364 research outputs found
HATS-6b: A Warm Saturn Transiting an Early M Dwarf Star, and a Set of Empirical Relations for Characterizing K and M Dwarf Planet Hosts
We report the discovery by the HATSouth survey of HATS-6b, an extrasolar
planet transiting a V=15.2 mag, i=13.7 mag M1V star with a mass of 0.57 Msun
and a radius of 0.57 Rsun. HATS-6b has a period of P = 3.3253 d, mass of
Mp=0.32 Mjup, radius of Rp=1.00 Rjup, and zero-albedo equilibrium temperature
of Teq=712.8+-5.1 K. HATS-6 is one of the lowest mass stars known to host a
close-in gas giant planet, and its transits are among the deepest of any known
transiting planet system. We discuss the follow-up opportunities afforded by
this system, noting that despite the faintness of the host star, it is expected
to have the highest K-band S/N transmission spectrum among known gas giant
planets with Teq < 750 K. In order to characterize the star we present a new
set of empirical relations between the density, radius, mass, bolometric
magnitude, and V, J, H and K-band bolometric corrections for main sequence
stars with M < 0.80 Msun, or spectral types later than K5. These relations are
calibrated using eclipsing binary components as well as members of resolved
binary systems. We account for intrinsic scatter in the relations in a
self-consistent manner. We show that from the transit-based stellar density
alone it is possible to measure the mass and radius of a ~0.6 Msun star to ~7%
and ~2% precision, respectively. Incorporating additional information, such as
the V-K color, or an absolute magnitude, allows the precision to be improved by
up to a factor of two.Comment: 21 pages, 11 figures, 10 tables. Submitted to AJ. Data available at
http://hatsouth.org Code implementing empirical model available at
http://www.astro.princeton.edu/~jhartman/kmdwarfparam.htm
HATS-15 b and HATS-16 b: Two massive planets transiting old G dwarf stars
We report the discovery of HATS-15 b and HATS-16 b, two massive transiting
extrasolar planets orbiting evolved ( Gyr) main-sequence stars. The
planet HATS-15 b, which is hosted by a G9V star ( mag), is a hot
Jupiter with mass of and radius of
, and completes its orbit in nearly 1.7 days.
HATS-16 b is a very massive hot Jupiter with mass of and radius of ; it orbits around
its G3 V parent star ( mag) in days. HATS-16 is slightly
active and shows a periodic photometric modulation, implying a rotational
period of 12 days which is unexpectedly short given its isochronal age. This
fast rotation might be the result of the tidal interaction between the star and
its planet.Comment: 16 pages, 8 figures, submitted to PAS
HATS-60bâHATS-69b: 10 Transiting Planets from HATSouth
We report the discovery of 10 transiting extrasolar planets by the HATSouth survey. The planets range in mass from the super-Neptune HATS-62b, with M-p < 0.179 M-J, to the super-Jupiter HATS-66b, with M-p = 5.33 M-J, and in size from the Saturn HATS-69b, with R-p = 0.94 R-J, to the inflated Jupiter HATS-67b, with R-p = 1.69 R-J. The planets have orbital periods between 1.6092 days (HATS-67b) and 7.8180 days (HATS-61b). The hosts are dwarf stars with masses ranging from 0.89 M-circle dot (HATS-69) to 1.56 M-circle dot (HATS-64) and have apparent magnitudes between V = 12.276 +/- 0.020 mag (HATS-68) and V = 14.095 +/- 0.030 mag (HATS-66). The super-Neptune HATS-62b is the least massive planet discovered to date with a radius larger than Jupiter. Based largely on the Gaia DR2 distances and broadband photometry, we identify three systems (HATS-62, HATS-64, and HATS-65) as having possible unresolved binary star companions. We discuss in detail our methods for incorporating the Gaia DR2 observations into our modeling of the system parameters and into our blend analysis procedures
Comprehensive prediction of chromosome dimer resolution sites in bacterial genomes
