Wine and Cheese Fall 2016

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

Wine and Cheese sessions with one talk will have a 50 minute talk with 10 minutes for questions. Sessions with two speakers will have two 25 minute talks, each with 5 minutes for questions.

September 19th

Massimo Robberto

GMOX and SAMOS
NSF has recently funded a JHU-led collaboration to build SAMOS, a novel multi-slit spectograph for the 4.1m SOAR telescope in Chile. SAMOS exploits the ground-layer AO system to take hundreds of faint spectra in parallel at R~2000 over a 3’x’3’ field of view. At the same time, Gemini has contracted us with the study of an expanded version of SAMOS, GMOX, to be installed at the Multi-Conjugate extreme-AO system of Gemini South. GMOX covers the full U to K bandpass at R~5000 and can synthetize slits as small as a single HST/WFC3-vis pixel (40mas), reaching unpredentented levels of sensitivity in the near-IR from the ground. I will present the main characteristics of the instruments, their current status, and an outline of the type of science programs that can be carried out in the substantial amount of GTO time.

Bram Ochsendorf

The Location, Clustering, and Propagation of Massive Star Formation in Giant Molecular Clouds
Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this talk, I will present results from a project utilizing data from several galaxy-wide surveys to build an unbiased dataset of ∼700 massive young stellar objects (MYSOs), ∼200 giant molecular clouds (GMCs), and ∼100 young (< 10 Myr) optical stellar clusters (SCs) in the Large Magellanic Cloud. We have employed this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. The main results are as follows: (1) Massive stars do not typically form at the highest column densities nor centers of their parent GMCs. (2) Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. (3) The rate of massive star formation is significantly boosted in clouds near SCs. Yet, comparison of molecular clouds associated with SCs with those that are not reveals no significant difference in their global properties. These results reveal a connection between different generations of massive stars on timescales up to 10 Myr. I will compare our findings with Galactic studies and discuss this in terms of GMC collapse, triggered star formation, and a potential dichotomy between low- and high-mass star formation.

September 26th

David Jones

Contaminated Cosmology: Measuring w with Photometrically Classified Supernovae from Pan-STARRS
The Pan-STARRS (PS1) Medium Deep Survey discovered over 5,000 likely supernovae (SNe) but obtained spectral classifications for only 10% of its SN candidates. We measured spectroscopic host galaxy redshifts for 2,979 of these likely SNe and estimate that ∼1,100 are Type Ia SNe (SNeIa) with light-curve quality sufficient for a cosmological analysis. We use PS1 data and simulations to determine the impact of core-collapse SN (CC SN) contamination on measurements of the dark energy equation of state, w. With the Bayesian Estimation Applied to Multiple Species (BEAMS) method, we simultaneously determine distances to SNe Ia and the contaminating CC SN distribution as a function of redshift. We use light-curve based SN classification priors for BEAMS as well as a new classification method based solely on host galaxy spectra. By applying several independent SN classification methods and CC SN parameterizations, we investigate the systematic error on w due to CC SN contamination. We find that w has an average systematic error of 0.012 due to CC SNe, ∼25% of the statistical error on w when using a cosmic microwave background prior. We find that Ia-like CCSNe in our sample are much brighter than expected from known CC SN luminosity functions.

Clément Bonnerot

Stream evolution in tidal disruption events
Tidal disruption events occur when a star gets scattered on a trajectory that takes it so close to a supermassive black hole that it is torn apart by strong tidal forces. Such events represent unique probes of otherwise quiescent black holes, which constitute the majority of black holes in the local universe. However, this great potential is hampered by the lack of a clear picture of how exactly these events take place. One particular uncertainty concerns the circularization process during which the stellar debris dissipate their large orbital energy to form an accretion disc around the black hole. Hydrodynamical simulations point towards shocks driven by debris self-intersections as an efficient dissipation mechanism. In my talk, I will present a recently developed semi-analytical model that treats the circularization process, accounting for the impact of both shocks and magnetic stresses. This model proves that the net effect of magnetic stresses is to strengthen shocks, thus accelerating circularization. It also allows to predict the form of the lightcurve associated to shock luminosity and demonstrates that the thermal energy excess imparted by shocks is most likely to cause the rapid formation of a thick structure. To conclude the talk, I will present latest advances on ongoing projects and mention future research directions.

October 3rd

David Hogg

Chemical tagging of stars with a data-driven model
We have used tens of thousands of high-quality stellar spectra taken in the SDSS-III APOGEE survey to build a data-driven model of stars, and measure detailed chemical abundances at a scale and precision substantially better than any previous experiment. I discuss the model, its successes, and its potential as a tool for understanding stars and the Galaxy.

October 10th

Cole Miller

CDM versus Perceived Structure
Cold dark matter, along with dark energy, constitute 96% of the universe. Calculations using these components have successfully explained many aspects of structure formation, but as is appropriate for such a broad framework there have also been multiple challenges along the way. One recent challenge involves the existence of structure in the satellite galaxy distributions of the Galaxy and M31, such as thin planes with apparent kinematic coherence, which have been claimed to be inconsistent with the results from dark matter simulations. However, these are a posteriori claims: a pattern is seen in data, and then that particular pattern is analyzed for significance, which can easily lead to misleading assessments of improbability. I will discuss different statistical methods to determine more objectively whether observed patterns are consistent with data, and will also discuss planned future work to help compare different models of cold dark matter.

October 24th

Nathan Roth

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October 31st

Special Halloween Speakers

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Attendance in costume is optional

November 7th

Anthony Pullen

Revealing Intensity Fluctuations with LSS Tracers
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November 28th

Aki Roberge

Star-Grazing Exocomets Around Nearby Young Stars and Big Bang to Biosignatures: The LUVOIR Decadal Mission Concept
A double-barreled talk!

December 5th

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