TY  - JOUR
A1  - Wells, Robert
A1  - Poppenhäger, Katja
A1  - Watson, C. A.
T1  - Validation of a temperate fourth planet in the K2-133 multiplanet system
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present follow-up observations of the K2-133 multiplanet system. Previously, we announced that K2-133 contained three super-Earths orbiting an M1.5V host star – with tentative evidence of a fourth outer-planet orbiting at the edge of the temperate zone. Here, we report on the validation of the presence of the fourth planet, determining a radius of 1.73+0.14−0.13 R⊕. The four planets span the radius gap of the exoplanet population, meaning further follow-up would be worthwhile to obtain masses and test theories of the origin of the gap. In particular, the trend of increasing planetary radius with decreasing incident flux in the K2-133 system supports the claim that the gap is caused by photo-evaporation of exoplanet atmospheres. Finally, we note that K2-133 e orbits on the edge of the star's temperate zone, and that our radius measurement allows for the possibility that this is a rocky world. Additional mass measurements are required to confirm or refute this scenario.
KW  - techniques: photometric
KW  - planets and satellites: general
KW  - stars: individual: LP 358-499
KW  - stars: individual: K2-133
KW  - stars: low-mass
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/stz1334
SN  - 0035-8711
SN  - 1365-2966
VL  - 487
IS  - 2
SP  - 1865
EP  - 1873
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Ilić Petković, Nikoleta
A1  - Poppenhäger, Katja
A1  - Hosseini, Seyede Marzieh
T1  - Tidal star-planet interaction and its observed impact on stellar activity in planet-hosting wide binary systems
JF  - Monthly notices of the Royal Astronomical Society
N2  - Tidal interaction between an exoplanet and its host star is a possible pathway to transfer angular momentum between the planetary orbit and the stellar spin. In cases where the planetary orbital period is shorter than the stellar rotation period, this may lead to angular momentum being transferred into the star's rotation, possibly counteracting the intrinsic stellar spin-down induced by magnetic braking. Observationally, detecting altered rotational states of single, cool field stars is challenging, as precise ages for such stars are rarely available. Here we present an empirical investigation of the rotation and magnetic activity of a sample of planet-hosting stars that are accompanied by wide stellar companions. Without needing knowledge about the absolute ages of the stars, we test for relative differences in activity and rotation of the planet hosts and their co-eval companions, using X-ray observations to measure the stellar activity levels. Employing three different tidal interaction models, we find that host stars with planets that are expected to tidally interact display elevated activity levels compared to their companion stars. We also find that those activity levels agree with the observed rotational periods for the host stars along the usual rotation-activity relationships, implying that the effect is indeed caused by a tidal interaction and not a purely magnetic interaction that would be expected to affect the stellar activity, but not necessarily the rotation. We conclude that massive, close-in planets have an impact on the stellar rotational evolution, while the smaller, more distant planets do not have a significant influence.
KW  - planet-star interactions
KW  - stars: activity
KW  - binaries: general
KW  - stars:
KW  - evolution
KW  - planets and satellites: general
KW  - X-rays: stars
Y1  - 2022
U6  - https://doi.org/10.1093/mnras/stac861
SN  - 0035-8711
SN  - 1365-2966
VL  - 513
IS  - 3
SP  - 4380
EP  - 4404
PB  - Oxford Univ. Press
CY  - Oxford
ER  -