Abstract
Proxima~Centauri is known as the closest star from the Sun. Recently, radial
velocity observations revealed the existence of an Earth--mass planet around
it. With an orbital period of $\sim$11 days, the surface of Proxima Centauri b
is temperate and might be habitable. We took a photometric monitoring campaign
to search for its transit, using the Bright Star Survey Telescope at the
Zhongshan Station in Antarctica. A transit--like signal appearing on September
8th, 2016, is identified tentatively. Its midtime,
$T_C=2,457,640.1990\pm0.0017$~HJD, is consistent with the predicted ephemeris
based on RV orbit in a 1$\sigma$ confidence interval. Time--correlated noise is
pronounced in the light curve of Proxima Centauri, affecting detection of
transits. We develop a technique, in a Gaussian process framework, to gauge the
statistical significance of potential transit detection. The tentative transit
signal reported here, has a confidence level of $2.5\sigma$. Further detection
of its periodic signals is necessary to confirm the planetary transit of
Proxima Centauri b. We plan to monitor Proxima Centauri in next Polar night at
Dome A in Antarctica, taking the advantage of continuous darkness.
Kipping17 reported two tentative transit--like signals of Proxima
Centauri b, observed by the Microvariability and Oscillation of Stars space
Telescope in 2014 and 2015, respectively. The midtransit time of our detection
is 138 minutes later than that predicted by their transit ephemeris. If all the
signals are real transits, the misalignment of the epochs plausibly suggests
transit timing variations of Proxima Centauri b induced by an outer planet in
this system.
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