Wine and Cheese Spring 2016

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Spring 2016.

If not specified otherwise, the talks are a 25-min presentation plus a 5-min Q/A session.

February 1st

Ilias Cholis

Towards a predictive analytic model for the solar modulation of cosmic rays
An important factor limiting our ability to understand the production and propagation of cosmic rays pertains to the effects of heliospheric forces, commonly known as solar modulation. The solar wind is capable of generating time and charge-dependent effects on the spectrum and intensity of low energy (~10 GeV) cosmic rays reaching Earth. Previous analytic treatments of solar modulation have utilized the force-field approximation, in which a simple potential is adopted whose amplitude is selected to best fit the cosmic-ray data taken over a given period of time. Making use of recently available cosmic-ray data from the Voyager 1 spacecraft, along with measurements of the heliospheric magnetic field and solar wind, I will show a time, charge and rigidity-dependent model of solar modulation that can be directly compared to data from a variety of cosmic-ray experiments. This is a simple analytic formula that can be easily utilized in a variety of applications, allowing us to better predict the effects of solar modulation and reduce the number of free parameters involved in cosmic ray propagation models.

William Blair

Understanding the Curious Young Supernova Remnant Population in M83
The nearby starburst galaxy M83 has been host to at least six (and likely seven!) supernovae in the last century, many of the core-collapse type. Hence, one might expect dozens of young SN remnants similar to, say, Cas A in our Galaxy or E0102-7219 in the SMC. We have used deep Chandra observations in conjunction with HST WFC3 imaging to find and diagnose the young SN remnants in M83 and, by in large, they do not look like Cas A (that is to say, dominated by emission from SN ejecta). Rather, they appear to be bright radiative remnants like the Cygnus Loop even though they are much smaller and younger. This rapid evolution into the radiative phase may be unique to the M83 population, due to high metal abundances and a high pressure ISM. Our investigation is ongoing, with Gemini GMOS spectroscopy of many of these young SN remnants providing additional clues.

February 8th

David Hogg

Postponed
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February 15th

Saleem Zaroubi

Probing the Epoch of Reionization from LOFAR
The Epoch of Reionization is one of the least explored epochs in the history of the Universe. The redshifted 21 cm line from neutral hydrogen emitted during this epoch is the most promising probe for exploring it. To date there are a number of low frequency radio telescope that are aiming at detecting this radiation. The LOw Frequency ARray, LOFAR, which a European telescope centred in the Netherlands, has started collecting data on December 2012. I will discuss the current status of the experiment and the main results coming out of it.

February 22nd

Mubdi Rahman

Early-time Feedback in the Milky Way
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Richard Anderson

On the effect of rotation on populations of Cepheids
Rotation affects the evolution of intermediate-mass stars by inducing mixing processes that alter mass-luminosity relations as well as main sequence lifetimes. Classical Cepheids are evolved intermediate-mass stars observed during a comparatively brief evolutionary phase that offers sensitive diagnostics for testing stellar evolution models and renders them accurate cosmic yardsticks.

In this talk I present recent work that investigates the evolutionary effect of rotation on classical Cepheid variable stars. The talk will focus on 1) the long-standing Cepheid mass discrepancy, 2) observational tests of model predictions, and 3) the significance of rotation for the period-luminosity relation.

Finally, we show that Cepheids obey a tight flux-weighted gravity-luminosity relation, which offers a novel approach for determining Cepheid distances using spectroscopy.

February 29th

Ethan Visniac

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March 7th

Nathan Miller

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Duncan Watts

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March 21st

Tony Sohn

HST Proper Motions along Stellar Streams: Constraining Dark Halo Properties of the Milky Way
Stellar streams in the Milky Way are unique dynamical tracers of the dark matter halo, and provide strong tests of galaxy formation models. However, lack of proper motion data limits our understanding of stream orbits and dark halo properties. Thanks to the HST's excellent astrometric accuracy, we are now able to obtain high quality proper motions along stellar streams in the Milky Way. In this talk, I will present our results on HST projects for measuring proper motions along two stellar streams in the halo: the Sagittarius Stream and the Orphan Stream.

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March 28th

Ravi Sankrit

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Zhilei Xu

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April 4th

Michael Fall

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April 11th

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April 18th

Joel Green

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April 25th

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May 2nd

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