12,171 research outputs found
The spectroscopic indistinguishability of red giant branch and red clump stars
Stellar spectroscopy provides useful information on the physical properties
of stars such as effective temperature, metallicity and surface gravity (log
g). However, those photospheric characteristics are often hampered by
systematic uncertainties. The joint spectro-seismo project (APOKASC) of field
red giants has revealed a puzzling offset between the log g determined
spectroscopically and those determined using asteroseismology, which is largely
dependent on the stellar evolutionary status. Therefore, in this letter, we aim
to shed light on the spectroscopic source of the offset using the APOKASC
sample. We analyse the log g discrepancy as a function of stellar mass and
evolutionary status and discuss the impact of He and carbon isotopic ratio.
We first show that for stars at the bottom of the red giant branch, the
discrepancy between spectroscopic and asteroseismic log g depends on stellar
mass. This indicates that the discrepancy is related to CN cycling. We
demonstrate that the C isotopic ratio () has the largest
impact on the stellar spectrum. We find that this log g discrepancy shows a
similar trend in mass as the ratios expected by stellar
evolution theory. Although we do not detect a direct signature of ,
the data suggests that the discrepancy is tightly correlated to the production
of . Moreover, by running a data-driven algorithm (the Cannon) on a
synthetic grid trained on the APOGEE data, we quantitatively evaluate the
impact of various ratios. While we have demonstrated that
impacts all parameters, the size of the impact is smaller than the
observed offset in log g. If further tests confirm that is not the
main element responsible of the log g problem, the number of spectroscopic
effects remaining to be investigated is now relatively limited. [Abridged]Comment: 4 Pages, 6 Figures. Accepted for publication in A&
Metamodulation of a spinal locomotor network by nitric oxide
Flexibility in the output of spinal networks can be accomplished by the actions of neuromodulators; however, little is known about how the process of neuromodulation itself may be modulated. Here we investigate the potential "meta"-modulatory hierarchy between nitric oxide (NO) and noradrenaline (NA) in Xenopus laevis tadpoles. NO and NA have similar effects on fictive swimming; both potentiate glycinergic inhibition to slow swimming frequency and GABAergic inhibition to reduce episode durations. In addition, both modulators have direct effects on the membrane properties of motor neurons. Here we report that antagonism of noradrenergic pathways with phentolamine dramatically influences the effect of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) on swimming frequency, but not its effect on episode durations. In contrast, scavenging extracellular NO with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(PTIO) does not influence any of the effects of NA on fictive swimming. These data place NO above NA in the metamodulatory hierarchy, strongly suggesting that NO works via a noradrenergic pathway to control glycine release but directly promotes GABA release. We confirmed this possibility using intracellular recordings from motor neurons. In support of a natural role for NO in the Xenopus locomotor network, PTIO not only antagonized all of the effects of SNAP on swimming but also, when applied on its own, modulated both swimming frequency and episode durations in addition to the underlying glycinergic and GABAergic pathways. Collectively, our results illustrate that NO and NA have parallel effects on motor neuron membrane properties and GABAergic inhibition, but that NO serially metamodulates glycinergic inhibition via NA.Publisher PDFPeer reviewe
The Species Richness of Lepidoptera in a Fragmented Landscape: A Supplement to the Checklist of Moths of Butler County, Ohio
Land conversion for agriculture or urban expansion has fragmented the midwestern landscape and isolated native biotas in remnant habitat patches. Identification of priority renmants to be targeted for conservation, however, requires an understanding of the species diversity and distributions in such fragmented landscapes. During a 3-year inventory, we estimated the species richness of Lepidoptera in forests and old fields within an agricultural region of southwest Ohio, Butler County. A combination of casual collecting (butterflies) and a systematic field study (moths) were used to sample lepidopteran species at several sites from 1998-2000. Our inventory added 207 new species to the checklist of the Lepidoptera of Butler County, bringing the total described species richness of the region to 599 species (including Peoria tetradella (Pyralidae), a state record). The species accumulation curve produced from our 1999 moth inventory did not reach saturation, suggesting that additional species remain to be recorded. These results indicate that even highly modified landscapes can support a substantial species diversity of Lepidoptera if there are sufficient areas of native habitat. Since short-term insect inventories tend to be biased toward common, well-known species, rapid diversity assessments may miss important elements of conservation interest. Checklists should remain an important data source for species occurrences and biogeography. Without a well-established knowledge of species geography, critical areas of conservation interest may be overlooked or left unprotected
Distinguishing Dynamical Dark Matter at the LHC
Dynamical dark matter (DDM) is a new framework for dark-matter physics in
which the dark sector comprises an ensemble of individual component fields
which collectively conspire to act in ways that transcend those normally
associated with dark matter. Because of its non-trivial structure, this DDM
ensemble --- unlike most traditional dark-matter candidates --- cannot be
characterized in terms of a single mass, decay width, or set of scattering
cross-sections, but must instead be described by parameters which describe the
collective behavior of its constituents. Likewise, the components of such an
ensemble need not be stable so long as lifetimes are balanced against
cosmological abundances across the ensemble as a whole. In this paper, we
investigate the prospects for identifying a DDM ensemble at the LHC and for
distinguishing such a dark-matter candidate from the candidates characteristic
of traditional dark-matter models. In particular, we focus on DDM scenarios in
which the component fields of the ensemble are produced at colliders alongside
some number of Standard-Model particles via the decays of additional heavy
fields. The invariant-mass distributions of these Standard-Model particles turn
out to possess several unique features that cannot be replicated in most
traditional dark-matter models. We demonstrate that in many situations it is
possible to differentiate between a DDM ensemble and a traditional dark-matter
candidate on the basis of such distributions. Moreover, many of our results
also apply more generally to a variety of other extensions of the Standard
Model which involve multiple stable or metastable neutral particles.Comment: 17 pages, LaTeX, 10 figure
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