Wine and Cheese Fall 2017

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2017.

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 11th

Lauren Corlies (JHU)

Figuring Out Gas & Galaxies In Enzo (FOGGIE): Connecting Simulations and Observations

The circumgalactic medium (CGM) is host to a number of fundamental processes driving galaxy formation and evolution: gas accretion from the IGM, gas stripping from in-falling satellites, the ejection of gas by multiple feedback processes, and the recycling of gas by the disk. Yet its diffuse nature makes observations difficult and thus, the CGM is one of the least constrained aspects of hydrodynamical simulations. In this talk, I’ll discuss two ways we are trying to connect the simulated CGM to current and future observations. First, I’ll present observationally constrained emission predictions from a high-resolution cosmological simulation of a Milky Way-like galaxy and demonstrate how this emission reflects the evolution of the CGM at late times and discuss the detection likelihoods for such emission. Second, I’ll present a novel implementation of a mesh refinement scheme wherein we achieve unprecedentedly high resolution in the CGM of a MW-like galaxy. I’ll highlight some preliminary results from these tests that indicate that resolution alone has a large impact on the physical structure and observational properties of this gas.

Ivan Padilla (JHU)

SPIDER: Searching for the echoes of inflation from atop the atmosphere

Balloon-borne platforms have long served as a shortcut to space-quality science and as pathfinder instruments for satellite missions. NASA's Long Duration Balloon platform allows for flights lasting roughly 20 days, carrying payloads weighing upwards of 6000 lbs. Spider is a balloon-borne microwave polarimeter that aims to take advantage of this platform to obtain very high sensitivity maps of the polarized cosmic microwave background, over a 10% patch of the sky and at 3 different frequencies -- 95, 150, and 285 GHz. The spatial and frequency coverage should allow for effective separation of foregrounds from the signal, potentially reaching an upper limit of r < 0.03.

Designed as a two-flight mission, Spider completed its first flight in January of 2015 after a 16 day voyage, suspended 36 km over the Antarctic continent. During the first flight, Spider observed a high Galactic latitude patch of the sky with over 2,000 polarization sensitive bolometers at 95 and 150 GHz. The second flight will replace some of the receivers with three high frequency 285 GHz channels containing 512 channels each. I will go over some preliminary results from the first flight, discuss some of the challenges involved, and motivate the need for a second flight. I will also give an update on the status of preparation for the second flight, which is scheduled for the end of 2018.

September 18th

David Neufeld (JHU)

What the Largest Atoms in the Galaxy Tell Us About the Density of Cosmic Rays

I'll discuss how the cosmic-ray ionization rate in diffuse molecular clouds can be inferred from observations of radio recombination lines emitted by atoms in high-lying "Rydberg" states. Our preliminary results are in good agreement with those obtained from observations of molecular ions such as OH+ and H3+.

Richard Conn Henry (JHU)

The Mental Universe
Forty-nine years ago I was hired (a PhD astronomer) by the JHU Physics department. I’d never understood physics from the classes I’d taken: physics did not seem to make much sense, especially, of course, quantum mechanics. So I decided I should teach physics myself, in the hope of understanding it at last. So, for about 35 years I taught Special Relativity, General Relativity, and Quantum Mechanics. The result was fascinating, and disturbing: it was clear that the universe is not what we astronomers think it is. I also discovered, by reading Nature and Science every week for all those years, that this was not a secret! For example, in Science, 1995, 270, 1439, “Measurements are the Only Reality, Say Quantum Tests.” But, the scientific community did not teach that fact to the young! What was going on? I decided, twelve years ago, to put the matter to the test: my wife and I were skiing in Colorado and in the evenings, I composed an essay entitled “The mental Universe,” and submitted it to Nature. Shortly after we returned to Baltimore, I received a phone call from England and was told that my essay “needed to be shortened by about a factor of two” before it could appear. I swallowed hard, shortened it, and it duly appeared (436, 29, 2005). I waited for blowback, but that never came. I will try to explain why this is not a joke, but is, well, real.

