Research

I am the project scientist for EXPRES, the EXtreme PREcision SPectrograph. EXPRES is a R=137,000, environmentally-stabilized, fiber-fed, optical spectrograph mounted on the 4.3-m Lowell Discovery Telescope (LDT). EXPRES has demonstrated an instrument precision of 4-7 cm/s and an on-sky single measurement precision of 30 cm/s for a SNR of 250.

I helped align and commission EXPRES, contributed to the observing software, and aided with survey design. I co-wrote the EXPRES extraction pipeline and now develop novel data-driven methods to improve instrument calibration, modeling telluric lines, and other.

• Instrument Design
• Performance Verification
• Pipeline

I founded and lead the Extreme Stellar Signals Project (ESSP), an international collaboration of researchers working on disentangling stellar signals from planetary signals. Measured spectral shifts due to intrinsic stellar variability (e.g. pulsations, granulation) and activity (e.g. spots, plages) have become the largest source of error for extreme precision radial velocity measurements.

By sharing EXPRES data at all levels, the first round of the ESSP established the current state of the field through a self-consistent comparison of 21 different methods. The second round makes use of contemporaneous Sun-as-a-star observations taken by HARPS, HARPS-N, EXPRES, and NEID, from which planetary and instrumental signals can be isolated. With simulatenous observations from four different instruments, I was able to conduct the first direct benchmark of instrument precision, finding agreement to within 15-30 cm/s.

• Round I Summary Report
• EXPRES Data Site
• Solar Comparison

I developed excalibur, a non-parametric, hierarchical method for precision wavelength calibration. Excalibur utilizes all calibration images to construct a model of the accessible calibration space of an instrument and de-noise line positions, which can then be fit with a more flexible, non-parametric model. This allows for more precise wavelengths while also learning how an instrument varies.

When applied to EXPRES data, the overall RMS of RV data sets for quiet targets decreased by 0.2-0.5 m/s. This reduction in overall RMS implies that excalibur addreses an instrumental, red-noise component that would otherwise permeate all exposures.

• Paper
• GitHub Repository

I ran simulations to understand what planets may still exist, undetected, around α Centauri A, B, and Proxima Centauri. The simulations made use of more than a decade of archival radial-velocity measurements of this star system from CHIRON, HARPS, and UVES. Existing data rules out planets in the classically defined habitable zones at an m sin(i) of greater than about 53 M_⊕ for α Cen A, 8.4 M_⊕ for α Cen B, and 0.47 M_⊕ for Proxima Centauri.

I use similar simulations to determine planet detectability based on either archival data or survey design. This allows us to make informed decisions in optimizing planet surveys.

• Paper
• Yale Press
• Scientific American

The atmosphere of a planet provides key constraints to the composition, formation conditions, and habitability of a planet. EXPRES observations taken during a planet's transit enables high-resolution transmission spectroscopy. With MASCARA-2b, we confirmed previous detections of Fe I, Fe II, and Na I as well as detected MG I and Cr II.

As a member of the Bean Exoplanet Group, I used transit spectroscopy to investigate the composition of Wasp-12 b's atmosphere. I analyzed data of Wasp-12 b from the Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS) to construct the transmission spectrum at wavelengths of 0.3-1.0 microns.

• MASCARA-2 b Paper
• Bean Exoplanet Group