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Post Info TOPIC: CoRoT-Exo-2a


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Posts: 131433
Date:
CoRoT-2b
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Star blasts planet with X-rays

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A nearby star is pummeling a companion planet with a barrage of X-rays a hundred thousand times more intense than the Earth receives from the Sun.
New data from NASA's Chandra X-ray Observatory and the European Southern Observatory's Very Large Telescope suggest that high-energy radiation is evaporating about 5 million tons of matter from the planet every second. This result gives insight into the difficult survival path for some planets.
The planet, known as CoRoT-2b, has a mass about 3 times that of Jupiter (1000 times that of Earth) and orbits its parent star, CoRoT-2a at a distance roughly ten times the distance between Earth and the Moon.

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Posts: 131433
Date:
CoRoT-2A
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Title: The corona and companion of CoRoT-2A. Insights from X-rays and optical spectroscopy
Authors: S. Schröter, S. Czesla, U. Wolter, H.M. Müller, K.F. Huber, J.H.M.M. Schmitt

CoRoT-2 is one of the most unusual planetary systems known to date. Its host star is exceptionally active, showing a pronounced, regular pattern of optical variability caused by magnetic activity. The transiting hot Jupiter, CoRoT-2b, shows one of the largest known radius anomalies. We analyse the properties and activity of CoRoT-2A in the optical and X-ray regime by means of a high-quality UVES spectrum and a 15 ks Chandra exposure both obtained during planetary transits. The UVES data are analysed using various complementary methods of high-resolution stellar spectroscopy. We characterise the photosphere of the host star by deriving accurate stellar parameters such as effective temperature, surface gravity, and abundances. Signatures of stellar activity, Li abundance, and interstellar absorption are investigated to provide constraints on the age and distance of CoRoT-2. Furthermore, our UVES data confirm the presence of a late-type stellar companion to CoRoT-2A that is gravitationally bound to the system. The Chandra data provide a clear detection of coronal X-ray emission from CoRoT-2A, for which we obtain an X-ray luminosity of 1.9e29 erg/s. The potential stellar companion remains undetected in X-rays. Our results indicate that the distance to the CoRoT-2 system is approximately 270 pc, and the most likely age lies between 100 and 300 Ma. Our X-ray observations show that the planet is immersed in an intense field of high-energy radiation. Surprisingly, CoRoT-2A's likely coeval stellar companion, which we find to be of late-K spectral type, remains X-ray dark. Yet, as a potential third body in the system, the companion could account for CoRoT-2b's slightly eccentric orbit.

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Posts: 131433
Date:
CoRoT-2
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Title: Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry
Authors: Adriana Silva-Valio, A. F. Lanza

CoRoT-2, the second planet-hosting star discovered by the CoRoT satellite, is a young and active star. A total of 77 transits were observed for this system over a period of 135 days. Small modulations detected in the optical light curve of the planetary transits are used to study the position, size, intensity, and temporal evolution of the photospheric spots on the surface of the star that are occulted by the planetary disk. We apply a spot model to these variations and create a spot map of the stellar surface of CoRoT-2 within the transit band for every transit. From these maps, we estimate the stellar rotation period and obtain the longitudes of the spots in a reference frame rotating with the star. Moreover, the spots temporal evolution is determined. This model achieves a spatial resolution of 2°. Mapping of 392 spots vs. longitude indicates the presence of a region free of spots, close to the equator, reminiscent of the coronal holes observed on the Sun during periods of maximum activity. With this interpretation, the stellar rotation period within the transit latitudes of -14.° 6 ±10° is found to be 4.48 days. This rotation period is shorter than the 4.54 days as derived from the out-of-transit light modulation. Since the transit data samples a region close to the stellar equator, while the period determined from out-of-transit data reflects the average rotation of the star, this is taken as an indication of a latitudinal differential rotation of about 3% or 0.042 rad/d.

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Posts: 131433
Date:
CoRoT-2b
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Title: Bright optical dayside emission from extrasolar planet CoRoT-2b
Authors: I.A.G. Snellen, E.J.W. de Mooij, A. Burrows

We present our analysis of the red-channel CoRoT data of extrasolar planet CoRoT-2b. A deep secondary eclipse is detected at a level of 1.02±0.20x10^-4, which suggests that all of the planet-signal detected previously in white light by Alonso et al. (2009) originates from the red channel. CoRoT-2b is the coolest exoplanet that has been detected in the optical so far. In contrast to the other planets, its measured brightness temperature of 2170±50 K is significantly higher than its maximum hemisphere-averaged effective day-side temperature. However, it is not expected that a hot Jupiter radiates as a black body, and its thermal spectrum can deviate significantly from a Planck curve. We present models of the planet/star flux ratio as function of wavelength, which are calculated for a T/P profile in radiative and hydrostatic equilibrium, using a self-consistent atmosphere code. These are compared with the CoRoT detection. We estimate that reflected light contributes only at a 10-20% level to the total optical eclipse depth. The models allow for an 'extra absorber' to be inserted at high altitude in the planet's atmosphere. This produces a thermal inversion layer, recently invoked to explain the photometric reversals and flux enhancements seen in some planets in the infrared. In the 0.5-1.5 um wavelength range, the model-spectra of planets with an extra absorber at high altitude, are relatively suppressed in flux compared to those without such absorber. We therefore argue that, in contrast to the other exoplanets detected in the optical so far, CoRoT-2b may not exhibit a significant thermal inversion in its atmosphere, causing its optical brightness temperature to be boosted above its maximum effective day-side temperature.

