41,066 research outputs found
Red Runaways II: Low mass Hills stars in SDSS Stripe 82
Stars ejected from the Galactic centre can be used to place important
constraints on the Milky Way potential. Since existing hypervelocity stars are
too distant to accurately determine orbits, we have conducted a search for
nearby candidates using full three-dimensional velocities. Since the efficacy
of such studies are often hampered by deficiencies in proper motion catalogs,
we have chosen to utilize the reliable, high-precision SDSS Stripe 82 proper
motion catalog. Although we do not find any candidates which have velocities in
excess of the escape speed, we identify 226 stars on orbits that are consistent
with Galactic centre ejection. This number is significantly larger than what we
would expect for halo stars on radial orbits and cannot be explained by disk or
bulge contamination. If we restrict ourselves to metal-rich stars, we find 29
candidates with [Fe/H] > -0.8 dex and 10 with [Fe/H] > -0.6 dex. Their
metallicities are more consistent with what we expect for bulge ejecta, and so
we believe these candidates are especially deserving of further study. We have
supplemented this sample using our own radial velocities, developing an
algorithm to use proper motions for optimizing candidate selection. This
technique provides considerable improvement on the blind spectroscopic sample
of SDSS, being able to identify candidates with an efficiency around 20 times
better than a blind search.Comment: 13 pages, accepted for publication in Ap
Nearby Low-Mass Hypervelocity Stars
Hypervelocity stars are those that have speeds exceeding the escape speed and
are hence unbound from the Milky Way. We investigate a sample of low-mass
hypervelocity candidates obtained using data from the high-precision SDSS
Stripe 82 catalogue, which we have combined with spectroscopy from the 200-inch
Hale Telescope at Palomar Observatory. We find four good candidates, but
without metallicities it is difficult to pin-down their distances and therefore
total velocities. Our best candidate has a significant likelihood that it is
escaping the Milky Way for a wide-range of metallicities.Comment: 5 pages; Contribution to proceedings for "The Milky Way Unravelled by
Gaia" conference, Barcelona, Dec 201
A Study of The Influence of Reworked Fibers on Dimensional Stability and Physical Characteristics of Paper
Secondary or re-pulped fibers, refined to the same degree in terms of freeness, exhibit different physical and optical characteristics than the same fiber in the virgin state. Paper which contains various ·per cent of secondary fibers have better opacity, less sensitivity to moisture and humidity, in the sense of hygro-expansivity, reduction of tendency to curl with addition of moisture to one side of the sheet, and less tensile elongation. The advantages listed above are offset to some extent by a loss in tensile strength, fold endurance and porosity
Discovery of a Spin-Down State Change in the LMC Pulsar B0540-69
We report the discovery of a large, sudden, and persistent increase in the
spin-down rate of B0540-69, a young pulsar in the Large Magellanic Cloud, using
observations from the Swift and RXTE satellites. The relative increase in the
spin-down rate of 36% is unprecedented for B0540-69. No accompanying change in
the spin rate is seen, and no change is seen in the pulsed X-ray emission from
B0540-69 following the change in the spin-down rate. Such large relative
changes in the spin-down rate are seen in the recently discovered class of
'intermittent pulsars', and we compare the properties of B0540-69 to such
pulsars. We consider possible changes in the magnetosphere of the pulsar that
could cause such a large change in the spin-down rate.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
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Free atmospheric CO2 enrichment increased above ground biomass but did not affect symbiotic N2-fixation and soil carbon dynamics in a mixed deciduous stand in Wales
