14,205 research outputs found
Primary transit of the planet HD189733b at 3.6 and 5.8 microns
The hot Jupiter HD 189733b was observed during its primary transit using the
Infrared Array Camera on the Spitzer Space Telescope. The transit depths were
measured simultaneously at 3.6 and 5.8 microns. Our analysis yields values of
2.356 +- 0.019 % and 2.436 +- 0.020$ % at 3.6 and 5.8 microns respectively, for
a uniform source. We estimated the contribution of the limb-darkening and
star-spot effects on the final results. We concluded that although the limb
darkening increases by ~0.02-0.03 % the transit depths, and the differential
effects between the two IRAC bands is even smaller, 0.01 %. Furthermore, the
host star is known to be an active spotted K star with observed photometric
modulation. If we adopt an extreme model of 20 % coverage with spots 1000K
cooler of the star surface, it will make the observed transits shallower by
0.19 and 0.18 %. The difference between the two bands will be only of 0.01 %,
in the opposite direction to the limb darkening correction. If the transit
depth is affected by limb darkening and spots, the differential effects between
the 3.6 and 5.8 microns bands are very small. The differential transit depths
at 3.6 and 5.8 microns and the recent one published by Knutson et al.(2007) at
8 microns are in agreement with the presence of water vapour in the upper
atmosphere of the planet. This is the companion paper to Tinetti et al.
(2007b), where the detailed atmosphere models are presented.Comment: 6 pages, 4 figures, Astrophysical Journal 675. Accepted Nov 21,
20007, to appear on March 10, 200
Spitzer/IRS investigation of MIPSGAL 24 microns compact bubbles
The MIPSGAL 24 m Galactic Plane Survey has revealed more than 400
compact-extended objects. Less than 15% of these MIPSGAL bubbles (MBs) are
known and identified as evolved stars. We present Spitzer observations of 4 MBs
obtained with the InfraRed Spectrograph to determine the origin of the mid-IR
emission. We model the mid-IR gas lines and the dust emission to infer physical
conditions within the MBs and consequently their nature. Two MBs show a
dust-poor spectrum dominated by highly ionized gas lines of [\ion{O}{4}],
[\ion{Ne}{3}], [\ion{Ne}{5}], [\ion{S}{3}] and [\ion{S}{4}]. We identify them
as planetary nebulae with a density of a few 10 and a central
white dwarf of K. The mid-IR emission of the two other MBs is
dominated by a dust continuum and lower-excitation lines. Both of them show a
central source in the near-IR (2MASS and IRAC) broadband images. The first
dust-rich MB matches a Wolf-Rayet star of K at 7.5 kpc with dust
components of and K. Its mass is about $10^{-3}\
\rm{M_\odot}10^{-6}\ \rm{M_\odot/yr}. The second
dust-rich MB has recently been suggested as a Be/B[e]/LBV candidate. The gas
lines of [\ion{Fe}{2}] as well as hot continuum components (\sim300\sim1250\sim7510^{-3}\ \rm{M_\odot}10^{-5}\ \rm{M_\odot/yr}$.Comment: accepted for publication in Ap
Suppression of spin-torque in current perpendicular to the plane spin-valves by addition of Dy cap layers
We demonstrate that the addition of Dy capping layers in current
perpendicular to the plane giant magneto-resistive spin-valves can increase the
critical current density beyond which spin-torque induced instabilities are
observed by about a factor of three. Current densities as high as 5e7 A/cm2 are
measured provided that the electron current flows from the free to the
reference layer. While Dy capped samples exhibit nonmagnetic 1/f noise, it is
sufficiently small to be unimportant for read head operation at practical data
rates.Comment: 13 pages (manuscript form), with 5 figures. Submitted for publicatio
Measuring the muon's anomalous magnetic moment to 0.14 ppm
The anomalous magnetic moment (g-2) of the muon was measured with a precision
of 0.54 ppm in Experiment 821 at Brookhaven National Laboratory. A difference
of 3.2 standard deviations between this experimental value and the prediction
of the Standard Model has persisted since 2004; in spite of considerable
experimental and theoretical effort, there is no consistent explanation for
this difference. This comparison hints at physics beyond the Standard Model,
but it also imposes strong constraints on those possibilities, which include
supersymmetry and extra dimensions. The collaboration is preparing to relocate
the experiment to Fermilab to continue towards a proposed precision of 0.14
ppm. This will require 20 times more recorded decays than in the previous
measurement, with corresponding improvements in the systematic uncertainties.
