Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Thomas Barclay
Kyle B. Sheppard
Natasha Latouf
Avi M. Mandell
Elisa V. Quintana
Emily A. Gilbert
Giuliano Liuzzi
Geronimo L. Villanueva
Giada Arney
Jonathan Brande
Knicole D. Colón
Giovanni Covone
Ian J. M. Crossfield
Mario Damiano
Shawn D. Domagal-Goldman
Thomas J. Fauchez
Stefano Fiscale
Francesco Gallo
Christina L. Hedges
Renyu Hu
Abstract： We present observations of the 1.35+/-0.07 Earth-radius planet L 98-59 c using Wide Field Camera~3 on the Hubble Space Telescope. L 98-59 is a nearby (10.6 pc), bright (H=7.4 mag), M3V star that harbors three small, transiting planets. As one of the closest known transiting multi-planet systems, L 98-59 offers one of the best opportunities to probe and compare the atmospheres of rocky planets that formed in the same stellar environment. We measured the transmission spectrum of L 98-59 c during a single transit, with the extracted spectrum showing marginal evidence for wavelength-dependent transit depth variations which would indicate the presence of an atmosphere. Forward modeling was used to constrain possible atmospheric compositions of the planet based on the shape of the transmission spectrum. Although L 98-59 is a fairly quiet star, we have seen evidence for stellar activity, and therefore we cannot rule out a scenario where the source of the signal originates with inhomogeneities on the host-star surface. While intriguing, our results are inconclusive and additional data is needed to verify any atmospheric signal. Fortunately, additional data will soon be collected from both HST and JWST. Should this result be confirmed with additional data, L 98-59 c would be the first planet smaller than 2 Earth-radii with a detected atmosphere, and among the first small planets with a known atmosphere to be studied in detail by the JWST.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Justin M. Wittrock
Peter Plavchan
Bryson L. Cale
Thomas Barclay
Emily A. Gilbert
Mathis R. Ludwig
Richard P. Schwarz
Djamel Mekarnia
Amaury Triaud
Lyu Abe
Olga Suarez
Tristan Guillot
Dennis M. Conti
Karen A. Collins
Ian A. Waite
John F. Kielkopf
Kevin I. Collins
Stefan Dreizler
Mohammed El Mufti
Dax Feliz
Abstract： AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess TTVs that cannot be accounted for by the two known transiting planets nor stellar activity. In this work, we present the validation of the candidate planet AU Mic d. We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O-C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for the period of planet d and then follow those up with detailed TTV and RV MCMC modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73812+/-0.00128 days (T_{C,d}=2458333.32110+/-0.35836 BJD), which puts the three planets near a 4:6:9 mean-motion orbital resonance. The mass for d is M_d=1.013+/-0.146 M_E, making this planet Earth-like in mass. The presence of orbital resonances in a very young system implies that compact planetary systems can develop resonant chains very early on, which can quickly establish the stability of the systems. Additional TTV observation of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c.
Peer Review Status:Awaiting Review
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