Developing new tools and techniques to probe the M dwarf planet population
Open Access
- Author:
- Kanodia, Shubham
- Graduate Program:
- Astronomy and Astrophysics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 19, 2022
- Committee Members:
- Suvrath Mahadevan, Chair & Dissertation Advisor
Randy McEntaffer, Major Field Member
Jason Wright, Major Field Member
Eric Ford, Major Field Member
James Kasting, Outside Unit & Field Member
Frederick Hearty, Major Field Member
Rebekah Ilene Dawson, Professor in Charge/Director of Graduate Studies - Keywords:
- exoplanets
astronomical instrumentation
m dwarfs
astrostatistics - Abstract:
- We do not understand the largest planets around the smallest and most numerous stars in the Galaxy. M dwarfs are the most common type of stars in the Galaxy. Empirical studies show that they also play host to more inner planets than FGK stars, despite this, of the currently $\sim 5000$ confirmed exoplanets, only about 250 orbit M dwarfs, of which only $\sim 65$ have precise mass and radii measurements! The population of planets around M dwarfs is poorly understood. In this thesis I will discuss our efforts to detect and obtain precise measurements for planets around M dwarfs, and then to place this sample of M dwarfs in context of the larger sample of planets around FGK stars. The first part of my dissertation focusses on the instrumentation efforts for the Habitable zone Planet Finder (HPF), and NEID. HPF is a stabilized near-infrared (NIR) fiber-fed radial velocity (RV) spectrograph at the 10 m Hobby Eberly Telescope (HET) at McDonald Observatory, Texas, USA, while NEID is a new high-precision spectrograph in the red-optical installed at the 3.5 m WIYN telescope at Kitt Peak, Arizona, USA. I was in charge of developing, integrating and testing the fiber-feed for HPF, as well as the optical simulations to verify the alignment of the instrument. For NEID, not only did I lead a similar effort for the fiber-feed and simulations, but was also responsible for the chromatic exposure meter which is essential to measure exposure midpoints for barycentric corrections. In conjunction, I developed the algorithm for performing these corrections, which are now used in HPF, NEID and numerous other RV spectrographs. HPF with its large aperture and near-infrared bandpass, and NEID with its red-optical coverage have already started to enable the RV follow up of planets around mid-to-late and early M dwarfs respectively. I then discuss some results from the HPF RV survey, where first I test the scrambling performance of HPF on the fixed altitude HET using on-sky data on an M dwarf. Then I present the results of a serendipitous observation of a flare around the ultracool dwarf vB 10. The HPF spectra taken during the flare show a red excess in the He 10830 \AA~triplet which is similar to observations of coronal rain for the Sun, while also placing a limit on the atmospheric mass loss from flares for planets orbiting such stars. Alongside the instrumentation and observational efforts, I also built upon a nonparametric framework to model exoplanet masses and radii (M-R), which was then applied to a sample of planets around M dwarfs. By comparing the results for M dwarf planets with those from FGK stars we notice some systemic differences in their distributions. However, further inferences were deterred by the small sample of transiting M dwarf planets with mass measurements. I then discuss the efforts to use HPF and NEID to follow up on M dwarf planet candidates discovered by TESS. Not only do these planets help fill in the M-R plane for M dwarfs, but also highlight interesting correlations with stellar properties. Finally, I conclude by giving an overview of how my work on instrumentation, algorithms and novel statistical frameworks has helped develop our understanding of the M dwarf planet population. The ongoing transiting gas giant follow-up will be continued in the future, which will help us shed further light on how these giant planets form around the smallest stars.