We describe the theoretical developments and the experimental upgrades that
provide a compelling motivation for the new measurement.Comment: 5 pages, 1 figure, presented at International Nuclear Physics
Conference 2010 (INPC 2010
Differential Effects of Race and Poverty on Ambulatory Care Sensitive Conditions
This study is a continuation of an earlier study that examined hospitalization rates for ambulatory care sensitive (ACS) conditions, as a proxy for quality of care, and found evidence of a racial disparity among African American and White Medicare beneficiaries. The current study sought to determine whether neighborhood socioeconomic status (SES) explained this disparity. Differences in rates of ACS hospitalizations by race were assessed using Cochran-Mantel Haenszel tests and Poisson regression. Unadjusted rate ratios for ACS hospitalization for African Americans vs. Whites were found to be higher in low poverty areas (rate ratio (RR)=1.13; 95% CI (1.08, 1.17)) than in high poverty areas (RR=0.97; 95% CI (0.89, 1.05)). After controlling for various indicators of area SES in multivariate analyses race differences in ACS hospitalization rates persisted. Rural neighborhoods and those with higher percent of non-high school graduates were associated with greater risk of ACS hospitalizations
L^2 torsion without the determinant class condition and extended L^2 cohomology
We associate determinant lines to objects of the extended abelian category
built out of a von Neumann category with a trace. Using this we suggest
constructions of the combinatorial and the analytic L^2 torsions which, unlike
the work of the previous authors, requires no additional assumptions; in
particular we do not impose the determinant class condition. The resulting
torsions are elements of the determinant line of the extended L^2 cohomology.
Under the determinant class assumption the L^2 torsions of this paper
specialize to the invariants studied in our previous work. Applying a recent
theorem of D. Burghelea, L. Friedlander and T. Kappeler we obtain a Cheeger -
Muller type theorem stating the equality between the combinatorial and the
analytic L^2 torsions.Comment: 39 page
Proper Motions of Young Stellar Outflows in the Mid-Infrared with Spitzer. II. HH 377/Cep E
We have used multiple mid-infrared observations at 4.5 micron obtained with
the Infrared Array Camera, of the compact (~1.4 arcmin) young stellar bipolar
outflow Cep E to measure the proper motion of its brightest condensations. The
images span a period of ~6 yr and have been reprocessed to achieve a higher
angular resolution (~0.8 arcsec) than their normal beam (2 arcsec).
We found that for a distance of 730 pc, the tangential velocities of the
North and South outflow lobes are 62+/-29 and 94+/-6 km/s respectively, and
moving away from the central source roughly along the major axis of the flow. A
simple 3D hydrodynamical simulation of the H2 gas in a precessing outflow
supports this idea. Observations and model confirm that the molecular Hydrogen
gas, traced by the pure rotational transitions, moves at highly supersonic
velocities without being dissociated. This suggests either a very efficient
mechanism to reform H2 molecules along these shocks or the presence of some
other mechanism (e.g. strong magnetic field) that shields the H2 gas.Comment: Accepted for publication in New Journal of Physics (Special Issue
article
Anomalies and Schwinger terms in NCG field theory models
We study the quantization of chiral fermions coupled to generalized Dirac
operators arising in NCG Yang-Mills theory. The cocycles describing chiral
symmetry breaking are calculated. In particular, we introduce a generalized
locality principle for the cocycles. Local cocycles are by definition
expressions which can be written as generalized traces of operator commutators.
In the case of pseudodifferential operators, these traces lead in fact to
integrals of ordinary local de Rham forms. As an application of the general
ideas we discuss the case of noncommutative tori. We also develop a gerbe
theoretic approach to the chiral anomaly in hamiltonian quantization of NCG
field theory.Comment: 30 page
The MIPSGAL View of Supernova Remnants in the Galactic Plane
We report the detection of Galactic supernova remnants (SNRs) in the mid-infrared (at 24 and 70 Ī¼m), in the coordinate ranges 10Ā° < l < 65Ā° and 285Ā° < l < 350Ā°, |b| < 1Ā°, using MIPS aboard the Spitzer Space Telescope. We search for infrared counterparts to SNRs in Green's catalog and identify 39 out of 121, i.e., a detection rate of about 32%. Such a relatively low detection fraction is mainly due to confusion with nearby foreground/background sources and diffuse emission. The SNRs in our sample show a linear trend in [F_8/F_(24)] versus [F_(70)/F_(24)]. We compare their infrared fluxes with their corresponding radio flux at 1.4 GHz and find that most remnants have a ratio of 70 Ī¼m to 1.4 GHz which is similar to those found in previous studies of SNRs (with the exception of a few that have ratios closer to those of H II regions). Furthermore, we retrieve a slope close to unity when correlating infrared (24 and 70 Ī¼m) with 1.4 GHz emission. Our survey is more successful in detecting remnants with bright X-ray emission, which we find is well correlated with the 24 Ī¼m morphology. Moreover, by comparing the power emitted in the X-ray, infrared, and radio, we conclude that the energy released in the infrared is comparable to the cooling in the X-ray range
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