774 research outputs found
An L Band Spectrum of the Coldest Brown Dwarf
The coldest brown dwarf, WISE 0855, is the closest known planetary-mass,
free-floating object and has a temperature nearly as cold as the solar system
gas giants. Like Jupiter, it is predicted to have an atmosphere rich in
methane, water, and ammonia, with clouds of volatile ices. WISE 0855 is faint
at near-infrared wavelengths and emits almost all its energy in the
mid-infrared. Skemer et al. 2016 presented a spectrum of WISE 0855 from 4.5-5.1
micron (M band), revealing water vapor features. Here, we present a spectrum of
WISE 0855 in L band, from 3.4-4.14 micron. We present a set of atmosphere
models that include a range of compositions (metallicities and C/O ratios) and
water ice clouds. Methane absorption is clearly present in the spectrum. The
mid-infrared color can be better matched with a methane abundance that is
depleted relative to solar abundance. We find that there is evidence for water
ice clouds in the M band spectrum, and we find a lack of phosphine spectral
features in both the L and M band spectra. We suggest that a deep continuum
opacity source may be obscuring the near-infrared flux, possibly a deep
phosphorous-bearing cloud, ammonium dihyrogen phosphate. Observations of WISE
0855 provide critical constraints for cold planetary atmospheres, bridging the
temperature range between the long-studied solar system planets and accessible
exoplanets. JWST will soon revolutionize our understanding of cold brown dwarfs
with high-precision spectroscopy across the infrared, allowing us to study
their compositions and cloud properties, and to infer their atmospheric
dynamics and formation processes.Comment: 19 pages, 21 figures. Accepted for publication in Ap
The Sonora Brown Dwarf Atmosphere and Evolution Models. I. Model Description and Application to Cloudless Atmospheres in Rainout Chemical Equilibrium
We present a new generation of substellar atmosphere and evolution models , appropriate for application to studies of L-, T-, and Y-type brown dwarfs and self-luminous extrasolar planets. The models describe the expected temperature-pressure proïŹles and emergent spectra of atmospheres in radiative-convective equilibrium with effective temperatures and gravities within the ranges †Teff †2400 K and . These ranges encompass masses from about 0.5 to 85 Jupiter masses for a set of metallicities ([M/H] = â 0.5 to + 0.5),C/O ratios (from 0.5 to 1.5 times that of solar), and ages. These models expand the diversity of model atmospheres currently available, notably to cooler effective temperatures and greater ranges in C/O. Notable improvements from past such models include updated opacities and atmospheric chemistry. Here we describe our modeling approach and present our initial tranche of models for cloudless, chemical equilibrium atmospheres. We compare the modeled spectra, photometry, and evolution to various data sets
Cosmological parameter estimation using Very Small Array data out to l=1500
We estimate cosmological parameters using data obtained by the Very Small
Array (VSA) in its extended configuration, in conjunction with a variety of
other CMB data and external priors. Within the flat CDM model, we find
that the inclusion of high resolution data from the VSA modifies the limits on
the cosmological parameters as compared to those suggested by WMAP alone, while
still remaining compatible with their estimates. We find that , , , , and
for WMAP and VSA when no external prior is
included.On extending the model to include a running spectral index of density
fluctuations, we find that the inclusion of VSA data leads to a negative
running at a level of more than 95% confidence (),
something which is not significantly changed by the inclusion of a stringent
prior on the Hubble constant. Inclusion of prior information from the 2dF
galaxy redshift survey reduces the significance of the result by constraining
the value of . We discuss the veracity of this result in the
context of various systematic effects and also a broken spectral index model.
