publications

2023

1. The TESS-Keck Survey. XV. Precise Properties of 108 TESS Planets and Their Host Stars MacDougall, Mason G., Petigura, Erik A., Gilbert, Gregory J., Angelo, Isabel, Batalha, Natalie M., and 36 more authors, including Yee, S. W.. Beard, Corey, Behmard, Aida, Blunt, Sarah, Brinkman, Casey, Chontos, Ashley, Crossfield, Ian J. M., Dai, Fei, Dalba, Paul A., Dressing, Courtney, Fetherolf, Tara, Fulton, Benjamin, Giacalone, Steven, Hill, Michelle L., Holcomb, Rae, Howard, Andrew W., Huber, Daniel, Isaacson, Howard, Kane, Stephen R., Kosiarek, Molly, Lubin, Jack, Mayo, Andrew, Močnik, Teo, Akana Murphy, Joseph M., Pidhorodetska, Daria, Polanski, Alex S., Rice, Malena, Robertson, Paul, Rosenthal, Lee J., Roy, Arpita, Rubenzahl, Ryan A., Scarsdale, Nicholas, Turtelboom, Emma V., Tyler, Dakotah, Van Zandt, Judah, Weiss, Lauren M., and Yee, Samuel W. (hide). (2023) The Astronomical Journal, 166, 33 [Abs] [arXiv] [URL]

   We present the stellar and planetary properties for 85 TESS Objects of Interest (TOIs) hosting 108 planet candidates that compose the TESS-Keck Survey (TKS) sample. We combine photometry, high- resolution spectroscopy, and Gaia parallaxes to measure precise and accurate stellar properties. We then use these parameters as inputs to a light-curve processing pipeline to recover planetary signals and homogeneously fit their transit properties. Among these transit fits, we detect significant transit-timing variations among at least three multiplanet systems (TOI-1136, TOI-1246, TOI-1339) and at least one single-planet system (TOI-1279). We also reduce the uncertainties on planet-to-star radius ratios R _p /R _\ensuremath⋆ across our sample, from a median fractional uncertainty of 8.8% among the original TOI Catalog values to 3.0% among our updated results. With this improvement, we are able to recover the Radius Gap among small TKS planets and find that the topology of the Radius Gap among our sample is broadly consistent with that measured among Kepler planets. The stellar and planetary properties presented here will facilitate follow-up investigations of both individual TOIs and broader trends in planet properties, system dynamics, and the evolution of planetary systems.

2. Three Saturn-mass planets transiting F-type stars revealed with TESS and HARPS. TOI-615b, TOI-622b, and TOI-2641b Psaridi, Angelica, Bouchy, François, Lendl, Monika, Akinsanmi, Babatunde, Stassun, Keivan G., and 60 more authors, including Yee, S. W.. Smalley, Barry, Armstrong, David J., Howard, Saburo, Ulmer-Moll, Solène, Grieves, Nolan, Barkaoui, Khalid, Rodriguez, Joseph E., Bryant, Edward M., Suárez, Olga, Guillot, Tristan, Evans, Phil, Attia, Omar, Wittenmyer, Robert A., Yee, Samuel W., Collins, Karen A., Zhou, George, Galland, Franck, Parc, Léna, Udry, Stéphane, Figueira, Pedro, Ziegler, Carl, Mordasini, Christoph, Winn, Joshua N., Seager, Sara, Jenkins, Jon M., Twicken, Joseph D., Brahm, Rafael, Jones, Matı́as I., Abe, Lyu, Addison, Brett, Briceño, César, Briegal, Joshua T., Collins, Kevin I., Daylan, Tansu, Eigmüller, Phillip, Furesz, Gabor, Guerrero, Natalia M., Hagelberg, Janis, Heitzmann, Alexis, Hounsell, Rebekah, Huang, Chelsea X., Krenn, Andreas, Law, Nicholas M., Mann, Andrew W., McCormac, James, Mékarnia, Djamel, Mounzer, Dany, Nielsen, Louise D., Osborn, Ares, Reinarz, Yared, Sefako, Ramotholo R., Steiner, Michal, Strøm, Paul A., Triaud, Amaury H. M. J., Vanderspek, Roland, Vanzi, Leonardo, Vines, Jose I., Watson, Christopher A., Wright, Duncan J., and Zapata, Abner (hide). (2023) Astronomy & Astrophysics, 675, A39 [Abs] [arXiv] [URL]

