Research

Current Research

My current research interests center around determining what factors change the radii of M dwarf stars. M dwarfs are the most abundant stars in the Galaxy, yet their fundamental parameters are still not well constrained. Radii of M dwarfs will be particularly important for upcoming exoplanet detections surveys such as TESS, and WFIRST’s exoplanet microlensing survey. As a visiting graduate student fellow at IPAC, I worked with J. Davy Kirkpatrick to determine how extreme metallicity variations (over 2.0 dex) can severely change the stellar radii. At Boston University I work with Professor Phil Muirhead on the well-known problem of radius inflation of M dwarfs (e.g., Torres & Ribas 2002).

At IPAC, I measured the radii of M subdwarfs with metallicities ranging from +0.5 to -2.0 dex compared to solar metallicity. We fit models to optical spectra to derive effective temperatures and we measured bolometric luminosities by combining broad wavelength coverage photometry with Gaia parallaxes. Radii were then computed by combining the effective temperature and bolometric luminosity using the Stefan-Boltzman law. We found that for a given temperature, ultra-subdwarfs (-2.0 dex) can be as much as five times smaller than their solar-metallicity counterparts. To aid in future radius determinations of low-metallicity M subdwarfs, we present radius relations that extend down to [Fe/H] of -2.0 dex. 

TeffvsRad

Along with my advisor, Phil Muirhead, we developed a novel way to test for inflated radii using single (non-binary) M dwarfs with known rotation periods (MEarth: Newton et al. 2016) in combination with projected rotational velocities (v sin i) to extract a distribution of radii modulated by the sin of the inclination. I am using the Immersion Grating Infrared Spectrograph (IGRINS) instrument on the Discovery Channel Telescope (DCT) and iSHELL on NASA’s Infrared Telescope Facility (IRTF) to obtain v sin measurements of ~100 mid-to-late M dwarfs. We found that stellar evolution models underestimate the radii of the most rapidly rotating (and magnetically active) M dwarfs by 10-15%, and that empirical relations do a much better job at estimating the radii of theses stars. We find no statistically significant evidence that the radii of the stars in our sample are inflated compared to the empirical estimates. For more details on our method see our paper on ADS.

Inflations2

Previously at BU I worked with Andrew West, also on stellar characterization. I created an empirical template library for the full range of spectral types (O through L), luminosity classes (dwarf and giant) and metallicity bins (-2.0 to +0.5 dex) by co-adding individual stellar spectra from the Sloan Digital Sky Survey’s Baryon Oscillation Spectroscopic Survey (BOSS). This work was recently published in the Astrophysical Journal Supplements (ApJS paper). Accompanying the empirical template library we released PyHammer, which automatically (and/or visually) determines the spectral type and metallicity of any optical stellar spectrum (screenshot of the GUI, used for the optional visual classification, shown below). Click here to go to our github page.

PyHammer

Past Research

1.) While at Colby College I worked on massive highly redshifted galaxies, with Elizabeth McGrath.  We were attempting to morphologically classify the galaxies, to determine if there was a pattern in the abundance of disk dominated galaxies with redshift. I classified 140 galaxies from the CANDELS survey. We concluded that there seemed to be more disk dominated massive galaxies in the past than there are in the present day universe. Below are two examples of the highly redshifted galaxies I was looking at.

ds9_8485ds9_5355

My thesis, entitled “Massive Quiescent Disk Galaxies in the CANDELS Survey” is available for download here: http://digitalcommons.colby.edu/honorstheses/707/

 

2.) I participated in an REU (Research Experience for Undergraduates) program at the University of Wisconsin in Madison. There I worked with Barbara Whitney, modeling variability young stellar objects. I used her radiative transfer code to model disks, warps in disks, hotspots, and spiral arms to try to match our models to observational data. 3col_180

Here is an example of an output image of an accretion disk with a warp in it. More information can be found on my REU website, or in the accompanying paper.