Search Publications
A High Merger Fraction in the Rich Cluster MS 1054-03 at Z = 0.83: Direct Evidence for Hierarchical Formation of Massive Galaxies
van Dokkum, Pieter G.; Franx, Marijn; Kelson, Daniel D. +2 more
We present a morphological study of the galaxy population of the luminous X-ray cluster MS 1054-03 at z=0.83. The sample consists of 81 spectroscopically confirmed cluster members in a 3×2 h-150 Mpc area imaged in F606W and F814W with WFPC2. We find 13 ongoing mergers in MS 1054-03, comprising 17% of the L>~L* c…
Slow Magnetosonic Waves in Coronal Plumes
Nakariakov, V. M.; DeForest, C. E.; Ofman, L.
Recent observations of polar plumes in the southern solar coronal hole by the Extreme-Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft show signatures of quasi-periodic compressional waves with periods of 10-15 minutes. The relative wave amplitude was found to increase with height in the plumes up to about 1.2 Rsolar. Us…
On the Origin of Impulsive Electron Events Observed at 1 AU
Krucker, Säm; Thompson, Barbara J.; Lin, Robert P. +1 more
A statistical survey of 12 impulsive electron events detected at energies down below 1 keV and 58 events detected above 25 keV observed at 1 AU by the 3-D Plasma and Energetic Particles experiment on the Wind spacecraft is presented. Timing analysis of the velocity dispersion reveals two different kinds of electron events: (1) events released from…
R-Process Abundances and Chronometers in Metal-poor Stars
Beers, Timothy C.; Burles, Scott; Tytler, David +5 more
Rapid neutron-capture (i.e., r-process) nucleosynthesis calculations, employing internally consistent and physically realistic nuclear physics input (quasi-particle random-phase approximation [QRPA] β-decay properties and the recent extended Thomas-Fermi with Strutinsky integral and quenching (ETFSI-Q) nuclear mass model), have been performed. The…
LASCO and EIT Observations of Helical Structure in Coronal Mass Ejections
Michels, D. J.; Howard, R. A.; Dere, K. P. +2 more
Observations of coronal mass ejections (CMEs) by the Large Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) show a significant fraction with circular intensity patterns. In the past, these would have been called ``disconnection'' events, but we suggest that these are evidence of CMEs containing helical magne…
Hubble Space Telescope and Palomar Imaging of GRB 990123: Implications for the Nature of Gamma-Ray Bursts and Their Hosts
Fruchter, Andrew S.; Hogg, David W.; Livio, Mario +13 more
We report on Hubble Space Telescope and Palomar optical images of the field of GRB 990123, obtained in 1999 February 8 and 9. We find that the optical transient (OT) associated with GRB 990123 is located on an irregular galaxy, with a magnitude of V=24.20+/-0.15. The strong metal absorption lines seen in the spectrum of the OT, along with the low …
Hot Horizontal-Branch Stars: The Ubiquitous Nature of the ``Jump'' in Strömgren u, Low Gravities, and the Role of Radiative Levitation of Metals
Grundahl, F.; Stetson, P. B.; Catelan, M. +2 more
A ``jump'' in the blue horizontal-branch (HB) distribution in the (V, u-y) color-magnitude diagram has recently been detected in the globular cluster (GC) M13 (NGC 6205) by Grundahl and coworkers. Such an effect is morphologically best characterized as a discontinuity in the (u, u-y) locus, with stars in the range 11,500 K<~Teff<~…
A Test of Pre-Main-Sequence Evolutionary Models across the Stellar/Substellar Boundary Based on Spectra of the Young Quadruple GG Tauri
Ghez, A. M.; Reid, I. Neill; White, Russel J. +1 more
We present spatially separated optical spectra of the components of the young hierarchical quadruple GG Tau. Spectra of GG Tau Aa and Ab (separation 0.25"~35 AU) were obtained with the Faint Object Spectrograph on board the Hubble Space Telescope. Spectra of GG Tau Ba and Bb (separation 1.48"~207 AU) were obtained with both the HIRES and the LRIS …
Silicate Mineralogy of the Dust in the Inner Coma of Comet C/1995 01 (Hale-Bopp) Pre- and Postperihelion
Woodward, Charles E.; Koike, Chiyoe; Witteborn, Fred C. +4 more
We present 7.5-13.4 µm infrared (IR) spectrophotometry (R~=180-360) of the 10 µm silicate emission from dust in the inner coma (i.e., within a diameter of 3") of comet C/1995 O1 (Hale-Bopp) at four temporal epochs from 1996 October through 1997 June during Hale-Bopp's approach to, arrival at, and recession from perihelion. Hale-Bopp's …
The Circumstellar Disk of HD 141569 Imaged with NICMOS
Zuckerman, B.; Schneider, G.; Silverstone, M. D. +5 more
Coronagraphic imaging with the Near-Infrared Camera and Multiobject Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4") radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected light image at 1.1 µm shows the disk oriented at a position angle of 356deg+/-5deg and inclined to ou…