Keivan Stassun at Vanderbilt University

UVEX will address outstanding questions in our understanding of the Universe, including the nature of the low-mass, low-metallicity galaxy population and the early ultraviolet emission of explosive transients. UVEX will also leave a rich legacy of all-sky ultraviolet data.

Astronomers discover an exoplanet hotter than most stars.
An international team of astronomers have discovered a planet like Jupiter zipping around its host star every day, boiling at temperatures hotter than most stars and sporting a giant, glowing gas tail like a comet. The discovery was made with Vanderbilt's KELT telescope and is published in the journal Nature. See the Vanderbilt News press release for more details.

IT'S OFFICIAL: WORLD RECORD SETTING STELLAR ECLIPSE
The longest stellar eclipse lasts around 3.45 years and takes place in a binary star system called TYC 2505-672-1. The discovery was made by the Stassun Research Group, and published on 19 January 2016. The eclipse takes place once every 69 years. From the viewpoint of an observer on Earth, the red giant component of the binary system is eclipsed by its companion star. The companion star - which the research team think could be a 'stripped red giant', which is on its way to becoming a white dwarf - is surrounded by a huge disc of opaque dust which blocks out almost all of the light from the red giant.

THIS IS WHAT HAPPENS WHEN STARS EAT ROCKY PLANETS
Some stars ingest material from rocky planets like Earth, and now we have a way to study the effect of such a diet on a star’s chemical composition. The result is a new modeling technique that may help scientists identify Earth-like exoplanets. The research is published in The Astrophysical Journal, featured on a video from Vanderbilt News, and on Futurity and Slate.

Twinkling stars:
A simple but powerful way to measure fundamental stellar properties, improve knowledge of exoplanet characteristics, and understand how stars evolve.
Variations in the brightness of solar-type stars are driven by many factors including granulation, a consequence of heat convection below the photosphere. And as granulation is correlated with surface gravity, variations in brightness can be used as a measure of surface gravity. Fisk-Vanderbilt Bridge student Fabienne Bastien and collaborators analyze archival data from NASA's Kepler mission and show that brightness fluctuations on timescales of less than 8 hours are correlated with the surface gravity in Sun-like stars in various evolutionary phases. Using straightforward measurements of this type it should be possible to determine the surface gravities of many of the stars observed by Kepler, and will permit much more accurate determination of the characteristics of planets orbiting these stars. The research is published in Nature, featured on the Vanderbilt News site, on the Nature Podcast, Nature Video, and in a related Nature News & Views article.

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), through which we participate in the Sloan Digital Sky Survey and other large-scale collaborations.

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?
Under what conditions are planets destroyed?
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.

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.