250 research outputs found
<3D> NLTE line formation in the atmospheres of red supergiants
Red supergiants with their enormous brightness at J-band are ideal probes of
cosmic chemical composition. It is therefore crucial to have realistic models
of radiative transfer in their atmospheres, which will permit determination of
abundances accurate to 0.15 dex, the precision attainable with future telescope
facilities in galaxies as distant as tens of Mpc. Here, we study the effects of
non-local thermodynamic equilibrium (NLTE) on the formation of iron, titanium,
and silicon lines, which dominate J-band spectra of red supergiants. It is
shown that the NLTE radiative transfer models enable accurate derivation of
metallicity and effective temperature in the J-band. We also discuss
consequences for RSG spectrum synthesis in different spectral windows,
including the heavily TiO-blanketed optical region, and atmospheric structure.
We then touch upon challenges of NLTE integration with new generation of 3D
hydrodynamical RSG models and present the first calculations of NLTE spectra
with the mean 3D model of Betelgeuse.Comment: 7 pages, proceedings of the Betelgeuse Workshop, Paris, 201
Searching for GC-like abundance patterns in young massive clusters
Studies during the last decade have revealed that nearly all Globular Clusters (GCs) host multiple populations (MPs) of stars with a distinctive chemical patterns in light elements. No evidence of such MPs has been found so far in lower-mass ( M) clusters in the Local Group. Young massive clusters (YMCs) have masses and densities similar to those expected of young GCs in the early universe, and their near-infrared (NIR) spectra are dominated by the light of red super giants (RSGs). The spectra of these stars may be used to determine the cluster's abundances, even though the individual stars cannot be spatially resolved from one another. We carry out a differential analysis between the Al lines of YMC NGC 1705: 1 and field Small Magellanic Cloud RSGs with similar metallicities. We exclude at high confidence extreme [Al/Fe] enhancements similar to those observed in GCs like NGC 2808 or NGC 6752. However, smaller variations cannot be excluded
Transit Analysis Package (TAP and autoKep): IDL Graphical User Interfaces for Extrasolar Planet Transit Photometry
We present an IDL graphical user interface-driven software package designed
for the analysis of extrasolar planet transit light curves. The Transit
Analysis Package (TAP) software uses Markov Chain Monte Carlo (MCMC) techniques
to fit light curves using the analytic model of Mandel and Agol (2002). The
package incorporates a wavelet based likelihood function developed by Carter
and Winn (2009) which allows the MCMC to assess parameter uncertainties more
robustly than classic chi-squared methods by parameterizing uncorrelated
"white" and correlated "red" noise. The software is able to simultaneously
analyze multiple transits observed in different conditions (instrument, filter,
weather, etc). The graphical interface allows for the simple execution and
interpretation of Bayesian MCMC analysis tailored to a user's specific data set
and has been thoroughly tested on ground-based and Kepler photometry. AutoKep
provides a similar GUI for the preparation of Kepler MAST archive data for
analysis by TAP or any other analysis software. This paper describes the
software release and provides instructions for its use.Comment: 8 pages, 2 figure
A Third Exoplanetary System with Misaligned Orbital and Stellar Spin Axes
We present evidence that the WASP-14 exoplanetary system has misaligned
orbital and stellar-rotational axes, with an angle lambda = 33.1 +/- 7.4 deg
between their sky projections. The evidence is based on spectroscopic
observations of the Rossiter-McLaughlin effect as well as new photometric
observations. WASP-14 is now the third system known to have a significant
spin-orbit misalignment, and all three systems have "super-Jupiter" planets
(M_P > 3 Mjup) and eccentric orbits. This finding suggests that the migration
and subsequent orbital evolution of massive, eccentric exoplanets is somehow
different from that of less massive close-in Jupiters, the majority of which
have well-aligned orbits.Comment: 8 pages, 5 figures, 3 tables, PASP accepte
Age Dating Stellar Populations in the Near Infrared: An absolute age indicator from the presence/absence of red supergiants
