Greg Feiden Publishes Findings on Low-Mass Stars

On June 17, 2013 by Elizabeth Molina-Markham

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The Graduate Forum would like to congratulate Greg Feiden on his recent publication in the Astrophysical Journal. Feiden collaborated on the publication, entitled “The Interior Structure Constants as an Age Diagnostic for Low-Mass Pre-Main-Sequence Detached Eclipsing Binary Stars,” with Aaron Dotter of the Australian National Observatory. Dotter received his PhD from Dartmouth in 2007.

The core of Feiden’s research is accurately determining the properties of stars with masses less than our Sun. This is achieved by modeling the evolution of the stellar interior from birth to death and at each stage in life comparing the model to observed characteristics.

In the past few years, however, researchers have shown that current models are not accurate representations of these stars. The inherent errors within the models affect the radius and effective temperature of these less massive systems, adding a large degree of uncertainty.

While these low-mass stars may seem small and unimportant, they actually make up the bulk of stars in the Universe. Since they are so prevalent, they have significant implications for extra-solar planet (exoplanet) searches. With the increased interest in low-mass star-planet systems, having accurate radii and temperatures is important for classification and determination of exoplanetary properties.

The focus of Feiden’s thesis is testing the influence of magnetic fields on stellar size. Using the Dartmouth Stellar Evolution code, he studied how magnetic fields alter the evolution and intrinsic properties of various types of low-mass stars. Feiden determined that for certain types, the magnetic fields are a plausible explanation for the differences in structure between the models and observations. This is not the case, however, for fully convective stars (i.e. stars that undergo energy transfer from core to surface similar to water boiling in a pot). These stars remain resilient and unchanged. The inability to explain the inconsistency for fully convective stars suggests another explanation may be necessary.

In his recent article, Feiden further explored the issues with the stellar structure models and proposed a possible method to circumvent some of the associated errors. The core of this correction lies with using the dynamical motion of eclipsing binary orbits, or two stars orbiting each other in such a way that one star blocks the other. This movement, also known as apsidal motion, is used to determine fixed properties of the stellar interior. Models of the apsidal motion are significantly less sensitive to whatever may be causing the stellar inflation. So, by using the apsidal motion instead of the individual stellar properties to determine the interior structures, Feiden found that the uncertainty associated with the stellar age was significantly lower using these fixed properties than by using the individual properties. This method is restricted to very precise observations of the apsidal motion, which are difficult to obtain presently due to observational limitations.

While at Dartmouth, Feiden has been recognized for his exemplary research, receiving a William H. Neukom Fellowship from the Neukom Institute for Computational Science at Dartmouth, and the Gordon F. Hull Fellowship presented by the Dartmouth Department of Physics and Astronomy to an outstanding senior graduate student. In addition, he has been awarded the Selamawit Tsehaye Excellence in Teaching Award, as well as a student nominated teaching award. While he is proud of these accomplishments, Feiden says his most rewarding experience during his tenure was his involvement for the past two and a half years as a hockey goalie coach for local youth hockey organizations.

Feiden’s research has sent him to exotic places. Among his favorites are a conference in Barcelona, Spain, and a workshop in Roscoff, France. Feiden, who defended his dissertation in May of this year, also spent four months in Sweden at Uppsala University where he plans to return in the fall for a post-doctoral position. Feiden plans on continuing an extension of his thesis work, but will also be involved in other projects such as examining exoplanets around red dwarf stars, and looking at the properties of stars on the asymptotic giant branch. We wish him the best of luck!

by Mackenzie Jones

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