Search Publications
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…
Distance to the Coma Cluster and a Value for HO Inferred from Globular Clusters in IC 4051
Ajhar, Edward A.; Grillmair, Carl J.; Groth, Edward J. +4 more
We report HST-WFPC2 observations of the giant E2 galaxy IC 4051 located 14' east of the center of the Coma Cluster. Eight full-orbit exposures were obtained with the F606W filter, and two with the F814W filter. Counts of globular clusters (GCs) in 0.2-mag wide bins were made within the PC1 (f/28) frame, where faint GCs can be distinguished from no…
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…
Nitrogen V in the wind of the pre-main sequence Herbig AE star AB Aurigae
Bouret, J. -C.; Catala, C.; Simon, T.
Recent GHRS observations of the Herbig Ae star AB Aur demonstrate the presence of N V in the wind of this star. This result reveals temperatures much higher than those previously considered for the wind of AB Aur. We show that homogeneous spherically symmetric models are unable to reproduce the available observations, including the C IV resonance …
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…
The high-excitation planetary nebula NGC 6741
Hyung, Siek; Aller, Lawrence H.
The compact, bright Peimbert type I planetary nebula NGC 6741 shows an unusually rich spectrum which is studied here from 3700 to 10 370 A with the Hamilton Echelle spectrograph at the Lick Observatory. By combining Hamilton Echelle observations with archive UV data secured with the International Ultraviolet Explorer (IUE), and with available IR d…
Ulysses observations of wave activity at interplanetary shocks and implications for type II radio bursts
MacDowall, R. J.; Phillips, J. L.; Stone, R. G. +2 more
We present the first quantitative investigation of interplanetary type II radio emission in which in situ waves measured at interplanetary shocks are used to compute radio wave intensities for comparison with type II observations. This study is based on in situ measurements of 42 in-ecliptic forward shocks as well as 10 intervals of type II emissi…
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…