Young Planets in Star Clusters

While thousands of exoplanets are known, most orbit anonymous stars in the Milky Way that are between one and ten billion years old. I have been using TESS, Gaia, and Kepler to find and study planets around stars in clusters younger than one billion years. The stellar ensembles in which these planets reside enable precise age measurements, which helps us map out how planets evolve. Related articles include:

Kepler and the Behemoth: Three Mini-Neptunes in a 40 Million Year Old Association [Paper],
with R. Kerr, J. Curtis, H. Isaacson, and friends, in AJ (2022)

A 38 Million Year Old Neptune-Sized Planet in the Kepler Field [Paper]
with J. Curtis, K. Masuda, L. Hillenbrand, and friends, in AJ (2022)

Cluster Difference Imaging Photometric Survey. II. TOI 837: A Young Validated Planet in IC 2602 [Paper]
with J. Hartman, R. Brahm, P. Evans, and friends, in AJ (2020)

PTFO 8-8695: Two Stars, Two Signals, No Planet [Paper]
with J. Winn, G. Ricker, R. Vanderspek and friends,, in AJ (2020)

Cluster Difference Imaging Photometric Survey. I. Light Curves of Stars in Open Clusters from TESS Sectors 6 and 7 [Paper, light curves, planet candidates, supplementary documentation]
with J. Hartman, W. Bhatti, J Winn, and G. Bakos, in ApJS (2019)

Ages of Field Stars

While stars in clusters yield gold-standard ages for a select set of planets, age-dating methods applicable to field stars might let us study planet evolution across hundreds to even thousands of planets. Rotation-based age dating (gyrochronology) is one of the most promising methods to age-date FGK stars on the main-sequence. A recent study that addresses some previous issues in the accuracy and precision of gyrochronology follows:

The Empirical Limits of Gyrochronology [Paper, gyro-interp software package, movie #1, movie #2]
with E. Palumbo and L. Hillenbrand, in ApJL (2023).

Complex Periodic Variables

The “complex periodic variables” are young and low-mass stars that show highly structured and periodic optical light curves. We believe that they are explained by clumps of either gas or dust that are forced to corotate with the star for hundreds of stellar rotation cycles. While only a few percent of young low-mass stars show the phenomenon, after correcting for the viewing angle, up to a quarter of young M dwarfs might host this type of circumstellar gunk. The origin of the material is not known. One possible source of dust could be collisions between small and close-in planets or planetesimals. Alternatively, the stars themselves could have strong winds, which might be a source for gas. I’ve recently submitted a study that describes our current state of understanding:

Transient Corotating Clumps Around Adolescent Low-Mass Stars From Four Years of TESS [Preprint]
with R. Jayaraman, S. Rappaport, L. Rebull, and friends, AJ (2024).

Dissolving Star Clusters

Stars form in clusters when molecular clouds collapse (see this video). After the gas from the birth cloud disperses, most of the stars escape the cluster’s gravitational pull and gradually populate the galactic disk. Using many of the same tools that I use to study exoplanets, I also study cluster dissolution. The near-term goals are to reconstruct the initial cluster configurations, and to understand the processes that dictate the shapes, sizes, and orientations of dissolving star clusters. The long-term goal is to understand whether we might be able to identify and study stars in the Sun’s birth cluster. See:

Stellar Rotation and Structure of the α Persei Complex: When Does Gyrochronology Start to Work? [Paper]
led by A. Boyle, in AJ (2023)

Rotation and Lithium Confirmation of a 500 Parsec Halo for the Open Cluster NGC 2516 [Paper, supplementary data]
with J. Curtis, J. Hartman, J. Winn, and G. Bakos, in AJ (2021)

Long-term Fates of Hot Jupiters

Tides are expected to cause hot Jupiters to inspiral into their stars and be torn apart, but it is not clear how long this takes. Beyond determining the lifespan of hot Jupiters, the answer also has implications for whether the Earth will be consumed by the Sun in the distant future. Related contributions:

WASP-4 is Accelerating Toward the Earth [Paper]
with J. Winn, A. Howard, S. Howell and friends, in ApJL (2020)

WASP-4b Arrived Early for the TESS Mission [Paper]
with J. Winn, C. Baxter, W. Bhatti, and friends, in AJ (2019)

Empirical Tidal Dissipation in Exoplanet Hosts From Tidal Spin-up [Paper]
led by K. Penev, with J. Winn and J. Hartman, in AJ (2018)

Design and Analysis of Transit Surveys

I’m broadly interested in the design, execution, and analysis of planet-hunting surveys, particularly using the transit method. Related studies include:

Biases in Planet Occurrence Caused by Unresolved Binaries in Transit Surveys [Paper]
with K. Masuda and J. Winn, in AJ (2018)

Planet Detection Simulations for Several Possible TESS Extended Missions [White paper, data products]
with J. Winn, J. Kosiarek, and P. McCullough, arXiv:1705.08891.