Search Publications
The Structure and Evolution of a Sigmoidal Active Region
Liu, Y.; Mason, H. E.; Thompson, B. J. +13 more
Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejections. Sigmoids, or S-shaped structures, may be indicators of twisted or helical magnetic structures, having an increased likelihood of eruption. We present here an analysis of a sigmoidal region's three-dimensional structure and how it evolves in rela…
Spectral Evidence for Widespread Galaxy Outflows at z > 4
Broadhurst, Tom; Frye, Brenda; Benítez, Narciso
We present discovery spectra of a sample of eight lensed galaxies at high redshift, 3.7<z<5.2, selected by their red colors in the fields of four massive clusters: A1689, A2219, A2390, and AC 114. Metal absorption lines are detected and observed to be blueshifted by 300-800 km s-1 with respect to the centroid of Lyα emission. A co…
Speckle interferometry of nearby multiple stars
Weigelt, G.; Hofmann, K. -H.; Schertl, D. +5 more
We present the results of diffraction-limited optical speckle interferometry and infrared bispectrum speckle interferometry of 111 double and 10 triple systems performed in 1998-1999 with the 6-m telescope of the Special Astrophysical Observatory in Zelenchuk. The observations concentrated on nearby close binaries discovered during the Hipparcos m…
Hubble Space Telescope Space Telescope Imaging Spectrograph Observations of the Bipolar Jet from RW Aurigae: Tracing Outflow Asymmetries Close to the Source
Bacciotti, Francesca; Eislöffel, Jochen; Davis, Christopher J. +2 more
We have observed the bipolar jet from RW Aur A with STIS on board the Hubble Space Telescope. After continuum subtraction, morphological and kinematic properties of this outflow can be traced to within 0.1" from the source in forbidden emission lines. The jet appears well collimated, with typical FWHMs of 20-30 AU in the first 2" and, surprisingly…
The Population of Weak Mg II Absorbers. II. The Properties of Single-Cloud Systems
Charlton, Jane C.; Churchill, Christopher W.; Rigby, Jane R.
We present an investigation of Mg II absorbers characterized as single-cloud ``weak systems'' [defined by Wr(λ2796)<0.3 Å] at z~1. We measured column densities and Doppler parameters for Mg II and Fe II in 15 systems found in High Resolution Echelle Spectrometer/Keck spectra at 6.6 km s-1. Using these quantities and C IV, …
X-ray observations of a large-scale solar coronal shock wave
Aurass, H.; Khan, J. I.
We report observations of a propagating disturbance in the solar corona observed in emission in soft X-ray images from the Yohkoh Soft X-ray Telescope (SXT). The disturbance was associated with a flare which began at about 09:04 UT on 1997 November 03. This flare was associated with a type II radio burst observed at decimetric-dekametric wavelengt…
Composition of Anomalous Cosmic Rays and Other Heliospheric Ions
Cummings, A. C.; Stone, E. C.; Steenberg, C. D.
Interstellar pickup ions accelerated by the termination shock of the solar wind dominate the anomalous cosmic-ray (ACR) intensities observed by the Voyager spacecraft in the outer heliosphere. Using a two-dimensional acceleration and propagation model, we derive the relative abundances of these interstellar ACRs and determine the mass dependence o…
Dynamical masses of young star clusters in NGC 4038/4039
Genzel, R.; Lehnert, M. D.; Mengel, S. +1 more
In order to estimate the masses of the compact, young star clusters in the merging galaxy pair, NGC 4038/4039 (``the Antennae''), we have obtained medium and high resolution spectroscopy using ISAAC on VLT-UT1 and UVES on VLT-UT2 of five such clusters. The velocity dispersions were estimated using the stellar absorption features of CO at 2.29 mu m…
Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Lindegren, Lennart; Madsen, Søren; Dravins, Dainis
Radial motions of stars in nearby moving clusters are determined from accurate proper motions and trigonometric parallaxes, without any use of spectroscopy. Assuming that cluster members share the same velocity vector (apart from a random dispersion), we apply a maximum-likelihood method on astrometric data from Hipparcos to compute radial and spa…
Infrared Views of the TW Hydra Disk
Zuckerman, B.; Schneider, G.; Hines, D. C. +6 more
The face-on disk around TW Hya is imaged in scattered light at 1.1 and 1.6 µm using the coronagraph in the Near Infrared Camera and Multi Object Spectrometer aboard the Hubble Space Telescope. Stellar light scattered from the optically thick dust disk is seen from 20 to 230 AU. The surface brightness declines as a power law of r-2.6+/-0…