January 31, 2017
12:00 PM to 1:00 PM
Chelsea Huang, Massachusetts Institute of Technology
Linking Giant Planets to Super Earths
Giant planets and super Earths are often studied as they were two isolated population. The loneliness of hot Jupiters (except for the WASP-47 system) suggests that they may be mutually exclusive with super Earths in the formation path. In this talk, I will examine systems which cohabiting giant-planets (outside of 1 AU) and super-Earths, and discuss how these giant planets shape up the architectures of their planetary systems.
System like this-cold Jupiters have close-in super-Earth companions have been discovered in Radial velocity surveys. Using N-body simulations, we show the formation of these cold Jupiters, through scattering events, would excite the super-Earths in the same system, leaving them dynamically hot. The recent discoveries of eccentric and inclined Kepler single-transiting planets is consistent with the predicted dynamically hot super Earths from this mechanism.
February 14, 2017
12:00 PM to 1:00 PM
Tad Komacek, University of Arizona
A Predictive Theory for the Atmospheric Circulation of Hot Jupiters
The atmospheres of extremely close-in extrasolar giant planets, or "hot Jupiters," are beginning to be analyzed as a population. Synthesizing observations of many different planets provides insight into the nature of the atmospheric circulation of these objects. Notably, the dayside-to-nightside brightness temperature difference from infrared observations of these tidally locked objects appears to increase with increasing incident stellar flux. Additionally, there is an eastward infrared phase shift on these planets, which shows tentative evidence of decreasing longitudinal offset from the substellar point with increasing stellar flux. Motivated by these observations, I will present an analytic theory from first principles that predicts dayside-nightside temperature differences and wind speeds as a function of incident stellar flux, rotation rate, atmospheric composition, potential frictional drag strength, and pressure level in the atmosphere. This analytic theory predicts that, as hinted at from observations, there should be a trend of increasing dayside-nightside temperature difference with increasing incident stellar flux. Additionally, the analytic theory can be used to predict vertical mixing rates (i.e. K_zz) for use as input into one-dimensional atmospheric chemistry models. Lastly, to understand in greater detail how atmospheric circulation varies with incident stellar flux and drag strength, I will present three-dimensional numerical simulations including a double-grey radiative transfer scheme. These simulations broadly confirm our theoretically predicted trends for the day-to-night temperature difference and vertical mixing rates.
February 28, 2017
12:00 PM to 1:00 PM
Phil Nicholson, Cornell
Kronoseismology: Probing Saturn’s Interior via its Rings
In previous work (Hedman & Nicholson  Astron. J. 146, 12; Ibid  MNRAS 444, 1369) we have identified several inward-propagating density waves in Saturn's C ring with outer Lindblad resonances (OLRs) generated by internal oscillations in Saturn. The oscillations involved are sectoral f-modes (ie., fundamental modes with l = m) with m = 1, 2, 3, 4 and 10, as originally discussed by Marley & Porco . In addition, five outward-propagating waves between radii of 84,800 and 86,600 km have been identified as density waves driven by 3:2 tesseral resonances with fixed gravitational anomalies within the planet. I will present stellar occultation data for six additional waves from the catalog of Baillie et al. , which are both weaker and shorter in wavelength than the previously-identified waves. We use a modified version of our wavelet-based technique to coadd phase-corrected spectra from multiple occultations, using trial values of `m` and the pattern speed to predict their relative phases. This enables us to detect waves too weak to see in individual data sets. Two of the new waves appear to be due to additional saturnian f-modes with m = 2 and m = 9. The other four waves appear to be in a new class: outward-propagating bending waves driven at outer vertical resonances (OVRs) with asymmetric Saturn internal oscillations for which l = m + 1. We identify four such waves with m = 4, 7, 8 & 9. All of the newly-identified waves are at radii less than 77,000 km. Only the m = 4 wave is near the location predicted by Marley & Porco .