127 research outputs found
On the heat redistribution of the hot transiting exoplanet WASP-18b
The energy deposition and redistribution in hot Jupiter atmospheres is not
well understood currently, but is a major factor for their evolution and
survival. We present a time dependent radiative transfer model for the
atmosphere of WASP-18b which is a massive (10 MJup) hot Jupiter (Teq ~ 2400 K)
exoplanet orbiting an F6V star with an orbital period of only 0.94 days. Our
model includes a simplified parametrisation of the day-to-night energy
redistribution by a modulation of the stellar heating mimicking a solid body
rotation of the atmosphere. We present the cases with either no rotation at all
with respect to the synchronously rotating reference frame or a fast
differential rotation. The results of the model are compared to previous
observations of secondary eclipses of Nymeyer et al. (2011) with the Spitzer
Space Telescope. Their observed planetary flux suggests that the efficiency of
heat distribution from the day-side to the night-side of the planet is
extremely inefficient. Our results are consistent with the fact that such large
day-side fluxes can be obtained only if there is no rotation of the atmosphere.
Additionally, we infer light curves of the planet for a full orbit in the two
Warm Spitzer bandpassses for the two cases of rotation and discuss the
observational differences.Comment: 4 figures, accepted for publication in Icaru
The contribution of the major planet search surveys to EChO target selection
The EChO core science will be based on a three tier survey, each with
increasing sensitivity, in order to study the population of exo-planets from
super-Earths to Jupiter-like planets, in the very hot to temperate zones
(temperatures of 300 K - 3000 K) of F to M-type host stars. To achieve a
meaningful outcome an accurate selection of the target sample is needed. In
this paper we analyse the targets, suitable for EChO observations, expected to
result from a sample of present and forthcoming detection surveys. Exoplanets
currently known are already sufficient to provide a large and diverse sample.
However we expect the results from these surveys to increase the sample of
smaller planets that will allow us to optimize the EChO sample selection.Comment: Submitted to Experimental Astronom
BEBOP III. Observations and an independent mass measurement of Kepler-16 (AB) b - the first circumbinary planet detected with radial velocities
The radial velocity method is amongst the most robust and most established means of detecting exoplanets. Yet, it has so far failed to detect circumbinary planets despite their relatively high occurrence rates. Here, we report velocimetric measurements of Kepler-16A, obtained with the SOPHIE spectrograph, at the Observatoire de Haute-Provence’s 193cm telescope, collected during the BEBOP survey for circumbinary planets. Our measurements mark the first radial velocity detection of a circumbinary planet, independently determining the mass of Kepler-16 (AB) b to be 0.313±0.039MJup?, a value in agreement with eclipse timing variations. Our observations demonstrate the capability to achieve photon-noise precision and accuracy on single-lined binaries, with our final precision reaching 1.5 ms-1 on the binary and planetary signals. Our analysis paves the way for more circumbinary planet detections using radial velocities which will increase the relatively small sample of currently known systems to statistically relevant numbers, using a method that also provides weaker detection biases. Our data also contain a long-term radial velocity signal, which we associate with the magnetic cycle of the primary star
Examining the orbital decay targets KELT-9 b, KELT-16 b, and WASP-4 b, and the transit-timing variations of HD 97658 b
Context. Tidal orbital decay is suspected to occur for hot Jupiters in particular, with the only observationally confirmed case of this being WASP-12b. By examining this effect, information on the properties of the host star can be obtained using the so-called stellar modified tidal quality factor Q*', which describes the efficiency with which the kinetic energy of the planet is dissipated within the star. This can provide information about the interior of the star.Aims. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16, and WASP-4 systems in order to find evidence for or against the presence of tidal orbital decay. With this, we want to constrain the Q*' value for each star. In addition, we aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period.Methods. Making use of newly acquired photometric observations from CHEOPS (CHaracterising ExOplanet Satellite) and TESS (Transiting Exoplanet Survey Satellite), combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models to the data, namely a constant-period model, an orbital-decay model, and an apsidal-precession model.Results. We find that the KELT-9 system is best described by an apsidal-precession model for now, with an orbital decay trend at over 2 s being a possible solution as well. A Keplerian orbit model with a constant orbital period provides the best fit to the transit timings of KELT-16 b because of the scatter and scale of their error bars. The WASP-4 system is best represented by an orbital decay model at a 5 s significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data
Period and amplitude variations in post-common-envelope eclipsing binaries observed with SuperWASP
