 more
Using both the Short- and Long-wavelength Spectrometers on board the Infrared Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae systems AB Aur and HD 163296. In addition, we obtained ground-based N band images of HD 163296. Our results can be summarized as follows: (1) The main dust components in AB Aur are amorphous sili…
Hubble Space Telescope observations of X-ray-selected active galactic nuclei
Schade, David J.; Boyle, B. J.; Letawsky, Michael
We report on the initial results of a comprehensive Hubble Space Telescope (HST) snapshot imaging survey of 76 low-redshift (z<0.15) X-ray-selected active galactic nuclei (AGN) in the Einstein Extended Medium Sensitivity Survey. This survey is expected to show no bias with respect to host galaxy types, and so is arguably one of the best availab…
The massive stellar content of the Hii region NGC 604 and its evolutionary state
Pérez, Enrique; González Delgado, Rosa M.
This paper analyses the integrated ultraviolet spectra taken with the International Ultraviolet Explorer (IUE) and optical ground-based spectra taken with the William Herschel Telescope (WHT) of the giant Hii region NGC 604. These data are complemented with ultraviolet (WFPC2 through F170W) and Hα (WFPC2 through F656N) images retrieved from the Hu…
Phase-sensitive Holography of Solar Activity
Braun, D. C.; Lindsey, C.
Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. We have now applied techniques in phase-sensitive seismic holography to data from the Solar Oscillation…
The γ Velorum binary system. II. WR stellar parameters and the photon loss mechanism
Schmutz, W.; Hillier, D. J.; Crowther, P. A. +4 more
In this paper we derive stellar parameters for the Wolf-Rayet star in the gamma Velorum binary system (WR11), from a detailed non-LTE model of its optical and infrared spectra. Compared to the study of Schaerer et al., the parameters of the WC8 star are revised to a hotter effective temperature (T_eff ~ 57 kK), a higher luminosity (log (L/Lsu…
A Redetermination of the Mass of Procyon
Brown, R. H.; Provencal, J. L.; Wu, H. +12 more
The parallax and astrometric orbit of Procyon have been redetermined from PDS measurements of over 250 photographic plates spanning 83 years, with roughly 600 exposures used in the solution. These data are combined with two modern measurements of the primary-white dwarf separation, one utilizing a ground-based coronagraph, the other, the Planetary…
Water in Emission in the Infrared Space Observatory Spectrum of the Early M Supergiant Star µ Cephei
Tsuji, Takashi
We report a detection of water in emission in the spectrum of the M2 supergiant star µ Cephei (M2 Ia) observed by the Short-Wavelength Spectrometer on board Infrared Space Observatory (ISO) and now released in the ISO archives. The emission first appears in the 6 µm region (ν2 fundamental bands) and then in the 40 µm r…
The Distribution and Physical State of H 2O on Charon
Buie, M. W.; Grundy, W. M.
We present new 1.4- to 2.5-µm geometric albedo spectra of Charon taken with HST/NICMOS in 1998. These new data provide global coverage of the surface with four spectra at evenly spaced longitudes. The surface of Charon is seen to be globally dominated by H 2O ice. The data indicate that the ice is in the crystalline phase at a tem…