KOI-13.01, a planet-sized companion in an optical double star was announced as one of the 1235 Kepler planet candidates in February 2011. The transit curves show significant distortion that was stable over the ~130 days time-span of the data. Here we
investigate the phenomenon via detailed analyses of the two components of the double star and a re-reduction of the Kepler data with pixel-level photometry. Our results indicate that KOI-13 is a common proper motion binary, with two rapidly rotating components (v sin i ~ 65--70 km/s). We identify the host star of KOI-13.01 and conclude that the transit curve asymmetry is consistent with a companion orbiting a rapidly rotating, possibly elongated star on an oblique orbit. After correcting the Kepler light curve to the second light of the optical companion star, we derive a radius of 2.2 R_J for the transiter, implying an irradiated late-type dwarf, probably a hot brown dwarf rather than a planet. KOI-13 is the first example for detecting orbital obliquity for a substellar companion without measuring the Rossiter-McLaughlin effect from spectroscopy.
A possible transit of HAT-P-13c has been predicted to occur on 2010 April 28. Here we report on the results of a multi-site campaign that has been organised to detect the event. CCD photometric observations have been carried out at five observatories
in five countries. We reached 30% time coverage in a 5 days interval centered on the suspected transit of HAT-P-13c. Two transits of HAT-P-13b were also observed. No transit of HAT-P-13c has been detected while the campaign was on. By a numerical experiment with 10^5 model systems we conclude that HAT-P-13c is not a transiting exoplanet with a significance level from 65% to 72%, depending on the planet parameters and the prior assumptions. We present two times of transit of HAT-P-13b ocurring at BJD 2455141.5522 +- 0.0010 and BJD 2455249.4508 +- 0.0020. The TTV of HAT-P-13b is consistent with zero within 0.001 days. The refined orbital period of HAT-P-13b is 2.916293 +- 0.000010 days.
New photometric series of BE Lyncis are presented. With template curve fitting we re-determined the $O-C$ for BE Lyncis. The phase shift diagram is apparently constant, disproving the suspected period variations of BE Lyn.
