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Observations of T Tauri Stars using Hubble Space Telescope GHRS. I. Far-Ultraviolet Emission Lines
Valenti, Jeff A.; Walter, Frederick M.; Ardila, David R. +2 more
We have analyzed Goddard High Resolution Spectrograph data of eight classical T Tauri stars (CTTSs) and one weak-lined T Tauri star (WTTS). The GHRS data consist of spectral ranges 40 Å wide centered on 1345, 1400, 1497, 1550, and 1900 Å. These UV spectra show strong Si IV and C IV emission and large quantities of sharp (~40 km s-1) H
Crossing the Yellow Void: Spatially Resolved Spectroscopy of the Post-Red Supergiant IRC +10420 and Its Circumstellar Ejecta
Smith, Nathan; Humphreys, Roberta M.; Davidson, Kris
IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the H-R diagram. During their post-red supergiant evolution, these massive stars enter a temperature range (6000-9000 K) of increased dynamical instability, high mass loss, and increasing opacity, a semiforbidden region that de Jager and his co…
Impulsive Variations of the Magnetic Helicity Change Rate Associated with Eruptive Flares
Moon, Y. -J.; Wang, Haimin; Chae, Jongchul +2 more
In this paper, we investigate impulsive variations of the magnetic helicity change rate associated with eruptive solar flares (three X class flares and one M class flare) accompanying halo coronal mass ejections. By analyzing four sets of 1 minute cadence full-disk magnetograms taken by the Michelson Doppler Imager on board the Solar and Heliosphe…
Photometry of Mercury from SOHO/LASCO and Earth. The Phase Function from 2 to 170 deg.
Howard, Russell A.; Mallama, Anthony; Wang, Dennis
CCD observations of Mercury were obtained with the large angle spectrometric coronograph (LASCO) on the solar and heliospheric observatory spacecraft, near superior and inferior solar conjunctions. Whole disk photometry was extracted from the orange and blue filter images and transformed to V magnitudes on the UBV system. The LASCO data were combi…
Combined VLT ISAAC/ISO SWS spectroscopy of two protostellar sources. The importance of minor solid state features
van Dishoeck, E. F.; Pontoppidan, K. M.; Dartois, E. +2 more
We discuss the L band infrared spectra of two massive protostars in the region of the so-called 3.47 mu m absorption feature. The high sensitivity VLT-ISAAC spectra of the two differently evolved massive protostars GL 989 and GL 2136, together with dedicated infrared laboratory experiments on ice molecular interactions, allow us to propose the ide…
The Optical Counterpart of an Ultraluminous X-Ray Object in M81
Bregman, Joel N.; Seitzer, Patrick; Liu, Ji-Feng
Ultraluminous X-ray objects (ULXs) are off-nucleus point sources with LX=1039-1041 ergs s-1 they are among the most poorly understood X-ray sources. To help understand their nature, we are trying to identify their optical counterparts by combining images from the Hubble Space Telescope and the Chandra X-…
The Variability of the Hg II λ3984 Line of the Mercury-Manganese Star α Andromedae
Adelman, Saul J.; Gulliver, Austin F.; Kochukhov, Oleg P. +1 more
The variability of the Hg II λ3984 line in the primary of the binary star α And was discovered through the examination of high-dispersion spectra with signal-to-noise ratios greater than 500. This first definitively identified spectrum variation in any mercury-manganese star is not due to the orbital motion of the companion. Rather, the variation …
Soho Contribution to Prominence Science
Patsourakos, Spiros; Vial, Jean-Claude
We present the main current issues concerning prominence studies. We recall the large range of plasma parameters found in prominences which makes the work of the MHD modeler more difficult. We also summarize the capabilities of the SOHO instrumentation. We present and discuss the most recent SOHO results concerning the determination of temperature…
Prediction of Earth orientation parameters by artificial neural networks
Ulrich, M.; Müller, J.; Schuh, H. +2 more
Earth orientation parameters (EOPs) [polar motion and length of day (LOD), or UT1-UTC] were predicted by artificial neural networks. EOP series from various sources, e.g. the C04 series from the International Earth Rotation Service and the re-analysis optical astrometry series based on the HIPPARCOS frame, served for training the neural network fo…
The Luminosity Function of QSO Host Galaxies
Turnshek, David A.; Casertano, Stefano; Hamilton, Timothy S.
We present some results from our HST archival image study of 71 QSO host galaxies. The objects are selected to have z<=0.46 and total absolute magnitude MV<=-23 in our adopted cosmology (H0=50 km s-1 Mpc-1, q0=0.5, and Λ=0). The aim of this initial study is to investigate the composition…