No asymmetries in the transit of hot Jupiter CoRoT-29b

The GTC exoplanet transit spectroscopy survey III. No asymmetries in the transit of CoRoT-29b

Authors:

Pallé et al

Abstract:

Context.

The launch of the exoplanet space missions obtaining exquisite photometry from space has resulted in the discovery of thousands of planetary systems with very different physical properties and architectures. Among them, the exoplanet CoRoT-29b was identified in the light curves the mission obtained in summer 2011, and presented an asymmetric transit light curve, which was tentatively explained via the effects of gravity darkening.

Aims.

Transits of CoRoT-29b are measured with precision photometry, to characterize the reported asymmetry in their transit shape.

Methods.

Using the OSIRIS spectrograph at the 10-m GTC telescope, we perform spectro-photometric differential observations, which allow us to both calculate a high-accuracy photometric light curve, and a study of the color-dependence of the transit.

Results.

After careful data analysis, we find that the previously reported asymmetry is not present in either of two transits, observed in July 2014 and July 2015 with high photometric precisions of 300 ppm over 5 min. Due to the relative faintness of the star, we do not reach the precision necessary to perform transmission spectroscopy of its atmosphere, but we see no signs of color-dependency of the transit depth or duration.

Conclusions.

We conclude that the previously reported asymmetry may have been a time-dependent phenomenon, which did not occur in more recent epochs. Alternatively, instrumental effects in the discovery data may need to be reconsidered.

No Asymmetries in the Transit of Corot-29b

The GTC exoplanet transit spectroscopy survey. IV.: No asymmetries in the transit of Corot-29b

Authors:

Palle et al

Abstract:

Context.

The launch of the exoplanet space missions obtaining exquisite photometry from space has resulted in the discovery of thousands of planetary systems with very different physical properties and architectures. Among them, the exoplanet CoRoT-29b was identified in the light curves the mission obtained in summer 2011, and presented an asymmetric transit light curve, which was tentatively explained via the effects of gravity darkening.

Aims.

Transits of CoRoT-29b are measured with precision photometry, to characterize the reported asymmetry in their transit shape.

Methods.

Using the OSIRIS spectrograph at the 10-m GTC telescope, we perform spectro-photometric di?erential observations, which allow us to both calculate a high-accuracy photometric light curve, and a study of the color-dependence of the transit.

Results.

After careful data analysis, we find that the previously reported asymmetry is not present in either of two transits, observed in July 2014 and July 2015 with high photometric precisions of 300ppm over 5 minutes. Due to the relative faintness of the star, we do not reach the precision necessary to perform transmission spectroscopy of its atmosphere, but we see no signs of color-dependency of the transit depth or duration.

Conclusions.

We conclude that the previously reported asymmetry may have been a time-dependent phenomenon, which did not occur in more recent epochs. Alternatively, instrumental effects in the discovery data may need to be reconsidered.

KIC 8462852 is an Excellent SETI Target

The Ĝ Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. The Signatures and Information Content of Transiting Megastructures

Authors:

Wright et al

Abstract:

Arnold (2005), Forgan (2013), and Korpela et al. (2015) noted that planet-sized artificial structures could be discovered with Kepler as they transit their host star. We present a general discussion of transiting megastructures, and enumerate ten potential ways their anomalous silhouettes, orbits, and transmission properties would distinguish them from exoplanets. We also enumerate the natural sources of such signatures.

Several anomalous objects, such as KIC 12557548 and CoRoT-29, have variability in depth consistent with Arnold's prediction and/or an asymmetric shape consistent with Forgan's model. Since well motivated physical models have so far provided natural explanations for these signals, the ETI hypothesis is not warranted for these objects, but they still serve as useful examples of how nonstandard transit signatures might be identified and interpreted in a SETI context. Boyajian et al. 2015 recently announced KIC 8462852, an object with a bizarre light curve consistent with a "swarm" of megastructures. We suggest this is an outstanding SETI target.

We develop the normalized information content statistic M to quantify the information content in a signal embedded in a discrete series of bounded measurements, such as variable transit depths, and show that it can be used to distinguish among constant sources, interstellar beacons, and naturally stochastic or artificial, information-rich signals. We apply this formalism to KIC 12557548 and a specific form of beacon suggested by Arnold to illustrate its utility.

The Odd Hot Jupiters CoRoT-28b and Comet-like (?) CoRoT-29b Orbit Giant Stars

Transiting exoplanets from the CoRoT space mission XXVIII. CoRoT-28b, a planet orbiting an evolved star, and CoRoT-29b, a planet showing an asymmetric transit

Authors:

Cabrera et al

Abstract:

Context.

We present the discovery of two transiting extrasolar planets by the satellite CoRoT.

Aims.

We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars.

Methods.

We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g,Teff,v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical.

Results.

We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484+/-0.087MJup; radius 0.955+/-0.066RJup) orbiting an evolved star with an orbital period of 5.208 51 +/- 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 +/- 0.20MJup; radius 0.90 +/- 0.16RJup) orbiting an oblate star with an orbital period of 2.850 570 +/- 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point.

Conclusions.

These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29.