Kavli Affiliate: Andrew Vanderburg
| First 5 Authors: Erica Thygesen, Joseph E. Rodriguez, Zoë L. De Beurs, Andrew Vanderburg, John H. Livingston
| Summary:
K2-2 b/HIP 116454 b, the first exoplanet discovery by K2 during its
Two-Wheeled Concept Engineering Test, is a sub-Neptune (2.5 $pm$ 0.1
$R_oplus$, 9.7 $pm$ 1.2 $M_oplus$) orbiting a relatively bright (KS = 8.03)
K-dwarf on a 9.1 day period. Unfortunately, due to a spurious follow-up transit
detection and ephemeris degradation, the transit ephemeris for this planet was
lost. In this work, we recover and refine the transit ephemeris for K2-2 b,
showing a $sim40{sigma}$ discrepancy from the discovery results. To
accurately measure the transit ephemeris and update the parameters of the
system, we jointly fit space-based photometric observations from NASA’s K2,
TESS, and Spitzer missions with new photometric observations from the ground,
as well as radial velocities from HARPS-N that are corrected for stellar
activity using a new modeling technique. Ephemerides becoming lost or
significantly degraded, as is the case for most transiting planets, highlights
the importance of systematically updating transit ephemerides with upcoming
large efforts expected to characterize hundreds of exoplanet atmospheres. K2-2
b sits at the high-mass peak of the known radius valley for sub-Neptunes, and
is now well-suited for transmission spectroscopy with current and future
facilities. Our updated transit ephemeris will ensure no more than a 13-minute
uncertainty through 2030.
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