The determination of age is a critical component in the study of a population
of stellar clusters. In this letter we present a new absolute age indicator for
young massive star clusters based on J-H colour. This novel method identifies
clusters as older or younger than 5.7 +/- 0.8 Myr based on the appearance of
the first population of red supergiant stars. We test the technique on the
stellar cluster population of the nearby spiral galaxy, M83, finding good
agreement with the theoretical predictions. The localisation of this technique
to the near-IR promises that it may be used well into the future with space--
and ground--based missions optimised for near-IR observations.Comment: 5 pages, 5 figures. Accepted to MNRAS, November 201
A Direct Stellar Metallicity Determination in the Disk of the Maser Galaxy NGC4258
We present the first direct determination of a stellar metallicity in the
spiral galaxy NGC4258 (D=7.6 Mpc) based on the quantitative analysis of a
low-resolution (~5 AE) Keck LRIS spectrum of a blue supergiant star located in
its disk. A determination of stellar metallicity in this galaxy is important
for the absolute calibration of the Cepheid Period-Luminosity relation as an
anchor for the extragalactic distance scale and for a better characterization
of its dependence as a function of abundance. We find a value 0.2 dex lower
than solar metallicity at a galactocentric distance of 8.7 kpc, in agreement
with recent HII region studies using the weak forbidden auroral oxygen line at
4363 AE. We determine the effective stellar temperature, gravity, luminosity
and line-of-sight extinction of the blue supergiant being studied. We show that
it fits well on the flux-weighted gravity--luminosity relation (FGLR),
strengthening the potential of this method as a new extragalactic distance
indicator.Comment: Accepted for publication by ApJ Letters, 5 pages, 5 figure
High frequency quasi-periodic oscillations in the X-ray radiation of the black hole binary GRS 1915+105
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 93-94).GRS 1915+105 is an accreting black-hole in a binary system located in the Milky Way. It is one of the most variable X-ray sources known, and 12 variability classifications have been defined, many of which appear to be repetitive cycles of accretion instability. We study one particular variability type, the p cycle, which is selected for its high frequency quasi-periodic oscillations (HFQPOs) and recurring double-peak flare in the light curve. We investigate the primary properties of the 82 p-type observations collected by RXTE. The range in flare recurrence time () is 33.73 s ± asample = 65.44 ± 19.83 s. The flaring fraction , defined by percent of cycle exposure > 1.2*mean count rate, ranges 12.11% ± asample = 20.05 ± 5.33%. We find a correlation between T and ( which divides the 82 observations into three sub-classes: pi; slow with low , P2; fast with low , and P3; fast with high . The evolution between sub-classes suggests two driving mechanisms, an unknown mechanism limiting T > 33 s and a process consistent with the Eddington limit that increases (at the lower limit of ) for the p3 group.(cont.) For each subclass we study the emission properties in four phase zones of the p cycle, where the phases are defined on the basis of the X-ray count rate (X) and soft color (S; rates at 6-12 keV / 2-5 keV). Two HFQPOs in the p cycle are isolated to different zones and sub-classes: one at 67 Hz is localized to the second (hard-spectrum) flare, and another QPO at 150 Hz in the low X, low S phase zone of the pi group. All phase zones display low-frequency QPOs, and they are particularly strong in the low-X, low-S zone (7.5 Hz) and the low-X, high-S zone (10.5 Hz). Classifications of X-ray spectral states for each zone indicate no zones in the thermal state, flaring zones (high X) in the steep power law (SPL) state, and quiet zones (low X) in either the hard or hard:SPL intermediate state. We conclude that the p cycle provides special opportunities to further study an instability cycle that is driven, in part, by the Eddington limit and that portions of the cycle contain the mechanism that produces two different HFQPOs. Further investigations should be made with increased phase resolution and with additional strategies to define the phases of the p cycle.by Jonathan Zachary Gazak.S.B
TERMS Photometry of Known Transiting Exoplanets
The Transit Ephemeris Refinement and Monitoring Survey (TERMS) conducts
