Showing papers by "Suzanne Aigrain published in 2011"
University of Exeter1, University of Oxford2, Harvard University3, Space Telescope Science Institute4, Tennessee State University5, University of California, Berkeley6, Institut d'Astrophysique de Paris7, Tel Aviv University8, University of California, Santa Barbara9, Las Cumbres Observatory Global Telescope Network10
TL;DR: In this article, the authors used time series spectra obtained during two transit events to determine the wavelength dependence of the planetary radius and measure the exoplanet's atmospheric transmission spectrum for the first time over this wavelength range.
Abstract: We present Hubble Space Telescope (HST) optical and near-ultraviolet transmission spectra of the transiting hot Jupiter HD 189733b, taken with the repaired Space Telescope Imaging Spectrograph (STIS) instrument. The resulting spectra cover the range 2900–5700 A and reach per exposure signal-to-noise ratio levels greater than 11 000 within a 500-A bandwidth. We used time series spectra obtained during two transit events to determine the wavelength dependence of the planetary radius and measure the exoplanet’s atmospheric transmission spectrum for the first time over this wavelength range. Our measurements, in conjunction with existing HST spectra, now provide a broad-band transmission spectrum covering the full optical regime. The STIS data also show unambiguous evidence of a large occulted stellar spot during one of our transit events, which we use to place constraints on the characteristics of the K dwarf’s stellar spots, estimating spot temperatures around T eff ∼ 4250 K. With contemporaneous ground-based photometric monitoring of the stellar variability, we also measure the correlation between the stellar activity level and transit-measured planet-to-star radius contrast, which is in good agreement with predictions. We find a planetary transmission spectrum in good agreement with that of Rayleigh scattering from a high-altitude atmospheric haze as previously found from HST Advanced Camera for Surveys. The high-altitude haze is now found to cover the entire optical regime and is well characterized by Rayleigh scattering. These findings suggest that haze may be a globally dominant atmospheric feature of the planet which would result in a high optical albedo at shorter optical wavelengths.
412 citations
TL;DR: In this article, the authors used time series spectra obtained during two transit events to determine the wavelength dependance of the planetary radius and measure the exoplanet's atmospheric transmission spectrum for the first time over this wavelength range.
Abstract: We present Hubble Space Telescope optical and near-ultraviolet transmission spectra of the transiting hot-Jupiter HD189733b, taken with the repaired Space Telescope Imaging Spectrograph (STIS) instrument. The resulting spectra cover the range 2900-5700 Ang and reach per-exposure signal-to-noise levels greater than 11,000 within a 500 Ang bandwidth. We used time series spectra obtained during two transit events to determine the wavelength dependance of the planetary radius and measure the exoplanet's atmospheric transmission spectrum for the first time over this wavelength range. Our measurements, in conjunction with existing HST spectra, now provide a broadband transmission spectrum covering the full optical regime. The STIS data also shows unambiguous evidence of a large occulted stellar spot during one of our transit events, which we use to place constraints on the characteristics of the K dwarf's stellar spots, estimating spot temperatures around Teff~4250 K. With contemporaneous ground-based photometric monitoring of the stellar variability, we also measure the correlation between the stellar activity level and transit-measured planet-to-star radius contrast, which is in good agreement with predictions. We find a planetary transmission spectrum in good agreement with that of Rayleigh scattering from a high-altitude atmospheric haze as previously found from HST ACS camera. The high-altitude haze is now found to cover the entire optical regime and is well characterised by Rayleigh scattering. These findings suggest that haze may be a globally dominant atmospheric feature of the planet which would result in a high optical albedo at shorter optical wavelengths.
355 citations
TL;DR: In this paper, the authors present a re-analysis of archival HST/NICMOS transmission spectroscopy of three exoplanet systems: HD 189733, GJ-436 and XO-1.
