The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

Christiansen, Jessie L.; Crossfield, Ian J. M.; Barentsen, Geert; Lintott, Chris; Barclay, Thomas; Simmons, Brooke; Petigura, Erik A.; Schlieder, Joshua E.; Dressing, Courtney D.; Vanderburg, Andrew; Allen, Campbell; McMaster, Adam; Miller, Grant; Veldthuis, Martin; Allen, Sarah; Wolfenbarger, Zach; Cox, B. E.; Zemiro, Julia; Howard, Andrew W.; Livingston, John H.; Sinukoff, Evan; Catron, Timothy; Grey, Andrew; Kusch, Joshua J. E.; Terentev, Ivan A.; Vales, Martin; Kristiansen, Martti H.

doi:10.3847/1538-3881/aa9be0

Cited by 95 publications

(79 citation statements)

References 69 publications

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“…A detailed analysis of the light curve revealed the presence of potentially six planets. The first five form a compact inner system with radii ranging from 1.6 R ⊕ to 3.3 R ⊕ and periods between 2.35 days and 12.76 days (Christiansen et al 2018). For the outer planet, only two transits are available in the K2 data, indicating a potential period of 42 days.…”

Section: Introductionmentioning

confidence: 99%

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Lopez

Barros

Santerne

et al. 2019

A&A

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The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0 M ⊕ with a precision of 34%, 20%, 18%, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8 g cm −3 , ranging from Earth to Neptune-like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses.

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Section: Introductionmentioning

confidence: 99%

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Lopez

Barros

Santerne

et al. 2019

A&A

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“…We first convert the raw cadence data into target pixel files with kadenza 22 (Barentsen & Cardoso 2018), following the approach described in Christiansen et al (2018).…”

Section: Time-series Photometrymentioning

confidence: 99%

Planetary Candidates from K2 Campaign 16

Crossfield

Schlieder

et al. 2018

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Given that Campaign 16 of the K2 mission is one of just two K2 campaigns observed so far in "forward-facing" mode, which enables immediate follow-up observations from the ground, we present a catalog of interesting targets identified through photometry alone. Our catalog includes 30 high-quality planet candidates (showing no signs of being non-planetary in nature), 48 more ambiguous events that may be either planets or false positives, 164 eclipsing binaries, and 231 other regularly periodic variable sources. We have released light curves for all targets in C16 and have also released system parameters and transit vetting plots for all interesting candidates identified in this paper. Of particular interest is a candidate planet orbiting the bright F dwarf HD73344 (V=6.9, K=5.6) with an orbital period of 15 days. If confirmed, this object would correspond to a 2.56±0.18 R ⊕ planet and would likely be a favorable target for radial velocity characterization. This paper is intended as a rapid release of planet candidates, eclipsing binaries, and other interesting periodic variables to maximize the scientific yield of this campaign, and as a test run for the upcoming TESS mission, whose frequent data releases call for similarly rapid candidate identification and efficient follow up.

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“…The platform today hosts about 21 live projects related to astronomy [25,26], resulting in an increasing number of scientific discoveries, e.g. [27,28,29].…”

Section: Citizen Astronomy and Its Implementationmentioning

confidence: 99%

A citizen science exploration of the X-ray transient sky using the EXTraS science gateway

D’Agostino

Law-Green

Watson

et al. 2020

Future Generation Computer Systems

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Modern soft X-ray observatories can yield unique insights into time domain astrophysics, and a huge amount of information is stored -and largely unexploited -in data archives. Like a treasure-hunt, the EXTraS project harvested the hitherto unexplored temporal domain information buried in the serendipitous data collected by the European Photon Imaging Camera instrument onboard the XMM-Newton satellite in 20 years of observations. The result is a vast catalog, describing the temporal behaviour of hundreds of thousands of X-ray sources. But the catalogue is just a starting point because it has to be, in its turn, further analysed. During the project an education activity has been defined and run in several workshops for high school students in Italy, Germany and UK. The final goal is to engage the students, and in perspective citizen scientists, to go through the whole validation process: they look into the data and try to discover new sources, or to characterize already known sources. This paper describes how the EXTraS science gateway is used to accomplish these tasks and highlights the first discovery, a flaring X-ray source in the globular cluster NGC 6540.1 lying by chance in the instrument field of view, in the portion of the sky surrounding the target of the observation 2 http://nxsa.esac.esa.int/nxsa-web 3 https://heasarc.gsfc.nasa.gov/W3Browse/xmm-newton/xmmssc.html 7

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The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

Cited by 95 publications

References 69 publications

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS

Planetary Candidates from K2 Campaign 16

A citizen science exploration of the X-ray transient sky using the EXTraS science gateway

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