TESS Revisits WASP-12: Updated Orbital Decay Rate and Constraints on Atmospheric Variability

Kavli Affiliate: Avi Shporer

| First 5 Authors: Ian Wong, Avi Shporer, Shreyas Vissapragada, Michael Greklek-McKeon, Heather A. Knutson

| Summary:

After observing WASP-12 in the second year of the primary mission, the
Transiting Exoplanet Survey Satellite (TESS) revisited the system in late 2021
during its extended mission. In this paper, we incorporate the new TESS
photometry into a reanalysis of the transits, secondary eclipses, and phase
curve. We also present a new $K_s$-band occultation observation of WASP-12b
obtained with the Palomar/WIRC instrument. The latest TESS photometry span
three consecutive months, quadrupling the total length of the TESS WASP-12
light curve and extending the overall time baseline by almost two years. Based
on the full set of available transit and occultation timings, we find that the
orbital period is shrinking at a rate of $-29.81 pm 0.94$ ms yr$^{-1}$. The
additional data also increase the measurement precision of the transit depth,
orbital parameters, and phase-curve amplitudes. We obtain a secondary eclipse
depth of $466 pm 35$ ppm, a $2sigma$ upper limit on the nightside brightness
of 70 ppm, and a marginal $6overset{circ}{.}2 pm 2overset{circ}{.}8$
eastward offset between the dayside hotspot and the substellar point. The
voluminous TESS dataset allows us to assess the level of atmospheric
variability on timescales of days, months, and years. We do not detect any
statistically significant modulations in the secondary eclipse depth or
day-night brightness contrast. Likewise, our measured $K_s$-band occultation
depth of $2810 pm 390$ ppm is consistent with most $sim$2.2 $mu$m
observations in the literature.

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