4,839 research outputs found
Is the Sun Lighter than the Earth? Isotopic CO in the Photosphere, Viewed through the Lens of 3D Spectrum Synthesis
We consider the formation of solar infrared (2-6 micron) rovibrational bands
of carbon monoxide (CO) in CO5BOLD 3D convection models, with the aim to refine
abundances of the heavy isotopes of carbon (13C) and oxygen (18O,17O), to
compare with direct capture measurements of solar wind light ions by the
Genesis Discovery Mission. We find that previous, mainly 1D, analyses were
systematically biased toward lower isotopic ratios (e.g., R23= 12C/13C),
suggesting an isotopically "heavy" Sun contrary to accepted fractionation
processes thought to have operated in the primitive solar nebula. The new 3D
ratios for 13C and 18O are: R23= 91.4 +/- 1.3 (Rsun= 89.2); and R68= 511 +/- 10
(Rsun= 499), where the uncertainties are 1 sigma and "optimistic." We also
obtained R67= 2738 +/- 118 (Rsun= 2632), but we caution that the observed
12C17O features are extremely weak. The new solar ratios for the oxygen
isotopes fall between the terrestrial values and those reported by Genesis
(R68= 530, R6= 2798), although including both within 2 sigma error flags, and
go in the direction favoring recent theories for the oxygen isotope composition
of Ca-Al inclusions (CAI) in primitive meteorites. While not a major focus of
this work, we derive an oxygen abundance of 603 +/- 9 ppm (relative to
hydrogen; 8.78 on the logarithmic H= 12 scale). That the Sun likely is lighter
than the Earth, isotopically speaking, removes the necessity to invoke exotic
fractionation processes during the early construction of the inner solar
system
A systematic review of associations between environmental exposures and development of asthma in children aged up to 9 years
Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.Peer reviewedPublisher PD
Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and their Isotopes
A solar photospheric "thermal profiling" analysis is presented, exploiting
the infrared rovibrational bands of carbon monoxide (CO) as observed with the
McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above
the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum
intensities and center-limb behavior constrained the temperature profile of the
deep photosphere, while CO center-limb behavior defined the thermal structure
at higher altitudes. The oxygen abundance was self consistently determined from
weak CO absorptions. Our analysis was meant to complement recent studies based
on 3-D convection models which, among other things, have revised the historical
solar oxygen (and carbon) abundance downward by a factor of nearly two;
although in fact our conclusions do not support such a revision. Based on
various considerations, an oxygen abundance of 700+/-100 ppm (parts per million
relative to hydrogen) is recommended; the large uncertainty reflects the model
sensitivity of CO. New solar isotopic ratios also are reported for 13C, 17O,
and 18O.Comment: 90 pages, 19 figures (some with parts "a", "b", etc.); to be
published in the Astrophysical Journal Supplement
Search for the disappearance of muon antineutrinos in the NuMI neutrino beam
We report constraints on muon antineutrino oscillation parameters that were obtained by using the two MINOS detectors to measure the 7% antineutrino component of the NuMI neutrino beam. In the Far Detector, we select 130 events in the charged-current muon antineutrino sample, compared to a prediction of 136.4 +/- 11.7(stat) ^{+10.2}_{-8.9}(syst) events under the assumption |dm2bar|=2.32x10^-3 eV^2, snthetabar=1.0. A fit to the two-flavor oscillation approximation constrains |dm2bar|<3.37x10^-3 eV^2 at the 90% confidence level with snthetabar=1.0
Coexistence of orbital and quantum critical magnetoresistance in FeSeS
The recent discovery of a non-magnetic nematic quantum critical point (QCP)
in the iron chalcogenide family FeSeS has raised the prospect of
investigating, in isolation, the role of nematicity on the electronic
properties of correlated metals. Here we report a detailed study of the normal
state transverse magnetoresistance (MR) in FeSeS for a series of
S concentrations spanning the nematic QCP. For all temperatures and
\textit{x}-values studied, the MR can be decomposed into two distinct
components: one that varies quadratically in magnetic field strength
and one that follows precisely the quadrature scaling form
recently reported in metals at or close to a QCP and characterized by a
\textit{H}-linear MR over an extended field range. The two components evolve
systematically with both temperature and S-substitution in a manner that is
determined by their proximity to the nematic QCP. This study thus reveals
unambiguously the coexistence of two independent charge sectors in a quantum
critical system. Moreover, the quantum critical component of the MR is found to
be less sensitive to disorder than the quadratic (orbital) MR, suggesting that
detection of the latter in previous MR studies of metals near a QCP may have
been obscured.Comment: 19 pages (including Supplemental Material), 12 figure
Structure of the outer layers of cool standard stars
Context: Among late-type red giants, an interesting change occurs in the
structure of the outer atmospheric layers as one moves to later spectral types
in the Hertzsprung-Russell diagram: a chromosphere is always present, but the
coronal emission diminishes and a cool massive wind steps in.
Aims: Where most studies have focussed on short-wavelength observations, this
article explores the influence of the chromosphere and the wind on
long-wavelength photometric measurements.
Methods: The observational spectral energy distributions are compared with
the theoretical predictions of the MARCS atmosphere models for a sample of 9 K-
and M-giants. The discrepancies found are explained using basic models for flux
emission originating from a chromosphere or an ionized wind.
Results: For 7 out of 9 sample stars, a clear flux excess is detected at
(sub)millimeter and/or centimeter wavelengths. The precise start of the excess
depends upon the star under consideration. The flux at wavelengths shorter than
about 1 mm is most likely dominated by an optically thick chromosphere, where
an optically thick ionized wind is the main flux contributor at longer
wavelengths.
Conclusions: Although the optical to mid-infrared spectrum of the studied K-
and M-giants is well represented by a radiative equilibrium atmospheric model,
the presence of a chromosphere and/or ionized stellar wind at higher altitudes
dominates the spectrum in the (sub)millimeter and centimeter wavelength ranges.
The presence of a flux excess also has implications on the role of these stars
as fiducial spectrophotometric calibrators in the (sub)millimeter and
centimeter wavelength range.Comment: 13 pages, 6 figures, 7 pages of online material, submitted to A&
Multimodel Analysis of the Atmospheric Response to Antarctic Sea Ice Loss at Quadrupled CO2
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordAntarctic sea ice cover is projected to significantly decrease by the end of the twenty-first century if greenhouse gas concentrations continue to rise, with potential consequences for Southern Hemisphere weather and climate. Here we examine the atmospheric response to projected Antarctic sea ice loss at quadrupled CO2, inferred from 11 Coupled Model Intercomparison Project phase 5 models. Our study is the first multimodel analysis of the atmospheric response to Antarctic sea ice loss. Projected sea ice loss enhances the negative phase of the Southern Annular Mode, which slightly damps the positive Southern Annular Mode response to increased CO2, particularly in spring. The negative Southern Annular Mode response largely reflects a weakening of the eddy-driven jet, and to a lesser extent, an equatorward shift of the jet. Sea ice loss induces near-surface warming over the high-latitude Southern Ocean, but warming does not penetrate over the Antarctic continent. In spring, we find multimodel evidence for a weakened polar stratospheric vortex in response to sea ice loss.NER
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