10^th Annual MKI Postdoctoral Symposium

Schedule for Friday May 12^th

Moderator: Rana Ezzeddine

11:45 – 12:00  Lunch catered by Bertucci’s (not pizza!)

12:00 – 12:30  Clara Sousa-Silva, “Will we know it when we see it? Resolving ambiguities in the spectroscopic detection of life”

Characterizing stars and their planetary companions in order to search for evidence of biosignatures requires a deep understanding of the molecules within them. Given that obtaining physical samples from other planetary systems is beyond our current abilities, our best bet is to remotely identify the existence of a molecule through its spectral signature. A comprehensive study of biosignatures requires understanding thousands of molecular species. However, knowledge of molecular spectra currently only exists for a few hundred molecules and, other than a handful of exceptions (e.g. water, CO), most molecular spectra are either incomplete, inaccurate or (most often) a dangerous combination of both. Measuring these spectra experimentally can be difficult, perilous, and sometimes altogether impossible. Fortunately, accurately calculating molecular spectra through theoretical means offers an excellent alternative. For the majority of molecules, however, this process remains computationally or mathematically impossible. I propose that, given the relatively low level of accuracy that astronomical observations require, there is value in creating approximate models of the spectra of molecules, particularly those about which we know very little or nothing at all. ATMOS (Approximate Theoretical MOlecular Spectra) aims to do just that, using a combination of experimental measurements, organic chemistry and quantum mechanics. Disclaimer: it still may not work, but it will be really cool if it does.

12:35 – 1:05  Paul Hemphill, “Yes, I Have Considered Magnetic Fields: Cyclotron Resonance Scattering Features in High-Mass X-ray Binaries”

Around two dozen accreting X-ray pulsars display cyclotron resonance scattering features (CRSFs) in their high-energy X-ray spectra. These broad pseudo-absorption features originate in the resonant scattering of photons on electrons moving in a strong magnetic field, and provide us with the only direct measurement of a pulsar’s magnetic field strength. Additionally, as they must be produced near or on the surface of the neutron star, their variability can be used as a probe of the physical conditions close to the magnetic pole.  In this talk I will give an overview of the current scientific picture of CRSFs and go into some of our recent results regarding these features and the high-energy X-ray continuum of neutron star HMXBs in general.

1:10 – 1:40  DJ Pashman, “Disk–Jet Coupling Following a Stellar Tidal Disruption Flare”

The tidal disruption of a star by a supermassive black hole can result in transient radio emission. The electrons producing these synchrotron radio flares could either be accelerated inside a relativistic jet or externally by shocks resulting from an outflow interacting with the circumnuclear medium. Until now, evidence for internal emission has been lacking and nearly all tidal disruption flare studies have adopted the external shock model to explain the observed properties of radio flares. Here we report the discovery of a correlation between changes in the x-ray and radio flux of a tidal disruption flare. The radio lags the x-ray emission by about 13 days. This demonstrates that the x-ray emitting accretion disk regulates the radio emission. This coupling is inconsistent with all previous external models but is naturally explained if the radio emission originates from a freely expanding jet.

NOTE: Immediately following the postdoc symposium on Friday, May 12, the MKI community will honor Steve Kissel’s 25+ years of service to MKI. Please stay and join us for cake!

2017 Postdoctoral Symposium Organizers: Rana Ezzeddine, Allison Noble, and DJ Pasham