115 research outputs found
A Precise Estimate of the Radius of HD 149026b
We present Spitzer 8 micron transit observations of the extrasolar planet
system HD 149026. At this wavelength, transit light curves are weakly affected
by stellar limb-darkening, allowing for a simpler and more accurate
determination of planetary parameters. We measure a planet-star radius ratio of
R_p/R_s = 0.05158 +/- 0.00077, and in combination with ground-based data and
independent constraints on the stellar mass and radius, we derive an orbital
inclination of i = 85.4 +0.9/-0.8 deg. and a planet radius of 0.755 +/- 0.040
Jupiter radii. These measurements further support models in which the planet is
greatly enriched in heavy elements.Comment: To appear in the Proceedings of the 253rd IAU Symposium: "Transiting
Planets", May 2008, Cambridge, M
Observational study of the association of first insulin type in uncontrolled type 2 diabetes with macrovascular and microvascular disease
<p>Aims: To compare the risk of vascular disease, HbA1c and weight change, between first prescribed insulins in people with type 2 diabetes.</p>
<p>Methods: People included in THIN United Kingdom primary care record database who began insulin (2000–2007) after poor control on oral glucose-lowering agents (OGLD) were grouped by the number of OGLDs in their treatment regimen immediately before starting insulin (n = 3,485). Within OGLD group, Cox regression compared macrovascular (all-cause mortality, myocardial infarction, acute coronary syndrome and stroke) and microvascular disease (peripheral neuropathy, nephropathy, and retinopathy) between insulin type (basal, pre-mix or Neutral Protamine Hagedorn, NPH) while ANCOVAs compared haemoglobin A1c (HbA1c) and weight change.</p>
<p>Results: Mean follow-up was 3.6 years. Rates of incident macrovascular events were similar when basal insulin was compared to pre-mix or NPH, adjusted hazard ratio versus basal: pre-mix 1.08 (95% CI 0.73, 1.59); NPH 1.00 (0.63, 1.58) after two OGLDs, and pre-mix 0.97 (0.46, 2.02); NPH 0.77 (0.32, 1.86) after three OGLDs. An increased risk of microvascular disease in NPH versus basal after 3 OGLDs, adjusted hazard ratio1.87 (1.04, 3.36), was not seen after two agents or in comparisons of basal and pre-mix. At one year, after two OGLDs, weight increase was less with basal compared with pre-mix. After three OGLDs, mean HbA1c had reduced less in basal versus pre-mix or NPH at 6–8 and at 9–11 months, and versus pre-mix at 12–14 months.</p>
<p>Conclusion: We found no difference in the risk of macrovascular events between first insulins in the medium term when started during poor glycaemia control. The increased risk of microvascular events with NPH warrants further study. In certain groups, first use of basal insulin was associated with less gain in weight and decrease in HbA1c compared to other insulins.</p>
The Transit Light Curve Project. XIII. Sixteen Transits of the Super-Earth GJ 1214b
We present optical photometry of 16 transits of the super-Earth GJ 1214b,
allowing us to refine the system parameters and search for additional planets
via transit timing. Starspot-crossing events are detected in two light curves,
and the star is found to be variable by a few percent. Hence, in our analysis,
special attention is given to systematic errors that result from star spots.
The planet-to-star radius ratio is 0.11610+/-0.00048, subject to a possible
upward bias by a few percent due to the unknown spot coverage. Even assuming
this bias to be negligible, the mean density of planet can be either
3.03+/-0.50 g cm^{-3} or 1.89+/-0.33 g cm^{-3}, depending on whether the
stellar radius is estimated from evolutionary models or from an empirical
mass-luminosity relation combined with the light curve parameters. One possible
resolution is that the orbit is eccentric (e approximately equal to 0.14),
which would favor the higher density, and hence a much thinner atmosphere for
the planet. The transit times were found to be periodic within about 15s,
ruling out the existence of any other super-Earths with periods within a
factor-of-two of the known planet.Comment: Accepted in Ap
Accurately Reflecting Uncertainty When Using Patient-Level Simulation Models to Extrapolate Clinical Trial Data.
