I study the detection, validation, and characterization of exoplanets via the transit and radial velocity methods. I'm interested in developing a better understanding of the exoplanet population, investigating the nature of exoplanet habitability, and finding and characterizing an Earth twin.

I completed my bachelor's degree at Harvard College in the spring of 2017, followed by a Fulbright Fellowship at the University of Copenhagen and the Technical University of Denmark. I moved to the Bay Area in the Fall of 2018, where I am now pursuing my PhD at UC Berkeley.

## Research

### Current Project: Mass Estimation via Radial Velocity Modeling

My current project involves modeling the mass of exoplanet via radial velocity observations (measurements of how fast the host star is moving toward or away from observers). This method is also sometimes called "The Wobble Method", since observers look for tiny wobbles in the motion of the star to detect the gravitational tug of an orbiting planet. The frequency of this wobble tells you what the orbital period of the planet is, while the amplitude of the wobble tells you the planet's mass. When the signal is very small compared to the noise from the star, advanced extraction and modeling techniques are required in order to detect and analyze the signal from the planet.

### August 2016 - February 2018: Exoplanet Validation

Exoplanet validation is the process of determining the probability of planethood for an exoplanet candidate. In other words, validation is how you sort out real exoplanets from fake ones. Exoplanets are commonly found using the transit method, where observers identify the small dip in light caused by the shadow of a planet as it crosses in front of its star. Whenever such a planet completes an orbit it will transit again, so these dips occur very regularly. However, periodic dips in light can also be caused by star/star eclipses in a binary or trinary star system, or by stellar oscillations, or by periodic systematic effects in the telescope. Exoplanet validation is how you rule out or assess the likelihoods of these possibilities.

Validation is a very important process for a few reasons. Consider an astronomer who wants to do follow up observations on an exoplanet candidate, like measuring its mass or trying to analyze its atmosphere. The last thing she wants to do is spend hours or days of extremely expensive telescope time only to learn that her exoplanet isn't real. Additionally, some astronomers are interested in studying the full exoplanet population to identify trends and test hypotheses about how different types of planets may have formed. This kind of work demands that the exoplanet sample being studied is made up of only exoplanets, and that all of the junk caused by other instrumental or astrophysical sources has been removed. Validation gives astronomers the (relative) certainty that they need to study individual planets and conduct careful studies of the general exoplanet population.

From August 2016 until February 2018, I worked with exoplanet candidates from the K2 mission identified by Andrew Vanderburg (currently a postdoctoral fellow at UT Austin) through his K2 data reduction and candidate identification pipeline. K2 is a space-based mission to detect transiting exoplanets. I built my own exoplanet transit model based on the BATMAN and emcee packages to determine exoplanet radius, inclination, distance from host star, and other transit parameters for each of these candidates. I determined stellar parameters (e.g. temperature, surface gravity, metallicity) for the exoplanet candidate host stars using spectra previously collected with the Tillinghast Reflector Echelle Spectrograph. Additionally, I made use of any available high-contrast images of the host stars to identify nearby stellar companions or otherwise determine how dim a stellar companion would have to be to escape detection.

With all of this information in hand, I then utilized VESPA, an exoplanet validation package. Essentially, VESPA creates a synthetic population of stars (some with planets, some without), determines which of these synthetic systems matches observations, and then calculates what fraction of those allowed systems actually contains a planet. This final value is the same as the likelihood that the exoplanet candidate is real. For my purposes, I classified exoplanet candidates as validated (i.e. real) planets only if the likelihood returned by VESPA was greater than 99.9%. In other words, I validated candidates only if the likelihood that they are fake was less than 1 in 1000.

