20 research outputs found
Three Dimensional Modeling of Hot Jupiter Atmospheric Flows
We present a three dimensional hot Jupiter model, extending from 200 bar to 1
mbar, using the Intermediate General Circulation Model from the University of
Reading. Our horizontal spectral resolution is T31 (equivalent to a grid of
48x96), with 33 logarithmically spaced vertical levels. A simplified
(Newtonian) scheme is employed for the radiative forcing. We adopt a physical
set up nearly identical to the model of HD 209458b by Cooper & Showman
(2005,2006) to facilitate a direct model inter-comparison. Our results are
broadly consistent with theirs but significant differences also emerge. The
atmospheric flow is characterized by a super-rotating equatorial jet, transonic
wind speeds, and eastward advection of heat away from the dayside. We identify
a dynamically-induced temperature inversion ("stratosphere") on the planetary
dayside and find that temperatures at the planetary limb differ systematically
from local radiative equilibrium values, a potential source of bias for transit
spectroscopic interpretations. While our model atmosphere is quasi-identical to
that of Cooper & Showman (2005,2006) and we solve the same meteorological
equations, we use different algorithmic methods, spectral-implicit vs.
grid-explicit, which are known to yield fully consistent results in the Earth
modeling context. The model discrepancies identified here indicate that one or
both numerical methods do not faithfully capture all of the atmospheric
dynamics at work in the hot Jupiter context. We highlight the emergence of a
shock-like feature in our model, much like that reported recently by Showman et
al. (2009), and suggest that improved representations of energy conservation
may be needed in hot Jupiter atmospheric models, as emphasized by Goodman
(2009).Comment: 25 pages, 6 figures, minor revisions, ApJ accepted, version with
hi-res figures:
http://www.astro.columbia.edu/~kristen/Hires/hotjup.3d.deep.ps.g
Radiation-Hydrodynamics of Hot Jupiter Atmospheres
Radiative transfer in planetary atmospheres is usually treated in the static
limit, i.e., neglecting atmospheric motions. We argue that hot Jupiter
atmospheres, with possibly fast (sonic) wind speeds, may require a more
strongly coupled treatment, formally in the regime of radiation-hydrodynamics.
To lowest order in v/c, relativistic Doppler shifts distort line profiles along
optical paths with finite wind velocity gradients. This leads to flow-dependent
deviations in the effective emission and absorption properties of the
atmospheric medium. Evaluating the overall impact of these distortions on the
radiative structure of a dynamic atmosphere is non-trivial. We present
transmissivity and systematic equivalent width excess calculations which
suggest possibly important consequences for radiation transport in hot Jupiter
atmospheres. If winds are fast and bulk Doppler shifts are indeed important for
the global radiative balance, accurate modeling and reliable data
interpretation for hot Jupiter atmospheres may prove challenging: it would
involve anisotropic and dynamic radiative transfer in a coupled
radiation-hydrodynamical flow. On the bright side, it would also imply that the
emergent properties of hot Jupiter atmospheres are more direct tracers of their
atmospheric flows than is the case for Solar System planets.
Radiation-hydrodynamics may also influence radiative transfer in other classes
of hot exoplanetary atmospheres with fast winds.Comment: 25 pages, 4 figures, accepted for publication in ApJ (minor
revisions
A New 24 micron Phase Curve for upsilon Andromedae b
We report the detection of 24 micron variations from the planet-hosting
upsilon Andromedae system consistent with the orbital periodicity of the
system's innermost planet, upsilon And b. We find a peak-to-valley phase curve
amplitude of 0.00130 times the mean system flux. Using a simple model with two
hemispheres of constant surface brightness and assuming a planetary radius of
1.3 Jupiter radii gives a planetary temperature contrast of >900 K and an
orbital inclination of >28 degrees. We further report the largest phase offset
yet observed for an extrasolar planet: the flux maximum occurs ~80 degrees
before phase 0.5. Such a large phase offset is difficult to reconcile with most
current atmospheric circulation models. We improve on earlier observations of
this system in several important ways: (1) observations of a flux calibrator
star demonstrate the MIPS detector is stable to 10^-4 on long timescales, (2)
we note that the background light varies systematically due to spacecraft
operations, precluding use of this background as a flux calibrator (stellar
flux measured above the background is not similarly affected), and (3) we
calibrate for flux variability correlated with motion of the star on the MIPS
detector. A reanalysis of our earlier observations of this system is consistent
with our new result.Comment: Submitted to ApJ. 15 pages, 6 figures, 4 table
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29
Puzzlecluster: A novel unsupervised clustering algorithm for binning dna fragments in metagenomics
Metagenomic datasets are composed of DNA fragments from large numbers of different and potentially novel organisms. These datasets can contain up to several million sequences taken from heterogeneous populations of extremely varied abundance. Unlike traditional genomic studies, metagenomic analysis requires an additional binning step. This process groups DNA fragments from the same or similar species of origin. However, existing unsupervised metagenomic binning programs cannot accurately analyze datasets containing a large number of species or with significantly unbalanced abundance ratios. To improve upon these current limitations, we present PuzzleCluster, a novel unsupervised binning algorithm. PuzzleCluster incorporates a unique cluster refinement step by automatically grouping reads which share a nucleotide word (i.e. reverse complement pairs) of a predetermined length. Additionally, the clustering parameters are estimated by fitting the Jensen-Shannon distance among sequences using the expectation maximization algorithm. Since clustering parameters are computed based on each dataset, our approach can adapt to the peculiarities of each dataset and is not confined by universal parameters. Furthermore, PuzzleCluster utilizes no prior assumptions about the genetic makeup or number of organisms present in the sample, making it well-suited for applications with a large amount of biodiversity and completely unknown organisms. As a comparison, PuzzleCluster has an accuracy 9%, 19.8%, 15.7%, and 19.5% higher than MetaCluster 3.0 for taxonomic levels phylum, class, order, and family, respectively. PuzzleCluster source code is freely available at http://math.stanford.edu/~ksiegel/PuzzleCluster.html © 2015 Bentham Science Publisher