* Astronomy

Darkest exoplanet spotted by astronomers

A dark alien world, blacker than coal, has been spotted by astronomers.
The Jupiter-sized planet is orbiting its star at a distance of just five million km, and is likely to be at a temperature of some 1200C.
The planet may be too hot to support reflective clouds like those we see in our own Solar System, but even that would not explain why it is so dark.
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Title: Analysis of Kepler's short-cadence photometry for TrES-2b
Authors: David M. Kipping, Gáspár Á. Bakos
(Version v3)

We present an analysis of 18 short-cadence (SC) transit lightcurves of TrES-2b using quarter 0 (Q0) and quarter 1 (Q1) from the Kepler Mission. The photometry is of unprecedented precision, 237ppm per minute, allowing for the most accurate determination of the transit parameters yet obtained for this system. Global fits of the transit photometry, radial velocities and known transit times are used to obtain a self-consistent set of refined parameters for this system, including updated stellar and planetary parameters. Special attention is paid to fitting for limb darkening and eccentricity. We place an upper limit on the occultation depth to be <72.9ppm to 3-sigma confidence, indicating TrES-2b has the lowest determined geometric albedo for an exoplanet, of Ag<0.146. We also produce a transit timing analysis using Kepler's short-cadence data and demonstrate exceptional timing precision at the level of a few seconds for each transit event. With 18 fully-sampled transits at such high precision, we are able to produce stringent constraints on the presence of perturbing planets, Trojans and extrasolar moons. We introduce the novel use of control data to identify phasing effects. We also exclude the previously proposed hypotheses of short-period TTV and additional transits but find the hypothesis of long-term inclination change is neither supported nor refuted by our analysis.

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Title: Multi-band transit observations of the TrES-2b exoplanet
Authors: D. Mislis, S. Schroter, J.H.M.M. Schmitt, O. Cordes, K. Reif
(Version v2)

We present a new data set of transit observations of the TrES-2b exoplanet taken in spring 2009, using the 1.2m Oskar-Luhning telescope (OLT) of Hamburg Observatory and the 2.2m telescope at Calar Alto Observatory using BUSCA (Bonn University Simultaneous CAmera). Both the new OLT data, taken with the same instrumental setup as our data taken in 2008, as well as the simultaneously recorded multicolour BUSCA data confirm the low inclination values reported previously, and in fact suggest that the TrES-2b exoplanet has already passed the first inclination threshold (i_min,1 = 83.417) and is not eclipsing the full stellar surface any longer. Using the multi-band BUSCA data we demonstrate that the multicolour light curves can be consistently fitted with a given set of limb darkening coefficients without the need to adjust these coefficients, and further, we can demonstrate that wavelength dependent stellar radius changes must be small as expected from theory. Our new observations provide further evidence for a change of the orbit inclination of the transiting extrasolar planet TrES-2b reported previously. We examine in detail possible causes for this inclination change and argue that the observed change should be interpreted as nodal regression. While the assumption of an oblate host star requires an unreasonably large second harmonic coefficient, the existence of a third body in the form of an additional planet would provide a very natural explanation for the observed secular orbit change. Given the lack of clearly observed short-term variations of transit timing and our observed secular nodal regression rate, we predict a period between approximately 50 and 100 days for a putative perturbing planet of Jovian mass. Such an object should be detectable with present-day radial velocity (RV) techniques.

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