I identified 275 candidates from the K2 pipeline that had enough follow up observations to conduct validation. And out of those 275, I found that 149 had planethood probabilities high enough (>99.9%) to be called validated planets (the rest may or may not be exoplanets, but there just isn't enough data to be sure either way). About a third of these have already been validated elsewhere, another third were only candidates before, and the final third haven't been identified anywhere yet. As a result, this research will add 95 exoplanets to the known exoplanet sample, increasing the number of validated exoplanets found by K2 by about 50%! This project has been a great experience because it's helped me develop a useful framework for careful and thorough exoplanet validation, which should help astronomers with upcoming validation efforts on future K2 campaigns and especially the Transiting Exoplanet Survey Satellite mission!

Let me just finally mention that you can also view the paper on this project here. It has already been accepted and published by the Astronomical Journal. This paper has more than two dozen co-authors and they have my sincere thanks. I would never have completed this project without their combined effort, including mentoring, proof-reading, and large amounts of data collection, reduction, and analysis.

## Publications

Mayo A. W. et al. "An 11 Earth-mass, Long-period Sub-Neptune Orbiting a Sun-like Star" The Astronomical Journal, 158, 165 (2019). [arXiv] [ADS] [view here]

Mayo A. W. et al., "275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0-10" The Astronomical Journal, 155, 136 (2018) [arXiv] [ADS] [view here]

Malavolta, L., Mayo, A. W., et al., "An ultra-short period rocky super-Earth with a secondary eclipse and a Neptune-like companion around K2-141" The Astronomical Journal, 155, 107 (2018) [arXiv] [ADS]

Dholakia, S., Dholakia, S., Mayo, A. W., et al., "Constraining Orbital Periods from Nonconsecutive Observations: Period Estimates for Long-Period Planets in Six Systems Observed by K2 During Multiple Campaigns" (2020, in press) [arXiv] [ADS]

Rice, K., Malavolta, L., Mayo, A. W., et al., "Masses and radii for the three super-Earths orbiting GJ 9827, and implications for the composition of small exoplanets" Monthly Notices of the Royal Astronomical Society, stz130 (2019) [arXiv] [ADS]

Vanderburg, A., Rappaport, S. A., Mayo, A. W., et al., "Detecting Exomoons via Doppler Monitoring of Directly Imaged Exoplanets" The Astronomical Journal, 156, 184 (2018) [arXiv] [ADS]

RodrÃ­guez MartÃ­nez, R., Ballard, S., Mayo, A. W., et al., "Characterization of Low Mass K2 Planet Hosts Using Near-Infrared Spectroscopy" (2019) [arXiv] [ADS]

Rodriguez, J. E. et al., including Mayo, A. W. "A Compact Multi-planet System with a Significantly Misaligned Ultra Short Period Planet" The Astronomical Journal, 156, 245 (2018) [arXiv] [ADS]

Vanderburg, A. et al., including Mayo, A. W. "Zodiacal Exoplanets in Time (ZEIT). VII. A Temperate Candidate Super-Earth in the Hyades Cluster" The Astronomical Journal, 156, 46 (2018) [arXiv] [ADS]

Plavchan, P. et al., including Mayo, A. W. "EarthFinder: A Precise Radial Velocity Probe Mission Concept For the Detection of Earth-Mass Planets Orbiting Sun-like Stars" arXiv:1803.03960 (2018) [arXiv] [ADS]

Rodriguez, J. E. et al., including Mayo A. W. "A Multi-Planet System Transiting the V = 9 Rapidly Rotating F-Star HD 106315" The Astronomical Journal, 153, 256 (2017) [arXiv] [ADS]

Vanderburg, A. et al., including Mayo A. W. "Two Small Planets Transiting HD 3167" The Astrophysical Journal Letters, 829, L9 (2016) [arXiv] [ADS]

## Kepler-538

This paper details how my team and I measured the mass of the exoplanet Kepler-538b using radial velocity measurements and a variant of a sophisticated modeling technique called a Gaussian process. As of publication, Kepler-538b is the smallest planet beyond an orbital period of 50 days with a precise mass from the radial velocity method.

You can view and download the paper here and an associated erratum here.

## K2 Validation Press Release

This paper details how my team and I analyzed 275 exoplanet candidates detected through the K2 mission and determined which of them are real exoplanets.

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