Abstract: We present a re-analysis of archival HST/NICMOS transmission spectroscopy of three exoplanet systems: HD 189733, GJ-436 and XO-1. Detections of several molecules, including H 2 O, CH 4 and CO 2 , have been claimed for HD 189733 and XO-1, but similarly sized features are attributed to systematic noise for GJ-436. The data consist of time-series grism spectra covering a planetary transit. After extracting light curves in independent wavelength channels, we use a linear decorrelation technique to account for instrumental systematics (which is becoming standard in the field), and measure the planet-to-star radius ratio as a function of wavelength. We use a residual permutation algorithm to calculate the uncertainties, in an effort to evaluate the effects of systematic noise on the resulting transmission spectra. For HD 189733, the uncertainties in the transmission spectrum are significantly larger than those previously reported. We also find that the transmission spectrum is considerably altered when using different out-of-transit orbits to remove the systematics, when some parameters are left out of the decorrelation procedure, or when we perform the decorrelation with quadratic functions rather than linear functions. Given that there is no physical reason to believe that the baseline flux should be modelled as a linear function of any particular set of parameters, we interpret this as evidence that the linear decorrelation technique is not a robust method to remove systematic effects from the light curves for each wavelength channel. For XO-1, the parameters measured to decorrelate the light curves would require extrapolation to the in-transit orbit to remove the systematics, and we cannot reproduce the previously reported results. We conclude that the resulting NICMOS transmission spectra are too dependent on the method used to remove systematics to be considered robust detections of molecular species in planetary atmospheres, although the presence of these molecules is not ruled out.
153 citations
Institut d'Astrophysique de Paris1, University of Nice Sophia Antipolis2, University of Cologne3, University of Texas at Austin4, University of La Laguna5, University of Geneva6, Paris Diderot University7, University of Paris8, German Aerospace Center9, University of Vienna10, University of São Paulo11, European Space Research and Technology Centre12, University of Liège13, Austrian Academy of Sciences14, Tel Aviv University15
TL;DR: In this paper, the discovery of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days was reported, which is the second transiting companion lying in the theoretical mass domain of brown dwarfs.
Abstract: We report the discovery by the CoRoT space mission of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a radius of 1.12 R Jup and a mass of 63.3 ± 4.1 M Jup , and is thus the second transiting companion lying in the theoretical mass domain of brown dwarfs. CoRoT-15b is either very young or inflated compared to standard evolution models, a situation similar to that of M-dwarf stars orbiting close to solar-typestars. Spectroscopic constraints and an analysis of the lightcurve imply a spin period in the range 2.9–3.1 days for the central star, which is compatible with a double-synchronisation of the system.
119 citations
TL;DR: In this article, the authors revisited the published HARPS radial velocity measurements of the object, which were previously used to estimate the companion mass, but have been the subject of ongoing debate.
Abstract: CoRoT-7 is an 11 th magnitude K-star whose light curve shows transits with depth of 0.3 mmag and a period of 0:854 d, superimposed on variability at the 1% level, due to the modulation of evolving active regions with the star’s 23 d rotation period. In this paper, we revisit the published HARPS radial velocity measurements of the object, which were previously used to estimate the companion mass, but have been the subject of ongoing debate. We build a realistic model of the star’s activity during the HARPS observations, by tting simultaneously the line width (as measured by the width of the cross-correlation function) and the line bisector, and use it to evaluate the contribution of activity to the RV variations. The data show clear evidence of errors above the level of the formal uncertainties, which are accounted for neither by activity, nor by any plausible planet model, and which increase rapidly with decreasing signal-to-noise of the spectra. We cite evidence of similar systematics in mid-SNR spectra of other targets obtained with HARPS and other high-precision RV spectrographs, and discuss possible sources. Allowing for these, we re-evaluate the semi-amplitude of the CoRoT-7b signal, nding Kb = 1:6 1:3 m s 1 , a tentative detection with a much reduced signicance (1.2sigma) compared to previous estimates. We also argue that the combined presence of activity and additional errors preclude a meaningful search for additional low-mass companions, despite previous claims to the contrary. Taken at face value, our analysis points to a lower density for CoRoT-7b, the 1 mass range spanning 1{4MEarth, and allowing for a wide range of bulk compositions. In particular, an ice-rich composition is compatible with the RV constraints. More generally, this study highlights the importance of a realistic treatment of both activity and uncertainties, particularly in the medium signal-to-noise ratio regime, which applies to most small planet candidates from CoRoT and Kepler.