September 25th

Michael Crosley (JHU)

The Search for Transient Mass Loss in Active Stars
One factor important to habitability is the impact of stellar eruptive events on nearby exoplanets. Currently this is poorly constrained due to heavy reliance on solar scaling relationships and a lack of experimental evidence. Low frequency dynamic spectra of radio bursts from nearby stars offer the best chance to directly detect the stellar signature of transient mass loss on low mass stars. By using solar observations, analogous to those found in stellar studies, we test the validity and accuracy of the multi-wavelength analysis proposed to describe coronal mass ejections from radio bursts and flare observations. We take these results and apply them to 15 hours of radio observations of YZ CMi taken at Low Frequency Array and 20 hr simultaneously observed EQ Peg observations taken at the Jansky Very Large Array and Apache Point Observatory.

Matt Morris (JHU)

Stellar Atmospheric Modelling for the ACCESS Program
The goal of the ACCESS program (Absolute Color Calibration Experiment for Standard Stars) is to enable greater discrimination between theoretical astrophysical models and observations, where the comparison is limited by systematic errors associated with the relative flux calibration of the targets. To achieve these goals, ACCESS has been designed as a sub-orbital rocket borne payload and ground calibration program, to establish absolute flux calibration of stellar targets at <1% precision, with a resolving power of 500 across the 0.35 to 1.7 micron bandpass. Using calibrated high resolution spectra from Apache Point Observatory in addition to HST/CALSPEC data, I have developed stellar atmosphere models for ACCESS flight candidates, as well as a selection of A and G stars from the CALSPEC database using ATLAS9 and ATLAS12 Kurucz stellar atmosphere code. I will discuss the process of model fitting, and present preliminary results.

Raymond Simons (JHU)

z~2: An Epoch of Disk Assembly
At z = 0, the majority of massive star-forming galaxies contain thin, rotationally supported gas disks. It was once accepted that galaxies form thin disks early: collisional gas with high velocity dispersion should dissipate energy, conserve angular momentum, and develop rotational support in only a few galaxy crossing times (~few hundred Myr). However, this picture is not borne out at high redshift, where the processes governing galaxy assembly tend to be violent and inhospitable to disk formation. I will present results from our survey of star-forming galaxy kinematics at z ~ 2. I will show that this period is one of disk assembly, where galaxies are most rapidly building their stellar mass and only just beginning to develop the kinematic characteristics of local disks, i.e., low velocity dispersion and high rotation velocity.

Kirill Tchernyshyov (JHU)

Gas Dynamics in the Spiral Arms of the Milky Way
There is general agreement that the ISM of the Milky Way is arranged into a spiral-like structure of some sort, though there is not yet agreement on how regular this spiral-like structure is, how many arms it consists of, or how it evolves. In order to investigate the dynamics of gas associated with one of the spiral arms nearest to the Sun, the Perseus arm, we have developed techniques for inferring the line-of-sight component of the velocity field of the ISM using combinations of observations of dust reddening, gas emission, and gas absorption. Using these techniques, we have produced two maps of the line-of-sight velocity as a function of three dimensional position. In both of these maps, there are spatially coherent deviations from flat rotation which reach their peak amplitudes at approximately the location of the Perseus arm. We have compared these deviations to predictions from stationary spiral shock and dynamic spiral structure models and have found that both models predict features that are clearly not present in the observed velocity field.

October 2nd

Norman Murray (CITA)

Star Formation, GMCs, and Galaxies

Star formation on galactic scales is observed to be a slow process, a result known as the Kennicutt-Schmidt relation. I will argue, using observations, simulations, and analytic theory, that star formation on smaller scales, those of Giant Molecular Clouds (GMCs), that the star formation rate increases with GMC age. GMCs in the "five kiloparsec ring" of the Milky Way are contracting under self-gravity, a process that is halted and reversed by feedback from star clusters. I will then describe the results of the FIRE simulations, which show that in galaxies with higher gas surface density, and hence more massive GMCs, the feedback not only disrupts the GMCs, it drives winds from the simulated galaxies; at high redshifts, the simulated winds remove the interstellar medium of the galaxy, halting star formation for a dynamical time. Upcoming CO intensity mapping experiments will test this prediction of the FIRE simulations.

