103 research outputs found
A Search for Exozodiacal Clouds with Kepler
Planets embedded within dust disks may drive the formation of large scale
clumpy dust structures by trapping dust into resonant orbits. Detection and
subsequent modeling of the dust structures would help constrain the mass and
orbit of the planet and the disk architecture, give clues to the history of the
planetary system, and provide a statistical estimate of disk asymmetry for
future exoEarth-imaging missions. Here we present the first search for these
resonant structures in the inner regions of planetary systems by analyzing the
light curves of hot Jupiter planetary candidates identified by the Kepler
mission. We detect only one candidate disk structure associated with KOI 838.01
at the 3-sigma confidence level, but subsequent radial velocity measurements
reveal that KOI 838.01 is a grazing eclipsing binary and the candidate disk
structure is a false positive. Using our null result, we place an upper limit
on the frequency of dense exozodi structures created by hot Jupiters. We find
that at the 90% confidence level, less than 21% of Kepler hot Jupiters create
resonant dust clumps that lead and trail the planet by ~90 degrees with optical
depths >~5*10^-6, which corresponds to the resonant structure expected for a
lone hot Jupiter perturbing a dynamically cold dust disk 50 times as dense as
the zodiacal cloud.Comment: 22 pages, 6 figures, Accepted for publication in Ap
A novel decatenation assay for DNA topoisomerases using a singly-linked catenated substrate
Decatenation is a crucial in vivo reaction of DNA topoisomerases in DNA replication and is frequently used in in vitro drug screening. Usually this reaction is monitored using kinetoplast DNA as a substrate, although this assay has several limitations. Here we have engineered a substrate for Tn3 resolvase that generates a singly-linked catenane that can readily be purified from the DNA substrate after restriction enzyme digestion and centrifugation. We show that this catenated substrate can be used with high sensitivity in topoisomerase assays and drug-inhibition assays
Focusing Cosmic Telescopes: Exploring Redshift z~5-6 Galaxies with the Bullet Cluster 1E0657-56
The gravitational potential of clusters of galaxies acts as a cosmic
telescope allowing us to find and study galaxies at fainter limits than
otherwise possible and thus probe closer to the epoch of formation of the first
galaxies. We use the Bullet Cluster 1E0657-56 (z = 0.296) as a case study,
because its high mass and merging configuration makes it one of the most
efficient cosmic telescopes we know. We develop a new algorithm to reconstruct
the gravitational potential of the Bullet Cluster, based on a non-uniform
adaptive grid, combining strong and weak gravitational lensing data derived
from deep HST/ACS F606W-F775W-F850LP and ground-based imaging. We exploit this
improved mass map to study z~5-6 Lyman Break Galaxies (LBGs), which we detect
as dropouts. One of the LBGs is multiply imaged, providing a geometric
confirmation of its high redshift, and is used to further improve our mass
model. We quantify the uncertainties in the magnification map reconstruction in
the intrinsic source luminosity, and in the volume surveyed, and show that they
are negligible compared to sample variance when determining the luminosity
function of high-redshift galaxies. With shallower and comparable magnitude
limits to HUDF and GOODS, the Bullet cluster observations, after correcting for
magnification, probe deeper into the luminosity function of the high redshift
galaxies than GOODS and only slightly shallower than HUDF. We conclude that
accurately focused cosmic telescopes are the most efficient way to sample the
bright end of the luminosity function of high redshift galaxies and - in case
they are multiply imaged - confirm their redshifts.Comment: 12 pages, Accepted for publication in Ap
The James Webb Space Telescope Mission: Optical Telescope Element Design, Development, and Performance
The James Webb Space Telescope (JWST) is a large, infrared space telescope
that has recently started its science program which will enable breakthroughs
in astrophysics and planetary science. Notably, JWST will provide the very
first observations of the earliest luminous objects in the Universe and start a
new era of exoplanet atmospheric characterization. This transformative science
is enabled by a 6.6 m telescope that is passively cooled with a 5-layer
sunshield. The primary mirror is comprised of 18 controllable, low areal
density hexagonal segments, that were aligned and phased relative to each other
in orbit using innovative image-based wavefront sensing and control algorithms.
This revolutionary telescope took more than two decades to develop with a
widely distributed team across engineering disciplines. We present an overview
of the telescope requirements, architecture, development, superb on-orbit
performance, and lessons learned. JWST successfully demonstrates a segmented
aperture space telescope and establishes a path to building even larger space
telescopes.Comment: accepted by PASP for JWST Overview Special Issue; 34 pages, 25
figure
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
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The Redshift Evolution of the Mean Temperature, Pressure, and Entropy Profiles in 80 SPT-Selected Galaxy Clusters
We present the results of an X-ray analysis of 80 galaxy clusters selected in the 2500 deg2 South Pole Telescope survey and observed with the Chandra X-ray Observatory. We divide the full sample into subsamples of ∼20 clusters based on redshift and central density, performing a joint X-ray spectral fit to all clusters in a subsample simultaneously, assuming self-similarity of the temperature profile. This approach allows us to constrain the shape of the temperature profile over 0 R500) regions than their low-z (0.3 < z < 0.6) counterparts. Combining the average temperature profile with measured gas density profiles from our earlier work, we infer the average pressure and entropy profiles for each subsample. Confirming earlier results from this data set, we find an absence of strong cool cores at high z, manifested in this analysis as a significantly lower observed pressure in the central 0.1R500 of the high-z cool-core subset of clusters compared to the low-z cool-core subset. Overall, our observed pressure profiles agree well with earlier lower-redshift measurements, suggesting minimal redshift evolution in the pressure profile outside of the core. We find no measurable redshift evolution in the entropy profile at r . 0.7R500 – this may reflect a long-standing balance between cooling and feedback over long timescales and large physical scales. We observe a slight flattening of the entropy profile at r & R500 in our high-z subsample. This flattening is consistent with a temperature bias due to the enhanced (∼3×) rate at which group-mass (∼2 keV) halos, which would go undetected at our survey depth, are accreting onto the cluster at z ∼ 1. This work demonstrates a powerful method for inferring spatially-resolved cluster properties in the case where individual cluster signal-to-noise is low, but the number of observed clusters is high.Physic
Telomerecat: A ploidy-agnostic method for estimating telomere length from whole genome sequencing data.
Telomere length is a risk factor in disease and the dynamics of telomere length are crucial to our understanding of cell replication and vitality. The proliferation of whole genome sequencing represents an unprecedented opportunity to glean new insights into telomere biology on a previously unimaginable scale. To this end, a number of approaches for estimating telomere length from whole-genome sequencing data have been proposed. Here we present Telomerecat, a novel approach to the estimation of telomere length. Previous methods have been dependent on the number of telomeres present in a cell being known, which may be problematic when analysing aneuploid cancer data and non-human samples. Telomerecat is designed to be agnostic to the number of telomeres present, making it suited for the purpose of estimating telomere length in cancer studies. Telomerecat also accounts for interstitial telomeric reads and presents a novel approach to dealing with sequencing errors. We show that Telomerecat performs well at telomere length estimation when compared to leading experimental and computational methods. Furthermore, we show that it detects expected patterns in longitudinal data, repeated measurements, and cross-species comparisons. We also apply the method to a cancer cell data, uncovering an interesting relationship with the underlying telomerase genotype
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
A Roadmap for HEP Software and Computing R&D for the 2020s
Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.Peer reviewe
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