key publications

2025

1. Spot-crossing Variations Confirm a Misaligned Orbit for a Planet Transiting an M Dwarf Tamburo, Patrick, Yee, Samuel W., Garcı́a-Mejı́a, Juliana, Charbonneau, David, Bieryla, Allyson, and 2 more authors. Collins, Karen A., and Shporer, Avi (hide). (2025) The Astronomical Journal, 170, 200 [Abs] [arXiv] [Paper]

   TOI-3884 b is an unusual 6.4 R_⊕planet orbiting an M4 host, whose transits display large and persistent spot- crossing events. We used the Tierras Observatory to monitor both the long-term photometric variability of TOI-3884 and changes in the spot-crossing events across multiple transits of the planet. We show that the star rotates with a period of 11.020 \pm 0.015 days. We simultaneously model the rotational modulation of the star and variations in transit shapes that arise due to rotation of the spot, allowing us to determine the true stellar obliquity, \psi_⋆. The data are best described by a planet on a misaligned orbit around a highly inclined star (\psi_⋆= 77.4_-2.5^+2.3^∘; i_⋆= 22.3_-1.6^+1.8^∘) that hosts a large polar starspot (r_\mathrmspot = 31.2_-1.9^+2.4^∘; \lambda_\mathrmspot = 70.5^∘ \pm 1.2^∘). Archival photometry from the Zwicky Transient Facility suggests that this polar spot has persisted on TOI-3884 for at least seven years. The TOI-3884 system provides a benchmark for studying the evolution of a polar spot on an M dwarf.

2. The Polar Orbit of TOI-2374 b, a Planet in the Neptunian Ridge Yee, Samuel W., Tamburo, Patrick, Stefánsson, Gudmundur, Garcı́a-Mejı́a, Juliana, Charbonneau, David, and 9 more authors. Barkaoui, Khalid, Collins, Karen A., Schwarz, Richard P., Narita, Norio, Fukui, Akihiko, Howard, Andrew W., Isaacson, Howard, Fulton, Benjamin J., and Dai, Fei (hide). (2025) arXiv e-prints, arXiv:2509.11565 [Abs] [arXiv] [Paper]

   The “Neptunian ridge“ is a recently identified peak in the frequency of planets with sizes between that of Neptune and Saturn orbiting their host stars with periods between 3 and 6 days (A. Castro-González et al. 2024). These planets may have formed similarly to their larger, hot Jupiter counterparts in the “three-day pile-up”, through a dynamically excited migration pathway. The distribution of stellar obliquities in hot Neptune systems may therefore provide a vital clue as to their origin. We report a new stellar obliquity measurement for TOI-2374 b, a planet in the Neptunian ridge (P = 4.31 days, R_p = 7.5 R_⊕). We observed a spectroscopic transit of TOI-2374 b with the Keck Planet Finder, detecting the Rossiter-McLaughlin (RM) anomaly with an amplitude of 3 m/s, and measured a sky-projected obliquity of λ= 81^∘^+23^∘_-22^∘, indicating an orbit significantly misaligned with the spin axis of its host star. A reloaded RM analysis of the cross-correlation functions confirms this misalignment, measuring λ= 65^∘^+32^∘_-24^∘. Additionally, we measured a stellar rotation period of P_\mathrmrot = 26.4^+0.9_-0.8 days with photometry from the Tierras observatory, allowing us to deduce the three-dimensional stellar obliquity of ψ= 85.9^∘^+8.6^∘_-9.2^∘. TOI-2374 b joins a growing number of hot Neptunes on polar orbits. The high frequency of misaligned orbits for Neptunian ridge and desert planets, compared with their longer period counterparts, is reminiscent of patterns seen for the giant planets and may suggest a similar formation mechanism.