   While the sample of confirmed exoplanets continues to grow, the population of transiting exoplanets around early-type stars is still limited. These planets allow us to investigate the planet properties and formation pathways over a wide range of stellar masses and study the impact of high irradiation on hot Jupiters orbiting such stars. We report the discovery of TOI-615b, TOI-622b, and TOI-2641b, three Saturn-mass planets transiting main sequence, F-type stars. The planets were identified by the Transiting Exoplanet Survey Satellite (TESS) and confirmed with complementary ground-based and radial velocity observations. TOI-615b is a highly irradiated (\raisebox-0.5ex\textasciitilde1277 F^\ensuremath⊕) and bloated Saturn-mass planet (1.69_\ensuremath-0.06^+0.05 R_Jup and 0.43_\ensuremath-0.08^+0.09 M_Jup) in a 4.66 day orbit transiting a 6850 K star. TOI-622b has a radius of 0.82_\ensuremath-0.03^+0.03 R_Jup and a mass of 0.30_\ensuremath-0.08^+0.07 M_Jup in a 6.40 day orbit. Despite its high insolation flux (\raisebox-0.5ex\textasciitilde600 F^\ensuremath⊕), TOI-622b does not show any evidence of radius inflation. TOI-2641b is a 0.39_\ensuremath-0.04^+0.02 M_Jup planet in a 4.88 day orbit with a grazing transit (b = 1.04_\ensuremath-0.06^+0.05) that results in a poorly constrained radius of 1.61_\ensuremath-0.64^+0.46 R_Jup. Additionally, TOI-615b is considered attractive for atmospheric studies via transmission spectroscopy with ground-based spectrographs and JWST. Future atmospheric and spin-orbit alignment observations are essential since they can provide information on the atmospheric composition, formation, and migration of exoplanets across various stellar types. \\textbackslashThe photometric and radial velocity data in this work are only available at the CDS via anonymous ftp to <A href=“https://cdsa rc.cds.unistra.fr/”>cdsarc.cds.unistra.fr</A> (ftp://130.79.128.5) or via <A href=“https://cdsarc.cds.unistra.fr/viz- bin/cat/J/A+A/675/A39”>https://cdsarc.cds.unistra.fr/viz- bin/cat/J/A+A/675/A39</A>

3. 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] [URL]

   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.

4. Scaling K2. VI. Reduced Small-planet Occurrence in High-galactic-amplitude Stars Zink, Jon K., Hardegree-Ullman, Kevin K., Christiansen, Jessie L., Petigura, Erik A., Boley, Kiersten M., and 11 more authors, including Yee, S. W.. Bhure, Sakhee, Rice, Malena, Yee, Samuel W., Isaacson, Howard, Fernandes, Rachel B., Howard, Andrew W., Blunt, Sarah, Lubin, Jack, Chontos, Ashley, Pidhorodetska, Daria, and MacDougall, Mason G. (hide). (2023) The Astronomical Journal, 165, 262 [Abs] [arXiv] [URL]

   In this study, we performed a homogeneous analysis of the planets around FGK dwarf stars observed by the Kepler and K2 missions, providing spectroscopic parameters for 310 K2 targets -including 239 Scaling K2 hosts-observed with Keck/HIRES. For orbital periods less than 40 days, we found that the distribution of planets as a function of orbital period, stellar effective temperature, and metallicity was consistent between K2 and Kepler, reflecting consistent planet formation efficiency across numerous \raisebox-0.5ex\textasciitilde1 kpc sight-lines in the local Milky Way. Additionally, we detected a 3\texttimes excess of sub-Saturns relative to warm Jupiters beyond 10 days, suggesting a closer association between sub-Saturn and sub- Neptune formation than between sub-Saturn and Jovian formation. Performing a joint analysis of Kepler and K2 demographics, we observed diminishing super-Earth, sub-Neptune, and sub-Saturn populations at higher stellar effective temperatures, implying an inverse relationship between formation and disk mass. In contrast, no apparent host-star spectral-type dependence was identified for our population of Jupiters, which indicates gas- giant formation saturates within the FGK mass regimes. We present support for stellar metallicity trends reported by previous Kepler analyses. Using Gaia DR3 proper motion and radial velocity measurements, we discovered a galactic location trend; stars that make large vertical excursions from the plane of the Milky Way host fewer super-Earths and sub-Neptunes. While oscillation amplitude is associated with metallicity, metallicity alone cannot explain the observed trend, demonstrating that galactic influences are imprinted on the planet population. Overall, our results provide new insights into the distribution of planets around FGK dwarf stars and the factors that influence their formation and evolution.