94 citations
TL;DR: In this article, the photospheric activity of the star CoRoT-6 with a period of 8.886 days was modeled using a maximum entropy spot model to fit the optical modulation as observed by CoRoTs during an uninterrupted interval of similar to 140 days.
Abstract: Context. The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9 main-sequence star called CoRoT-6 with a period of 8.886 days. Aims. We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction. Methods. We apply a maximum entropy spot model to fit the optical modulation as observed by CoRoT during a uninterrupted interval of similar to 140 days. Photospheric active regions are assumed to consist of spots and faculae in a fixed proportion with solar-like contrasts. Results. Individual active regions have lifetimes up to 30-40 days. Most of them form and decay within five active longitudes whose different migration rates are attributed to the stellar differential rotation for which a lower limit of Delta Omega/Omega = 0.12 +/- 0.02 is obtained. Several active regions show a maximum of activity at a longitude lagging the subplanetary point by similar to 200 degrees with the probability of a chance occurrence being smaller than 1 percent. Conclusions. Our spot modelling indicates that the photospheric activity of CoRoT-6 could be partially modulated by some kind of star-planet magnetic interaction, while an interaction related to tides is highly unlikely because of the weakness of the tidal force.
57 citations
TL;DR: The CoRoT-20b is a super-dense giant planet with a mass of 4.24 +/- 0.23 MJ and a radius of 0.87 +/- 1.10 g/cm^3 as mentioned in this paper.
Abstract: We report the discovery by the CoRoT space mission of a new giant planet, CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/- 0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most compact planets known so far. Evolution models for the planet suggest a mass of heavy elements of the order of 800 ME if embedded in a central core, requiring a revision either of the planet formation models or of planet evolution and structure models. We note however that smaller amounts of heavy elements are expected from more realistic models in which they are mixed throughout the envelope. The planet orbits a G-type star with an orbital period of 9.24 days and an eccentricity of 0.56. The star's projected rotational velocity is vsini = 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its axis of rotation is perpendicular to the orbital plane. In the framework of Darwinian theories and neglecting stellar magnetic breaking, we calculate the tidal evolution of the system and show that CoRoT-20b is presently one of the very few Darwin-stable planets that is evolving towards a triple synchronous state with equality of the orbital, planetary and stellar spin periods.
54 citations
TL;DR: In this article, a simple spot model is proposed to predict activity-induced radial velocity variations using high-precision time-series photometry, which can reproduce variations well below the m/s level and show that RV amplitudes above that level may be expected for approximately two thirds of the candidates.
Abstract: We present a new, simple method to predict activity-induced radial velocity variations using high-precision time-series photometry. It is based on insights from a simple spot model, has only two free parameters (one of which can be estimated from the light curve) and does not require knowledge of the stellar rotation period. We test the method on simulated data and illustrate its performance by applying it to MOST/SOPHIE observations of the planet host-star HD189733, where it gives almost identical results to much more sophisticated, but highly degenerate models, and synthetic data for the Sun, where we demonstrate that it can reproduce variations well below the m/s level. We also apply it to Quarter 1 data for Kepler transit candidate host stars, where it can be used to estimate RV variations down to the 2-3m/s level, and show that RV amplitudes above that level may be expected for approximately two thirds of the candidates we examined.