3. The TESS Grand Unified Hot Jupiter Survey. III. Thirty More Giant Planets Yee, Samuel W., Winn, Joshua N., Hartman, Joel D., Rodriguez, Joseph E., Zhou, George, and 120 more authors. Latham, David W., Quinn, Samuel N., Bieryla, Allyson, Collins, Karen A., Eastman, Jason D., Collins, Kevin I., Conti, Dennis M., Jensen, Eric L. N., Baker, David, Barkaoui, Khalid, Baştürk, Özgür, Battley, Matthew P., Bayliss, Daniel, Beatty, Thomas G., Beletsky, Yuri, Belinski, Alexander A., Benkhaldoun, Zouhair, Benni, Paul, Bosch-Cabot, Pau, Briceño, César, Brudny, Andrzej, Burleigh, Matthew R., Butler, R. Paul, Chairetas, Stavros, Chontos, Ashley, Christiansen, Jessie, Ciardi, David R., Clark, Catherine A., Cloutier, Ryan, Craig, Matthew W., Crane, Jeffrey D., Dowling, Nicholas, Dressing, Courtney D., Emmanuel, Jehin, Evans, Phil, Everett, Mark E., Fernández-Rodrı́guez, Gareb, Fernández Fernández, Jorge, Forés-Toribio, Raquel, Fortenbach, Charles D., Fukui, Akihiko, Furlan, Elise, Gan, Tianjun, Ghachoui, Mourad, Giacalone, Steven, Gill, Samuel, Gillon, Michaël, Hall, Kylie, Hayashi, Yuya, Hedges, Christina, Higuera, Jesus, Hintz, Eric G., Hirsch, Lea, Holcomb, Rae, Horne, Keith, Grau Horta, Ferran, Howard, Andrew W., Howell, Steve B., Isaacson, Howard, Jenkins, Jon M., Kagetani, Taiki, Kamler, Jacob, Kendall, Alicia, Korth, Judith, Kroft, Maxwell A., Lacedelli, Gaia, Laloum, Didier, Law, Nicholas, de Leon, Jerome Pitogo, Levine, Alan M., Lewin, Pablo, Logsdon, Sarah E., Lund, Michael B., Madsen, Madelyn M., Mann, Andrew W., Mann, Christopher R., Maslennikova, Nataliia A., Matutano, Sandra, McCormack, Mason, McLeod, Kim K., Michaels, Edward J., Mireles, Ismael, Mori, Mayuko, Muñoz, Jose A., Murgas, Felipe, Narita, Norio, O’Brien, Sean M., Odden, Caroline, Palle, Enric, Patel, Yatrik G., Plavchan, Peter, Polanski, Alex S., Popowicz, Adam, Radford, Don J., Reed, Phillip A., Relles, Howard M., Rice, Malena, Ricker, George R., Safonov, Boris S., Savel, Arjun B., Schulte, Jack, Schwarz, Richard P., Schweiker, Heidi, Seager, Sara, Sefako, Ramotholo, Shectman, Stephen A., Shporer, Avi, Stephens, Denise C., Stockdale, Chris, Striegel, Stephanie, Tan, Thiam-Guan, Teske, Johanna K., Timmermans, Mathilde, Ulmer-Moll, Solène, Wang, Gavin, Wheatley, Peter J., Yalcinkaya, Selçuk, Zambelli, Roberto, Van Zandt, Judah, and Ziegler, Carl (hide). (2025) The Astrophysical Journal Supplement Series, 280, 30 [Abs] [arXiv] [Paper]

   We present the discovery of 30 transiting giant planets that were initially detected using data from NASA’s Transiting Exoplanet Survey Satellite mission. These new planets orbit relatively bright (G \ensuremath≤ 12.5) FGK host stars with orbital periods between 1.6 and 8.2 days, and have radii between 0.9 and 1.7 Jupiter radii. We performed follow-up ground-based photometry, high angular resolution imaging, high-resolution spectroscopy, and radial velocity monitoring for each of these objects to confirm that they are planets and determine their masses and other system parameters. The planets’ masses span more than an order of magnitude (0.17 M_J < M_p < 3.3 M_J). For two planets, TOI-3593 b and TOI-4961 b, we measured significant nonzero eccentricities of 0.11‑0.03+0.05 and 0.18‑0.05+0.04 , respectively, while for the other planets, the data typically provide a 1\ensuremathσ upper bound of 0.15 on the eccentricity. These discoveries represent a major step toward assembling a complete, magnitude-limited sample of transiting hot Jupiters around FGK stars. *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

4. The True Stellar Obliquity of a Sub-Saturn Planet from the Tierras Observatory and the Keck Planet Finder Tamburo, Patrick, Yee, Samuel W., Garcı́a-Mejı́a, Juliana, Stefánsson, Gudmundur, Charbonneau, David, and 5 more authors. Bieryla, Allyson, Howard, Andrew W., Isaacson, Howard, Fulton, Benjamin J., and Householder, Aaron (hide). (2025) The Astronomical Journal, 170, 34 [Abs] [arXiv] [Paper]