5. 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] [URL]

   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

6. NEID Reveals That the Young Warm Neptune TOI-2076 b Has a Low Obliquity Frazier, Robert C., Stefánsson, Gudmundur, Mahadevan, Suvrath, Yee, Samuel W., Cañas, Caleb I., and 25 more authors. Winn, Joshua N., Luhn, Jacob, Dai, Fei, Doyle, Lauren, Cegla, Heather, Kanodia, Shubham, Robertson, Paul, Wisniewski, John, Bender, Chad F., Dong, Jiayin, Gupta, Arvind F., Halverson, Samuel, Hawley, Suzanne, Hebb, Leslie, Holcomb, Rae, Kowalski, Adam, Libby-Roberts, Jessica, Lin, Andrea S. J., McElwain, Michael W., Ninan, Joe P., Petrovich, Cristobal, Roy, Arpita, Schwab, Christian, Terrien, Ryan C., and Wright, Jason T. (hide). (2023) The Astrophysical Journal Letters, 944, L41 [Abs] [arXiv] [URL]

   TOI-2076 b is a sub-Neptune-sized planet (R = 2.39 \ensuremath\pm 0.10 R _\ensuremath⊕) that transits a young (204 \ensuremath\pm 50 MYr) bright (V = 9.2) K-dwarf hosting a system of three transiting planets. Using spectroscopic observations obtained with the NEID spectrograph on the WIYN 3.5 m Telescope, we model the Rossiter-McLaughlin effect of TOI-2076 b, and derive a sky-projected obliquity of λ=-3_-15^+16^∘ . Using the size of the star (R = 0.775 \ensuremath\pm 0.015 R _\ensuremath⊙), and the stellar rotation period (P _rot = 7.27 \ensuremath\pm 0.23 days), we estimate an obliquity of ψ=18_-9^+10^∘ (\ensuremathψ < 34\textdegree at 95% confidence), demonstrating that TOI-2076 b is in a well- aligned orbit. Simultaneous diffuser-assisted photometry from the 3.5 m telescope at Apache Point Observatory rules out flares during the transit. TOI-2076 b joins a small but growing sample of young planets in compact multi-planet systems with well- aligned orbits, and is the fourth planet with an age \ensuremath≲300 Myr in a multi-transiting system with an obliquity measurement. The low obliquity of TOI-2076 b and the presence of transit timing variations in the system suggest the TOI-2076 system likely formed via convergent disk migration in an initially well-aligned disk.

7. TOI-1075 b: A Dense, Massive, Ultra-short-period Hot Super-Earth Straddling the Radius Gap Essack, Zahra, Shporer, Avi, Burt, Jennifer A., Seager, Sara, Cambioni, Saverio, and 27 more authors, including Yee, S. W.. Lin, Zifan, Collins, Karen A., Mamajek, Eric E., Stassun, Keivan G., Ricker, George R., Vanderspek, Roland, Latham, David W., Winn, Joshua N., Jenkins, Jon M., Butler, R. Paul, Charbonneau, David, Collins, Kevin I., Crane, Jeffrey D., Gan, Tianjun, Hellier, Coel, Howell, Steve B., Irwin, Jonathan, Mann, Andrew W., Ramadhan, Ali, Shectman, Stephen A., Teske, Johanna K., Yee, Samuel W., Mireles, Ismael, Quintana, Elisa V., Tenenbaum, Peter, Torres, Guillermo, and Furlan, Elise (hide). (2023) The Astronomical Journal, 165, 47 [Abs] [arXiv] [URL]

   Populating the exoplanet mass-radius diagram in order to identify the underlying relationship that governs planet composition is driving an interdisciplinary effort within the exoplanet community. The discovery of hot super-Earths - a high temperature, short-period subset of the super-Earth planet population - has presented many unresolved questions concerning the formation, evolution, and composition of rocky planets. We report the discovery of a transiting, ultra-short period hot super-Earth orbiting TOI-1075 (TIC 351601843), a nearby (d = 61.4 pc) late K-/early M-dwarf star, using data from the Transiting Exoplanet Survey Satellite (TESS). The newly discovered planet has a radius of 1.791^+0.116_-0.081 R_⊕, and an orbital period of 0.605 days (14.5 hours). We precisely measure the planet mass to be 9.95^+1.36_-1.30 M_⊕ using radial velocity measurements obtained with the Planet Finder Spectrograph (PFS), mounted on the Magellan II telescope. Our radial velocity data also show a long-term trend, suggesting an additional planet in the system. While TOI-1075 b is expected to have a substantial H/He atmosphere given its size relative to the radius gap, its high density (9.32^+2.05_-1.85 \rmg/cm^3) is likely inconsistent with this possibility. We explore TOI-1075 b’s location relative to the M-dwarf radius valley, evaluate the planet’s prospects for atmospheric characterization, and discuss potential planet formation mechanisms. Studying the TOI-1075 system in the broader context of ultra-short period planetary systems is necessary for testing planet formation and evolution theories, density enhancing mechanisms, and for future atmospheric and surface characterization studies via emission spectroscopy with JWST.