We also constrain the fraction of neutrinos and find that at
95% confidence which corresponds to when all neutrino
masses are the equal. Finally, we consider the global best fit within a general
cosmological model with 12 parameters and find consistency with other analyses
available in the literature. The evidence for is only marginal
within this model
Correlation Functions of Operators and Wilson Surfaces in the d=6, (0,2) Theory in the Large N Limit
We compute the two and three-point correlation functions of chiral primary
operators in the large N limit of the (0,2), d=6 superconformal theory. We also
consider the operator product expansion of Wilson surfaces in the (0,2) theory
and compute the OPE coefficients of the chiral primary operators at large N
from the correlation functions of surfaces.Comment: 34 pages, using utarticle.cls (included), array.sty, amsmath.sty,
amsfonts.sty, latexsym.sty, epsfig. Bibtex style: utphys.bst (.bbl file
included
Re-presenting the Paralympics: (contested) philosophies, production practices and the hypervisibility of disability
Studies that have engaged para-sport broadcasting, particularly through a narrative lens, have almost exclusively relied on textual and/or content analysis of the Paralympic Games as the source of cultural critique. We know far less about the decisions taken inside Paralympic broadcasters that have led to such representations. In this study â based on interviews with senior production and promotion staff at the UKâs Paralympic broadcaster, Channel 4 â we provide the first detailed examination of mediated para-sport from this vantage point. We explore the use of promotional devices such as athletesâ backstories â the âHollywood treatmentâ â to both hook audiences and serve as a vehicle for achieving its social enterprise mandate to change public attitudes toward disability. In so doing, we reveal myriad tensions that coalesce around representing the Paralympics; with respect to the efforts made to balance the competing goals of key stakeholders and a stated desire to make the Paralympics both a commercial and socially progressive success
The Carnegie Supernova Project: First Near-Infrared Hubble Diagram to z~0.7
The Carnegie Supernova Project (CSP) is designed to measure the luminosity
distance for Type Ia supernovae (SNe Ia) as a function of redshift, and to set
observational constraints on the dark energy contribution to the total energy
content of the Universe. The CSP differs from other projects to date in its
goal of providing an I-band {rest-frame} Hubble diagram. Here we present the
first results from near-infrared (NIR) observations obtained using the Magellan
Baade telescope for SNe Ia with 0.1 < z < 0.7. We combine these results with
those from the low-redshift CSP at z <0.1 (Folatelli et al. 2009). We present
light curves and an I-band Hubble diagram for this first sample of 35 SNe Ia
and we compare these data to 21 new SNe Ia at low redshift. These data support
the conclusion that the expansion of the Universe is accelerating. When
combined with independent results from baryon acoustic oscillations (Eisenstein
et al. 2005), these data yield Omega_m = 0.27 +/- 0.0 (statistical), and
Omega_DE = 0.76 +/- 0.13 (statistical) +/- 0.09 (systematic), for the matter
and dark energy densities, respectively. If we parameterize the data in terms
of an equation of state, w, assume a flat geometry, and combine with baryon
acoustic oscillations, we find that w = -1.05 +/- 0.13 (statistical) +/- 0.09
(systematic). The largest source of systematic uncertainty on w arises from
uncertainties in the photometric calibration, signaling the importance of
securing more accurate photometric calibrations for future supernova cosmology
programs. Finally, we conclude that either the dust affecting the luminosities
of SNe Ia has a different extinction law (R_V = 1.8) than that in the Milky Way
(where R_V = 3.1), or that there is an additional intrinsic color term with
luminosity for SNe Ia independent of the decline rate.Comment: 44 pages, 23 figures, 9 tables; Accepted for publication in the
Astrophysical Journa
Precision Primordial He Measurement with CMB Experiments
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are
two major pillars of cosmology. Standard BBN accurately predicts the primordial
light element abundances (He, D, He and Li), depending on one
parameter, the baryon density. Light element observations are used as a
baryometers. The CMB anisotropies also contain information about the content of
the universe which allows an important consistency check on the Big Bang model.
In addition CMB observations now have sufficient accuracy to not only determine
the total baryon density, but also resolve its principal constituents, H and
He. We present a global analysis of all recent CMB data, with special
emphasis on the concordance with BBN theory and light element observations. We
find and
(fraction of baryon mass as He) using CMB data alone, in agreement with
He abundance observations. With this concordance established we show that
the inclusion of BBN theory priors significantly reduces the volume of
parameter space. In this case, we find
and . We also find that the inclusion of deuterium
abundance observations reduces the and ranges by a factor
of 2. Further light element observations and CMB anisotropy experiments
will refine this concordance and sharpen BBN and the CMB as tools for precision
cosmology.Comment: 7 pages, 3 color figures made minor changes to bring inline with
journal versio
Constraining dark energy with Sunyaev-Zel'dovich cluster surveys
We discuss the prospects of constraining the properties of a dark energy
component, with particular reference to a time varying equation of state, using
future cluster surveys selected by their Sunyaev-Zel'dovich effect. We compute
the number of clusters expected for a given set of cosmological parameters and
propogate the errors expected from a variety of surveys. In the short term they
will constrain dark energy in conjunction with future observations of type Ia
supernovae, but may in time do so in their own right.Comment: 5 pages, 3 figures, 1 table, version accepted for publication in PR
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