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.


12:30 pm: High Energy Astrophysics Division Lunch Talk. "Evidence for Wave Heating of the Solar Corona," Michael Hahn, Columbia University. Pratt Conference Room.

Abstract: One of the major theories to explain the heating of the solar corona is that waves carry the required energy from lower layers of the solar atmosphere into the corona where the waves dissipate, thereby heating the plasma. Recent observational evidence has demonstrated that waves are ubiquitous in the corona, but a challenge for wave-driven heating models has been to determine if the waves are damped. In order to address this question, we analyzed observations from the Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. In particular, we studied the non-thermal line width, which is proportional to the amplitude of transverse Alfvenic waves. Our results indicate that Alfvenic waves both carry and dissipate enough energy to heat coronal holes as well as quiet Sun regions. Thus, our results imply that such waves are responsible for heating the corona outside of active regions. One of the questions raised by this work is the damping mechanism. The observed dissipation is faster than expected from viscosity or resistivity, but there are more complex theories that may explain the damping. I will describe some proposed laboratory plasma experiments that will test these theories.


4:00 pm: Colloquium. "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.