GRAD Alumni Research Award 2017 Recipient: Meridith Joyce, Physics and Astronomy

Thanks to the generosity of alumni from the School of Graduate and Advanced Studies, several current students are able to receive funds to support their research endeavor off campus. Each recipient is required to submit a short overview of how the award contributed to their work.

With the generous support of the Alumni Research Award, I successfully obtained preliminary spectroscopy of roughly 200 chemically interesting, low-mass stars using the SpUpNIC spectrograph on the 1.9m telescope at the South African Astronomical Observatory's site in Sutherland, South Africa.

These spectra have been used to classify the stars according to their heavy element content, from which a target list for high resolution follow-up has been devised. The most promising candidates are now slated for high-resolution spectroscopy on SAAO's South African Large Telescope (SALT), one of a small number of 10-meter class instruments and one in which Dartmouth owns an impressive 11% share.

My research at Dartmouth is overseen by Professor Brian Chaboyer in the department of Physics and Astronomy. Both he and the department have a long and fruitful history in stellar modeling, where the DSEP (Dartmouth Stellar Evolution Program) code and database have been used for decades to deduce basic stellar properties.

My research has demonstrated that there are certain evolutionary regimes where models fail to reproduce the observed properties of stars with sufficient accuracy. This is due in part to the fact that astronomers have relied on high precision data from the Sun to construct some of the formalisms that describe heat transport and chemical mixing inside stars.

There is mounting evidence, however, that such formalisms are ineffective for stars with significantly lower concentrations of heavy elements in their compositions than the Sun. The spectra I have obtained for a large number of metal-depleted stars will be used to calibrate critical components of theoretical stellar evolution models because they provide high fidelity data on stars whose physical properties deviate heavily from the Sun's.

Thanks to the Alumni Research Award, I was able to participate in a four- night observational training session in September of 2017, also in Sutherland, which in turn facilitated my leadership on the seven-night observing run in November 2017. Because my thesis work has been primarily theoretical, this was the first opportunity I had to go on an observing run for personal research.

The exposure to telescope operations alone was hugely beneficial to my academic development, as it fulfilled a vital component of my training as a professional astronomer.

Most crucially, the funding allowed me to capitalize on observing time I was allocated on the 1.9m as a principle investigator (PI). Observing time is competitive, and it is somewhat uncommon for graduate students to procure time for their own projects.

Receiving the allocation is merely the first step; there are then several subsequent financial and logistical barriers, not to mention uncertainty in the weather. Travel from Hanover, New Hampshire, to the southern tip of Africa is no small task, but the Alumni Fund defrayed these costs significantly.

Because I was a graduate student PI, the Allocation Committee requested that I receive training before operating the 1.9m on my own, and recommended hiring a support astronomer for the data collection. These unanticipated costs – which were necessary to the completion of my run – were easily absorbed thanks to the Alumni Research Award. As a consequence, I received four additional nights of observational training and financially supported a local South African student who assisted with my run.

In the end, I was lucky enough to receive observing time, financial support, and good weather. The data I have collected with SpUpNIC have already been used to drive the next phase of observation of these metal-depleted stars, and I have made a case for the necessity of continuing such observations in my recently accepted publication, “Not All Stars Are the Sun: Empirical Calibration of the Mixing Length for Metal-Poor Stars Using 1-D Stellar Evolution Models." This paper appeared in The Astrophysical Journal in March 2018.