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] [URL]

   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 +/- 0.073 and 0.195 +/- 0.030 Jupiter masses, respectively. We also measured a detectably eccentric orbit (e = 0.17 +/- 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] [URL]

   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 ≈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 ≈75% complete for stars brighter than Gaia G ≤ 10.5, falling to ≤ 50% for G ≤ 12. (2) There are probably a few undiscovered HJs with host stars brighter than G ≈ 10 located within 10 degrees 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 ≈ 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, S. W., Tamayo, D., Hadden, S., and Winn, J. N. (2021) The Astronomical Journal, 162, 55 [Abs] [arXiv] [URL]

   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, S. W., Winn, J. N., Knutson, H. A., Patra, K. C., Vissapragada, S., and 4 more authors. Zhang, M. M., Holman, M. J., Shporer, A., and Wright, J. T. (hide). (2020) The Astrophysical Journal Letters, 888, L5 [Abs] [arXiv] [URL]

   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 ± 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 ΔBIC 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/\dotP=3.25+/- 0.23 Myr. Interpreting the decay as the result of tidal dissipation, the modified stellar tidal quality factor is Q_⋆^\prime = 1.8 \times 10^5.

2018

1. HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities Yee, S. W., Petigura, E. A., Fulton, B. J., Knutson, H. A., Batygin, K., and 8 more authors. Bakos, G. Á., Hartman, J. D., Hirsch, L. A., Howard, A. W., Isaacson, H., Kosiarek, M. R., Sinukoff, E., and Weiss, L. M. (hide). (2018) The Astronomical Journal, 155, 255 [Abs] [arXiv] [URL]

   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 sin 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 ± 0.03). In our joint modeling of RV and stellar activity, we found an activity-induced RV signal of ∼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.

2. Planet Candidates from K2 Campaigns 5–8 and Follow-up Optical Spectroscopy Petigura, E. A., Crossfield, I. J. M., Isaacson, H., Beichman, C. A., Christiansen, J. L., and 8 more authors, including Yee, S. W.. Dressing, C. D., Fulton, B. J., Howard, A. W., Kosiarek, M. R., Lépine, S., Schlieder, J. E., Sinukoff, E., and Yee, S. W. (hide). (2018) The Astronomical Journal, 155, 21 [Abs] [arXiv] [URL]

   We present 151 planet candidates orbiting 141 stars from K2 campaigns 5–8 (C5–C8), identified through a systematic search of K2 photometry. In addition, we identify 16 targets as likely eclipsing binaries, based on their light curve morphology. We obtained follow-up optical spectra of 105/141 candidate host stars and 8/16 eclipsing binaries to improve stellar properties and to identify spectroscopic binaries. Importantly, spectroscopy enables measurements of host star radii with ≈10% precision, compared to ≈40% precision when only broadband photometry is available. The improved stellar radii enable improved planet radii. Our curated catalog of planet candidates provides a starting point for future efforts to confirm and characterize K2 discoveries.

2017

1. Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library Yee, S. W., Petigura, E. A., and von Braun, K. (2017) The Astrophysical Journal, 836, 77 [Abs] [arXiv] [URL] [Code]

   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 ≈ 60,000), high signal-to-noise ratio (S/N ≈ 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 ˜M5-F1 (Teff ≈ 3000-7000 K, R ⋆ ≈ 0.1-16 R ⊙). 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 (Teff), 15% in stellar radius (R ⋆), and 0.09 dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars ˜K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in T eff, 10% in R ⋆, 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.

2011

1. The vertical oscillations of coupled magnets Li, K., Lin, J., Kang, Z. Y., Yee, S. W., and Wong, S. J. (2011) European Journal of Physics, 32, S1 [Abs] [URL]

   The International Young Physicists’ Tournament (IYPT) is a worldwide, annual competition for high school students. This paper is adapted from the winning solution to Problem 14, Magnetic Spring, as presented in the final round of the 23rd IYPT in Vienna, Austria. Two magnets were arranged on top of each other on a common axis. One was fixed, while the other could move vertically. Various parameters of interest were investigated, including the effective gravitational acceleration, the strength, size, mass and geometry of the magnets, and damping of the oscillations. Despite its simplicity, this setup yielded a number of interesting and unexpected relations. The first stage of the investigation was concerned only with the undamped oscillations of small amplitudes, and the period of small amplitude oscillations was found to be dependent only on the eighth root of important magnet properties such as its strength and mass. The second stage sought to investigate more general oscillations. A numerical model which took into account magnet size, magnet geometry and damping effects was developed to model the general oscillations. Air resistance and friction were found to be significant sources of damping, while eddy currents were negligible.