About me

I am a third-year PhD student and NSF Graduate Research Fellow at the Institute for Astronomy, University of Hawai‘i at Mānoa.

My primary research interest is understanding the full lifetime of exoplanets. Currently, I study their evolution by detecting planets around evolved stars and developing methods to better constrain the ages of exoplanet host stars.

Before I arrived in Hawaii, I was a research support scientist at the Kepler/K2 Guest Observer Office at NASA Ames.

For my undergraduate degrees, I attended the University of Washington in Seattle. I earned a B.S. in Astronomy and Physics, and a B.A. in Comparative Literature (with an emphasis on Cinema Studies), and I was a member of the Washington NASA Space Grant Consortium.

View my CV for more information.

Research Projects

Completed and ongoing research

Constraining Weakened Magnetic Braking with Asteroseismic Rotation Rates

Advised by Prof. Jen van Saders

As stars age, they gradually lose angular momentum through stellar winds, and the rate at which they rotates decreases. Gyrochronology relates the rotation period of a star to its age. The spin-age relationship has been well characterized for young stars using nearby clusers, but remains unreliable for older stars. A population of old stars with faster than expected rotation prompted the theory of "Weakened Magnetic Braking," a stage of stellar evolution during which the star undergoes a magnetic transition that allows it to maintain rapid rotation.

With a new sample of benchmark stars with rotation periods measured from asteroseismology, I am creating stellar evolution models to constrain gyrochronology weakened magnetic braking models.

Detecting Planets Around Evolved Stars with TESS

Advised by Prof. Dan Huber and Dr. Sam Grunblatt

The explosion of exoplanet detection in the last decade has enabled astronomers to study the underlying characteristics of planet populations. Planets orbiting main-sequence stars have been characterized in detail, however planets orbiting evolved stars remain mysterious due to the small sample of observed transiting planets around post-main-sequence stars.

I am conducting a search for planets around evolved stars in the TESS Full Frame Images (FFIs). I wrote a pipeline to quickly remove the scattered light from TESS which uses linear regression to isolate and remove the bright background from light curves. After de-trending the light curve, my pipeline performs a Box Least Squares (BLS) search for transiting planet signals. We selected a sample of subgiant and red giant stars, and have generated and searched over 500,000 light curves. We have identified and confirmed three new planets which were not identified by the NASA SPOC or MIT QLP pipelines, and have multiple discovery papers in prep.

Creating High-precision K2 Light Curves

Advised by Prof. Rory Barnes and Dr. Rodrigo Luger

When the Kepler space telescope lost two of its four reaction wheels, the spacecraft lost the fine pointing necessary for high precision photometry. Engineers were able to reorient the telescope to observe along the ecliptic plane, held stable by the photon pressure from the solar wind, and the mission entered a second phase called K2. However, the spacecraft maintained a slow drift and was re-oriented every 6 hours by a stabilizing thruster fire, causing targets to traverse accross the CCD detector. Because of subtle variations in sensitivity between pixels, as well as within each pixel, K2 light curves have periodic systematic noise.

In order to better understand the characteristics of K2 noise and test noise removal methods, I developed a Python package called scope (Simulated CCD Observations for Photometric Experimentation) to simulate the pixel sensitivty variation of the Kepler detector and motion of targets, ultimately reproducing the noise properties of K2 light curves. Scope was used to test the performance of the everest pipeline, particularly in the case of high motion. The results of the paper linked below influenced the decision to continue observation and upload larger aperture masks for K2 campaign 17.

Publications:
Hedges, C., Angus, R., Barentsen, G., Saunders, N., Montet, B.T., Gully-Santiago, M. (2020) Systematics-insensitive Periodogram for Finding Periods in TESS Observations of Long-period Rotators. RNAAS, 4, 220

Saunders, N., Luger, R., Barnes, R. (2019) The Pointing Limits of Transiting Exoplanet Light Curve Characterization with Pixel Level De-correlation. AJ, 157, 197

Hedges, C., Saunders, N., Barentsen, G., Coughlin, J., Vinícius de Miranda Cardoso, J., Kostov, V., Dotson, J., Cody, A.M. (2019) Four Small Planets Buried in K2 Systems: What Can We Learn for TESS? ApJL, 880, 1