   We measure the true obliquity of TOI-2364, a K dwarf with a sub-Saturn- mass (M_p = 0.18 M_J) transiting planet on the upper edge of the hot-Neptune desert. We used new Rossiter–McLaughlin observations gathered with the Keck Planet Finder to measure the sky-projected obliquity \ensuremathλ = 7\textdegree + 10\textdegree–11\textdegree. Combined with a stellar rotation period of 23.47 \ensuremath\pm 0.29 days measured with photometry from the Tierras Observatory, this yields a stellar inclination of 90\textdegree \ensuremath\pm 13\textdegree and a true obliquity \ensuremathψ = 15.\textdegree6 + 7.\textdegree7–7.\textdegree3, indicating that the planet’s orbit is well aligned with the rotation axis of its host star. The determination of \ensuremathψ is important for investigating a potential bimodality in the orbits of short- period sub-Saturns around cool stars, which tend to be either aligned with or perpendicular to their host stars’ spin axes.

5. The Super-puff WASP-193 b is on a Well-aligned Orbit Yee, Samuel W., Stefánsson, Gudmundur, Thorngren, Daniel, Monson, Andy, Hartman, Joel D., and 6 more authors. Charbonneau, David B., Teske, Johanna K., Butler, R. Paul, Crane, Jeffrey D., Osip, David, and Shectman, Stephen A. (hide). (2025) The Astronomical Journal, 169, 225 [Abs] [arXiv] [Paper]

   The “super-puffs” are a population of planets that have masses comparable to that of Neptune but radii similar to Jupiter, leading to extremely low bulk densities (\ensuremathρ_p \ensuremath≲ 0.2 g cm^‑3) that are not easily explained by standard core accretion models. Interestingly, several of these super-puffs are found in orbits significantly misaligned with their host stars’ spin axes, indicating past dynamical excitation that may be connected to their low densities. Here, we present new Magellan/Planet Finder Spectrograph radial velocity measurements of WASP-193, a late F star hosting one of the least dense transiting planets known to date (, , \ensuremathρ_p = 0.060 \ensuremath\pm 0.019 g cm^‑3). We refine the bulk properties of WASP-193 b and use interior structure models to determine that the planet can be explained if it consists of roughly equal amounts of metals and H/He, with a metal fraction of Z = 0.42. The planet is likely substantially reinflated due to its host star’s evolution, and expected to be actively undergoing mass loss. We also measure the projected stellar obliquity using the Rossiter–McLaughlin effect, finding that WASP-193 b is on an orbit well aligned with the stellar equator, with degrees. WASP-193 b is the first Jupiter- sized super-puff on a relatively well-aligned orbit, suggesting a diversity of formation pathways for this population of planets. ^*This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile

6. A Planet Candidate Orbiting near the Hot Jupiter TOI-2818 b Inferred through Transit Timing McKee, Brendan J., Montet, Benjamin T., Yee, Samuel W., Hartman, Joel D., Winn, Joshua N., and 3 more authors. Martins, Jorge H. C., Silva, André M., and Wallace, Alexander L. (hide). (2025) The Astrophysical Journal, 981, 106 [Abs] [arXiv] [Paper]

   TOI-2818 b is a hot Jupiter orbiting a slightly evolved G-type star on a 4.04 day orbit that shows transit timing variations (TTVs) suggestive of a decreasing orbital period. In the most recent year of TESS observations, transits were observed \ensuremath∼8 minutes earlier than expected for a constant period. The implied orbital decay rate is 1.35 \ensuremath\pm 0.25 s yr^‑1, too fast to be explained by tidal dissipation, even considering the evolved nature of the host star. Radial velocity (RV) monitoring and astrometric data make the possibility of perturbations from a long-period companion unlikely; further Doppler spectroscopy observations can efficiently confirm or rule out such a companion. Apsidal precession due to the tidal distortion of the planet is also physically implausible. The most plausible explanation for the TTVs appears to be gravitational perturbations from a hitherto undetected planet with mass \ensuremath≲10 M_\ensuremath⊕ that is in (or near) a mean-motion resonance with the hot Jupiter. Such a planet could be responsible for the observed TTVs while avoiding detection with the available RV and transit data.

