摘要：We apply for the first time the transit least-squares (TLS) algorithm to search for new transiting exoplanets. TLS has been developed as a successor to the box least-squares (BLS) algorithm, which has served as a standard tool for the detection of periodic transits. In this proof-of-concept paper, we demonstrate that TLS finds small planets that have previously been missed. We show the capabilities of TLS using the K2 EVEREST-detrended light curve of the star K2-32 (EPIC 205071984), which has been known to have three transiting planets. TLS detects these known Neptune-sized planets K2-32 b, d, and c in an iterative search and finds an additional transit signal with a high signal detection efficiency (SDETLS) of 26.1 at a period of 4.34882−0.00075+0.00069d. We show that this additional signal remains detectable (SDETLS= 13.2) with TLS in theK2SFFlight curve of K2-32, which includes a less optimal detrending of the systematic trends. The signal is below common detection thresholds if searched with BLS in theK2SFFlight curve (SDEBLS= 8.9), however, as in previous searches. Markov chain Monte Carlo sampling with theemceesoftware shows that the radius of this candidate is 1.01−0.09+0.10R⊕. We analyzed its phase-folded transit light curve using thevespasoftware and calculated a false-positive probability FPP = 3.1 × 10−3. Taking into account the multiplicity boost of the system, we estimate an FPP < 3.1 × 10−4, which formally validates K2-32 e as a planet. K2-32 now hosts at least four planets that are very close to a 1:2:5:7 mean motion resonance chain. The offset of the orbital periods of K2-32 e and b from a 1:2 mean motion resonance agrees very well with the sample of transiting multiplanet systems fromKepler, lending further credence to the planetary nature of K2-32 e. We expect that TLS can find many more transits of Earth-sized and even smaller planets in theKeplerand K2 data that have so far remained undetected with algorithms that search for box-like signals.
关键词：Key wordseneclipsesmethods: data analysisplanets and satellites: detectionplanets and satellites: individual: K2-32planetary systemstechniques: photometric
