17,681 research outputs found
The Large Peculiar Velocity of the cD Galaxy in Abell 3653
We present a catalogue of galaxies in Abell 3653 from observations made with
the 2dF spectrograph at the Anglo-Australian Telescope. Of the 391 objects
observed, we find 111 are bone-fide members of Abell 3653. We show that the
cluster has a velocity of cz = 32214 +/- 83 km/s (z=0.10738 +/- 0.00027), with
a velocity dispersion typical of rich, massive clusters of sigma_{cz} =
880^{+66}_{-54}. We find that the cD galaxy has a peculiar velocity of 683 +/-
96 km/s in the cluster restframe - some 7sigma away from the mean cluster
velocity, making it one of the largest and most significant peculiar velocities
found for a cD galaxy to date. We investigate the cluster for signs of
substructure, but do not find any significant groupings on any length scale. We
consider the implications of our findings on cD formation theories.Comment: 16 pages, including 7 figures and a long table. Accepted for
publication in MNRA
Chromospheric Inversions of a Micro-flaring Region
We use spectropolarimetric observations of the Ca II 8542~\AA\ line, taken
from the Swedish 1-m Solar Telescope (SST), in an attempt to recover dynamic
activity in a micro-flaring region near a sunspot via inversions. These
inversions show localized mean temperature enhancements of 1000~K in the
chromosphere and upper photosphere, along with co-spatial bi-directional
Doppler shifting of 5 - 10 km s. This heating also extends along a
nearby chromospheric fibril, co-spatial to 10 - 15 km s down-flows.
Strong magnetic flux cancellation is also apparent in one of the footpoints,
concentrated in the chromosphere. This event more closely resembles that of an
Ellerman Bomb (EB), though placed slightly higher in the atmosphere than is
typically observed.Comment: 9 pages, 9 figures, accepted in ApJ. Movies are stored here:
https://star.pst.qub.ac.uk/webdav/public/areid/Microflare
Stock assessment and management recommendations for Pacific sardine (Sardinops sagax) in 1997
The primary goal of sardine management as directed by the California Fish and Game Code is rehabilitation of the resource with an added objective of maximizing sustained harvest. Accordingly, the Code states that the annual sardine quota can be set at an amount greater than
1,000 tons, providing that the level of take allows for continued increase in the spawning population.
We estimated the sardine population size to have been 464,000 short tons on July 1, 1997. Our estimate was based on output from a modified version of the integrated stock assessment model called CANSAR (Deriso et al. 1996). CANSAR is a forward-casting, age-structured analysis using fishery-dependent and fishery-independent data to obtain annual estimates of sardine abundance, year-class strength and age-specific fishing mortality for 1983 through the
first semester of 1997. Non-linear least-squares criteria are used to find the best fit between model estimates and input data.
Questions about stock structure and range extent remain major sources of uncertainty in assessing current sardine population biomass. Recent survey results and anecdotal evidence suggest increased sardine abundance in the Pacific Northwest and areas offshore from central and
southern California. It is difficult to determine if those fish were part of the stock available to the California fishery. In an attempt to address this problem, the original CANSAR model was reconfigured into a Two-Area Migration Model (CANSAR-TAM) which accounted for sardine
lost to the areas of the fishery and abundance surveys due to population expansion and net emigration. While the model includes guesses and major assumptions about net emigration and recruitment, it provides an estimate which is likely closer to biological reality than past
assessments. The original CANSAR model was also used and estimates are provided for comparison.
Based on the 1997 estimate of total biomass and the harvest formula used last year, we recommend a 1998 sardine harvest quota of 48,000 tons for the California fishery. The 1998 quota is a decrease of 11% from the final 1997 sardine harvest quota for California of 54,000
tons. (55pp.
A Dynamical Analysis of the Proposed Circumbinary HW Virginis Planetary System
In 2009, the discovery of two planets orbiting the evolved binary star system
HW Virginis was announced, based on systematic variations in the timing of
eclipses between the two stars. The planets invoked in that work were
significantly more massive than Jupiter, and moved on orbits that were mutually
crossing - an architecture which suggests that mutual encounters and strong
gravitational interactions are almost guaranteed. In this work, we perform a
highly detailed analysis of the proposed HW Vir planetary system. First, we
consider the dynamical stability of the system as proposed in the discovery
work. Through a mapping process involving 91,125 individual simulations, we
find that the system is so unstable that the planets proposed simply cannot
exist, due to mean lifetimes of less than a thousand years across the whole
parameter space. We then present a detailed re-analysis of the observational
data on HW Vir, deriving a new orbital solution that provides a very good fit
to the observational data. Our new analysis yields a system with planets more
widely spaced, and of lower mass, than that proposed in the discovery work, and
yields a significantly greater (and more realistic) estimate of the uncertainty
in the orbit of the outermost body. Despite this, a detailed dynamical analysis
of this new solution similarly reveals that it also requires the planets to
move on orbits that are simply not dynamically feasible. Our results imply that
some mechanism other than the influence of planetary companions must be the
principal cause of the observed eclipse timing variations for HW Vir. If the
sys- tem does host exoplanets, they must move on orbits differing greatly from
those previously proposed. Our results illustrate the critical importance of
performing dynamical analyses as a part of the discovery process for
multiple-planet exoplanetary systems.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Formation of van der Waals molecules in buffer gas cooled magnetic traps
We show that a large class of helium-containing cold polar molecules form
readily in a cryogenic buffer gas, achieving densities as high as 10^12 cm^-3.
We explore the spin relaxation of these molecules in buffer gas loaded magnetic
traps, and identify a loss mechanism based on Landau-Zener transitions arising
from the anisotropic hyperfine interaction. Our results show that the recently
observed strong T^6 thermal dependence of spin change in buffer gas trapped
silver (Ag) is accounted for by the formation and spin change of AgHe, thus
providing evidence for molecular formation in a buffer gas trap.Comment: 4 pages, 4 figure
Influence of low-level Pr substitution on the superconducting properties of YBa2Cu3O7-delta single crystals
We report on measurements on Y1-xPrxBa2Cu3O7-delta single crystals, with x
varying from 0 to 2.4%. The upper and the lower critical fields, Hc2 and Hc1,
the Ginzburg-Landau parameter and the critical current density, Jc(B), were
determined from magnetization measurements and the effective media approach
scaling method. We present the influence of Pr substitution on the pinning
force density as well as on the trapped field profiles analyzed by Hall probe
scanning.Comment: 4 pages, 5 figures, accepted for publication in J. Phys. Conf. Se
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