October 9th

Gabriele Betancourt-Martinez (UMCP)

Understanding Charge Exchange through Laboratory Astrophysics Measurements using an Electron Beam Ion Trap
X-ray emission due to charge exchange (CX) between solar wind ions and neutrals in comets and planetary atmospheres is ubiquitous in the solar system, and is also a significant contaminating foreground in all observations from low-Earth orbit. It is also likely that CX is common astrophysically, in any environment where hot plasma and cold gas interact. Theoretical models of CX spectra do not always accurately describe observations, and different spectral models often predict distinct CX spectra, even for the same initial assumptions. It is important to verify these models experimentally in order to exploit the diagnostic nature of CX, and in general to deduce the proper physics from the astrophysical environments we observe.

In order to improve our understanding and modeling of CX spectra, we use an Electron Beam Ion Trap (EBIT) to perform CX experiments and measure the spectra with the EBIT Calorimeter Spectrometer, a silicon thermistor microcalorimeter which has an energy resolution of ~4.5 eV at 6 keV. In this talk, I will present experimental data that we have used to benchmark CX models, and review our progress in understanding CX diagnostics and developing a more comprehensive and accurate CX theory.

Max Abitbol (Columbia)

The Impact of Foregrounds on Cosmic Microwave Background Polarization and Spectrum Measurements
I will present my recent work on foregrounds and their impact on cosmic microwave background (CMB) analysis and instrument design. There are four topics I will focus on: (i) self-calibration, (ii) forecasting for spectral distortion sensitivity, (iii) anomalous microwave emission (AME) observations and (iv) foreground moment expansion.

First, self-calibration is an analysis method that uses the EB and TB power spectrum to precisely determine the polarization angle of a CMB experiment. We show that foregrounds in principle can have non-zero EB and TB spectra which would bias the self-calibration angle and thus fidelity of B-mode detections. The susceptibility of experiments to this bias depends on their sky coverage and beam size. Second, I will talk about our effort to forecast the spectral distortion sensitivity of a space-based interferometric experiment such as PIXIE. We assumed foreground models from Planck and used Fisher and MCMC methods. We show that a 10 year PIXIE mission could detect the thermal-y and relativistic SZ distortions. However, it would not detect the LCDM-predicted chemical potential (mu) distortion as the synchrotron, free-free, and AME foregrounds strongly degrade the sensitivity below 30 GHz. Third, I will discuss our results from Green Bank Telescope C-band observations of a star forming region with known AME. The observations show that the diffuse emission is spatially correlated with H-alpha and 408MHz maps, and the star forming region is correlated with thermal dust emission identified by far IR data. Preliminary analysis suggests the emission is spinning dust which could be a polarized foreground in B-mode observations. Fourth, I will talk about applying a novel foreground parameterization method recently invented by Jens Chluba. Spatial variations of foreground emission integrated along the line-of-sight and within the beam of CMB experiments induce modeling residuals that can be significant for future experiments. To address this, we generalize foreground models using an expansion in parameter moments. This method allows for more flexible foreground models and reduces residual foreground contamination in CMB maps and power spectra.

October 16th

Jeffrey Iuliano (JHU)

CLASS CMB Polarization Survey
The Cosmic Microwave Background is a rich source of information about the universe. CLASS aims to measure CMB polarization – particularly large angular scale patterns, which are typically decomposed into E and B modes. Through this survey, CLASS will characterize inflation, measure the optical depth to re-ionization, and probe high energy physics in the early universe. CLASS will make a sample-limited measurement of large angular scale E-modes, and measure B-modes well enough to determine or constrain the tensor to scalar ratio, r, for r>~0.01. CLASS employs a front-end modulator that enables measurements of large scale patterns from the ground, four frequency bands to remove galactic foregrounds, and a receiver designed for high efficiency and low noise polarization measurement.

