2,362 research outputs found
Spitzer Infrared Observations and Independent Validation of the Transiting Super-Earth CoRoT-7b
The detection and characterization of the first transiting super-Earth,
CoRoT-7 b, has required an unprecedented effort in terms of telescope time and
analysis. Although the star does display a radial velocity signal at the period
of the planet, this has been difficult to disentangle from the intrinsic
stellar variability, and pinning down the velocity amplitude has been very
challenging. As a result, the precise value of the mass of the planet - and
even the extent to which it can be considered to be confirmed - have been
debated in the recent literature, with six mass measurements published so far
based on the same spectroscopic observations, ranging from about 2 to 8 Earth
masses. Here we report on an independent validation of the planet discovery,
using one of the fundamental properties of a transit signal: its achromaticity.
We observed four transits of CoRoT-7 b with Spitzer, in order to determine
whether the depth of the transit signal in the near-infrared is consistent with
that observed in the CoRoT bandpass, as expected for a planet. We detected the
transit and found an average depth of 0.426 {\pm} 0.115 mmag at 4.5 {\mu}m,
which is in good agreement with the depth of 0.350 {\pm} 0.011 mmag found by
CoRoT. These observations place important constraints on the kinds of
astrophysical false positives that could mimic the signal. Combining this with
additional constraints reported earlier, we performed an exhaustive exploration
of possible blends scenarios for CoRoT-7 b using the BLENDER technique. We are
able to rule out the vast majority of false positives, and the remaining ones
are found to be much less likely than a true transiting planet. We thus
validate CoRoT-7 b as a bona-fide planet with a very high degree of confidence,
independently of any radial-velocity information. Our Spitzer observations have
additionally allowed us to significantly improve the ephemeris of the planet.Comment: Accepted by Ap
The first radial velocity measurements of a microlensing event: no evidence for the predicted binary
The gravitational microlensing technique allows the discovery of exoplanets
around stars distributed in the disk of the galaxy towards the bulge. However,
the alignment of two stars that led to the discovery is unique over the
timescale of a human life and cannot be re-observed. Moreover, the target host
is often very faint and located in a crowded region. These difficulties hamper
and often make impossible the follow-up of the target and study of its possible
companions. Gould et al. (2013) predicted the radial-velocity curve of a binary
system, OGLE-2011-BLG-0417, discovered and characterised from a microlensing
event by Shin et al. (2012). We used the UVES spectrograph mounted at the VLT,
ESO to derive precise radial-velocity measurements of OGLE-2011-BLG-0417. To
gather high-precision on faint targets of microlensing events, we proposed to
use the source star as a reference to measure the lens radial velocities. We
obtained ten radial velocities on the putative V=18 lens with a dispersion of
~100 m/s, spread over one year. Our measurements do not confirm the
microlensing prediction for this binary system. The most likely scenario is
that the assumed V=18 mag lens is actually a blend and not the primary lens
that is 2 magnitude fainter. Further observations and analyses are needed to
understand the microlensing observation and infer on the nature and
characteristics of the lens itself.Comment: submitted on 3rd June 2015 to A&ALette
Fluctuation effects in ternary AB+A+B polymeric emulsions
We present a Monte Carlo approach to incorporating the effect of thermal
fluctuations in field theories of polymeric fluids. This method is applied to a
field-theoretic model of a ternary blend of AB diblock copolymers with A and B
homopolymers. We find a shift in the line of order-disorder transitions from
their mean-field values, as well as strong signatures of the existence of a
bicontinuous microemulsion phase in the vicinity of the mean-field Lifshitz
critical point. This is in qualitative agreement with a recent series of
experiments conducted with various three-dimensional realizations of this model
system. Further, we also compare our results and the performance of the
presently proposed simulation method to that of an alternative method involving
the integration of complex Langevin dynamical equations.Comment: minor changes, references adde
WASP-23b: a transiting hot Jupiter around a K dwarf and its Rossiter-McLaughlin effect
We report the discovery of a new transiting planet in the Southern
Hemisphere. It has been found by the WASP-south transit survey and confirmed
photometrically and spectroscopically by the 1.2m Swiss Euler telescope, LCOGT
2m Faulkes South Telescope, the 60 cm TRAPPIST telescope and the ESO 3.6m
telescope. The orbital period of the planet is 2.94 days. We find it is a gas
giant with a mass of 0.88 \pm 0.10 Mj and a radius estimated at 0.96 \pm 0.05
Rj . We have also obtained spectra during transit with the HARPS spectrograph
and detect the Rossiter-McLaughlin effect despite its small amplitude. Because
of the low signal to noise of the effect and of a small impact parameter we
cannot place a constraint on the projected spin-orbit angle. We find two
confiicting values for the stellar rotation. Our determination, via spectral
line broadening gives v sin I = 2.2 \pm 0.3 km/s, while another method, based
on the activity level using the index log R'HK, gives an equatorial rotation
velocity of only v = 1.35 \pm 0.20 km/s. Using these as priors in our analysis,