48 citations
Institut d'Astrophysique de Paris1, University of Geneva2, European Space Agency3, Tel Aviv University4, Spanish National Research Council5, Janssen Pharmaceutica6, University of Paris7, German Aerospace Center8, University of Cologne9, University of Vienna10, University of São Paulo11, University of Liège12, Austrian Academy of Sciences13, Paris Diderot University14
TL;DR: In this paper, a massive hot jupiter was detected transiting in front of its host star with a period of 1.9000693 +/- 0.0000028 days, which is the Rossiter-McLaughlin anomaly in the CoRoT-18 system.
Abstract: We report the detection of CoRoT-18b, a massive hot jupiter transiting in front of its host star with a period of 1.9000693 +/- 0.0000028 days. This planet was discovered thanks to photometric data secured with the CoRoT satellite combined with spectroscopic and photometric ground-based follow-up observations. The planet has a mass M_p = 3.47 +/- 0.38 M_Jup, a radius R_p = 1.31 +/- 0.18 R_Jup, and a density rho_p = 2.2 +/- 0.8 g/cm3. It orbits a G9V star with a mass M_* = 0.95 +/- 0.15 M_Sun, a radius R_* = 1.00 +/- 0.13 R_Sun, and a rotation period P_rot = 5.4 +/- 0.4 days. The age of the system remains uncertain, with stellar evolution models pointing either to a few tens Ma or several Ga, while gyrochronology and lithium abundance point towards ages of a few hundred Ma. This mismatch potentially points to a problem in our understanding of the evolution of young stars, with possibly significant implications for stellar physics and the interpretation of inferred sizes of exoplanets around young stars. We detected the Rossiter-McLaughlin anomaly in the CoRoT-18 system thanks to the spectroscopic observation of a transit. We measured the obliquity psi = 20 +/- 20 degrees (sky-projected value: lambda = -10 +/- 20 degrees), indicating that the planet orbits in the same way as the star is rotating and that this prograde orbit is nearly aligned with the stellar equator.
47 citations
TL;DR: A hot Jupiter-type exoplanet, CoRoT-17b, was detected by the coRoT satellite as discussed by the authors, which has a mass of $2.43\pm 0.30$\Mjup and a radius of $1.02\pm0.07$\Rjup.
Abstract: We report on the discovery of a hot Jupiter-type exoplanet, CoRoT-17b, detected by the CoRoT satellite. It has a mass of $2.43\pm0.30$\Mjup and a radius of $1.02\pm0.07$\Rjup, while its mean density is $2.82\pm0.38$ g/cm$^3$. CoRoT-17b is in a circular orbit with a period of $3.7681\pm0.0003$ days. The host star is an old ($10.7\pm1.0$ Gyr) main-sequence star, which makes it an intriguing object for planetary evolution studies. The planet's internal composition is not well constrained and can range from pure H/He to one that can contain $\sim$380 earth masses of heavier elements.
42 citations
German Aerospace Center1, Paris Diderot University2, European Space Research and Technology Centre3, University of Geneva4, University of Paris5, Institut d'Astrophysique de Paris6, University of Texas at Austin7, Spanish National Research Council8, University of Vienna9, University of São Paulo10, University of Nice Sophia Antipolis11, University of Liège12, Austrian Academy of Sciences13, Tel Aviv University14
TL;DR: A hot Jupiter-type exoplanet, CoRoT-17b, was detected by the coRoT satellite as mentioned in this paper, which has a mass of $2.43\pm 0.30$\Mjup and a radius of $1.02\pm0.07$\Rjup.
Abstract: We report on the discovery of a hot Jupiter-type exoplanet, CoRoT-17b, detected by the CoRoT satellite. It has a mass of $2.43\pm0.30$\Mjup and a radius of $1.02\pm0.07$\Rjup, while its mean density is $2.82\pm0.38$ g/cm$^3$. CoRoT-17b is in a circular orbit with a period of $3.7681\pm0.0003$ days. The host star is an old ($10.7\pm1.0$ Gyr) main-sequence star, which makes it an intriguing object for planetary evolution studies. The planet's internal composition is not well constrained and can range from pure H/He to one that can contain $\sim$380 earth masses of heavier elements.