Duncan Watts (JHU)

Cosmology with CLASS
The Cosmology Large Angular Scale Surveyor (CLASS) will use large-scale measurements of the polarized cosmic microwave background (CMB) to constrain the physics of inflation, reionization, and massive neutrinos. The experiment is designed to characterize the largest scales, which are inaccessible to most ground-based experiments, and remove Galactic foregrounds from the CMB maps. In this talk, I present simulations of CLASS data and demonstrate their ability to constrain the simplest single-field models of inflation and to reduce the uncertainty of the optical depth to reionization to near the cosmic variance limit, significantly improving on current constraints. These constraints will bring a qualitative shift in our understanding of standard $\Lambda$CDM cosmology. In particular, CLASS's measurement of $\tau$ breaks cosmological parameter degeneracies. Probes of large scale structure (LSS) test the effect of neutrino free-streaming at small scales, which depends on the mass of the neutrinos. CLASS's $\tau$ measurement, when combined with next-generation LSS and BAO measurements, will enable a $4\sigma$ detection of neutrino mass, compared with $2\sigma$ without CLASS data.

Ren Bin (JHU)

Non-negative Matrix Factorization: Robust Extraction of Extended Circumstellar Structures
In the post-processing of direct imaging observations, the vectorized Non-negative Matrix Factorization (NMF) method first creates a non-orthogonal and non-negative basis of components using the given reference images, then models a target with the components. The constructed model is then rescaled with a factor to compensate for the contribution from the circumstellar disks. I will compare NMF with existing methods (classical reference differential imaging method, and the Karhunen-Loeve image projection algorithm) using synthetic circumstellar disks, and demonstrate the superiority of NMF: with no need of prior selection of references, NMF can not only detect fainter circumstellar disks, but also better preserve their morphology. The application of NMF to direct imaging observations obtained from the Hubble Space Telescope will be presented and discussed.

Murdock Hart (JHU)

Reflectance Measurements of Backside Illuminated Charge Coupled Devices
The high quantum efficiencies (QE) of backside illuminated charge coupled devices (CCD) has ushered in the age of the large scale astronomical survey. The QE of these devices can be greater than 90%, and is dependent upon the operating temperature, device thickness, backside charging mechanisms, and anti-reflection (AR) coatings. But at optical wavelengths the QE is well approximated as one minus the reflectance, thus the measurement of the backside reflectivity of these devices provides a second independent measure of their QE.

We have designed and constructed a novel instrument to measure the relative specular reflectance of CCD detectors, with a significant portion of this device being constructed using a 3D fused deposition model (FDM) printer. This device implements both a monitor and measurement photodiode to simultaneously collect incident and reflected measurements reducing errors introduced by the relative reflectance calibration process. While most relative reflectometers are highly dependent upon a precisely repeatable target distance for accurate measurements, we have implemented a method of measurement which minimizes these errors.

Isha Nayak (JHU)

The Most Luminous Young Stellar Object in the Large Magellanic Cloud
The Large Magellanic Cloud has been the subject of star formation studies for decades due to its proximity to the Milky Way (50 kpc), a nearly face-on orientation, and a low metallicity (0.5 solar) similar to that of galaxies at the peak of star formation in the universe (z~2). The most luminous young stellar object (J72.97-69.39) is located in the N79 region of the Large Magellanic Cloud and has a luminosity over 2,000,000 L⨀. How can a massive star like J72.97-69.39 form in a seemingly quiescent environment? Is the N79 region actually quiescent? I will present a comprehensive multi-wavelength analysis of J72.97-69.39: SED fits to Spitzer and Herschel photometry, near-IR and mid-IR spectroscopy from Magellan/FIRE and Spitzer/IRS, low-J CO data from ALMA, and high-J CO data and a [CII] map from SOFIA/GREAT. Spectral energy distribution (SED) fits show this object is a O5V star. ALMA images indicate that J72.97-69.39 could be at the center of colliding filaments. Near-IR spectrum from Magellan/FIRE shows H, H2, He, and [Fe II] emission lines tracing radiative and shock excitation. SOFIA/GREAT observations probe the photodissociation region (PDR) surrounding this massive young stellar object. My work on J72.97-69.39 aims to study the most luminous young stellar object ever found with the goal of answering the questions: How do massive stars form? What is the impact of outflows on the local environment? What role does the local environment (metallicity, nearby star formation, molecular clump distribution) play in the creation of massive stars?

October 23rd

TBD (TBD)

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October 30th

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November 6th

TBD (TBD)

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November 13th

TBD (TBD)

Planning Solar System Observations with JWST
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November 27th

TBD (TBD)

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December 5th

TBD (TBD)

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