Research


Low-mass stars — M dwarfs — are the most common type of star in the Galaxy, and have main sequence lifetimes longer than the age of the Universe. They provide laboratories in which to test stellar physics models in a regime very different from the Sun, and can act as probes of galactic evolution and star formation history. They are also ideal targets around which to find Earth-sized, potentially-habitable planets that can be characterized with current technology. I am an observational astronomer researching stellar physics and the connection between stars and the planets that orbit them. I highlight some of my work below.

Stellar astrophysics Exoplanet host stars 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 obtained 270 new optical spectra in order to investigate how stellar activity relates to rotation period. We found that M dwarfs on either side of the fully convective boundary display the same type of relationship as do solar-type stars.

Newton et al., 2017, ApJ 834, 85

ADS | ArXiv

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

ADS | ArXiv

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

ADS | ArXiv

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

ADS | ArXiv

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 figures

Young 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

ADS | arXiv

TESS discovery data of DS Tuc Ab

A young hot Jupiter informs planet migration.
Rizzuto et al. 2020, AJ 160, 33 ADS | arXiv

Two multi-planet systems orbiting bright, young stars (HD 63433 and TOI 451) enable atmospheric study and comparative planetology, while HD 110082 is in a newly identified young association.

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.

10.5281/zenodo.35686
Available on github

tellrv: measure absolute radial velocities from NIR spectra, using telluric features to provide the wavelength calibration.

10.5281/zenodo.35687
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