TL;DR: In this paper, the authors presented a list of planetary transit candidates from the CoRoT LRa01 star field in the Monoceros constellation towards the Galactic anti-center towards the Earth.
Abstract: Context: CoRoT is a pioneering space mission whose primary goals are stellar seismology and extrasolar planets search. Its surveys of large stellar fields generate numerous planetary candidates whose lightcurves have transit-like features. An extensive analytical and observational follow-up effort is undertaken to classify these candidates. Aims: The list of planetary transit candidates from the CoRoT LRa01 star field in the Monoceros constellation towards the Galactic anti-center is presented. The CoRoT observations of LRa01 lasted from 24 October 2007 to 3 March 2008. Methods: 7470 chromatic and 3938 monochromatic lightcurves were acquired and analysed. Instrumental noise and stellar variability were treated with several filtering tools by different teams from the CoRoT community. Different transit search algorithms were applied to the lightcurves. Results: Fifty-one stars were classified as planetary transit candidates in LRa01. Thirty-seven (i.e., 73 % of all candidates) are "good" planetary candidates based on photometric analysis only. Thirty-two (i.e., 87 % of the "good" candidates) have been followed-up. At the time of this writing twenty-two cases have been solved and five planets have been discovered: three transiting hot-Jupiters (CoRoT-5b, CoRoT-12b, and CoRoT-21b), the first terrestrial transiting planet (CoRoT-7b), and another planet in the same system (CoRoT-7c, detected by radial velocity survey only). Evidences of another non-transiting planet in the CoRoT-7 system, namely CoRoT-7d, have been recently found.
Spanish National Research Council1, University of Texas at Austin2, University of Geneva3, Tel Aviv University4, Paris Diderot University5, University of Paris-Sud6, Institut d'Astrophysique de Paris7, European Space Research and Technology Centre8, University of Cologne9, German Aerospace Center10, University of Vienna11, University of São Paulo12, Austrian Academy of Sciences13
TL;DR: In this paper, the CoRoT Exoplanet Science Team announces its 14th discovery, a hot Jupiter with a mass of 7.6 ± 0.6 Jupiter masses orbiting a solar-type star (F9V) with a period of only 1.5 d, less than 5 stellar radii from its parent star.
Abstract: In this paper, the CoRoT Exoplanet Science Team announces its 14th discovery. Herein, we discuss the observations and analyses that allowed us to derive the parameters of this system: a hot Jupiter with a mass of 7.6 ± 0.6 Jupiter masses orbiting a solar-type star (F9V) with a period of only 1.5 d, less than 5 stellar radii from its parent star. It is unusual for such a massive planet to have such a small orbit: only one other known higher mass exoplanet orbits with a shorter period.
TL;DR: In this paper, the CoRoT Exoplanet Science Team announces its 14th discovery, a hot Jupiter with a mass of $7.6 \pm 0.6$ orbiting a solar-type star (F9V) with a period of only 1.5 d, less than 5 stellar radii from its parent star.
Abstract: In this paper, the CoRoT Exoplanet Science Team announces its 14th discovery. Herein, we discuss the observations and analyses that allowed us to derive the parameters of this system: a hot Jupiter with a mass of $7.6 \pm 0.6$ Jupiter masses orbiting a solar-type star (F9V) with a period of only 1.5 d, less than 5 stellar radii from its parent star. It is unusual for such a massive planet to have such a small orbit: only one other known exoplanet with a higher mass orbits with a shorter period.
