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  Transit least-squares survey: I. Discovery and validation of an Earth-sized planet in the four-planet system K2-32 near the 1:2:5:7 resonance

Heller, R., Rodenbeck, K., & Hippke, M. (2019). Transit least-squares survey: I. Discovery and validation of an Earth-sized planet in the four-planet system K2-32 near the 1:2:5:7 resonance. Astronomy and Astrophysics, 625: A31. doi:10.1051/0004-6361/201935276.

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Heller, René1, Author              
Rodenbeck, Kai1, Author              
Hippke, Michael, Author
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              


Free keywords: eclipses / methods: data analysis / planets and satellites: detection / planets and satellites: individual: K2-32 / planetary systems / techniques: photometric
 Abstract: 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+0.00069 d. We show that this additional signal remains detectable (SDETLS = 13.2) with TLS in the K2SFF light 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 the K2SFF light curve (SDEBLS = 8.9), however, as in previous searches. Markov chain Monte Carlo sampling with the emcee software shows that the radius of this candidate is 1.01−0.09+0.10 R⊕. We analyzed its phase-folded transit light curve using the vespa software 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 from Kepler, 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 the Kepler and K2 data that have so far remained undetected with algorithms that search for box-like signals.


Language(s): eng - English
 Dates: 2019
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1051/0004-6361/201935276
 Degree: -



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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 625 Sequence Number: A31 Start / End Page: - Identifier: Other: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1