Search Publications
The Orion Nebula: Structure, Dynamics, and Population
O'Dell, C. R.
The physical nature and evolution of the Orion Nebula has begun to be revealed by calibrated emission line images and high resolution spectroscopy. We review the evidence that the nebula is a thin wall of emission on the near side of the Orion Molecular Cloud and that its separation from the dominant ionizing star is about 0.3 pc. The density of t…
Spectropolarimetric Variability in OB Stars
Bjorkman, K. S.
Data from the Wisconsin spectropolarimetric monitoring program provide information about the polarimetric variability of numerous types of stars. Examining the data that exist thus far, we find, not surprisingly, that many OB stars, especially OB supergiants and Be stars, are polarimetric variables. Be stars show the most extreme variability as a …
Connection between X-Ray and Optical Variability in NGC 4151
Oknyanskij, V. L.
We have used long light curves in the X-ray (ARIEL V, EXOSAT, Ginga and others), UV (IUE), and optical (data of intensive ground-based monitoring) ranges of NGC 4151 to investigate connections between variations in these spectral fields. Applying Fourier (CLEAN algorithm) and modern cross-correlation analysis, we revealed the different character o…
High-Precision VLBI Astrometric Observations of Radio-Emitting Stars for Detection of Extra-Solar Planets
Preston, Robert A.; Jones, Dayton L.; Lestrade, Jean-Francois +1 more
The displacement of a radio-emitting star around the barycenter of a possible planetary system can be measured by astrometric very long baseline interferometry (VLBI) observations. We have observed the radio-emitting starσ2 CrB at 8 epochs over 5 years by VLBI and fitted its 5 astrometric parameters to the observed coordinates. The post…
The Evidence for Clumpy Accretion in the Herbig AE Star HR 5999
Grady, C. A.; Perez, M. R.; The, P. S.
Analysis of IUE high- and low-dispersion spectra of the young Herbig Ae star HR 5999 (HD 144668) covering 1978–1992 has revealed dramatic changes in the Mg II h and k (2795.5, 2802.7 Å) emission profiles, changes in the column density and distribution in radial velocity of accreting gas, and flux in the Lyα, OI and CIV emission lines, which are co…
Detection of Accreting Circumstellar Gas around Weak Emission-Line Herbig Ae/Be Stars
Grady, C. A.; Perez, M. R.; The, P. S.
We present archival and recent IUE high dispersion spectra of late B stars which reveal the presence of accreting gas with velocities as high as 350 km s‑1, collisional ionization of the accreting gas to temperatures above the stellar Teff, and column densities intermediate between those observed toward classical Herbig Ae/Be…
2800 MG II Emission in the Most Active Radio Stars
Gurzadyan, G. A.; Rustambekyan, S. S.
Spectral recordings in the region near 2800 Å are examined from the IUE archives for the twenty most active radio stars, which are also close binary systems. In all of these spectra, the doublet k and h Mg II is seen in strong emission. We find that the observed fluxes of the magnesium doublet emission are directly proportional to the mean fluxes …
Monitoring the Winds of Hot Stars with HST/GHRS
Heap, Sara R.
We present observations obtained with the Goddard High Resolution Spectrograph (GHRS) of three O-type stars:ξ per (O7 III),λ Cep (O6 Iaf) and 10 Lac (O9 V). These observations show evidence of instabilities in the winds of all three stars, although not necessarily those expected from current models of structured winds.
Pulsed Gamma Rays from Geminga
Cheng, K. S.; Ma, Y. Q.
The pulsed gamma ray spectrum is obtained by analyzing COS-B data of observation no. 14, 39, 54 and 64. We find that the pulsed spectrum differs significantly from that of previous reports in which the pulsed component and steady component are not separated. A clear spectral break of the pulsed spectrum occurs at ~ 100 MeV and the majority of the …
Column Densities of Interstellar Gas in the Direction of the Star \Epsilon ORI (B0 IA)
Mentese, H. H.
We have investigated the star ɛ Ori with IUE high resolution SWP spectrum in order to derive curve of growth and column densities of Al II, Si II, S II, Fe II, Ni II and Zn II. It has been possible to fit these ions on one empirical curve of growth with a velocity parameterb = 11 km s‑1 for the star studied.