Through increases in net primary production (NPP), elevated CO2 is hypothesizes to increase the amount of plant litter entering the soil. The fate of this extra carbon on the forest floor or in mineral soil is currently not clear. Moreover, increased rates of NPP can be maintained only if forests can escape nitrogen limitation. In a Free atmospheric CO2 Enrichment (FACE) experiment near Bangor, Wales, 4 ambient CO2 and 4 FACE plots were planted with patches of Betula pendula, Alnus glutinosa and Fagus sylvatica on a former arable field. Four years after establishment, only a shallow L forest floor litter layer had formed due to intensive bioturbation. Total soil C and N contents increased irrespective of treatment and species as a result of afforestation. We could not detect an additional C sink in the soil, nor were soil C stabilization processes affected by FACE. We observed a decrease of leaf N content in Betula and Alnus under FACE, while the soil C/N ratio decreased regardless of CO2 treatment. The ratio of N taken up from the soil and by N2-fixation in Alnus was not affected by FACE. We infer that increased nitrogen use efficiency is the mechanism by which increased NPP is sustained under elevated CO2 at this site
A Dense Gas Trigger for OH Megamasers
HCN and CO line diagnostics provide new insight into the OH megamaser (OHM)
phenomenon, suggesting a dense gas trigger for OHMs. We identify three physical
properties that differentiate OHM hosts from other starburst galaxies: (1) OHMs
have the highest mean molecular gas densities among starburst galaxies; nearly
all OHM hosts have = 10^3-10^4 cm^-3 (OH line-emitting clouds likely
have n(H2) > 10^4 cm^-3). (2) OHM hosts are a distinct population in the
nonlinear part of the IR-CO relation. (3) OHM hosts have exceptionally high
dense molecular gas fractions, L(HCN)/L(CO)>0.07, and comprise roughly half of
this unusual population. OH absorbers and kilomasers generally follow the
linear IR-CO relation and are uniformly distributed in dense gas fraction and
L(HCN), demonstrating that OHMs are independent of OH abundance. The fraction
of non-OHMs with high mean densities and high dense gas fractions constrains
beaming to be a minor effect: OHM emission solid angle must exceed 2 pi
steradians. Contrary to conventional wisdom, IR luminosity does not dictate OHM
formation; both star formation and OHM activity are consequences of tidal
density enhancements accompanying galaxy interactions. The OHM fraction in
starbursts is likely due to the fraction of mergers experiencing a temporal
spike in tidally driven density enhancement. OHMs are thus signposts marking
the most intense, compact, and unusual modes of star formation in the local
universe. Future high redshift OHM surveys can now be interpreted in a star
formation and galaxy evolution context, indicating both the merging rate of
galaxies and the burst contribution to star formation.Comment: 5 pages, 3 figures, 1 table, accepted by ApJ Letter
Direct determination of vibrational density of states change on ligand binding to a protein
The change in the vibrational density of states of a protein (dihydrofolate reductase) on binding a ligand (methotrexate) is determined using inelastic neutron scattering. The vibrations of the complex soften significantly relative to the unbound protein. The resulting free-energy change, which is directly determined by the density of states change, is found to contribute significantly to the binding equilibrium
DIRECT ESTIMATION OF ABOVEGROUND FOREST PRODUCTIVITY THROUGH HYPERSPECTRAL REMOTE SENSING OF CANOPY NITROGEN
The concentration of nitrogen in foliage has been related to rates of net photosynthesis across a wide range of plant species and functional groups and thus represents a simple and biologically meaningful link between terrestrial cycles of carbon and nitrogen. Although foliar N is used by ecosystem models to predict rates of leafâlevel photosynthesis, it has rarely been examined as a direct scalar to standâlevel carbon gain. Establishment of such relationships would greatly simplify the nature of forest C and N linkages, enhancing our ability to derive estimates of forest productivity at landscape to regional scales. Here, we report on a highly predictive relationship between wholeâcanopy nitrogen concentration and aboveground forest productivity in diverse forested stands of varying age and species composition across the 360â000âha White Mountain National Forest, New Hampshire, USA. We also demonstrate that hyperspectral remote sensing can be used to estimate foliar N concentration, and hence forest production across a large number of contiguous images. Together these data suggest that canopyâlevel N concentration is an important correlate of productivity in these forested systems, and that imaging spectrometry of canopy N can provide direct estimates of forest productivity across large landscapes
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