radial velocity and photometric monitoring of known exoplanets in order to
refine planetary orbits and predictions of possible transit times. This effort
is primarily directed towards planets not known to transit, but a small sample
of our targets consist of known transiting systems. Here we present precision
photometry for 6 WASP planets acquired during their transit windows. We perform
a Markov Chain Monte Carlo (MCMC) analysis for each planet and combine these
data with previous measurements to redetermine the period and ephemerides for
these planets. These observations provide recent mid-transit times which are
useful for scheduling future observations. Our results improve the ephemerides
of WASP-4b, WASP-5b and WASP-6b and reduce the uncertainties on the mid-transit
time for WASP-29b. We also confirm the orbital, stellar and planetary
parameters of all 6 systems.Comment: 12 pages; 6 figures; 9 tables; accepted for publication in AJ; two
references updated and minor improvements made to match the version to be
publishe
Kepler-445, Kepler-446 And The Occurrence Of Compact Multiples Orbiting Mid-M Dwarf Stars
We confirm and characterize the exoplanetary systems Kepler-445 and Kepler-446: two mid-M dwarf stars, each with multiple, small, short-period transiting planets. Kepler-445 is a metal-rich ([ Fe/H] = + 0.25 0.10) M4 dwarf with three transiting planets, and Kepler-446 is a metal-poor ([ Fe/H] = -0.30 0.10) M4 dwarf also with three transiting planets. Kepler-445c is similar toGJ 1214b: both in planetary radius and the properties of the host star. The Kepler-446 system is similar to the Kepler-42 system: both are metal-poor with large galactic space velocities and three short-period, likely rocky transiting planets that were initially assigned erroneously large planet-to-star radius ratios. We independently determined stellar parameters from spectroscopy and searched for and fitted the transit light curves for the planets, imposing a strict prior on stellar density in order to remove correlations between the fitted impact parameter and planet-to-star radius ratio for short-duration transits. Combining Kepler-445, Kepler-446, and Kepler-42, and isolating all mid-M dwarf stars observed by Kepler with the precision necessary to detect similar systems, we calculate that 21+ 7 -5 % of mid-M dwarf stars host compact multiples ( multiple planets with periods of less than 10 days) for a wide range of metallicities. We suggest that the inferred planet masses for these systems support highly efficient accretion of protoplanetary disk metals by mid-M dwarf protoplanets.NSF DGE1144152, AST-1005313NASA NAS5-26555NASA Office of Space Science NNX13AC07GAstronom
The novel 5-lipoxygenase inhibitor ABT-761 attenuates cerebral vasospasm in a rabbit model of subarachnoid hemorrhage
OBJECTIVE: Eicosanoids have been implicated in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). Leukotrienes, 5-hydroxyperoxyeicosatetraenoic acid, and 5-hydroxyeicosatetraenoic acid are part of this group of substances, resulting from the 5-lipoxygenase activity on arachidonic acid metabolism. This study examined the effects of ABT-761, a new 5-lipoxygenase inhibitor, on cerebral vasospasm in an in vivo rabbit model of SAH.
METHODS: A total of 48 rabbits were assigned to one of six groups: SAH + placebo (n = 8), SAH + ABT-761 20 mg/kg (n = 8), SAH + ABT-761 30 mg/kg (n = 8), control + placebo (n = 8), control + ABT-761 20 mg/kg (n = 8), and control + ABT-761 30 mg/kg (n = 8). Drug administration was initiated 30 minutes after induction of SAH and repeated 24 hours later. The animals were killed 48 hours after SAH, using the perfusion-fixation method. The cross sectional areas of basilar artery histological sections were measured by an investigator blinded to the treatment groups of the individual samples.
RESULTS: In placebo-treated animals, the average luminal cross sectional area of the basilar artery was reduced by 68% after SAH as compared with controls (P < 0.0001). After SAH, the vasospastic response was attenuated in animals treated with 20 or 30 mg/kg representing a 28 or 35% reduction, respectively (P = 0.0011 and P = 0.0038).
CONCLUSION: The results demonstrated that ABT-761 is effective in attenuating experimental cerebral vasospasm, indicating that this new drug represents a potential therapeutic agent for the treatment of vasospasm after SAH
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