Aix-Marseille University1, Institut d'Astrophysique de Paris2, Tel Aviv University3, Paris Diderot University4, German Aerospace Center5, University of Geneva6, Spanish National Research Council7, University of Paris-Sud8, Aarhus University9, University of Cologne10, European Space Research and Technology Centre11, University of La Laguna12, University of Göttingen13, University of Vienna14, University of São Paulo15, University of Liège16, Austrian Academy of Sciences17, Technical University of Berlin18
TL;DR: In this paper, the authors reported the discovery of CoRoT-19b, a gas-giant planet transiting an old, inactive F9V-type star with a period of four days.
Abstract: Observations of transiting extrasolar planets are of key importance to our understanding of planets because their mass, radius, and mass density can be determined. The CoRoT space mission allows us to achieve a very high photometric accuracy. By combining CoRoT data with high-precision radial velocity measurements, we derive precise planetary radii and masses. We report the discovery of CoRoT-19b, a gas-giant planet transiting an old, inactive F9V-type star with a period of four days. After excluding alternative physical configurations mimicking a planetary transit signal, we determine the radius and mass of the planet by combining CoRoT photometry with high-resolution spectroscopy obtained with the echelle spectrographs SOPHIE, HARPS, FIES, and SANDIFORD. To improve the precision of its ephemeris and the epoch, we observed additional transits with the TRAPPIST and Euler telescopes. Using HARPS spectra obtained during the transit, we then determine the projected angle between the spin of the star and the orbit of the planet. We find that the host star of CoRoT-19b is an inactive F9V-type star close to the end of its main-sequence life. The host star has a mass M*=1.21+/-0.05 Msun and radius R*=1.65+/-0.04 Rsun. The planet has a mass of Mp=1.11+/-0.06 Mjup and radius of Rp=1.29+/-0.03 Rjup. The resulting bulk density is only rho=0.71+/-0.06 gcm-3, which is much lower than that for Jupiter. The exoplanet CoRoT-19b is an example of a giant planet of almost the same mass as Jupiter but a 30% larger radius.
TL;DR: In this paper, the authors used achromatic properties of a transiting super-Earth, CoRoT-7 b, to determine whether the depth of the transit signal in the near-infrared is consistent with that observed in the Co RoT bandpass, as expected for a planet.
Abstract: 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.
Tel Aviv University1, University of Provence2, Institut d'Astrophysique de Paris3, University of Geneva4, European Space Research and Technology Centre5, Janssen Pharmaceutica6, University of Paris7, Spanish National Research Council8, University of São Paulo9, University of Vienna10, German Aerospace Center11, University of Liège12, University of Nice Sophia Antipolis13, Austrian Academy of Sciences14, University of Cologne15
TL;DR: The case of CoRoT LRa02_E2_0121, which was initially classified as a Neptune-size transiting-planet candidate on a relatively wide orbit of 36.3 days, was presented in this paper.
Abstract: This paper presents the case of CoRoT LRa02_E2_0121, which was initially classified as a Neptune-size transiting-planet candidate on a relatively wide orbit of 36.3 days. Follow-up observations were performed with UVES, Sandiford, SOPHIE and HARPS. These observations revealed a faint companion in the spectra. To find the true nature of the system we derived the radial velocities of the faint companion using TODMOR - a two-dimensional correlation technique, applied to the SOPHIE spectra. Modeling the lightcurve with EBAS we discovered a secondary eclipse with a depth of ~0.07%, indicating a diluted eclipsing binary. Combined MCMC modeling of the lightcurve and the radial velocities suggested that CoRoT LRa02_E2_0121 is a hierarchical triple system with an evolved G-type primary and an A-type:F-type grazing eclipsing binary. Such triple systems are difficult to discover.
Institut d'Astrophysique de Paris1, University of Geneva2, European Space Agency3, Tel Aviv University4, Spanish National Research Council5, Janssen Pharmaceutica6, University of Paris7, German Aerospace Center8, University of Cologne9, University of Vienna10, University of São Paulo11, University of Liège12, Austrian Academy of Sciences13, Paris Diderot University14
TL;DR: In this paper, a massive hot jupiter was detected transiting in front of its host star with a period of 1.9000693 +/- 0.0000028 days, which is the Rossiter-McLaughlin anomaly in the CoRoT-18 system.