2024

1. Additional Doppler Monitoring Corroborates HAT-P-11c as a Planet Yee, Samuel W., Petigura, Erik A., Isaacson, Howard, Howard, Andrew W., Blunt, Sarah, and 13 more authors. Dalba, Paul A., Dai, Fei, Fulton, Benjamin J., Giacalone, Steven, Kane, Stephen R., Kosiarek, Molly, Močnik, Teo, Rice, Malena, Rubenzahl, Ryan, Saunders, Nicholas, Tyler, Dakotah, Weiss, Lauren M., and Zhang, Jingwen (hide). (2024) Research Notes of the American Astronomical Society, 8, 187 [Abs] [arXiv] [Paper]

   In 2010, Bakos and collaborators discovered a Neptune-sized planet transiting the K-dwarf HAT-P-11 every five days. Later in 2018, Yee and collaborators reported an additional Jovian-mass companion on a nine year orbit based on a decade of Doppler monitoring. The eccentric outer giant HAT-P-11c may be responsible for the peculiar polar orbit of the inner planet HAT-P-11b. However, Basilicata et al. recently suggested that the HAT-P-11c Doppler signal could be caused by stellar activity. In this research note, we extend the Yee et al. Doppler time series by six years. The combined data set spanning 17 yr covers nearly two orbits of the outer planet. Importantly, we observe two periastron passages of planet c and do not observe a coherent activity signature. Together with the previously reported astrometric acceleration of HAT-P-11 from Hipparcos and Gaia, we believe there is strong evidence for HAT-P-11c as a bona fide planet.

2023

1. The Period Distribution of Hot Jupiters Is Not Dependent on Host Star Metallicity Yee, Samuel W., and Winn, Joshua N. (2023) The Astrophysical Journal Letters, 949, L21 [Abs] [arXiv] [Paper]

   The probability that a Sun-like star has a close-orbiting giant planet (period \ensuremath≲1 yr) increases with stellar metallicity. Previous work provided evidence that the period distribution of close-orbiting giant planets is also linked to metallicity, hinting that there two formation/evolution pathways for such objects, one of which is more probable in high- metallicity environments. Here, we check for differences in the period distribution of hot Jupiters (P < 10 days) as a function of host star metallicity, drawing on a sample of 232 transiting hot Jupiters and homogeneously derived metallicities from Gaia Data Release 3. We found no evidence for any metallicity dependence; the period distributions of hot Jupiters around metal-poor and metal-rich stars are indistinguishable. As a byproduct of this study, we provide transformations between metallicities from the Gaia Radial Velocity Spectrograph and from traditional high-resolution optical spectroscopy of main- sequence FGK stars.

2. The TESS Grand Unified Hot Jupiter Survey. II. Twenty New Giant Planets Yee, Samuel W., Winn, Joshua N., Hartman, Joel D., Bouma, Luke G., Zhou, George, and 82 more authors. Quinn, Samuel N., Latham, David W., Bieryla, Allyson, Rodriguez, Joseph E., Collins, Karen A., Alfaro, Owen, Barkaoui, Khalid, Beard, Corey, Belinski, Alexander A., Benkhaldoun, Zouhair, Benni, Paul, Bernacki, Krzysztof, Boyle, Andrew W., Butler, R. Paul, Caldwell, Douglas A., Chontos, Ashley, Christiansen, Jessie L., Ciardi, David R., Collins, Kevin I., Conti, Dennis M., Crane, Jeffrey D., Daylan, Tansu, Dressing, Courtney D., Eastman, Jason D., Essack, Zahra, Evans, Phil, Everett, Mark E., Fajardo-Acosta, Sergio, Forés-Toribio, Raquel, Furlan, Elise, Ghachoui, Mourad, Gillon, Michaël, Hellier, Coel, Helm, Ian, Howard, Andrew W., Howell, Steve B., Isaacson, Howard, Jehin, Emmanuel, Jenkins, Jon M., Jensen, Eric L. N., Kielkopf, John F., Laloum, Didier, Leonhardes-Barboza, Naunet, Lewin, Pablo, Logsdon, Sarah E., Lubin, Jack, Lund, Michael B., MacDougall, Mason G., Mann, Andrew W., Maslennikova, Natalia A., Massey, Bob, McLeod, Kim K., Muñoz, Jose A., Newman, Patrick, Orlov, Valeri, Plavchan, Peter, Popowicz, Adam, Pozuelos, Francisco J., Pritchard, Tyler A., Radford, Don J., Reefe, Michael, Ricker, George R., Rudat, Alexander, Safonov, Boris S., Schwarz, Richard P., Schweiker, Heidi, Scott, Nicholas J., Seager, S., Shectman, Stephen A., Stockdale, Chris, Tan, Thiam-Guan, Teske, Johanna K., Thomas, Neil B., Timmermans, Mathilde, Vanderspek, Roland, Vermilion, David, Watanabe, David, Weiss, Lauren M., West, Richard G., Van Zandt, Judah, Zejmo, Michal, and Ziegler, Carl (hide). (2023) The Astrophysical Journal Supplement Series, 265, 1 [Abs] [arXiv] [Paper]

