Accretion Machines


This post is the first of a series highlighting the fantastic summer astronomy research Amherst students conducted. For more information on the series, visit this post.

This week, Astronomy Department Editor William Balmer (that’s me) interviewed three of the six Follette Lab students who presented at the Colloquium. Beck Dacus ‘22, Cailin Plunkett ‘23, and Huichen “Will” Wang ‘23 worked on building and refining a database of accreting objects; we had the opportunity to interview all three to learn more about how stars grow and how they shaped and engaged with a large, multidimensional dataset.

Interviews with the Follette Lab Accretion Database Team

William B.: “Can you say a bit about yourself and where you worked this summer?”

Cailin P.: “I’m Cailin Plunkett, sophomore/class of ’23, and I’m a (declared! exciting!) physics major and prospective math or statistics major. I worked in Oakland, California doing remote SURF research for the Follette Laboratory.”

W: “What was the goal of your research with Dr. Follette?”

C: “Our goal was to perform a meta-analysis of a database of Brown Dwarfs to probe whether they form via the same mechanisms as planets and stars. Since different studies use drastically different methods, it’s difficult to tell whether scatter in the relationship is due to physical or methodological differences in the parameter estimation. We re-estimated the data in a unified way to mitigate that issue.”

W: “So you worked with a couple of other people on this, what did you do specifically and who else did you work with?”

C: “I worked alongside Beck Dacus ’22 and Will Wang ’23 under Kate Follette, Kim Ward-Duong, and graduate student Sarah Betti on this project. My particular role was to re-estimate the mass accretion rates—the y-axis of our main plot, the amount of mass the object gains each year—using a consistent methodology. This required hunting through literature for original data, transforming it into workable formats, and running the recalculations. There’s a ton of work left to do, but with the re-estimated data we should be able to more accurately explore differences in properties!”

This plot, courtesy of Cailin Plunkett ‘23 and the Accretion Database Team, shows the movement of stars across parameter space after their meticulous recalculations.

W: “Beck, we’re good friends, we’ve worked together on projects before. Pretend we don’t know each other—who are you and what are you doing?”

Beck D.: “My name is Beck Dacus, I’m a junior at Amherst majoring in astronomy, and this summer I worked in Professor Follette’s astronomy lab on the Accreting Objects Database team.”

W: “Cailin touched on this accretion concept, what’s your project goal and what is accretion?”

B: “Our goal was to find differences in the way young massive objects grow as you move from planets to brown dwarfs and up to stars, to see if they appear to form differently. Currently, there is too much spread to the data to be able to make compelling conclusions, so this summer we focused on estimating the masses and growth rates of these young objects more consistently than past research.”

This artist’s interpretation shows a young star pulling material onto its surface from its surrounding environment (a process known as accretion) and gaining mass. (Image credit: NASA/JPL-Caltech)

W: “So what did you do with this dataset?”

B: “My part in this was to more accurately constrain the distances to the objects we were interested in; a star’s mass and age are intimately related to its brightness, and without accurate distances, it’s not clear if, say, a star that appears dim compared to another is actually dim, or just farther away. In order to find the most up-to-date distance estimates, I turned to data from the Gaia spacecraft, a satellite that uses parallax to find accurate distances to billions of nearby stars in the galaxy, which will give us more confidence that any spread we observe in our data is due to physical effects and not methodological ones.”

W: “Fellow Will! Thank you for braving the monstrous time difference to chat! Tell us about yourself, your interests.”

Huichen W.: “My name is Huichen “Will” Wang. I am a sophomore interested in astronomy, psychology, and computer science.”

W: “You worked on the Accretion Database too. Tell me a bit more about the origin of this dataset and what you did with it.”

H: “Our project built on a database on accreting objects that was put together by Annie Peck, a Smith College graduate. There is a large scatter around the best fit line in the accretion rate vs. mass relationship in the brown dwarf regime, which we tried to understand from physical and non-physical perspectives. Aside from doing a literature search and adding new accreting brown dwarfs to the database, I re-estimated masses and radii of brown dwarfs using a uniform evolutionary model. The purpose of doing so was to account for the methodological differences in estimating stellar parameters since previous studies have adopted various models to estimate them. I managed to re-estimate masses and radii for over 85% of the brown dwarfs in the database. The new data were used to plot a new accretion rate vs. mass plot.”

W: “You’re currently abroad, correct? How did that change your remote experience compared to others?”

H: “Although my SURF experience was quite different from that of the previous students—I did research remotely in Shanghai, China, 12 hours away from the U.S.—I think my mentors, teammates, and I were still able to communicate and collaborate quite smoothly. I really enjoyed the process of learning about a previously unfamiliar area. With all the jargon and high-level physics in astronomy, this could be challenging, but at the end of the day, I couldn’t believe how much I had gained from this experience thanks to my mentors and teammates who helped me along the way.

One highlight from the summer was the opportunity to shadow an astronomical observation in real-time. Due to the time difference, I was lucky enough to shadow the observation run led by Professor Bary from Colgate University during my afternoon time. Professor Bary and his students used the Apache Point Telescope, located in New Mexico, to observe some targets, which included an accreting Brown Dwarf. It was truly an educational experience; jargon in papers suddenly came to life! Some observational strategies, such as observing an A0V star to determine atmospheric absorption, were simply eye-opening. Plus, I would never know some telescopes rotate really slowly had I not observed the run.”

An aerial view of Apache Point Observatory, where Huichen Wang ‘23 shadowed Colgate University’s Professor Jeff Bary in taking observations of accreting stars (Image credit: APO)

Final Thoughts

Thanks to the Physics and Astronomy Department for organizing these flash-talks, and thanks especially to Cailin, Beck, and Will for their amazing interviews. Look out for more coverage of astronomy summer research in the next few weeks, when we’ll be highlighting three more students who conducted astronomy research this summer.