Research
You can get quick tour of my PhD research on M dwarf stars through two short talks from my graduate school days. My more recent work has focused on exoplanet discovery and young stellar populations; as co-PI of the THYME collaboration, I've helped lead the discovery of more than a dozen young exoplanets.
M dwarf astrophysics M dwarfs as planet hosts Young exoplanets Public code and data
Stellar Physics
The interior structure of an M dwarf differs significantly from the Sun.
It is not fully understood how they organize their strong magnetic fields or how they lose angular momentum in order to spin down with time. I use observations of rotation and activity to investigate these mechanisms.
The M dwarf rotation-activity relation.
We used photometry from MEarth-North to measure rotation periods for nearly 400 nearby, mid-to-late M dwarfs. We found no correlation between period and amplitude for these objects, and used Galactic kinematics to estimate the M dwarf spin-down timescale.
Newton et al., 2016, ApJ 821, 93
New rotation period measurements.
Demonstratation of our RV precision. My RV code is freely available online.
We developed a new technique to measure absolute radial velocities from low-resolution near-infrared spectra. We used telluric absorption features to provide the absolute wavelength calibration, enabling RVs accurate to 4 km/s for spectra obtained with IRTF/SpeX. We applied this method to M dwarfs in my sample.
Newton et al., 2014, AJ 147, 20
Characterizing Exoplanet Hosts
The basic parameters of the average M dwarf are not well-constrained.
Because planet properties of measured only relative to the star, any uncertainties about M dwarfs directly impacts our ability to learn about the planets that orbit them. We developed empirical calibrations based on NIR spectra to overcome these challenges. We recently applied these relationships, for example, in Dressing et al. (2017). The code I developed is freely available online.
We developed an empirical calibration for the temperatures and radii of cool dwarfs, which use H-band EWs and can be applied to non-flux calibrated spectra. We revised the properties of the cool dwarfs hosting candidate Kepler planets, showing that the stars (and the planets) are about 15% larger than previously estimated.
Newton et al., 2015, ApJ 800, 85
M dwarf H-band spectra and feature definitions
Our M dwarf metallicity calibration
We obtained low resolution near-infrared spectra of 447 mid-to-late M dwarfs in order to estimate their metallicities. We presented a calibration to estimate metallicities from NIR spectral features as well as from NIR photometry (using 2MASS J, H and K magnitudes).
Newton et al., 2014, AJ 147, 20
ADS | arXiv | Data and figuresYoung Exoplanets
We do not know how planets form and evolve.
By studying the properties of planets at a range of ages, we can piece together how their orbits, sizes, and atmospheres change over time. NASA's TESS mission allows to search to new, young exoplanets all over the sky. Here are some highlights from the TESS Hunt for Young and Maturing Exoplanets (THYME) Collaboration, of which I am the co-PI.
We found and confirmed a planet around a 45 Myr solar mass star, DS Tuc Ab. The planet has a size in between that of Neptune and Saturn and an 8-day orbital period. The planetary orbit, the spin of the host star DS Tuc A, and the orbit of the stellar binary companion DS Tuc B, are likely aligned.
Newton et al., 2019, ApJL 880, 1
TESS discovery data of DS Tuc Ab
Mann et al. 2020, AJ 160, 4
ADS
| arXiv
Newton et al. 2021, AJ 161,
2 ADS
| arXiv
Tofflemire et al. 2021
accepted to AJ arXiv
Data and Code
nirew: measure EWs from NIR spectra and estimate metallicity, spectral type, temperature, radius, and luminosity.
Available on github
tellrv: measure absolute radial velocities from NIR spectra, using telluric features to provide the wavelength calibration.
Available on github
NIR spectra: Our NIR spectra, data tables, and figures from our survey of nearby M dwarfs. Data and figures
K2-25 photometry: Our ground-based transit data is available through CDS in conjunction with Kain et al. 2020
A quick tour of my research
Harvard Horizons (exoplanets, intended for a general audience)
ITC Luncheon (stellar physics, intended for a scientific audience)