   NASA’s Transiting Exoplanet Survey Satellite (TESS) mission promises to improve our understanding of hot Jupiters by providing an all- sky, magnitude-limited sample of transiting hot Jupiters suitable for population studies. Assembling such a sample requires confirming hundreds of planet candidates with additional follow-up observations. Here we present 20 hot Jupiters that were detected using TESS data and confirmed to be planets through photometric, spectroscopic, and imaging observations coordinated by the TESS Follow-up Observing Program. These 20 planets have orbital periods shorter than 7 days and orbit relatively bright FGK stars (10.9 < G < 13.0). Most of the planets are comparable in mass to Jupiter, although there are four planets with masses less than that of Saturn. TOI-3976b, the longest-period planet in our sample (P = 6.6 days), may be on a moderately eccentric orbit (e = 0.18 \ensuremath\pm 0.06), while observations of the other targets are consistent with them being on circular orbits. We measured the projected stellar obliquity of TOI-1937A b, a hot Jupiter on a 22.4 hr orbit with the Rossiter-McLaughlin effect, finding the planet’s orbit to be well aligned with the stellar spin axis (\ensuremath∣\ensuremathλ\ensuremath∣ = 4.\textdegree0 \ensuremath\pm 3.\textdegree5). We also investigated the possibility that TOI-1937 is a member of the NGC 2516 open cluster but ultimately found the evidence for cluster membership to be ambiguous. These objects are part of a larger effort to build a complete sample of hot Jupiters to be used for future demographic and detailed characterization work. *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile

2022

1. The TESS Grand Unified Hot Jupiter Survey. I. Ten TESS Planets Yee, Samuel W., Winn, Joshua N., Hartman, Joel D., Rodriguez, Joseph E., Zhou, George, and 67 more authors. Quinn, Samuel N., Latham, David W., Bieryla, Allyson, Collins, Karen A., Addison, Brett C., Angelo, Isabel, Barkaoui, Khalid, Benni, Paul, Boyle, Andrew W., Brahm, Rafael, Butler, R. Paul, Ciardi, David R., Collins, Kevin I., Conti, Dennis M., Crane, Jeffrey D., Dai, Fei, Dressing, Courtney D., Eastman, Jason D., Essack, Zahra, Forés-Toribio, Raquel, Furlan, Elise, Gan, Tianjun, Giacalone, Steven, Gill, Holden, Girardin, Eric, Henning, Thomas, Henze, Christopher E., Hobson, Melissa J., Horner, Jonathan, Howard, Andrew W., Howell, Steve B., Huang, Chelsea X., Isaacson, Howard, Jenkins, Jon M., Jensen, Eric L. N., Jordán, Andrés, Kane, Stephen R., Kielkopf, John F., Lasota, Slawomir, Levine, Alan M., Lubin, Jack, Mann, Andrew W., Massey, Bob, McLeod, Kim K., Mengel, Matthew W., Muñoz, Jose A., Murgas, Felipe, Palle, Enric, Plavchan, Peter, Popowicz, Adam, Radford, Don J., Ricker, George R., Rowden, Pamela, Safonov, Boris S., Savel, Arjun B., Schwarz, Richard P., Seager, S., Sefako, Ramotholo, Shporer, Avi, Srdoc, Gregor, Strakhov, Ivan S., Teske, Johanna K., Tinney, C. G., Tyler, Dakotah, Wittenmyer, Robert A., Zhang, Hui, and Ziegler, Carl (hide). (2022) The Astronomical Journal, 164, 70 [Abs] [arXiv] [Paper]

