Relativity and Space Science Seminar Series, Thursdays, 3-4p.m., Dayton Conference Room (EPS 258)

Date Presenter Topic
Sept 5 Laura Sampson Molecular Detectability in Exoplanetary Emission Spectra 5
Formation of Primordial Supermassive Stars by Rapid Mass Accretion 4
Sept 12 Katerina Chatziioannou Gravitational Waves from Spinning, Compact Binary Inspirals
Sept 19 Devin Hansen One Good Turn
Sept 26 Martin Harrington  
Oct 3 Sarah Jaeggli The Role of H2 in the Solar Atmosphere
Oct 10 Wenjuan Liu Determining Heating Rates in Reconnection Formed Flare Loops
Oct 17 Meg Millhouse Neutrino Tomography
Oct 24 David McKenzie Spatially Resolved Measurements of Turbulence in the Flare Reconnection Region
Oct 31 Kent Yagi Strong Binary Pulsar Constraints on Lorentz Violation in Gravity
Nov 7 Laura Sampson  
Nov14 Antoine Klein Inspiral waveforms for binary systems
Nov 21 Dana Longcope  
Dec 5 Nick Loutrel  


When: September 12th
Who: Katerina Chatziioannou
What: Gravitational Waves from Spinning, Compact Binary Inspirals

Binary inspirals, which are among the most promising gravitational wave sources for future detectors, are expected to be affected by the spins of the two components. This spin interaction will induce a precession of the orbital plane of the binary, which will alter the gravitational waves emitted, a detailed modeling of which is crucial for parameter estimation. In this talk, I will describe how one can analytically, perturbatively model the spin interactions and obtain accurate gravitational wave templates.


When: September 19th
Who: Devin Hansen (*undergraduate student*)
Title: One Good Turn

One method for producing rotating axisymmetric black hole metrics from stationary spherically-symmetric counterparts in general relativity is the Newman-Janis algorithm.  While there is currently no fundamental explanation for the algorithm's success, it has in recent years been used to ``rotate" metrics in modified gravity theories.  We find that such uses are without basis, and that the use of the algorithm on a generic non-GR spherically-symmetric metric introduces pathologies into the resulting metric.  This establishes that, in general, the algorithm cannot be used to generate new axisymmetric black hole solutions in modified gravity theories.


October 5th
Sarah Jaeggli
Title: The Role of H2 in the Solar Atmosphere

Molecules may not seem like a large portion of the solar atmosphere, but in sunspots, where the atmosphere is significantly cooler than the surrounding quiet-Sun, the molecular population becomes a major player.  Large molecular populations, primarily in the form of molecular hydrogen (H2), can have interesting consequences for the sunspot atmosphere.  However, detecting H2 is a significant problem.  In this talk I'll present a continuing study of H2 based on the observed magnetohydrostatic state in sunspots, observed traces of other, similar molecular species, and direct observations of H2 spectral lines in the far UV.  I will also discuss prospects for future observations with the UV spectrograph on IRIS.


Oct 10th.
Wenjuan Liu
Title: Determining Heating Rates in Reconnection Formed Flare Loops

High-cadence UV and EUV observations have revealed that flare loops are formed
and heated by magnetic reconnection events taking place successively. The UV 1600Å radiation
in the lower atmosphere is usually used to study the feet of flare loops. The UV light curve in
each flaring pixel is characterized by impulsive rise of several minutes and long decay with time
scale of more than ten minutes. Since the lower atmosphere responses within a few seconds to
the energy deposit during the flare, the rise of the UV light curves could be used to infer the
impulsive heating rates in these loops anchored at the foot-points. Using these heating rates and
the Enthalpy-Based Thermal Evolution of Loops (EBTEL) model, we can compute plasma
evolution in thousands of flare loops anchored at the UV foot-points, and calculate the synthetic
radiation from these loops and/or foot points to compare with observations to constrain the
heating rates. Furthermore, using RHESSI hard X-ray observations, we also infer the fraction
of non-thermal beam heating in the total heating rate of flare loops, and discuss its effect on
plasma evolution. In the talk, I’ll present studies of in two M-class flares and show the favorable
comparisons of the synthetic spectra and light curves with the observations. 


October 17th.
Meg Millhouse
Title: Neutrino Tomography

Neutrinos are produced in weak interactions as states with definite flavor—electron, muon, or tau—and these flavor states are superpositions of states of different mass. As a neutrino propagates through space, the different mass eigenstates interfere, resulting in time-dependent flavor oscillation. Though matter is transparent to neutrinos, the flavor oscillation probability is modified when neutrinos travel through matter. We present an introduction to neutrino propagation through matter. As an interesting application, we consider neutrino propagation through matter with a piecewise-constant density profile. This scenario has relevance in neutrino tomography, in which the density profile of matter, like the Earth’s interior, can be probed via a broad-spectrum neutrino beam. We provide an idealized example to demonstrate the principle of neutrino tomography.


October 24th
David McKenzie
David McKenzie will speak on Spatially Resolved Measurements of Turbulence in the Flare Reconnection Region

I will begin by recapping the key points from February's RelAstro seminar "Handwaves & Mosh Pits", as a lead-in to discussing why turbulence is relevant to reconnection in solar flares. Then I'll update you on work that Mike Freed & I are doing with image data from the Solar Dynamics Observatory, and how those measurements compare with EUV spectra from Hinode. Next I'll show how heating terms calculated from velocity shear, divergence, and curl in the sheet-like plasma structures compare with the observed temperature changes. If there's time, I will mention some of the other measurements we plan to make in the turbulent velocity fields.


October 31st
Kent Yagi.
Title: Strong Binary Pulsar Constraints on Lorentz Violation in Gravity

Binary pulsars are excellent laboratories to test the building blocks of Einstein's theory of General Relativity. One of these is Lorentz symmetry which states that physical phenomena appear the same for all inertially moving observers. We study the effect of violations of Lorentz symmetry in the orbital evolution of binary pulsars and find that it induces a much more rapid decay of the binary's orbital period due to the emission of dipolar radiation. The absence of such behavior in recent observations allows us to place the most stringent constraints on Lorentz violation in gravity, thus verifying one of the cornerstones of Einstein's theory much more accurately than any previous gravitational observation.


November 14th
Antoine Klein

Today I will be talking about inspiral waveforms for binary systems. I will try to address the question of what accuracy in the post-Newtonian expansion is required for good parameter recovery in case of a gravitational wave detection. I will focus on spin-aligned waveforms, and on the recovery of the masses and the spin parameters of the binary components.


Talks from the Spring 2013 semester can be found here...