K2-111 b - A short period super-Earth transiting a metal poor, evolved old star
Journal article, 2017
Context. From a light curve acquired through the K2 space mission, the star K2-111(EPIC 210894022) has been identified as possibly orbited by a transiting planet.
Aims: Our aim is to confirm the planetary nature of the object and derive its fundamental parameters.
Methods: We analyse the light curve variations during the planetary transit using packages developed specifically for exoplanetary transits. Reconnaissance spectroscopy and radial velocity observations have been obtained using three separate telescope and spectrograph combinations. The spectroscopic synthesis package SME has been used to derive the stellar photospheric parameters that were used as input to various stellar evolutionary tracks in order to derive the parameters of the system. The planetary transit was also validated to occur on the assumed host star through adaptive imaging and statistical analysis.
Results: The star is found to be located in the background of the Hyades cluster at a distance at least 4 times further away from Earth than the cluster itself. The spectrum and the space velocities of K2-111 strongly suggest it to be a member of the thick disk population. The co-added high-resolution spectra show that that it is a metal poor ([Fe/H] = - 0.53 ± 0.05 dex) and α-rich somewhat evolved solar-like star of spectral type G3. We find Teff = 5730 ± 50 K, log g⋆ = 4.15 ± 0.1 cgs, and derive a radius of R⋆ = 1.3 ± 0.1 R⊙ and a mass of M⋆ = 0.88 ± 0.02 M⊙. The currently available radial velocity data confirms a super-Earth class planet with a mass of 8.6 ± 3.9 M⊕ and a radius of 1.9 ± 0.2 R⊕. A second more massive object with a period longer than about 120 days is indicated by a long-term radial velocity drift.
Conclusions: The radial velocity detection together with the imaging confirms with a high level of significance that the transit signature is caused by a planet orbiting the star K2-111. This planet is also confirmed in the radial velocity data. A second more massive object (planet, brown dwarf, or star) has been detected in the radial velocity signature. With an age of ≳10 Gyr this system is one of the oldest where planets are hitherto detected. Further studies of this planetary system are important since it contains information about the planetary formation process during a very early epoch of the history of our Galaxy.
techniques: spectroscopic
techniques: photometric
planetary systems
stars: individual: K2-111 b
Author
Malcolm Fridlund
Astronomy and Plasmaphysics
E. Gaidos
University of Hawaii
O. Barragán
University of Turin
Carina Persson
Astronomy and Plasmaphysics
D. Gandolfi
University of Turin
J. Cabrera
German Aerospace Center (DLR)
T. Hirono
Tokyo Institute of Technology
M. Kuzuhara
National Astronomical Observatory of Japan
National Institutes of Natural Sciences
Sz. Csizmadia
German Aerospace Center (DLR)
G. Nowak
Instituto de Astrofísica de Canarias
University of La Laguna
M. Endl
The University of Texas at Austin
S. Grziwa
University of Cologne
J. Korth
University of Cologne
J. Pfaff
Technische Universität Berlin
B. Bitsch
Lund University
A. Johansen
Lund University
A. J. Mustill
Lund University
M. B. Davies
Lund University
H. Deeg
University of La Laguna
Instituto de Astrofísica de Canarias
E. Palle
Instituto de Astrofísica de Canarias
University of La Laguna
W. D. Cochran
The University of Texas at Austin
P. Eigmüller
German Aerospace Center (DLR)
A. Erikson
German Aerospace Center (DLR)
E. W. Guenther
Thüringer Landessternwarte Tautenburg
A. Hatzes
Thüringer Landessternwarte Tautenburg
A. Kiilerich
Massachusetts Institute of Technology (MIT)
Aarhus University
Princeton University
T. Kudo
National Astronomical Observatory of Japan
P. MacQueen
The University of Texas at Austin
N. Narita
University of Tokyo
National Astronomical Observatory of Japan
National Institutes of Natural Sciences
D. Nespral
Instituto de Astrofísica de Canarias
University of La Laguna
M. Patzold
University of Cologne
J. Prieto-Arranz
Instituto de Astrofísica de Canarias
University of La Laguna
H. Rauer
German Aerospace Center (DLR)
Technische Universität Berlin
V. Van Eylen
Heidelberg-Königstuhl State Observatory
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 604 A16- A16Exoplanets from space – CHEOPS and PLATO, ESA’s next two projects
Swedish National Space Board (174/18), 2017-01-01 -- 2022-12-31.
Subject Categories
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.1051/0004-6361/201730822