   Hot Jupiters-short-period giant planets-were the first extrasolar planets to be discovered, but many questions about their origin remain. NASA’s Transiting Exoplanet Survey Satellite (TESS), an all-sky search for transiting planets, presents an opportunity to address these questions by constructing a uniform sample of hot Jupiters for demographic study through new detections and unifying the work of previous ground-based transit surveys. As the first results of an effort to build this large sample of planets, we report here the discovery of 10 new hot Jupiters (TOI-2193A b, TOI-2207b, TOI-2236b, TOI-2421b, TOI-2567b, TOI-2570b, TOI-3331b, TOI-3540A b, TOI-3693b, TOI-4137b). All of the planets were identified as planet candidates based on periodic flux dips observed by TESS, and were subsequently confirmed using ground-based time-series photometry, high- angular-resolution imaging, and high-resolution spectroscopy coordinated with the TESS Follow-up Observing Program. The 10 newly discovered planets orbit relatively bright F and G stars (G < 12.5, T _eff between 4800 and 6200 K). The planets’ orbital periods range from 2 to 10 days, and their masses range from 0.2 to 2.2 Jupiter masses. TOI-2421b is notable for being a Saturn-mass planet and TOI-2567b for being a “sub-Saturn,” with masses of 0.322 \ensuremath\pm 0.073 and 0.195 \ensuremath\pm 0.030 Jupiter masses, respectively. We also measured a detectably eccentric orbit (e = 0.17 \ensuremath\pm 0.05) for TOI-2207b, a planet on an 8 day orbit, while placing an upper limit of e < 0.052 for TOI-3693b, which has a 9 day orbital period. The 10 planets described here represent an important step toward using TESS to create a large and statistically useful sample of hot Jupiters.

2021

1. How Complete Are Surveys for Nearby Transiting Hot Jupiters? Yee, Samuel W., Winn, Joshua N., and Hartman, Joel D. (2021) The Astronomical Journal, 162, 240 [Abs] [arXiv] [Paper]

   Hot Jupiters are a rare and interesting outcome of planet formation. Although more than 500 hot Jupiters (HJs) are known, most of them were discovered by a heterogeneous collection of surveys with selection biases that are difficult to quantify. Currently, our best knowledge of HJ demographics around FGK stars comes from the sample of \ensuremath≈40 objects detected by the Kepler mission, which have a well-quantified selection function. Using the Kepler results, we simulate the characteristics of the population of nearby transiting HJs. A comparison between the known sample of nearby HJs and simulated magnitude-limited samples leads to four conclusions. (1) The known sample of HJs appears to be \ensuremath≈75% complete for stars brighter than Gaia G \ensuremath≤ 10.5, falling to \ensuremath≲50% for G \ensuremath≤ 12. (2) There are probably a few undiscovered HJs with host stars brighter than G \ensuremath≈ 10 located within 10\textdegree of the Galactic plane. (3) The period and radius distributions of HJs may differ for F-type hosts (which dominate the nearby sample) and G-type hosts (which dominate the Kepler sample). (4) To obtain a magnitude-limited sample of HJs that is larger than the Kepler sample by an order of magnitude, the limiting magnitude should be approximately G \ensuremath≈ 12.5. This magnitude limit is within the range for which NASA’s Transiting Exoplanet Survey Satellite can easily detect HJs, presenting the opportunity to greatly expand our knowledge of hot-Jupiter demographics.

2. How Close are Compact Multiplanet Systems to the Stability Limit? Yee, Samuel W., Tamayo, Daniel, Hadden, Samuel, and Winn, Joshua N. (2021) The Astronomical Journal, 162, 55 [Abs] [arXiv] [Paper]

   Transit surveys have revealed a significant population of compact multiplanet systems, containing several sub-Neptune-mass planets on close-in, tightly-packed orbits. These systems are thought to have formed through a final phase of giant impacts, which would tend to leave systems close to the edge of stability. Here, we assess this hypothesis, comparing observed eccentricities in systems exhibiting transit-timing variations versus the maximum eccentricities compatible with long-term stability. We use the machine-learning classifier SPOCK (Tamayo et al.) to rapidly classify the stability of numerous initial configurations and hence determine these stability limits. While previous studies have argued that multiplanet systems are often maximally packed, in the sense that they could not host any additional planets, we find that the existing planets in these systems have measured eccentricities below the limits allowed by stability by a factor of 2-10. We compare these results against predictions from the giant-impact theory of planet formation, derived from both N-body integrations and theoretical expectations that, in the absence of dissipation, the orbits of such planets should be distributed uniformly throughout the phase space volume allowed by stability. We find that the observed systems have systematically lower eccentricities than this scenario predicts, with a median eccentricity about four times lower than predicted. This suggests that, if these systems formed through giant impacts, then some dissipation must occur to damp their eccentricities. This may occur through interactions with the natal gas disk or a leftover population of planetesimals, or over longer timescales through the coupling of tidal and secular processes.

