92 research outputs found
XO-5b: A Transiting Jupiter-sized Planet With A Four Day Period
The star XO-5 (GSC 02959-00729, V=12.1, G8V) hosts a Jupiter-sized,
Rp=1.15+/-0.12 Rjup, transiting extrasolar planet, XO-5b, with an orbital
period of P=4.187732+/-0.00002 days. The planet mass (Mp=1.15+/-0.08 Mjup) and
surface gravity (gp=22+/-5 m/s^2) are significantly larger than expected by
empirical Mp-P and Mp-P-[Fe/H] relationships. However, the deviation from the
Mp-P relationship for XO-5b is not large enough to suggest a distinct type of
planet as is suggested for GJ 436b, HAT-P-2b, and XO-3b. By coincidence XO-5
overlies the extreme H I plume that emanates from the interacting galaxy pair
NGC 2444/NGC 2445 (Arp 143).Comment: 10 pages, 9 Figures, Submitted to Ap
XO-2b: Transiting Hot Jupiter in a Metal-rich Common Proper Motion Binary
We report on a V=11.2 early K dwarf, XO-2 (GSC 03413-00005), that hosts a
Rp=0.98+0.03/-0.01 Rjup, Mp=0.57+/-0.06 Mjup transiting extrasolar planet,
XO-2b, with an orbital period of 2.615857+/-0.000005 days. XO-2 has high
metallicity, [Fe/H]=0.45+/-0.02, high proper motion, mu_tot=157 mas/yr, and has
a common proper motion stellar companion with 31" separation. The two stars are
nearly identical twins, with very similar spectra and apparent magnitudes. Due
to the high metallicity, these early K dwarf stars have a mass and radius close
to solar, Ms=0.98+/-0.02 Msolar and Rs=0.97+0.02/-0.01 Rsolar. The high proper
motion of XO-2 results from an eccentric orbit (Galactic pericenter, Rper<4
kpc) well confined to the Galactic disk (Zmax~100 pc). In addition, the phase
space position of XO-2 is near the Hercules dynamical stream, which points to
an origin of XO-2 in the metal-rich, inner Thin Disk and subsequent dynamical
scattering into the solar neighborhood. We describe an efficient Markov Chain
Monte Carlo algorithm for calculating the Bayesian posterior probability of the
system parameters from a transit light curve.Comment: 14 pages, 10 Figures, Accepted in ApJ. Negligible changes to XO-2
system properties. Removed Chi^2 light curve analysis section, and simplified
MCMC light curve analysis discussio
The XO Planetary Survey Project - Astrophysical False Positives
Searches for planetary transits find many astrophysical false positives as a
by-product. There are four main types analyzed in the literature: a
grazing-incidence eclipsing binary star, an eclipsing binary star with a small
radius companion star, a blend of one or more stars with an unrelated eclipsing
binary star, and a physical triple star system. We present a list of 69
astrophysical false positives that had been identified as candidates of
transiting planets of the on-going XO survey. This list may be useful in order
to avoid redundant observation and characterization of these particular
candidates independently identified by other wide-field searches for transiting
planets. The list may be useful for those modeling the yield of the XO survey
and surveys similar to it. Subsequent observations of some of the listed stars
may improve mass-radius relations, especially for low-mass stars. From the
candidates exhibiting eclipses, we report three new spectroscopic double-line
binaries and give mass function estimations for 15 single lined spectroscopic
binaries.Comment: 13 pages, 4 figures, accepted to ApJ
XO-3b: A Massive Planet in an Eccentric Orbit Transiting an F5V Star
We report the discovery of a massive (Mpsini = 13.02 +/- 0.64 Mjup; total
mass 13.25 +/- 0.64 Mjup), large (1.95 +/- 0.16 Rjup) planet in a transiting,
eccentric orbit (e = 0.260 +/- 0.017) around a 10th magnitude F5V star in the
constellation Camelopardalis. We designate the planet XO-3b, and the star XO-3,
also known as GSC 03727-01064. The orbital period of XO-3b is 3.1915426 +/-
0.00014 days. XO-3 lacks a trigonometric distance; we estimate its distance to
be 260 +/- 23 pc. The radius of XO-3 is 2.13 +/- 0.21 Rsun, its mass is 1.41
+/- 0.08 Msun, its vsini = 18.54 +/- 0.17 km/s, and its metallicity is [Fe/H] =
-0.177 +/- 0.027. This system is unusual for a number of reasons. XO-3b is one
of the most massive planets discovered around any star for which the orbital
period is less than 10 days. The mass is near the deuterium burning limit of 13
Mjup, which is a proposed boundary between planets and brown dwarfs. Although
Burrows et al. (2001) propose that formation in a disk or formation in the
interstellar medium in a manner similar to stars is a more logical way to
differentiate planets and brown dwarfs, our current observations are not
adequate to address this distinction. XO-3b is also unusual in that its
eccentricity is large given its relatively short orbital period. Both the
planetary radius and the inclination are functions of the spectroscopically
determined stellar radius. Analysis of the transit light curve of XO-3b
suggests that the spectroscopically derived parameters may be over estimated.
