HAO 2010 PROFILES IN SCIENCE: Dr. Travis Metcalfe

Contact

303-497-8326
travis@ucar.edu

Area of expertise: Sun and Upper Atmosphere

Specialties: asteroseismology (the study of the internal structure of stars through the interpretation of their pulsation periods) and magnetic activity cycles of Sun-like stars

Dr. Travis Metcalfe is a Scientist II in the High Altitude Observatory of the National Center for Atmospheric Research. He received his PhD in Astronomy in 2001 from the University of Texas, Austin. His first work with HAO was as a visitor in 2000 and as an NSF Fellow in 2004. His main focus of research is in asteroseismology of solar-type stars, understanding stellar magnetic activity cycles, interpreting interferometric observations of rapidly rotating stars, and exploring the solar-stellar connection. Travis Metcalfe is an astronomer who probes the interiors of distant, Sun-like stars to improve understanding of stellar structure and shed light on the behavior of our own Sun. He combines astronomical theory, computer science, and the few measurements available to piece together a portrait of magnetic plasma movement and other interior processes. For data, he relies on sound waves, or pulsation frequencies, that traverse the interiors of Sun-like stars and rise to the surface. Metcalfe has a cross-laboratory appointment in NCAR's High Altitude Observatory (HAO) and Scientific Computing Division (CISL).

Professional Website(s): Travis Metcalfe & Solar Stellar Coffee

Publication:

(1) A precise asteroseismic age and radius for an evolved Sun-like star

Abstract:

The primary science goal of the Kepler mission is to provide a census of exoplanets in the solar neighborhood, including the identification and characterization of habitable Earth-like planets. The asteroseismic capabilities of the mission are being used to determine precise radii and ages for the target stars from their solar-like oscillations. Chaplin et al. (2010) published observations of three bright G-type stars, which were monitored during the first 33.5 days of science operations. One of these stars exhibits a characteristic pattern of oscillation frequencies suggesting that it has evolved significantly. We derived asteroseismic estimates of the properties of KIC 11026764 from Kepler photometry combined with ground-based spectroscopic data. We determined both the radius and the age with a precision near 1%, and an accuracy near 2% for the radius and 15% for the age.

Acknowledgements: This work is partially supported by NASA grant NNX09AE59G and TeraGrid allocation TG-AST090107.

Team: Travis Metcalfe and Kepler Asteroseismic Science Consortium.

Figure: An "echelle diagram" showing the 26 oscillation frequencies in KIC 11026764 plotted against their deviations from the average spacing between consecutive radial overtones. The star exhibits modes that have radial (circles), dipole (triangles), and quadrupole (squares) geometry. Two of the best models (blue and red) are shown for comparison, and a greyscale map of the observed power spectrum (smoothed to 1 micro Hz resolution) is included in the background for reference.

Publication:

(2) The shortest measured magnetic activity cycle in a solar-type star

Abstract:

The Mount Wilson Ca HK survey revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 to 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and the depths of the surface convection zones for stars with various masses and ages. In 2007 we initiated a long-term monitoring campaign of Ca II H and K emission for a sample of 57 southern solar-type stars to measure their magnetic activity cycles and their rotational properties when possible. Using these data we discovered a 1.6-year magnetic activity cycle in the exoplanet host star iota Horologii, and we obtained an estimate of its rotation period near 8.5 days. This is the shortest activity cycle so far measured for a solar-type star, and may be related to the short-timescale magnetic variations recently identified in the Sun and HD 49933 from helio- and asteroseismic measurements. If such short activity cycles are common in F stars, then NASA's Kepler mission should observe their effects in many of its long-term asteroseismic targets.

Acknowledgements: This work is partially supported by Small and Moderate Aperture Research Telescope System Consortium, National Optical Astronomy Observatory long-term program 2008B-0039.

Team: Travis Metcalfe with scientists from Yale, Georgia State, Space Telescope Science Institute, and High Altitude Observatory.

Figure: Chromospheric activity measurements of iota Horologii from the southern HK survey, showing a clear variation with a cycle period of 1.6 years, the shortest cycle ever measured for a solar-type star. The scatter around the fitted sinusoid is primarily from rotational modulation with a period near 8.5 days.