Keivan Stassun at Vanderbilt University

Cosmic conundrum:
The binary star system Par 1802 within the Orion Nebula poses a riddle in stellar evolution.
Two stars, each with the same mass and in orbit around each other, are twins that one would expect to be identical. So the discovery of twin stars in the Orion Nebula that are not identical at all comes as a surprise. In fact, these stars exhibit significant differences in brightness, temperature, and radius. The study, which is published in Nature, suggests that one of the stars formed significantly earlier than its twin. The discovery provides an important new challenge for today's star formation theories. Look here for a video interview from the National Science Foundation. The discovery is also featured in Nature's Making the paper column and the Nature podcast. The Vanderbilt Explorations website features a multimedia presentation of the results.

Discovery of the first brown-dwarf eclipsing binary

Magnificent Failures:
Discovery of a rare brown-dwarf eclipsing binary
Brown dwarfs are often called “failed stars” because their low masses are intermediate to those of planets and stars. Until recently, the fundamental physical properties of brown dwarfs were largely unkown. The discovery of a pair of brown dwarfs in an eclipsing binary system provides the first direct measurements of the masses, diameters, temperatures, and luminosities of these failed stars. See the Vanderbilt Explorations website for a multimedia feature about this research. Also check out NPR's Earth & Sky interview and radio story.

The informatics revolution in astronomy and astrophysics
My research seeks to address questions related to the formation of stars and planetary systems. With the advent of all-sky surveys, large-format detectors, and high-performance computers, this work increasingly involves approaches at the interface of astronomy, physics, computer science, and informatics. This is the domain of the Vanderbilt Initiative in Data-Intensive Astrophysics (VIDA).

What are the physical processes involved in stellar birth, and which theory of star formation provides the most accurate description of a young star's evolution?
What are the physical processes involved in planet formation, and how long does this process take?
How do young stars produce energetic X-ray radiation, and what is the impact of this radiation on the environment of young Earth-like planets?
By what mechanism(s) do young stars slow down the very rapid rotation that should result from their gravitational collapse?

Stellar Mass
Mass is the most important property of a star, determining the course of its birth, life, and death. My work in this area seeks to test and inform theories of early stellar evolution, particularly via empirical mass measurements of young stars. The number of pre-main-sequence stars with empirically determined masses is increasing, but remains small. As such, the pre-main-sequence stellar evolutionary models that are used to infer stellar masses, ages, and other basic stellar properties, remain largely uncalibrated by observation. This limits the ability of astronomers to discriminate between different star-formation scenarios and to accurately determine the timescales for planet formation.

See the following features of our recent discovery of a brown dwarf eclipsing binary system, published in Nature:

Stellar Angular Momentum
The so-called "angular momentum conundrum" of how stars shed most of their initial angular momentum continues to pose a fundamental astrophysical challenge to our understanding of the star-for mation process. My work in this area includes:

modeling the rotational evolution of young, low-mass stars from the stellar birthline to the main sequence
determining the distribution of stellar rotation rates among stars at various ages
understanding the role of circumstellar disks in regulating angular momentum evolution
ascertaining the influence of stellar multiplicity on early stellar angular momentum evolution

Stellar X-rays
Young stars produce as much as 1000 times more X-ray radiation than the Sun. How do they do this? My work in this area seeks to understand how this intense X-ray radiation is produced and how these X-rays may affect the environment in which planets form.

Students Phillip Cargile (left) and Yilen Gómez Maqueo Chew (right)
presenting at a recent meeting of the American Astronomical Society.