Though relatively noisy, the light curves favor a smaller radius in order to
better match the steepness of the ingress and egress. The light curve fits
imply a planetary radius of 1.25 +/- 0.15 Rjup, which would correspond to a
mass of 12.03 +/- 0.46 Mjup.Comment: 26 pages, 10 figures. Accepted by ApJ. Current version has several
small corrections as a result of a bug in the fitting softwar
NICMOS Observations of the Transiting Hot Jupiter XO-1b
We refine the physical parameters of the transiting hot Jupiter planet XO-1b
and its stellar host XO-1 using HST NICMOS observations. XO-1b has a radius
Rp=1.21+/-0.03 RJup, and XO-1 has a radius Rs=0.94+/-0.02 RSun, where the
uncertainty in the mass of XO-1 dominates the uncertainty of Rp and Rs. There
are no significant differences in the XO-1 system properties between these
broad-band NIR observations and previous determinations based upon ground-based
optical observations. We measure two transit timings from these observations
with 9 s and 15 s precision. As a residual to a linear ephemeris model, there
is a 2.0 sigma timing difference between the two HST visits that are separated
by 3 transit events (11.8 days). These two transit timings and additional
timings from the literature are sufficient to rule out the presence of an Earth
mass planet orbiting in 2:1 mean motion resonance coplanar with XO-1b. We
identify and correct for poorly understood gain-like variations present in
NICMOS time series data. This correction reduces the effective noise in time
series photometry by a factor of two, for the case of XO-1.Comment: 13 pages, 8 figures, submitted to Ap
Elevated <scp>CO<sub>2</sub></scp> interacts with nutrient inputs to restructure plant communities in phosphorusâlimited grasslands
AbstractGlobally pervasive increases in atmospheric CO2 and nitrogen (N) deposition could have substantial effects on plant communities, either directly or mediated by their interactions with soil nutrient limitation. While the direct consequences of N enrichment on plant communities are well documented, potential interactions with rising CO2 and globally widespread phosphorus (P) limitation remain poorly understood. We investigated the consequences of simultaneous elevated CO2 (eCO2) and N and P additions on grassland biodiversity, community and functional composition in Pâlimited grasslands. We exposed soilâturf monoliths from limestone and acidic grasslands that have received >25âyears of N additions (3.5 and 14âgâmâ2âyearâ1) and 11 (limestone) or 25 (acidic) years of P additions (3.5âgâmâ2âyearâ1) to eCO2 (600âppm) for 3âyears. Across both grasslands, eCO2, N and P additions significantly changed community composition. Limestone communities were more responsive to eCO2 and saw significant functional shifts resulting from eCO2ânutrient interactions. Here, legume cover tripled in response to combined eCO2 and P additions, and combined eCO2 and N treatments shifted functional dominance from grasses to sedges. We suggest that eCO2 may disproportionately benefit P acquisition by sedges by subsidising the carbon cost of locally intense root exudation at the expense of coâoccurring grasses. In contrast, the functional composition of the acidic grassland was insensitive to eCO2 and its interactions with nutrient additions. Greater diversity of Pâacquisition strategies in the limestone grassland, combined with a more functionally even and diverse community, may contribute to the stronger responses compared to the acidic grassland. Our work suggests we may see large changes in the composition and biodiversity of Pâlimited grasslands in response to eCO2 and its interactions with nutrient loading, particularly where these contain a high diversity of Pâacquisition strategies or developmentally young soils with sufficient bioavailable mineral P.</jats:p
Age at quitting smoking as a predictor of risk of cardiovascular disease incidence independent of smoking status, time since quitting and pack-years