Introduction. Patient-level simulation models facilitate extrapolation of clinical trial data while allowing for heterogeneity, prior history, and nonlinearity. However, combining different types of uncertainty around within-trial and extrapolated results remains challenging. Methods. We tested 4 methods to combine parameter uncertainty (around the regression coefficients used to predict future events) with sampling uncertainty (uncertainty around mean risk factors within the finite sample whose outcomes are being predicted and the effect of treatment on these risk factors). We compared these 4 methods using a simulation study based on an economic evaluation extrapolating the AFORRD randomized controlled trial using the UK Prospective Diabetes Study Outcomes Model version 2. This established type 2 diabetes model predicts patient-level health outcomes and costs. Results. The 95% confidence intervals around life years gained gave 25% coverage when sampling uncertainty was excluded (i.e., 25% of 95% confidence intervals contained the "true" value). Allowing for sampling uncertainty as well as parameter uncertainty widened confidence intervals by 6.3-fold and gave 96.3% coverage. Methods adjusting for baseline risk factors that combine sampling and parameter uncertainty overcame the bias that can result from between-group baseline imbalance and gave confidence intervals around 50% wider than those just considering parameter uncertainty, with 99.8% coverage. Conclusions. Analyses extrapolating data for individual trial participants should include both sampling uncertainty and parameter uncertainty and should adjust for any imbalance in baseline covariates
Transit Timing Observations from Kepler: III. Confirmation of 4 Multiple Planet Systems by a Fourier-Domain Study of Anti-correlated Transit Timing Variations
We present a method to confirm the planetary nature of objects in systems
with multiple transiting exoplanet candidates. This method involves a
Fourier-Domain analysis of the deviations in the transit times from a constant
period that result from dynamical interactions within the system. The
combination of observed anti-correlations in the transit times and mass
constraints from dynamical stability allow us to claim the discovery of four
planetary systems Kepler-25, Kepler-26, Kepler-27, and Kepler-28, containing
eight planets and one additional planet candidate.Comment: Accepted to MNRA
NLTT 41135: a field M-dwarf + brown dwarf eclipsing binary in a triple system, discovered by the MEarth observatory
We report the discovery of an eclipsing companion to NLTT 41135, a nearby M5
dwarf that was already known to have a wider, slightly more massive common
proper motion companion, NLTT 41136, at 2.4 arcsec separation. Analysis of
combined-light and radial velocity curves of the system indicates that NLTT
41135B is a 31-34 +/- 3 MJup brown dwarf (where the range depends on the
unknown metallicity of the host star) on a circular orbit. The visual M-dwarf
pair appears to be physically bound, so the system forms a hierarchical triple,
with masses approximately in the ratio 8:6:1. The eclipses are grazing,
preventing an unambiguous measurement of the secondary radius, but follow-up
observations of the secondary eclipse (e.g. with the James Webb Space
Telescope) could permit measurements of the surface brightness ratio between
the two objects, and thus place constraints on models of brown dwarfs.Comment: 15 pages, 6 figures, 10 tables, emulateapj format. Accepted for
publication in Ap
SPECULOOS exoplanet search and its prototype on TRAPPIST
One of the most significant goals of modern science is establishing whether
life exists around other suns. The most direct path towards its achievement is
the detection and atmospheric characterization of terrestrial exoplanets with
potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs),
i.e. very-low-mass stars and brown dwarfs with effective temperatures lower
than 2700 K, represent a unique opportunity to reach this goal within the next
decade. The potential of the transit method for detecting potentially habitable
Earth-sized planets around these objects is drastically increased compared to
Earth-Sun analogs. Furthermore, only a terrestrial planet transiting a nearby
UCD would be amenable for a thorough atmospheric characterization, including
the search for possible biosignatures, with near-future facilities such as the
James Webb Space Telescope. In this chapter, we first describe the physical
properties of UCDs as well as the unique potential they offer for the detection
of potentially habitable Earth-sized planets suitable for atmospheric
characterization. Then, we present the SPECULOOS ground-based transit survey,
that will search for Earth-sized planets transiting the nearest UCDs, as well
as its prototype survey on the TRAPPIST telescopes. We conclude by discussing
the prospects offered by the recent detection by this prototype survey of a
system of seven temperate Earth-sized planets transiting a nearby UCD,
TRAPPIST-1.Comment: Submitted as a chapter in the "Handbook of Exoplanets" (editors: H.
Deeg & J.A. Belmonte; Section Editor: N. Narita). 16 pages, 4 figure
A Precise Estimate of the Radius of the Exoplanet HD 149026b from Spitzer Photometry
We present Spitzer 8 micron transit observations of the extrasolar planet HD
149026b. At this wavelength, transit light curves are weakly affected by
stellar limb-darkening, allowing for a simpler and more accurate determination
of planetary parameters. We measure a planet-star radius ratio of Rp/Rs =
0.05158 +/- 0.00077, and in combination with ground-based data and independent
constraints on the stellar mass and radius, we derive an orbital inclination of
i = 85.4 +0.9/-0.8 degrees and a planet radius of Rp = 0.755 +/- 0.040 R_jup.
These measurements further support models in which the planet is greatly
enriched in heavy elements.Comment: 18 pages, 4 figures, accepted to Ap
Type 2 diabetes impairs venous, but not arterial smooth muscle cell function: possible role of differential RhoA activity.
Coronary heart disease is the leading cause of morbidity in patients with type 2 diabetes mellitus (T2DM), frequently resulting in a requirement for coronary revascularization using the internal mammary artery (IMA) or saphenous vein (SV). Patency rates of SV grafts are inferior to IMA and further impaired by T2DM whilst IMA patencies appear similar in both populations. Smooth muscle cells (SMC) play a pivotal role in graft integration; we therefore examined the phenotype and proliferative function of IMA- and SV-SMC isolated from non-diabetic (ND) patients or those diagnosed with T2DM
- …