<p>Abstract</p> <p>Background</p> <p>During the replication process of bacteria with circular chromosomes, an odd number of homologous recombination events results in concatenated dimer chromosomes that cannot be partitioned into daughter cells. However, many bacteria harbor a conserved dimer resolution machinery consisting of one or two tyrosine recombinases, XerC and XerD, and their 28-bp target site, <it>dif</it>.</p> <p>Results</p> <p>To study the evolution of the <it>dif/</it>XerCD system and its relationship with replication termination, we report the comprehensive prediction of <it>dif </it>sequences <it>in silico </it>using a phylogenetic prediction approach based on iterated hidden Markov modeling. Using this method, <it>dif </it>sites were identified in 641 organisms among 16 phyla, with a 97.64% identification rate for single-chromosome strains. The <it>dif </it>sequence positions were shown to be strongly correlated with the GC skew shift-point that is induced by replicational mutation/selection pressures, but the difference in the positions of the predicted <it>dif </it>sites and the GC skew shift-points did not correlate with the degree of replicational mutation/selection pressures.</p> <p>Conclusions</p> <p>The sequence of <it>dif </it>sites is widely conserved among many bacterial phyla, and they can be computationally identified using our method. The lack of correlation between <it>dif </it>position and the degree of GC skew suggests that replication termination does not occur strictly at <it>dif </it>sites.</p
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
MEF2C Enhances Dopaminergic Neuron Differentiation of Human Embryonic Stem Cells in a Parkinsonian Rat Model
Human embryonic stem cells (hESCs) can potentially differentiate into any cell type, including dopaminergic neurons to treat Parkinson's disease (PD), but hyperproliferation and tumor formation must be avoided. Accordingly, we use myocyte enhancer factor 2C (MEF2C) as a neurogenic and anti-apoptotic transcription factor to generate neurons from hESC-derived neural stem/progenitor cells (NPCs), thus avoiding hyperproliferation. Here, we report that forced expression of constitutively active MEF2C (MEF2CA) generates significantly greater numbers of neurons with dopaminergic properties in vitro. Conversely, RNAi knockdown of MEF2C in NPCs decreases neuronal differentiation and dendritic length. When we inject MEF2CA-programmed NPCs into 6-hydroxydopamineâlesioned Parkinsonian rats in vivo, the transplanted cells survive well, differentiate into tyrosine hydroxylase-positive neurons, and improve behavioral deficits to a significantly greater degree than non-programmed cells. The enriched generation of dopaminergic neuronal lineages from hESCs by forced expression of MEF2CA in the proper context may prove valuable in cell-based therapy for CNS disorders such as PD
A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
A key legacy of the recently launched TESS mission will be to provide the
astronomical community with many of the best transiting exoplanet targets for
atmospheric characterization. However, time is of the essence to take full
advantage of this opportunity. JWST, although delayed, will still complete its
nominal five year mission on a timeline that motivates rapid identification,
confirmation, and mass measurement of the top atmospheric characterization
targets from TESS. Beyond JWST, future dedicated missions for atmospheric
studies such as ARIEL require the discovery and confirmation of several hundred
additional sub-Jovian size planets (R_p < 10 R_Earth) orbiting bright stars,
beyond those known today, to ensure a successful statistical census of
exoplanet atmospheres. Ground-based ELTs will also contribute to surveying the
atmospheres of the transiting planets discovered by TESS. Here we present a set
of two straightforward analytic metrics, quantifying the expected
signal-to-noise in transmission and thermal emission spectroscopy for a given
planet, that will allow the top atmospheric characterization targets to be
readily identified among the TESS planet candidates. Targets that meet our
proposed threshold values for these metrics would be encouraged for rapid
follow-up and confirmation via radial velocity mass measurements. Based on the
catalog of simulated TESS detections by Sullivan et al. (2015), we determine
appropriate cutoff values of the metrics, such that the TESS mission will
ultimately yield a sample of high-quality atmospheric
characterization targets across a range of planet size bins, extending down to
Earth-size, potentially habitable worlds.Comment: accepted to PAS
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