Background: Risk prediction for CVD events has been shown to vary according to current smoking status, pack-years smoked over a lifetime, time since quitting and age at quitting. The latter two are closely and inversely related. It is not known whether the age at which one quits smoking is an additional important predictor of CVD events. The aim of this study was to determine whether the risk of CVD events varied according to age at quitting after taking into account current smoking status, lifetime pack-years smoked and time since quitting. Findings. We used the Cox proportional hazards model to evaluate the risk of developing a first CVD event for a cohort of participants in the Framingham Offspring Heart Study who attended the fourth examination between ages 30 and 74 years and were free of CVD. Those who quit before the median age of 37 years had a risk of CVD incidence similar to those who were never smokers. The incorporation of age at quitting in the smoking variable resulted in better prediction than the model which had a simple current smoker/non-smoker measure and the one that incorporated both time since quitting and pack-years. These models demonstrated good discrimination, calibration and global fit. The risk among those quitting more than 5 years prior to the baseline exam and those whose age at quitting was prior to 44 years was similar to the risk among never smokers. However, the risk among those quitting less than 5 years prior to the baseline exam and those who continued to smoke until 44 years of age (or beyond) was two and a half times higher than that of never smokers. Conclusions: Age at quitting improves the prediction of risk of CVD incidence even after other smoking measures are taken into account. The clinical benefit of adding age at quitting to the model with other smoking measures may be greater than the associated costs. Thus, age at quitting should be considered in addition to smoking status, time since quitting and pack-years when counselling individuals about their cardiovascular risk
The same frequency of planets inside and outside open clusters of stars
Most stars and their planets form in open clusters. Over 95 per cent of such
clusters have stellar densities too low (less than a hundred stars per cubic
parsec) to withstand internal and external dynamical stresses and fall apart
within a few hundred million years. Older open clusters have survived by virtue
of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when
they formed. Such clusters represent a stellar environment very different from
the birthplace of the Sun and other planet-hosting field stars. So far more
than 800 planets have been found around Sun-like stars in the field. The field
planets are usually the size of Neptune or smaller. In contrast, only four
planets have been found orbiting stars in open clusters, all with masses
similar to or greater than that of Jupiter. Here we report observations of the
transits of two Sun-like stars by planets smaller than Neptune in the
billion-year-old open cluster NGC6811. This demonstrates that small planets can
form and survive in a dense cluster environment, and implies that the frequency
and properties of planets in open clusters are consistent with those of planets
around field stars in the Galaxy.Comment: 18 pages, 6 figures, 1 table (main text + supplementary information
Cell-intrinsic differences between human airway epithelial cells from children and adults
Summary
The airway epithelium is a protective barrier that is maintained by the self-renewal and differentiation of basal stem cells. Increasing age is a principle risk factor for chronic lung diseases, but few studies have explored age-related molecular or functional changes in the airway epithelium. We retrieved epithelial biopsies from histologically normal tracheobronchial sites from pediatric and adult donors and compared their cellular composition and gene expression profile (in laser capture-microdissected whole epithelium, fluorescence-activated cell-sorted basal cells and basal cells in cell culture). Histologically, pediatric and adult tracheobronchial epithelium were similar in composition. We observed age-associated changes in RNA sequencing studies, including higher interferon-associated gene expression in pediatric epithelium. In cell culture, pediatric cells had higher colony-formation ability, sustained in vitro growth and out-competed adult cells in a direct competitive proliferation assay. Our results demonstrate cell-intrinsic differences between airway epithelial cells from children and adults in both homeostatic and proliferative states
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