Abstract: We report the detection of CoRoT-18b, a massive hot jupiter transiting in front of its host star with a period of 1.9000693 +/- 0.0000028 days. This planet was discovered thanks to photometric data secured with the CoRoT satellite combined with spectroscopic and photometric ground-based follow-up observations. The planet has a mass M_p = 3.47 +/- 0.38 M_Jup, a radius R_p = 1.31 +/- 0.18 R_Jup, and a density rho_p = 2.2 +/- 0.8 g/cm3. It orbits a G9V star with a mass M_* = 0.95 +/- 0.15 M_Sun, a radius R_* = 1.00 +/- 0.13 R_Sun, and a rotation period P_rot = 5.4 +/- 0.4 days. The age of the system remains uncertain, with stellar evolution models pointing either to a few tens Ma or several Ga, while gyrochronology and lithium abundance point towards ages of a few hundred Ma. This mismatch potentially points to a problem in our understanding of the evolution of young stars, with possibly significant implications for stellar physics and the interpretation of inferred sizes of exoplanets around young stars. We detected the Rossiter-McLaughlin anomaly in the CoRoT-18 system thanks to the spectroscopic observation of a transit. We measured the obliquity psi = 20 +/- 20 degrees (sky-projected value: lambda = -10 +/- 20 degrees), indicating that the planet orbits in the same way as the star is rotating and that this prograde orbit is nearly aligned with the stellar equator.
TL;DR: In this article, the authors proposed a method to infer transit parameters in the presence of systematic noise using Gaussian processes, a technique widely used in the machine learning community for Bayesian regression and classification problems.
Abstract: Transmission spectroscopy, which consists of measuring the wavelength-dependent absorption of starlight by a planet's atmosphere during a transit, is a powerful probe of atmospheric composition. However, the expected signal is typically orders of magnitude smaller than instrumental systematics, and the results are crucially dependent on the treatment of the latter. In this paper, we propose a new method to infer transit parameters in the presence of systematic noise using Gaussian processes, a technique widely used in the machine learning community for Bayesian regression and classification problems. Our method makes use of auxiliary information about the state of the instrument, but does so in a non-parametric manner, without imposing a specific dependence of the systematics on the instrumental parameters, and naturally allows for the correlated nature of the noise. We give an example application of the method to archival NICMOS transmission spectroscopy of the hot Jupiter HD 189733, which goes some way towards reconciling the controversy surrounding this dataset in the literature. Finally, we provide an appendix giving a general introduction to Gaussian processes for regression, in order to encourage their application to a wider range of problems.
01 Feb 2011
TL;DR: The ASTEP project (Antarctic Search for Transiting ExoPlanets) aims at testing the quality of the Dome C site for photometry in the visible, as well as detecting and characterizing transiting exoplanets.
Abstract: The ASTEP project (Antarctic Search for Transiting ExoPlanets), aims at testing the quality of the Dome C site in Antarctica for photometry in the visible, as well as detecting and characterizing transiting exoplanets. A dedicated telescope, ASTEP400, has been developped and installed at Concordia. The first campaign took place during the winter 2010, and the telescope functionned nominally during all the winter. A first analysis of the data leads to a precision of 189 and 205 ppm for WASP-19 and WASP-18 respectively, for continuous observations during 1 month. This shows that extremely high precision photometry is achievable from Dome C.
01 Sep 2011
TL;DR: In this article, the variability properties of main-sequence stars in the first month of Kepler data, using a new astrophysically robust systematics correction, were investigated, and 36% appeared more variable than the Sun, and confirm the trend of increasing variability with decreasing effective temperature.
