2,765 research outputs found
White Dwarf - Red Dwarf Systems Resolved with the Hubble Space Telescope. II. Full Snapshot Survey Results
Results are presented for a Hubble Space Telescope Advanced Camera for
Surveys high-resolution imaging campaign of 90 white dwarfs with known or
suspected low mass stellar and substellar companions. Of the 72 targets which
remain candidate and confirmed white dwarfs with near-infrared excess, 43 are
spatially resolved into two or more components, and a total of 12 systems are
potentially triples. There is a possible, slight deficit of earlier spectral
types (bluer colors) among the spatially unresolved companions, exactly the
opposite of expectations if significant mass is transferred to the companion
during the common envelope phase. Using the best available distance estimates,
the low mass companions to white dwarfs exhibit a bimodal distribution in
projected separation. This result supports the hypothesis that during the giant
phases of the white dwarf progenitor, any unevolved companions either migrate
inward to short periods of hours to days, or outward to periods of hundreds to
thousands of years. No intermediate projected separations of a few to several
AU are found among these pairs. However, a few double M dwarfs (within triples)
are spatially resolved in this range, empirically demonstrating that such
separations were readily detectable among the binaries with white dwarfs. A
straightforward and testable prediction emerges: all spatially unresolved, low
mass stellar and substellar companions to white dwarfs should be in short
period orbits. This result has implications for substellar companion and
planetary orbital evolution during the post-main sequence lifetime of their
stellar hosts.Comment: Accepted to ApJ Supplement Series, emulateapj format, 14 figures, 8
table
Mid-Infrared Circumstellar Shell Sources Discovered with Spitzer: An Obscured Population of Massive Stars?
We have discovered a large number of circular and elliptical shells around luminous central sources at 24 μm with the MIPS instrument on board the Spitzer Space Telescope. Most of these shells are not visible in the shorter wavelengths bands of IRAC or archival 2MASS and optical images. On the other hand, many of the central stars are detected in the 2MASS catalog, but lack an optical counterpart, indicating that we are dealing with a population of highly obscured objects. Our archival follow-up effort has revealed 90% of these shell sources to be previously unknown
Recent Results from Infrared Observations of White Dwarfs, their Companions, and the Dust that Surrounds Them
Although "traditionally" observed at short wavelengths, white dwarfs have displayed many surprising features when probed in the infrared. We present an overview of recent results from ground- and space-based near- to mid-infrared observations of white dwarfs. These include the discovery of many new candidate binary stars containing low mass stellar or sub-stellar companions from a sample of objects previously thought to be single white dwarfs, and Spitzer Space Telescope observations that suggest that dust is common in the environs of white dwarfs in cataclysmic variables
The WISE InfraRed Excesses around Degenerates (WIRED) Survey
The Wide-field Infrared Survey Explorer (WISE) is a NASA medium class Explorer
mission that performed an all sky survey in four infrared bands. We present an overview of the WISE
InfraRed Excesses around Degenerates (WIRED) Survey, which has the goals of characterizing
white dwarf stars in the WISE bands, confirming objects known to have infrared excess from past
observations, and revealing new examples of white dwarfs with infrared excess that can be attributed
to unresolved companions or debris disks. We obtained preliminary WISE detections (S/N > 2) in
at least one band of 405 white dwarfs from the 9316 unique possible targets in the Sloan Digital
Sky Survey Data Release 4 Catalog of Spectroscopically Identified White Dwarfs (not all potential
targets were available in the sky coverage used here). A companion paper in this volume discusses
specific results from our target detections
The COLD-SAT Experiment for Cryogenic Fluid Management Technology
Future national space transportation missions will depend on the use of cryogenic fluid management technology development needs for these missions. In-space testing will be conducted in order to show low gravity cryogenic fluid management concepts and to acquire a technical data base. Liquid H2 is the preferred test fluid due to its propellant use. The design of COLD-SAT (Cryogenic On-orbit Liquid Depot Storage, Acquisition, and Transfer Satellite), an Expendable Launch Vehicle (ELV) launched orbital spacecraft that will perform subcritical liquid H2 storage and transfer experiments under low gravity conditions is studied. An Atlas launch vehicle will place COLD-SAT into a circular orbit, and the 3-axis controlled spacecraft bus will provide electric power, experiment control, and data management, attitude control, and propulsive accelerations for the experiments. Low levels of acceleration will provide data on the effects that low gravity might have on the heat and mass transfer processes used. The experiment module will contain 3 liquid H2 tanks; fluid transfer, pressurization and venting equipment; and instrumentation
Evolution of Spatially Inhomogeneous Eco-Systems: An Unified Model Based Approach
Recently we have extended our the "unified" model of evolutionary ecology to
incorporate the {\it spatial inhomogeneities} of the eco-system and the {\it
migration} of individual organisms from one patch to another within the same
eco-system. In this paper an extension of our recent model is investigated so
as to describe the {\it migration} and {\it speciation} in a more realistic
way.Comment: Latex, 10 pages, 8 figure
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