710 research outputs found
The Apparently Decaying Orbit of WASP-12
We present new transit and occultation times for the hot Jupiter WASP-12b.
The data are compatible with a constant period derivative:
ms yr and Myr. However, it is difficult to tell whether
we have observed orbital decay, or a portion of a 14-year apsidal precession
cycle. If interpreted as decay, the star's tidal quality parameter is
about . If interpreted as precession, the planet's Love number is
. Orbital decay appears to be the more parsimonious model: it is
favored by despite having two fewer free parameters than the
precession model. The decay model implies that WASP-12 was discovered within
the final 0.2% of its existence, which is an unlikely coincidence but
harmonizes with independent evidence that the planet is nearing disruption.
Precession does not invoke any temporal coincidence, but does require some
mechanism to maintain an eccentricity of 0.002 in the face of rapid
tidal circularization. To distinguish unequivocally between decay and
precession will probably require a few more years of monitoring. Particularly
helpful will be occultation timing in 2019 and thereafter.Comment: 10 pages [AAS journals, in press, note added in proof
Metabolic control of gene transcription in non-alcoholic fatty liver disease: the role of the epigenome
Non-alcoholic fatty liver disease (NAFLD) is estimated to affect 24% of the global adult population. NAFLD is a major risk factor for the development of cirrhosis and hepatocellular carcinoma, as well as being strongly associated with type 2 diabetes and cardiovascular disease. It has been proposed that up to 88% of obese adults have NAFLD, and with global obesity rates increasing, this disease is set to become even more prevalent. Despite intense research in this field, the molecular processes underlying the pathology of NAFLD remain poorly understood. Hepatic intracellular lipid accumulation may lead to dysregulated tricarboxylic acid (TCA) cycle activity and associated alterations in metabolite levels. The TCA cycle metabolites alpha-ketoglutarate, succinate and fumarate are allosteric regulators of the alpha-ketoglutarate-dependent dioxygenase family of enzymes. The enzymes within this family have multiple targets, including DNA and chromatin, and thus may be capable of modulating gene transcription in response to intracellular lipid accumulation through alteration of the epigenome. In this review, we discuss what is currently understood in the field and suggest areas for future research which may lead to the development of novel preventative or therapeutic interventions for NAFLD
TITAN Wireless Camera Control System
The Titan Camera Control System is an eletromechanical device that allows the user to wirelessly control a camera’s digital operations as well as physical orientation through the use of a mobile device application. The Titan system accepts input in the form of virtual user commands on the mobile app and performs system output in the form of sending photos/video from the camera back to the app as well as changing the orientation of the camera in accordance with the user’s commands
Understanding extreme quasar optical variability with CRTS: I. Major AGN flares
There is a large degree of variety in the optical variability of quasars and
it is unclear whether this is all attributable to a single (set of) physical
mechanism(s). We present the results of a systematic search for major flares in
AGN in the Catalina Real-time Transient Survey as part of a broader study into
extreme quasar variability. Such flares are defined in a quantitative manner as
being atop of the normal, stochastic variability of quasars. We have identified
51 events from over 900,000 known quasars and high probability quasar
candidates, typically lasting 900 days and with a median peak amplitude of
mag. Characterizing the flare profile with a Weibull
distribution, we find that nine of the sources are well described by a
single-point single-lens model. This supports the proposal by Lawrence et al.
