Search Publications
PG 2131+066: A Test of Pre-White Dwarf Asteroseismology
Reed, M. D.; Kawaler, Steven D.; O'Brien, M. Sean
PG 2131+066 is a composite-spectrum binary with a hot pulsating PG 1159-type pre-white dwarf and an early M-type main-sequence star. Analysis of Whole Earth Telescope observations of the pulsating pre-white dwarf component provided an asteroseismological determination of its mass, luminosity, and effective temperature. These determinations allowed…
Hubble Space Telescope Infrared Imaging Polarimetry of Centaurus A: Implications for the Unified Scheme and the Existence of a Misdirected BL Lacertae Nucleus
Marconi, Alessandro; Capetti, Alessandro; Hough, J. H. +6 more
We report results from the Hubble Space Telescope (HST)/near-infrared camera and multiobject spectrometer (NICMOS) 2 µm imaging polarimetry of the central region of Centaurus A. In the vicinity of the nucleus we observe a complex polarization structure, which we explain by a combination of scattering of nuclear light and dichroic polarizatio…
Distance Dependence in the Solar Neighborhood Age-Metallicity Relation
Garnett, D. R.; Kobulnicky, H. A.
The age-metallicity relation for F and G dwarf stars in the solar neighborhood, based on the stellar metallicity data of Edvardsson et al., shows an apparent scatter that is larger than expected considering the uncertainties in metallicities and ages. A number of theoretical models have been put forward to explain the large scatter. However, we pr…
The Nature of Solar Polar Rays
Jewitt, David; Li, Jing; LaBonte, Barry
We use time series observations from the Solar and Heliospheric Observatory and Yohkoh spacecraft to study solar polar rays. Contrary to our expectations, we find that the rays are associated with active regions on the Sun and are not features of the polar coronal holes. They are extended, hot plasma structures formed in the active regions and pro…
Evolution of Global-Scale Coronal Magnetic Field due to Magnetic Reconnection: The Formation of the Observed Blob Motion in the Coronal Streamer Belt
Plunkett, S. P.; Michels, D. J.; Wu, S. T. +1 more
Recent SOHO/LASCO/EIT observations showed that the global corona at the minimum phase of cycle 22 is an organized, simple, and persistent dipolar configuration streamer belt (Michels). But the low-lying, closed-loop, multipolar magnetic structure of the inner corona at low- to mid-latitudes revealed in EIT and LASCO images is not static. It stretc…
Small Scale Structure in the Solar Transition Region
Winebarger, Amy R.; Warren, Harry P.
We present analysis of a high spatial resolution (~1.5") O VI λ1032 spectroheliogram taken with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory. This image shows numerous narrow, looplike structures. The widths of the narrowest resolved features are at the spatial resolution of…
Interplanetary Network Localization of GRB 991208 and the Discovery of its Afterglow
Cline, T.; Hurley, K.; Golenetskii, S. +9 more
The extremely energetic (~10-4 ergs cm-2) gamma-ray burst (GRB) of 1999 December 8 was triangulated to an ~14 arcmin2 error box ~1.8 days after its arrival at Earth with the third interplanetary network (IPN), which consists of the Ulysses, Near-Earth Asteroid Rendezvous, and Wind spacecraft. Radio observations wit…
Secondary Fragmentation of the Solar and Heliospheric Observatory Sungrazing Comets at Very Large Heliocentric Distance
Sekanina, Zdenek
The temporal distribution of the Kreutz group of sungrazing comets has been known to have an episodic character on timescales from weeks to tens of years. With the large number of minor members of this group being nowadays discovered in images taken with the Solar and Heliospheric Observatory coronagraphs, it has become apparent that the distribut…
A New Look at Globular Cluster Colors in NGC 3311 and the Case for Exclusively Metal-rich Globular Cluster Systems
Larsen, S. S.; Kissler-Patig, M.; Brodie, J. P.
NGC 3311, the central cD galaxy in the Hydra Cluster, was previously thought to host the most metal-rich globular cluster system known. Ground-based Washington photometry had indicated the almost complete absence of the population of globular clusters near [Fe/H]~-1 dex; these globular clusters are normally dominant in the metallicity distribution…
The Infrared Einstein Ring in the Gravitational Lens MG J1131+0456 and the Death of the Dusty Lens Hypothesis
Peng, C. Y.; Keeton, C. R.; Kochanek, C. S. +6 more
We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131+0456, which show that its lens galaxy is an H=18.6 mag, transparent, early-type galaxy at a redshift of zl~=0.84 it has a major axis effective radius Re=0.7"+/-0.1", projected axis ratio b/a=0.6+/-0.1, and major axis P.A.=55deg+/-9…