7,945 research outputs found
How to Make a Singleton sdB Star via Accelerated Stellar Evolution
Many hot subdwarf B stars (sdBs) are in close binaries, and the favored
formation channels for subdwarfs rely on mass transfer in a binary system to
strip a core He burning star of its envelope. However, these channels cannot
account for sdBs that have been observed in long period binaries nor the narrow
mass distribution of isolated (or "singleton") sdBs. We propose a new formation
channel involving the merger of a helium white dwarf and a low mass, hydrogen
burning star, which addresses these issues. Hierarchical triples whose inner
binaries merge and form sdBs by this process could explain the observed long
period subdwarf+main sequence binaries. This process would also naturally
explain the observed slow rotational speeds of singleton sdBs. We also briefly
discuss the implications of this formation channel for extreme horizontal
branch morphology in globular clusters and the UV upturn in elliptical
galaxies.Comment: 5 pages, 3 figures, accepted for publication ApJ
MUCHFUSS - Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS
The project Massive Unseen Companions to Hot Faint Underluminous Stars from
SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact
companions (white dwarfs with masses , neutron stars or
black holes). The existence of such systems is predicted by binary evolution
calculations and some candidate systems have been found. We identified
hot subdwarf stars from the Sloan Digital Sky Survey (SDSS). Stars
with high velocities have been reobserved and individual SDSS spectra have been
analysed. About 70 radial velocity variable subdwarfs have been selected as
good candidates for follow-up time resolved spectroscopy to derive orbital
parameters and photometric follow-up to search for features like eclipses in
the light curves. Up to now we found nine close binary sdBs with short orbital
periods ranging from to . Two of them are
eclipsing binaries with companions that are most likely of substellar nature.Comment: 6 pages, 4 figures, AN, in pres
Organic grapes - More than Wine and Statistics
The chapter presents inforamtion on the status of organic viticulture world wide and also includes a global organic wine statistics (hectares per country; not all wine producing countries covered though)
Moving Environments: Affect, Emotion, Ecology, and Film edited by Alexa Weik von Mossner
Ted Geier reviews Completely Affecting: The Cinematics of Environmental Concern and Real Change, edited by Alexa Weik von Mossner
The fast rotating, low gravity subdwarf B star EC 22081-1916 - Remnant of a common envelope merger event
Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very
thin hydrogen envelopes. In order to form an sdB, the progenitor has to lose
almost all of its hydrogen envelope right at the tip of the red giant branch.
In binary systems, mass transfer to the companion provides the extraordinary
mass loss required for their formation. However, apparently single sdBs exist
as well and their formation is unclear since decades. The merger of helium
white dwarfs leading to an ignition of core helium-burning or the merger of a
helium core and a low mass star during the common envelope phase have been
proposed. Here we report the discovery of EC 22081-1916 as a fast rotating,
single sdB star of low gravity. Its atmospheric parameters indicate, that the
hydrogen envelope must be unusually thick, which is at variance with the He-WD
merger scenario, but consistent with a common envelope merger of a low-mass,
possibly substellar object with a red-giant core.Comment: 16 pages, 4 figures, ApJL, accepte
Born Naked by Farley Mowat
Farley Mowat\u27s charming childhood memoir covers the usual Mowat terrain: riotous humour, humble reverence, and a meticulous accounting of the little things that make life--all life--dear to us. Mowat\u27s work deserves regular attention in animal studies and environmental literary studies. His autobiographical techniques, as this review suggests, can be both assets and occasional impediments. But there is no replacing or replicating a Farley Mowat, and Born Naked deserves to be read immediately and repeatedly as one of the lasting legacies of a long life, well-lived
Novel shock absorber features varying yield strengths
A shock absorbent webbing of partially drawn synthetic strands is arranged in sections of varying density related to the varying mass of the human body. This is contoured to protect the body at points of contact, when subjected to large acceleration or deceleration forces
On Oblivious Amplification of Coin-Tossing Protocols
We consider the problem of amplifying two-party coin-tossing protocols: given a protocol where it is possible to bias the common output by at most ?, we aim to obtain a new protocol where the output can be biased by at most ?* < ?. We rule out the existence of a natural type of amplifiers called oblivious amplifiers for every ?* < ?. Such amplifiers ignore the way that the underlying ?-bias protocol works and can only invoke an oracle that provides ?-bias bits.
We provide two proofs of this impossibility. The first is by a reduction to the impossibility of deterministic randomness extraction from Santha-Vazirani sources. The second is a direct proof that is more general and also rules outs certain types of asymmetric amplification. In addition, it gives yet another proof for the Santha-Vazirani impossibility
- …