Feinstein, A.D., Montet, B.T., Bean, J.L., Bedell, M.E., Christiansen, J., Foreman-Mackey, D., Hedges, C., Luger, R., Saunders, N., Scolnic, D., Vinícius de Miranda Cardoso, J. (2019) eleanor: A tool for extracting light curves from the TESS Full-Frame Images. PASP, 131, 1003

David, T., Cody, A., Hedges, C., Mamajek, E., Hillenbrand, L., Ciardi, D., Beichman, C., Petigura, E., Fulton, B., Isaacson, H., Howard, A., Gagné, J., Saunders, N., Rebull, L., Stauffer, J., Vasisht, G., Hinkley, S. (2019) A warm Jupiter-sized planet transiting the pre-main sequence star V1298 Tau. AJ, 158, 2

Mahabal, A., Rebbapragada, U., Walters, R. et al. (including Saunders, N.) (2019) Machine Learning for the Zwicky Transient Facility. PASP, 131, 997

Hedges, C., Saunders, N., Barensen, G., Gully-Santiago, M., Cody, A.M., Vinícius de Miranda Cardoso, J. (2019) A Hot Jupiter Exoplanet Candidate towards the Galactic Center Identified in Kepler/K2 Campaign 9 Microlensing Survey. RNAAS, 3, 1

Barentsen, G., Hedges, C., Saunders, N., Cody, A.M., Gully-Santiago, M., Bryson, S., Dotson, J. (2018) Kepler’s Discoveries Will Continue: 21 Important Scientific Opportunities with Kepler & K2 Archive Data. arXiv:1810.12554

Cody, A.M., Barentsen, G., Hedges, G., Gully-Santiago, M., Dotson, J., Barclay, T., Bryson, S., Saunders, N. (2018) A catalog of 29 open clusters and associations observed by the Kepler and K2 Mission. RNAAS, 2, 4

Luger, R., Kruse, E., Foreman-Mackey, D., Agol, E., Saunders, N. (2018) An Update to the EVEREST K2 Pipeline: Short Cadence, Saturated Stars, and Kepler-like Photometry down to Kp = 15. AJ, 156, 99

Click below for a full list of my publications.

Codes

Software projects to which I've contributed

lightkurve

A friendly package for Kepler & TESS time series analysis

I am a core developer of the lightkurve package. The goal of lightkurve is to lower the bar for astronomical time series analysis by providing clear and easy to use tools to the astronomy community. Lightkurve is a great software package for introducing undergraduate and graduate students to the basic principles of exoplanet or binary system detection and characterization, stellar variability, or transient detection in space telescope photometry.

Adorable image created by Christina Hedges.

eleanor

Simple light curve extraction from TESS FFIs

I am also a member of the core development team for the eleanorTESS pipeline. This pipeline provides systematics-corrected light curves for hundreds of thousands of targets in the TESS FFIs, and enables users to produce custom systematics-corrected light curves for any target with a given TIC ID, Gaia source ID, or RA and dec coordinates.

scope

Simulated CCD Observations for Photometric Experimentation

I am the lead developer for the scope simulation tool. This package was used to test the performance of the everest pipeline, particularly in the case of high motion. The results of the paper linked below influenced the decision to continue observation and upload larger aperture masks for K2 campaign 17.

everest

Pixel Level Decorrelation of K2 Light Curves

I contributed to the development of the everest K2 pipeline. This pipeline was developed by Luger et al. (2016, 2018) to remove systematic noise from K2 light curves. Using a method called Pixel Level Decorrelation (PLD) based on the work of Deming et al. (2015), we achieved Kepler-like precision in de-trended K2 light curves down to 15th magnitude.

All of my software can be found on my GitHub.

Outreach

Since 2015, I have been an active volunteer for outreach events and planetarium shows. While at UW, I gave weekly shows for visiting elementary and high school classes, groups of teachers, UW students, members of local Indian Reservations, and the public. I also organized a new set of free monthly public shows, and managed ticket sales and social media for the planetarium.

During the 2017 solar eclipse, I visited the Warm Springs Reservation in Oregon and taught middle school students about solar system science. I also helped organize public viewing through telescopes at night and solar telescopes during the day.

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