the planet could either be misaligned or aligned. This should send strong
warnings regarding the use of such priors. There is no evidence for
eccentricity nor of any radial velocity drift with time.Comment: 13 pages, 8 figures, 7 tables, accepted for publication in A&
Threshold Regression for Survival Analysis: Modeling Event Times by a Stochastic Process Reaching a Boundary
Many researchers have investigated first hitting times as models for survival
data. First hitting times arise naturally in many types of stochastic
processes, ranging from Wiener processes to Markov chains. In a survival
context, the state of the underlying process represents the strength of an item
or the health of an individual. The item fails or the individual experiences a
clinical endpoint when the process reaches an adverse threshold state for the
first time. The time scale can be calendar time or some other operational
measure of degradation or disease progression. In many applications, the
process is latent (i.e., unobservable). Threshold regression refers to
first-hitting-time models with regression structures that accommodate covariate
data. The parameters of the process, threshold state and time scale may depend
on the covariates. This paper reviews aspects of this topic and discusses
fruitful avenues for future research.Comment: Published at http://dx.doi.org/10.1214/088342306000000330 in the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
HAT-P-11b: A Super-Neptune Planet Transiting a Bright K Star in the Kepler Field
We report on the discovery of HAT-P-11b, the smallest radius transiting
extrasolar planet (TEP) discovered from the ground, and the first hot Neptune
discovered to date by transit searches. HAT-P-11b orbits the bright (V=9.587)
and metal rich ([Fe=H] = +0.31 +/- 0.05) K4 dwarf star GSC 03561-02092 with P =
4.8878162 +/- 0.0000071 days and produces a transit signal with depth of 4.2
mmag. We present a global analysis of the available photometric and
radial-velocity data that result in stellar and planetary parameters, with
simultaneous treatment of systematic variations. The planet, like its near-twin
GJ 436b, is somewhat larger than Neptune (17Mearth, 3.8Rearth) both in mass Mp
= 0.081 +/- 0.009 MJ (25.8 +/- 2.9 Mearth) and radius Rp = 0.422 +/- 0.014 RJ
(4.73 +/- 0.16 Rearth). HAT-P-11b orbits in an eccentric orbit with e = 0.198
+/- 0.046 and omega = 355.2 +/- 17.3, causing a reflex motion of its parent
star with amplitude 11.6 +/- 1.2 m/s, a challenging detection due to the high
level of chromospheric activity of the parent star. Our ephemeris for the
transit events is Tc = 2454605.89132 +/- 0.00032 (BJD), with duration 0.0957
+/- 0.0012 d, and secondary eclipse epoch of 2454608.96 +/- 0.15 d (BJD). The
basic stellar parameters of the host star are M* = 0.809+0.020-0.027 Msun, R* =
0.752 +/- 0.021 Rsun and Teff = 4780 +/- 50 K. Importantly, HAT-P-11 will lie
on one of the detectors of the forthcoming Kepler mission. We discuss an
interesting constraint on the eccentricity of the system by the transit light
curve and stellar parameters. We also present a blend analysis, that for the
first time treats the case of a blended transiting hot Jupiter mimicing a
transiting hot Neptune, and proves that HAT-P-11b is not such a blend.Comment: Accepted for publication in ApJ, 24 pages, 14 figures, 6 tables. All
RV data presented in this versio
The SOPHIE search for northern extrasolar planets VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions
Long-period brown dwarf companions detected in radial velocity surveys are
important targets for direct imaging and astrometry to calibrate the
mass-luminosity relation of substellar objects. Through a 20-year radial
velocity monitoring of solar-type stars that began with ELODIE and was extended
with SOPHIE spectrographs, giant exoplanets and brown dwarfs with orbital
periods longer than ten years are discovered. We report the detection of five
new potential brown dwarfs with minimum masses between 32 and 83 Jupiter mass
orbiting solar-type stars with periods longer than ten years. An upper mass
limit of these companions is provided using astrometric Hipparcos data,
high-angular resolution imaging made with PUEO, and a deep analysis of the
cross-correlation function of the main stellar spectra to search for blend
effects or faint secondary components. These objects double the number of known
brown dwarf companions with orbital periods longer than ten years and reinforce
the conclusion that the occurrence of such objects increases with orbital
separation. With a projected separation larger than 100 mas, all these brown
dwarf candidates are appropriate targets for high-contrast and high angular
resolution imaging.Comment: 17 pages, 9 figures, accepted in A&
An ingress and a complete transit of HD 80606 b
We have used four telescopes at different longitudes to obtain
near-continuous lightcurve coverage of the star HD 80606 as it was transited by
its \sim 4-MJup planet. The observations were performed during the predicted
transit windows around the 25th of October 2008 and the 14th of February 2009.
Our data set is unique in that it simultaneously constrains the duration of the
transit and the planet's period. Our Markov-Chain Monte Carlo analysis of the
light curves, combined with constraints from radial-velocity data, yields
system parameters consistent with previously reported values. We find a
planet-to-star radius ratio marginally smaller than previously reported,
corresponding to a planet radius of Rp = 0.921 \pm 0.036RJup .Comment: 6 pages, 2 figures, MNRAS accepte
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