JANUARY 26 - 30, 2015


Noon: Solar, Stellar, and Planetary Sciences Division Seminar. "The UV and Extreme-UV Radiation of Exoplanet Host Stars," Dr. Jeff Linsky, University of Colorado. Pratt Conference Room.

Abstract: I will describe our program to observe, reconstruct, and compute by various techniques the radiation environment of exoplanet host stars, in particular M dwarf stars. Stellar UV radiation, dominated by Lyman-alpha, controls the photochemistry of important molecules in the outer atmospheres of exoplanets, and the extreme-UV (EUV) radiation phoenixes hydrogen leading to mass loss from these atmospheres. The solar EUV radiation (see figure) and new HST UV spectra provide partial answers to the radiation environment seen by exoplanets, but interstellar absorption removes most of the Lyman-alpha and EUV flux seen from Earth. I will present the results of our HST observing program, methods for reconstructing or estimating the intrinsic flux in the Lyman-alpha line, and our approach to estimating the intrinsic EUV flux seen by exoplanets.


4:00 pm: Colloquium. Lecar Prize Lecture: "The Exo-planet Obliquity as a Fingerprint of Planetary Formation and Evolution," Prof. Tsevi Mazeh, Wise Observatory, Tel Aviv. Preceded by tea at 3:30 pm. Phillips Auditorium.

Abstract: The angle between the stellar spin axis and the orbital planetary angular momentum of a planet, also referred to as the obliquity of the system, is a matter of intense study in recent years, for the transiting planets of the Kepler mission in particular. Some evidence was found for two populations of hot Jupiters - one around cool stars with orbits well-aligned with the stellar rotational axes, and the other around hot stars with isotropic distribution of obliquities, including planets with retrograde motion. It was suggested that the primordial planetary obliquity is isotropic, and cool stars have reached their zero-obliquity state by tidal re-alignment. The talk will discuss some observational techniques for measuring planetary obliquities, and will present a surprising statistical result that emerges from the study of Kepler light curves of stellar rotation, suggesting the alignment of cool stars is probably not the result of tidal interaction.


The CfA will be hosting the 26th International Symposium on Space Terahertz Technology, March 16-18, 2015, at the Knafel Center in the Radcliffe Yard on the Harvard University campus. Additional information can be found here.