Issue |
A&A
Volume 625, May 2019
|
|
---|---|---|
Article Number | A31 | |
Number of page(s) | 8 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/201935276 | |
Published online | 06 May 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
1
Max Planck Institute for Solar System Research,
Justus-von-Liebig-Weg 3,
37077
Göttingen,
Germany
e-mail: heller@mps.mpg.de
2
Institute for Astrophysics, Georg-August-Universität Göttingen,
Friedrich-Hund-Platz 1,
37077
Göttingen,
Germany
e-mail: rodenbeck@mps.mpg.de
3
Sonneberg Observatory,
Sternwartestraße 32,
96515
Sonneberg,
Germany
e-mail: michael@hippke.org
Received:
14
February
2019
Accepted:
30
March
2019
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.
Key words: eclipses / methods: data analysis / planets and satellites: detection / planets and satellites: individual: K2-32 / planetary systems / techniques: photometric
© R. Heller et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open Access funding provided by Max Planck Society.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.