Search Publications
GHRS Observations of Cool Low-Gravity Stars. III. Plasma Flows and Turbulence in the Outer Atmosphere of α Orionis (M2 Iab)
Robinson, Richard D.; Carpenter, Kenneth G.
We present the results of a Goddard High Resolution Spectrograph (GHRS) study of flow and turbulent velocities in the outer atmosphere of the M2 Iab supergiant α Ori. Ions with observed chromospheric emission features include C I, C II, Si I, Si II, O I, Co II, Al II, Mg II, Cr II, Fe I, and Fe II, while the photospheric absorption spectrum is dom…
A New Luminous Blue Variable in the Giant Extragalactic H II Region NGC 2363
Drissen, Laurent; Robert, Carmelle; Roy, Jean-René
We report the discovery of an erupting luminous blue variable (LBV) star in the giant H II region NGC 2363, the most massive star-forming region in the Magellanic irregular galaxy NGC 2366. This LBV, presently the visually brightest star in the galaxy (MV ~ -10.2), was first noticed in Hubble Space Telescope Wide Field Planetary Camera …
The O-Type Binary 15 Monocerotis Nears Periastron
Gies, Douglas R.; Penny, Laura R.; Bagnuolo, William G., Jr. +6 more
We present new radial velocity measurements for the massive binary 15 Monocerotis which indicate that the system is now very close to periastron (1996.9) in its 24 yr orbit. The velocity separation in the coming year may be large enough to permit an accurate estimate of mass ratio. We also present our first astrometric measurement of 15 Mon made w…
The High Chromospheres of the Late A Stars
Simon, Theodore; Landsman, Wayne B.
We report the detection of N V 1239 Å transition region emission in HST/Goddard High Resolution Spectrograph spectra of the A7 V stars, α Aql and α Cep. Our observations provide the first direct evidence of 1-3 × 105 K material in the atmospheres of normal A-type stars. For both stars, and for the mid A-type star τ3 Eri, we a…
Non-LTE Line-blanketed Model Atmospheres of Hot Stars. III. Hot Subdwarfs: The sdO Star BD +75°325
Hubeny, Ivan; Heap, Sara R.; Lanz, Thierry
We have made a detailed comparison of results of spectroscopic analysis using three differents types of model atmospheres: classical non-LTE H-He models; approximate non-LTE line-blanketed models (with only a subset of Fe and Ni lines: those originating from transitions between levels with measured energies); and non-LTE fully blanketed models. Th…
The Dust-to-Gas Ratio in the Damped Lyα Clouds toward the Gravitationally Lensed QSO 0957+561
Cohen, Ross D.; Junkkarinen, Vesa T.; Lyons, R. W. +3 more
We present HST/FOS1 spectra of the two bright images (A and B) of the gravitationally lensed QSO 0957+561 in the wavelength range 2200-3300 Å. We find that the absorption system (zabs = 1.3911) near zem is a weak, damped Lyα system with strong Lyα absorption lines seen in both images. However, the H I column densities are dif…
The Giant 1991 June 1 Flare: Evidence for Gamma-Ray Production in the Corona and Accelerated Heavy Ion Abundance Enhancements from Gamma-Ray Spectroscopy
Ramaty, Reuven; Mandzhavidze, Natalie; Barat, Claude +1 more
We investigated the implications of the gamma-ray line emission observed with Granat/PHEBUS from the behind-the-limb flare on 1991 June 1. We showed that thin target interactions are required to account for the very high observed ratio of the nuclear line emission in the 1.1-1.8 MeV and 4.1-7.6 MeV energy bands, which are populated predominantly b…
Digging Deeper in the Coronal Graveyard
Ayres, Thomas R.; Brown, Alexander; Carpenter, K. G. +4 more
Soft X-ray detections of stellar coronae (T ~ 106 K) are rare in the giant branch redward of ~K1 III. We have conducted a less direct--but more sensitive--search using the Hubble Space Telescope Goddard High-Resolution Spectrograph to probe for far-ultraviolet proxies of the hot coronal gas in representative ``noncoronal'' red giants. I…
Ultraviolet Interstellar Absorption Lines toward the Starburst Dwarf Galaxy NGC 1705
Blades, J. Chris; Sahu, M. S.
Archival Goddard High Resolution Spectrograph (GHRS) low-resolution spectra of NGC 1705, with wavelength ranges of 1170.3-1461.7 Å and 1453.5-1740.1 Å and a velocity resolution of ~120 kms-1, have been used to derive the velocity structure and equivalent widths of the absorption lines of Si II λ1190.42, λ1260.42, λ1304.37, and λ1526.71,…
The Initial Mass Function of Low-Mass Stars in Globular Clusters
Paresce, Francesco; De Marchi, Guido
We compare deep I-band luminosity functions of two globular clusters (NGC 6397 and NGC 6656) that have similar metal content but have experienced very different dynamical histories, both in terms of internal dynamics and as a result of different interactions with the Galactic tidal field. Their luminosity functions measured at the half-mass radius…