Abstract: We investigate the variability properties of main-sequence stars in the first month of Kepler data, using a new astrophysically robust systematics correction. We find that 36% appear more variable than the Sun, and confirm the trend of increasing variability with decreasing effective temperature. We define lowand high-variability samples, with a cut at twice the level of the active Sun, and compare properties of the stars belonging to each sample. We find tentative evidence that the more active stars have lower proper motions. The frequency content of the variability shows clear evidence for periodic or quasi-periodic behaviour in 16% of stars, and highlights significant differences in the nature of variability between spectral types. Most A and F stars have short periods ( 5 days, with a trend towards longer periods at later spectral types) and show a mixture of periodic and stochastic variability, indicative of activity. Finally, we use autoregressive models to characterise the stochastic component of the variability, and show that its typical amplitude and time-scale increase towards later spectral types, which we interpret as an increase in the characteristic size and life-time of active regions. Full details will be published shortly.
Austrian Academy of Sciences1, University of Vienna2, University of Provence3, Spanish National Research Council4, University of La Laguna5, German Aerospace Center6, Centre national de la recherche scientifique7, University of Nice Sophia Antipolis8, University of Exeter9, University of Oxford10, University of Geneva11, University of Bern12, University of Paris13, Paris Diderot University14, University of Cologne15, European Space Research and Technology Centre16, NASA Exoplanet Science Institute17, University of São Paulo18, University of Liège19, University of Sydney20, Las Cumbres Observatory Global Telescope Network21, Tel Aviv University22, Technical University of Berlin23
TL;DR: In this paper, the variability properties of main sequence stars in the first month of Kepler data, using a new astrophysically robust systematics correction, were investigated, and 60% of stars are more variable then the active Sun.
Abstract: We investigate the variability properties of main sequence stars in the first month of Kepler data, using a new astrophysically robust systematics correction, and find that 60% of stars are more variable then the active Sun. We define low and high variability samples, with a cut corresponding to twice the variability level of the active Sun, and compare the properties of the stars belonging to each sample. We show tentative evidence that the more active stars have lower proper motions and may be located closer to the galactic plane. We also investigate the frequency content of the variability, finding clear evidence for periodic or quasi-periodic behaviour in 16% of stars, and showing that there exist significant differences in the nature of variability between spectral types. Of the periodic objects, most A and F stars have short periods ( 5 days, with a trend towards longer periods at later spectral types) and show a mixture of periodic and stochastic variability, indicative of activity. Finally, we use auto-regressive models to characterise the stochastic component of the variability, and show that its typical amplitude and time-scale both increase towards later spectral types, which we interpret as a corresponding increase in the characteristic size and life-time of active regions.
Tel Aviv University1, University of Provence2, Institut d'Astrophysique de Paris3, University of Geneva4, European Space Research and Technology Centre5, Janssen Pharmaceutica6, University of Paris7, Spanish National Research Council8, University of São Paulo9, University of Vienna10, German Aerospace Center11, University of Liège12, University of Nice Sophia Antipolis13, Austrian Academy of Sciences14, University of Cologne15
TL;DR: The case of CoRoT LRa02_E2_0121, which was initially classified as a Neptune-size transiting-planet candidate on a relatively wide orbit of 36.3 days, was presented in this article.
Abstract: This paper presents the case of CoRoT LRa02_E2_0121, which was initially classified as a Neptune-size transiting-planet candidate on a relatively wide orbit of 36.3 days. Follow-up observations were performed with UVES, Sandiford, SOPHIE and HARPS. These observations revealed a faint companion in the spectra. To find the true nature of the system we derived the radial velocities of the faint companion using TODMOR - a two-dimensional correlation technique, applied to the SOPHIE spectra. Modeling the lightcurve with EBAS we discovered a secondary eclipse with a depth of ~0.07%, indicating a diluted eclipsing binary. Combined MCMC modeling of the lightcurve and the radial velocities suggested that CoRoT LRa02_E2_0121 is a hierarchical triple system with an evolved G-type primary and an A-type:F-type grazing eclipsing binary. Such triple systems are difficult to discover.