(2016) that microlensing is a plausible physical mechanism for extreme
variability. However, we attribute the majority of our events to explosive
stellar-related activity in the accretion disk: superluminous supernovae, tidal
disruption events, and mergers of stellar mass black holes.Comment: 25 pages, 18 figures, accepted for publication by MNRA
Connecting the time domain community with the Virtual Astronomical Observatory
The time domain has been identified as one of the most important areas of
astronomical research for the next decade. The Virtual Observatory is in the
vanguard with dedicated tools and services that enable and facilitate the
discovery, dissemination and analysis of time domain data. These range in scope
from rapid notifications of time-critical astronomical transients to annotating
long-term variables with the latest modeling results. In this paper, we will
review the prior art in these areas and focus on the capabilities that the VAO
is bringing to bear in support of time domain science. In particular, we will
focus on the issues involved with the heterogeneous collections of (ancillary)
data associated with astronomical transients, and the time series
characterization and classification tools required by the next generation of
sky surveys, such as LSST and SKA.Comment: Submitted to Proceedings of SPIE Observatory Operations: Strategies,
Processes and Systems IV, Amsterdam, 2012 July 2-
A systematic search for close supermassive black hole binaries in the Catalina Real-Time Transient Survey
Hierarchical assembly models predict a population of supermassive black hole
(SMBH) binaries. These are not resolvable by direct imaging but may be
detectable via periodic variability (or nanohertz frequency gravitational
waves). Following our detection of a 5.2 year periodic signal in the quasar PG
1302-102 (Graham et al. 2015), we present a novel analysis of the optical
variability of 243,500 known spectroscopically confirmed quasars using data
from the Catalina Real-time Transient Survey (CRTS) to look for close (< 0.1
pc) SMBH systems. Looking for a strong Keplerian periodic signal with at least
1.5 cycles over a baseline of nine years, we find a sample of 111 candidate
objects. This is in conservative agreement with theoretical predictions from
models of binary SMBH populations. Simulated data sets, assuming stochastic
variability, also produce no equivalent candidates implying a low likelihood of
spurious detections. The periodicity seen is likely attributable to either jet
precession, warped accretion disks or periodic accretion associated with a
close SMBH binary system. We also consider how other SMBH binary candidates in
the literature appear in CRTS data and show that none of these are equivalent
to the identified objects. Finally, the distribution of objects found is
consistent with that expected from a gravitational wave-driven population. This
implies that circumbinary gas is present at small orbital radii and is being
perturbed by the black holes. None of the sources is expected to merge within
at least the next century. This study opens a new unique window to study a
population of close SMBH binaries that must exist according to our current
understanding of galaxy and SMBH evolution.Comment: 29 pages, 10 figures, accepted for publication in MNRAS - this
version contains extended table and figur
A possible close supermassive black-hole binary in a quasar with optical periodicity
Quasars have long been known to be variable sources at all wavelengths. Their
optical variability is stochastic, can be due to a variety of physical
mechanisms, and is well-described statistically in terms of a damped random
walk model. The recent availability of large collections of astronomical time
series of flux measurements (light curves) offers new data sets for a
systematic exploration of quasar variability. Here we report on the detection
of a strong, smooth periodic signal in the optical variability of the quasar PG
1302-102 with a mean observed period of 1,884 88 days. It was identified
in a search for periodic variability in a data set of light curves for 247,000
known, spectroscopically confirmed quasars with a temporal baseline of
years. While the interpretation of this phenomenon is still uncertain, the most
plausible mechanisms involve a binary system of two supermassive black holes
with a subparsec separation. Such systems are an expected consequence of galaxy
mergers and can provide important constraints on models of galaxy formation and
evolution.Comment: 19 pages, 6 figures. Published online by Nature on 7 January 201
Self-Assembly of Patterns in the abstract Tile Assembly Model
In the abstract Tile Assembly Model, self-assembling systems consisting of
tiles of different colors can form structures on which colored patterns are
``painted.'' We explore the complexity, in terms of the numbers of unique tile
types required, of assembling various patterns. We first demonstrate how to
efficiently self-assemble a set of simple patterns, then show tight bounds on
the tile type complexity of self-assembling 2-colored patterns on the surfaces
of square assemblies. Finally, we demonstrate an exponential gap in tile type
complexity of self-assembling an infinite series of patterns between systems
restricted to one plane versus those allowed two planes
A Search for a Sub-Earth Sized Companion to GJ 436 and a Novel Method to Calibrate Warm Spitzer IRAC Observations
We discovered evidence for a possible additional 0.75 R_Earth transiting
planet in the NASA EPOXI observations of the known M dwarf exoplanetary system
GJ 436. Based on an ephemeris determined from the EPOXI data, we predicted a
transit event in an extant Spitzer Space Telescope 8 micron data set of this
star. Our subsequent analysis of those Spitzer data confirmed the signal of the
predicted depth and at the predicted time, but we found that the transit depth
was dependent on the aperture used to perform the photometry. Based on these
suggestive findings, we gathered new Warm Spitzer Observations of GJ 436 at 4.5
microns spanning a time of transit predicted from the EPOXI and Spitzer 8
micron candidate events. The 4.5 micron data permit us to rule out a transit at
high confidence, and we conclude that the earlier candidate transit signals
resulted from correlated noise in the EPOXI and Spitzer 8 micron observations.
In the course of this investigation, we developed a novel method for correcting
the intrapixel sensitivity variations of the 3.6 and 4.5 micron channels of the
Infrared Array Camera (IRAC) instrument. We demonstrate the sensitivity of Warm
Spitzer observations of M dwarfs to confirm sub-Earth sized planets. Our
analysis will inform similar work that will be undertaken to use Warm Spitzer
observations to confirm rocky planets discovered by the Kepler mission.Comment: 22 pages, 8 figures, accepted for publication in PAS
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