ITC Pizza Lunch


Wednesday, May 2, 2018, 11:00am to 12:00pm




Xiawei Wang (Harvard)
Self-sustaining star formation fronts in filaments during cosmic dawn
Abstract: We propose a new model for the ignition of star formation in low-mass halos by a self-sustaining shock front in cosmic filaments at high redshifts. The gaseous fuel for star formation resides in low mass halos which can not cool on their own due to their primordial composition and low virial temperatures. We show that star formation can be triggered in these filaments by a passing shock wave. The shells swept-up by the shock cool and fragment into cold clumps that form massive stars via thermal instability on a timescale shorter than the front's dynamical timescale. The shock, in turn, is self-sustained by energy injection from supernova explosions. The star formation front is analogous to a detonation wave, which drives exothermic reactions powering the shock. We find that sustained star formation would typically propel the front to a speed of ~ 300-700 km/s during the epoch of reionization. Future observations by the James Webb Space Telescope could reveal the illuminated regions of cosmic filaments, and constrain the initial mass function of stars in them.



Sofia Moschou (CfA)

Title: Modeling Radio Loud Coronal Mass Ejections

Ground-based radio observations offer access to a diverse range of
physical processes, from thermal to eruptive ones, that take place in
the solar atmosphere. Radio waves have a strong dependence on the
refraction index and thus follow curved paths when they travel in
stratified media, such as the stellar coronae. The effect of
refraction is stronger for lower radio frequencies. Inspired by the
solar paradigm that has revealed a “1-1” relation between Type II
radio bursts and CME shock waves, stellar radio astronomers are
conducting surveys to incontrovertibly observe stellar CMEs. I will
present a newly developed radio synthetic imaging tool integrated in
state-of-the-art computational simulations of the solar corona and
wind. The tool calculates and visualizes the Bremsstrahlung radio
emission for both the quiescent corona and CMEs along the actual
curved paths of the radio rays. Our results are in good agreement with
high frequency observations of the solar corona.


See also: Pizza Lunch, 2017-18