Weekly Calendar of Events

MARCH 30 - APRIL 3, 2015


Noon: Solar, Stellar, and Planetary Sciences Division Seminar. "A Magnetically-Driven Model of Flux-Rope Expansion from the Sun to 1AU in Order to Compute Bz at 1AU," Valbona Kunkel, George Mason University. Pratt Conference Room.

Abstract: In this talk I will present the results of the HelioXM model that simulates the propagation of (CME-like) idealized magnetic flux ropes from the Sun to the Earth by including both the dynamics of the apex and the legs of the flux ropes. Therefore the model calculates the expansion of a flux rope in three orthogonal directions based on physical forces: apex expansion, transverse expansion, and minor radial expansion. The model provides two new important predictions: (1) estimates of the magnetic field strength and orientation of the CME Bz component at 1AU (2) estimates of the arrival time of the magnetized CME ejecta. The model calculates the evolving magnetic field of a CME ejecta (in three dimension Bx, By, Bz), pressure, temperature and density in relation to the initial geometry of the CME at the Sun and height-time data measured directly in white-light images. I will present the limitations of the model and future improvements that could be made to it. I will also present an application based on this type of model that computes the magnetic field vector components seen by a probe/planet traversing through the flux rope for any orientation of the CME.


11:00 am: Seamless Astronomy Colloquium. "The Diffuse Universe: Catalogs, Continuum, Combination," Josh Peek, Space Telescope Science Institute. Refreshments will be provided. Phillips Auditorium.

Abstract: Astronomy has always been a science of catalogs: catalogs of stars, galaxies, quasars, and planets. While most of the light in the Universe comes from these dense objects in the darkness, the contents of the universe are largely diffuse. Dark energy, dark matter, plasma, and gas make up 99.8% of the mass-energy budget of the Universe and cannot be easily cataloged. If we want to understand how the objects in the universe came to be,we must appeal to the largely invisible diffuse phase that formed them. I will try to make sense of this conundrum in three ways. The first is to use the cataloged objects to discern things about the intervening gas: through dust reddening we can measure the location and density of metal enriched gas in the Galaxy and beyond. The second is to examine the velocity-resolved emission from the gas. To do this we invent statistically robust ways to measure the shape structure of the gas, where much of the information about the diffuse phases hides. The third is to combine the two, catalogs and continuum, to delve into the 4D structure of our Galaxy. I will discuss a method in development, Kinetic Tomography, which will hopefully help us understand how the Galaxy came to be the way it is today.

1:00 pm: Institute for Theory and Computation (ITC) Pizza Lunch. Speakers: Josh Peek, Space Telescope Science Institute, and Dr. Chat Hull, CfA. Topics: To be announced. Phillips Auditorium.


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

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: Special Institute for Theory and Computation (ITC) Colloquium. "Is Statistical Mechanics Useful for Describing Galaxies and Planetary Systems," Prof. Scott Tremaine, Institute for Advanced Study. Phillips Auditorium.


11:00 am: Institute for Theory and Computation (ITC) Colloquium. "Head in the Clouds: Decoding the Spectral Features Produced by Brown Dwarf and Exoplanent Atmospheres," Prof. Kelle Cruz, Hunter College/CUNY. Pratt Conference Room.

Abstract: Brown dwarfs, with low temperature atmospheres dominated by condensate clouds, are promising analogs for young, massive exoplanets. In this talk, I will first give a brief overview of the brown dwarf-exoplanet connections and the current roadblocks in interpreting their spectra. I will then describe our ongoing observational efforts to identify and exploit well-characterized benchmark brown dwarfs with well-constrained ages to empirically disentangle the effects of temperature, age, and condensate clouds on brown dwarf spectra. This work is creatively advancing our understanding of the key physical parameters that sculpt observed spectral data of exoplanet atmospheres: a critical component to interpreting results from the next generation of telescopes and instrumentation.

4:00 pm: Colloquium. "Understanding Haze Formation in Planetary Atmospheres: Lessons from the Lab," Dr. Sarah Horst, Johns Hopkins University. Preceded by tea at 3:30 pm. Phillips Auditorium.

Abstract: From exoplanets, with their surprising lack of spectral features, to Titan and its characteristic haze layer, numerous planetary atmospheres may possess photochemically produced particles or haze. With few exceptions, we lack strong observational constraints (in situ or remote sensing) on the size, shape, density, and composition of these particles. Photochemical models, which can generally explain the observed abundances of smaller, gas phase species, are not well suited for investigations of much larger, solid phase species. Laboratory investigations of haze formation in planetary atmospheres therefore play a key role in improving our understanding of the formation and composition of haze particles. I will discuss a series of experiments aimed at improving our understanding of haze in the atmospheres of Titan, the early Earth, exoplanets, and any other atmospheres composed of a combination of N2, CH4, CO, CO2, and/or O2. In particular, I will discuss investigations of the density of Titan aerosol analogues ("tholins"), the effect of energy source on incorporation of nitrogen into tholin, the effect of CO on haze formation, and the possible presence of haze during the rise of oxygen on the early Earth.

The Calendar is prepared by the Web Services Group. Entries may be submitted via email to weekly_cal@cfa.


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