Period or amplitude variations in eclipsing binaries may reveal the presence of additional massive bodies in the system, such as circumbinary planets. Here, we have studied twelve previously-known eclipsing post-common-envelope binaries for evidence of such light curve variations, on the basis of multi-year observations in the SuperWASP archive. The results for HW Vir provided strong evidence for period changes consistent with those measured by previous studies, and help support a two-planet model for the system. ASAS J102322-3737.0 exhibited plausible evidence for a period increase not previously suggested; while NY Vir, QS Vir and NSVS 14256825 afforded less significant support for period change, providing some confirmation to earlier claims. In other cases, period change was not convincingly observed; for AA Dor and NSVS 07826147, previous findings of constant period were confirmed. This study allows us to present hundreds of new primary eclipse timings for these systems, and further demonstrates the value of wide-field high-cadence surveys like SuperWASP for the investigation of variable stars
The EBLM Project—From False Positives to Benchmark Stars and Circumbinary Exoplanets
The EBLM project aims to characterise very-low-mass stars that are companions to solar-type stars in eclipsing binaries. We describe the history and motivation for this project, the methodology we use to obtain the precise mass, radius, and effective temperature estimates for very-low-mass M dwarfs, and review the results of the EBLM study and those from related projects. We show that radius inflation in fully convective stars is a more subtle effect than what was previously thought based on less precise measurements, i.e., the mass–radius–effective temperature relations we observe for fully convective stars in single-line eclipsing binaries show reasonable agreement with the theoretical models, particularly if we account for the M-dwarf metallicity, as inferred from the analysis of the primary star spectrum.<br/
The TESS light curve of the eccentric eclipsing binary 1SWASP J011351.29+314909.7 -- no evidence for a very hot M-dwarf companion
A 2014 study of the eclipsing binary star 1SWASPJ011351.29+314909.7
(J0113+31) reported an unexpectedly high effective temperature for the M-dwarf
companion to the 0.95-M primary star. The effective temperature
inferred from the secondary eclipse depth was 600 K higher than the value
predicted from stellar models. Such an anomalous result questions our
understanding of low-mass stars and might indicate a significant uncertainty
when inferring properties of exoplanets orbiting them. We seek to measure the
effective temperature of the M-dwarf companion using the light curve of
J0113+31 recently observed by the Transiting Exoplanet Survey Satellite (TESS).
We use the pycheops modelling software to fit a combined transit and eclipse
model to the TESS light curve. To calculate the secondary effective
temperature, we compare the best-fit eclipse depth to the predicted eclipse
depths from theoretical stellar models. We determined the effective temperature
of the M dwarf to be = 3208 43 K, assuming = 5, [Fe/H] = and no alpha-element enhancement. Varying these
assumptions changes by less than 100 K. These results do
not support a large anomaly between observed and theoretical low-mass star
temperatures.Comment: 5 pages, 3 figures, published in MNRA
Substellar companions and the formation of hot subdwarf stars
"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics."We give a brief review over the observational evidence for close substellar companions to hot subdwarf stars. The formation of these core helium-burning objects requires huge mass loss of their red giant progenitors. It has been suggested that besides stellar companions substellar objects in close orbits may be able to trigger this mass loss. Such objects can be easily detected around hot subdwarf stars by medium or high resolution spectroscopy with an RV accuracy at the km s(-1)-level. Eclipsing systems of Vir type stick out of transit surveys because of their characteristic light curves. The best evidence that substellar objects in close orbits around sdBs exist and that they are able to trigger the required mass loss is provided by the eclipsing system SDSS J0820+0008, which was found in the course of the MUCHFUSS project. Furthermore, several candidate systems have been discovered.Final Accepted Versio
WASP-80b has a dayside within the T-dwarf range
AHMJT is a Swiss National Science Foundation (SNSF) fellow under grant number P300P2-147773. MG and EJ are Research Associates at the F.R.S-FNRS; LD received the support the support of the F.R.I.A. fund of the FNRS. DE, KH, and SU acknowledge the financial support of the SNSF in the frame of the National Centre for Competence in Research ‘PlanetS’. EH and IR acknowledge support from the Spanish Ministry of Economy and Competitiveness (MINECO) and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER) through grants AYA2012-39612-C03-01 and ESP2013-48391-C4-1-R.WASP-80b is a missing link in the study of exo-atmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterisation, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer. Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 m Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L-T transition, our results would imply this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour-magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, like brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter-McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated. [abridged]Publisher PDFPeer reviewe
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