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Posts: 131433
Date:
CoRoT-2a
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Title: A planetary eclipse map of CoRoT-2a. Comprehensive lightcurve modeling combining rotational-modulation and transits
Authors: K. F. Huber, S. Czesla, U. Wolter, J. H. M. M. Schmitt

We analyse the surface structure of the planet host star CoRoT-2a using a consistent model for both the 'global' (i.e., rotationally modulated) lightcurve and the transit lightcurves, using data provided by the CoRoT mission. Selecting a time interval covering two stellar rotations and six transits of the planetary companion CoRoT-2b, we adopt a 'strip' model of the surface to reproduce the photometric modulation inside and outside the transits simultaneously. Our reconstructions show that it is possible to achieve appropriate fits for the entire sub-interval using a low-resolution surface model with 36 strips. The surface reconstructions indicate that the brightness on the eclipsed section of the stellar surface is (6 ±1)% lower than the average brightness of the remaining surface. This result suggests a concentration of stellar activity in a band around the stellar equator similar to the behaviour observed on the Sun.

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Posts: 131433
Date:
CoRoT-2b
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Title: The secondary eclipse of the transiting exoplanet CoRoT-2b
Authors: R. Alonso, T. Guillot, T. Mazeh, S. Aigrain, A. Alapini, P. Barge, A. Hatzes, and F. Pont

We present a study of the light curve of the transiting exoplanet CoRoT-2b, aimed at detecting the secondary eclipse and measuring its depth. The data were obtained with the CoRoT satellite during its first run of more than 140 days. After filtering the low frequencies with a pre-whitening technique, we detect a 0.0060 ±0.0020% secondary eclipse centred on the orbital phase 0.494 ±0.006. Assuming a black-body emission of the planet, we estimate a surface brightness temperature of T_{p,CoRoT} =1910^_ K. We provide the planet's equilibrium temperature and re-distribution factors as a function of the unknown amount of reflected light. The upper limit for the geometric albedo is 0.12. The detected secondary is the shallowest ever found.

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Posts: 131433
Date:
RE: CoRoT-Exo-2b
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Astronomers observing exoplanets around other stars may be underestimating their size, according to a German study.
The researchers believe the error may be due to active stars adding 'noise' to the observation of exoplanets using the transit method.
The transit method detects exoplanets as they pass in front of their parent star, reducing the amount of light reaching telescopes on, and orbiting, Earth.
Although the transit method isn't the best method for detecting exoplanets, it provides a reliable estimate of its size and mass.

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Posts: 131433
Date:
CoRoT-2b
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Title: Transit mapping of a starspot on CoRoT-2 - Probing a stellar surface by planetary transits
Authors:
U. Wolter, J.H.M.M. Schmitt, K.F. Huber, S. Czesla, H.M. Mueller, E.W. Guenther, A.P. Hatzes

We analyse variations in the transit lightcurves of CoRoT-2b, a massive hot Jupiter orbiting a highly active G star. We use one transit lightcurve to eclipse-map a photospheric spot occulted by the planet. In this case study we determine the size and longitude of the eclipsed portion of the starspot and systematically study the corresponding uncertainties. We determine a spot radius between 4.5° and 10.5° on the stellar surface and the spot longitude with a precision of about ± 1 degree. Given the well-known transit geometry of the CoRoT-2 system, this implies a reliable detection of spots on latitudes typically covered by sunspots; also regarding its size the modelled spot is comparable to large spot groups on the Sun. We discuss the future potential of eclipse mapping by planetary transits for the high-resolution analysis of stellar surface features.

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Posts: 131433
Date:
Exoplanet CoRoT-2b
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Title: The secondary eclipse of the transiting exoplanet CoRoT-2b
Authors: R. Alonso, T. Guillot, T. Mazeh, S. Aigrain, A. Alapini, P. Barge, A. Hatzes, F. Pont

We present a study of the light curve of the transiting exoplanet CoRoT-2b, aimed at detecting the secondary eclipse and measuring its depth. The data were obtained with the CoRoT satellite during its first run of more than 140 days. After filtering the low frequencies with a pre-whitening technique, we detect a 0.0060 ±0.0020% secondary eclipse centred on the orbital phase 0.494 ±0.006. Assuming a black-body emission of the planet, we estimate a surface brightness temperature of T_{p,CoRoT}=1910^{+90}_{-100} K. We provide the planet's equilibrium temperature and re-distribution factors as a function of the unknown amount of reflected light. The upper limit for the geometric albedo is 0.12. The detected secondary is the shallowest ever found.

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Posts: 131433
Date:
CoRoT-2a
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Title: CoRoT-2a magnetic activity: hints for possible star-planet interaction
Authors: Isabella Pagano, Antonino F. Lanza, Giuseppe Leto, Sergio Messina, Pierre Barge, Annie Baglin

CoRoT-2a is a young (about 0.5 Gyr) G7V star accompanied by a transiting hot-Jupiter, discovered by the CoRoT satellite (Alonso et al. 2008; Bouchy et al. 2008). An analysis of its photospheric activity, based on spot modelling techniques previously developed by our group for the analysis of the Sun as a star, shows that the active regions on CoRoT-2a arose within two active longitudes separated by about 180 degrees and rotating with periods of 4.5221 and 4.5543 days, respectively, at epoch of CoRoT observations (112 continuous days centred at 2007.6). We show that the total spotted area oscillates with a period of about 8.9 days, a value close to 10 times the synodic period of the planet with respect to the active longitude pattern rotating in 4.5221 days. Moreover, the variance of the stellar flux is modulated in phase with the planet orbital period. This suggests a possible star-planet magnetic interaction, a phenomenon already seen in other extrasolar planetary systems hosting hot-Jupiters.

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