The 13th and 14th PlanetHunters Habitable Zone Candidates

Follow up to some visual transit hunting done earlier this year has exposed two additional targets with possible habitable zone exoplanets on PH Talk: one candidate seems comparable with Neptune while the other is smaller and may be reside in either the mini-Neptune or super-Earth domain, depending on how it accreted. Neither appears in the current Kepler Object of Interest or False Positive lists on MAST.

KIC 6106282

The host star is listed in the KIC as a Type M with radius 0.8 compared to Sol at a Teff of 3912(K). The magnitude is 15.1 and the light curve is fairly variable even after pipeline corrections. Two transits appear to be lost in data gaps for the public time series, but the four remaining do not appear to exhibit clear pixel offsets which would indicate they are the result of a background eclipsing binary.

Source

 Transits display a period of ~101 days and initial characterization suggests the exoplanet may exist as a 2.58x RE orbiting at 0.385 to 0.409AU with an effective temperature of 237 to 245K. This is a little on the chilly side, but if accurate could still be offset by a variety of atmospheric conditions and provide an environment where liquid water states can exist.

KIC 9147029

The star is listed as a magnitude15.3 Type F with a stellar radius just short of Sol and a Teff of 6216(K). Two potential issues exist for this longer period candidate: there are currently only two transits visible in the public data set (one at BJD 419 in Q4 and another at BJD 816 in Q9) and a second point source in the form of KIC 9147033 lies right nearby in the FOV.

However the two transits look pretty good and appear to be free of APOs; if initial characterization is accurate this could be a 4.5x RE exoplanet orbiting in a 397 day period at a distance of 1.026AU. Similar to KIC 6106282, this candidate may be a bit questionable as a habitable zone contender with a slightly chilly potential Teq of 243 to 250K. But the suspected radius and potential for exomoons that receive additional heat generated by tidal forces tipped the scales for its inclusion on the PH HZ list. A third transit and spectroscopic follow up of the system will be required to lock this down further

Source

The search continues at PlanetHunters for smaller exoplanets that would truly rank as potentially habitable candidates, as opposed to just orbiting within the habitable zone of the host star.