2020

1. The Orbit of WASP-12b Is Decaying Yee, Samuel W., Winn, Joshua N., Knutson, Heather A., Patra, Kishore C., Vissapragada, Shreyas, and 4 more authors. Zhang, Michael M., Holman, Matthew J., Shporer, Avi, and Wright, Jason T. (hide). (2020) The Astrophysical Journal Letters, 888, L5 [Abs] [arXiv] [Paper]

   WASP-12b is a transiting hot Jupiter on a 1.09 day orbit around a late-F star. Since the planet’s discovery in 2008, the time interval between transits has been decreasing by 29 \ensuremath\pm 2 ms yr^-1. This is a possible sign of orbital decay, although the previously available data left open the possibility that the planet’s orbit is slightly eccentric and is undergoing apsidal precession. Here, we present new transit and occultation observations that provide more decisive evidence for orbital decay, which is favored over apsidal precession by a {{\ensuremath∆ }}{BIC} of 22.3 or Bayes factor of 70,000. We also present new radial- velocity data that rule out the Rømer effect as the cause of the period change. This makes WASP-12 the first planetary system for which we can be confident that the orbit is decaying. The decay timescale for the orbit is P/\textbackslashdot{P}=3.25+/- 0.23 {Myr}. Interpreting the decay as the result of tidal dissipation, the modified stellar tidal quality factor is {Q}_\textbackslashstar ^{\textbackslashprime }=1.8\texttimes {10}^5.

2018

1. HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities Yee, Samuel W., Petigura, Erik A., Fulton, Benjamin J., Knutson, Heather A., Batygin, Konstantin, and 8 more authors. Bakos, Gáspár Á., Hartman, Joel D., Hirsch, Lea A., Howard, Andrew W., Isaacson, Howard, Kosiarek, Molly R., Sinukoff, Evan, and Weiss, Lauren M. (hide). (2018) The Astronomical Journal, 155, 255 [Abs] [arXiv] [Paper]

   HAT-P-11 is a mid-K dwarf that hosts one of the first Neptune-sized planets found outside the solar system. The orbit of HAT-P-11b is misaligned with the star’s spin—one of the few known cases of a misaligned planet orbiting a star less massive than the Sun. We find an additional planet in the system based on a decade of precision radial velocity (RV) measurements from Keck/High Resolution Echelle Spectrometer. HAT-P-11c is similar to Jupiter in its mass ({M}_P\textbackslashsin i=1.6+/- 0.1 M _ J ) and orbital period (P={9.3}_-0.5^+1.0 year), but has a much more eccentric orbit (e = 0.60 \ensuremath\pm 0.03). In our joint modeling of RV and stellar activity, we found an activity-induced RV signal of \ensuremath∼7 {{m}} {{{s}}}^-1, consistent with other active K dwarfs, but significantly smaller than the 31 {{m}} {{{s}}}^-1 reflex motion due to HAT-P-11c. We investigated the dynamical coupling between HAT-P-11b and c as a possible explanation for HAT-P-11b’s misaligned orbit, finding that planet-planet Kozai interactions cannot tilt planet b’s orbit due to general relativistic precession; however, nodal precession operating on million year timescales is a viable mechanism to explain HAT-P-11b’s high obliquity. This leaves open the question of why HAT-P-11c may have such a tilted orbit. At a distance of 38 pc, the HAT-P-11 system offers rich opportunities for further exoplanet characterization through astrometry and direct imaging.

2017

1. Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library Yee, Samuel W., Petigura, Erik A., and von Braun, Kaspar (2017) The Astrophysical Journal, 836, 77 [Abs] [arXiv] [Paper]

   Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution (R \ensuremath≈ 60,000), high signal-to-noise ratio (S/N \ensuremath≈ 150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well- characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types \ensuremath∼M5-F1 (T _eff \ensuremath≈ 3000-7000 K, R _\ensuremath⋆ \ensuremath≈ 0.1-16 R _\ensuremath⊙). We also present “Empirical SpecMatch” (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100 K in effective temperature (T _eff), 15% in stellar radius (R _\ensuremath⋆), and 0.09 dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars \ensuremath∼K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in T _eff, 10% in R _\ensuremath⋆, and 0.12 dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.