Browsing by Author "Llama, Joe"

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    Amplitude Modulation of Short-timescale Hot Spot Variability
    (IOP Publishing, 2021) Biddle, Lauren I.; Llama, Joe; Cameron, Andrew; Prato, L.; Jardine, Moira; Johns-Krull, Christopher M.
    Variability of Classical T Tauri stars (CTTS) occurs over a vast range of timescales. CTTS in particular are subject to variability caused by accretion shocks, which can occur stochastically, periodically, or quasi-periodically on timescales over a few days. The detectability of young planets within these systems is likely hampered by activity; therefore, it is essential that we understand the origin of young star variability over a range of timescales to help disentangle stellar activity from signatures of planetary origin. We present an analysis of the stochastic small-amplitude photometric variability in the K2 lightcurve of CI Tau occurring on timescales of  lesssim1 day. We find the amplitude of this variability exhibits the same periodic signatures as detected in the large-amplitude variability, indicating that the physical mechanism modulating these brightness features is the same. The periods detected are also in agreement with the rotation period of the star (~6.6 days) and the orbital period of the planet (~9.0 days) known to drive pulsed accretion onto the star.
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    K2ﾠReveals Pulsed Accretion Driven by the 2 Myr Old Hot Jupiter CI Tau b
    (IOP Publishing, 2018) Biddle, Lauren I.; Johns-Krull, Christopher M.; Llama, Joe; Prato, Lisa; Skiff, Brian A.
    CIﾠTau is a young (~2 Myr) classical T Tauri star located in the Taurus star-forming region. Radial velocity observations indicate it hosts a Jupiter-sized planet with an orbital period of approximately 9 days. In this work, we analyze time series of CIﾠTau's photometric variability as seen byﾠK2. The light curve reveals the stellar rotation period to be ~6.6 days. Although there is no evidence that CIﾠTau b transits the host star, a ~9 day signature is also present in the light curve. We believe this is most likely caused by planetﾖdisk interactions that perturb the accretion flow onto the star, resulting in a periodic modulation of the brightness with the ~9 day period of the planet's orbit.
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    TESS Hunt for Young and Maturing Exoplanets (THYME). VI. An 11 Myr Giant Planet Transiting a Very-low-mass Star in Lower Centaurus Crux
    (IOP Publishing, 2022) Mann, Andrew W.; Wood, Mackenna L.; Schmidt, Stephen P.; Barber, Madyson G.; Owen, James E.; Tofflemire, Benjamin M.; Newton, Elisabeth R.; Mamajek, Eric E.; Bush, Jonathan L.; Mace, Gregory N.; Kraus, Adam L.; Thao, Pa Chia; Vanderburg, Andrew; Llama, Joe; Johns-Krull, Christopher M.; Prato, L.; Stahl, Asa G.; Tang, Shih-Yun; Fields, Matthew J.; Collins, Karen A.; Collins, Kevin I.; Gan, Tianjun; Jensen, Eric L. N.; Kamler, Jacob; Schwarz, Richard P.; Furlan, Elise; Gnilka, Crystal L.; Howell, Steve B.; Lester, Kathryn V.; Owens, Dylan A.; Suarez, Olga; Mekarnia, Djamel; Guillot, Tristan; Abe, Lyu; Triaud, Amaury H. M. J.; Johnson, Marshall C.; Milburn, Reilly P.; Rizzuto, Aaron C.; Quinn, Samuel N.; Kerr, Ronan; Ricker, George R.; Vanderspek, Roland; Latham, David W.; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Guerrero, Natalia M.; Shporer, Avi; Schlieder, Joshua E.; McLean, Brian; Wohler, Bill
    Mature super-Earths and sub-Neptunes are predicted to be ≃ Jovian radius when younger than 10 Myr. Thus, we expect to find 5–15 R ⊕ planets around young stars even if their older counterparts harbor none. We report the discovery and validation of TOI 1227b, a 0.85 ± 0.05 R J (9.5 R ⊕) planet transiting a very-low-mass star (0.170 ± 0.015 M ⊙) every 27.4 days. TOI 1227's kinematics and strong lithium absorption confirm that it is a member of a previously discovered subgroup in the Lower Centaurus Crux OB association, which we designate the Musca group. We derive an age of 11 ± 2 Myr for Musca, based on lithium, rotation, and the color–magnitude diagram of Musca members. The TESS data and ground-based follow-up show a deep (2.5%) transit. We use multiwavelength transit observations and radial velocities from the IGRINS spectrograph to validate the signal as planetary in nature, and we obtain an upper limit on the planet mass of ≃0.5 M J. Because such large planets are exceptionally rare around mature low-mass stars, we suggest that TOI 1227b is still contracting and will eventually turn into one of the more common <5 R ⊕ planets.