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The Formation of Broad-Line Clouds in the Accretion Shocks of Active Galactic Nuclei
Fromerth, Michael J.; Melia, Fulvio
Recent work on the gas dynamics in the Galactic center has improved our understanding of the accretion processes in galactic nuclei, particularly with regard to properties such as the specific angular momentum distribution, density, and temperature of the inflowing plasma. With the appropriate extrapolation of the physical conditions, this informa…
Hubble Space Telescope STIS Observations of GRB 000301C: CCD Imaging and Near-Ultraviolet MAMA Spectroscopy
Fruchter, Andrew S.; Hogg, David W.; Livio, Mario +24 more
We present Space Telescope Imaging Spectrograph observations of the optical transient (OT) counterpart of the γ-ray burster GRB 000301C obtained 5 days after the burst, on 2000 March 6. CCD clear-aperture imaging reveals a R~=21.50+/-0.15 source with no apparent host galaxy. An 8000 s, 1150 Å<λ<3300 Å near-ultraviolet MAMA prism spectrum sho…
Far-Ultraviolet Intensities and Center-to-Limb Variations of Active Regions and Quiet Sun Using UARS SOLSTICE Irradiance Measurements and Ground-based Spectroheliograms
Woods, Thomas N.; Worden, John R.; Bowman, Kevin W.
The average intensity and center-to-limb variation of active regions, enhanced network (large-scale active region fragments), and quiet Sun are estimated by minimizing the variance between time series of the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) far-ultraviolet (FUV) irradiance measurements and a model of the solar irradiance t…
Ultraviolet spectra for lambda Boo (HD 125162) computed with H2 opacities and Lyman-alpha H-H and H-H+ opacities
Castelli, F.; Kurucz, R. L.
New opacity distribution functions (ODF) have been computed for use with the ATLAS9 model atmosphere code of Kurucz. One of the improvements upon the Kurucz (\cite{kur90}) ODFs is the addition to the line blanketing of the Lyman-alpha H-H and H-H+ quasi-molecular absorptions near 1600 Å and 1400 Å. New-ODF fluxes are expected to reprodu…
UBVRIJH photometry of two new luminous δ Scuti stars and the discovery of δ Scuti pulsation in the most evolved Ap star known
Handler, G.; Kurtz, D. W.; Kilkenny, D. +5 more
Time-series photometry of the Hipparcos variable stars HD 199434 and 21190 is reported. Both stars are pulsators of the δ Scuti type. Reclassifications of the MK types of the stars, based on new spectrograms, are given. HD 21190 is found to be F2III SrEuSi:, making it the most evolved Ap star known. Its Strömgren photometric indices support the pe…
Rapid Temporal Variations of Interstellar Absorption Lines in the Carina Nebula
Walborn, Nolan R.; Danks, Anthony C.; Landsman, Wayne B. +3 more
Two observations of the complex interstellar absorption-line profiles in the UV spectrum of CPD -59°2603, obtained 22 months apart in the R~110,000 mode of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, reveal substantial variations in the intensities of several high-velocity components, including the virtual disappearance…
Binary systems with post-T Tauri secondaries
Gerbaldi, M.; Faraggiana, R.; Balin, N.
The identification of post-T Tauri (pTT) stars selected through spectroscopic criteria by Pallavicini et al. (\cite{Pallavicini92}) and by Martín et al. (1992) among the candidates belonging to visual binary systems is revisited in the present paper by studying their position in the HR diagram. These stars belong to the so-called Lindroos binary s…
A model for the origin of the anomalous and very bright UV lines of Fe II in gaseous condensations of the star η Carinae
Johansson, S.; Letokhov, V. S.
We present a qualitative physical model of the origin of two very bright UV lines of Fe II at 2507-2509 Å, present in high-resolution spectra of gaseous condensations (blobs) close to the central star of eta Carinae. The spectra have been obtained with the Hubble Space Telescope (HST). The model is based on a type of Bowen mechanism with selective…
The Inner Nebula and Central Binary of the Symbiotic Star HM Sagittae
Davis, R. J.; Eyres, S. P. S.; Bode, M. F. +2 more
We present contemporaneous Hubble Space Telescope Wide Field Planetary Camera 2 and Very Large Array observations of the symbiotic nova HM Sge. We identify a number of discreet features at spatial scales smaller than ~0.1" embedded in the extended nebula, with radio and optical emission well correlated in the inner 1". For the first time we measur…
WIYN Open Cluster Study. VII. NGC 2451A and the Hipparcos Distance Scale
Deliyannis, Constantine P.; Kozhurina-Platais, Vera; Girard, Terrence M. +5 more
We provide new evidence that NGC 2451A is undoubtedly a young open cluster, although sparsely populated. New cluster membership has been derived from relative proper motions of 5868 stars. In total, 136 stars down to V~15 have membership probability Pµ>=2%. New CCD BV photometry indicates that about 70 stars are indeed main-seq…