Wine and Cheese Fall 2020

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2020.

Wine and Cheese sessions with one speaker 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. Sessions in the Graduate Student Series will have three 15 minute talks, each with 5 minutes for questions.

21 September

Jose Luis Bernal Mera (JHU)

Cosmology with Large-Scale Structure Clustering and Implications for Early Dark Energy Models
During the last decade, measurements of the galaxy clustering have become one of the cornerstones for our understanding of the Universe. With next-generation galaxy surveys and the promise of line-intensity mapping experiments, observations will be more precise will probe regimes that have been unexplored so far. In this talk we will review the cosmological information encoded in large-scale structure clustering and discuss the validity and reach of standard measurements. We also will review recent claims of galaxy clustering ruling out early dark energy models as a solution for the Hubble constant tension: although we agree with the results of the analyses performed, we reckon that such results are driven by the choice of prior and potential tensions between different observables, hence concluding that early dark energy is still a viable model and potential solution for the Hubble constant tension.

David Nataf (JHU)

Recent developments in the study of the distance and extinction to the Large and Small Magellanic Cloud
The Small and in particular the Large Magellanic Clouds (LMC) remain important anchors both to the extragalactic distance scale and to stellar astrophysics in general. As virtually all classes of variable stars and all classes of distance indicators have been studied in the LMC, it is possible and necessary to evaluate if these are consistent. I will begin my talk by first reviewing a surprising recent development. There is a 0.18 mag in the zero-point of the V-band extinction to the LMC, which vastly exceeds the quoted errors of virtually all prior studies of the matter. I will then discuss how our recent paper (https://arxiv.org/abs/2006.03603) resolved this issue, concurrently with another independent effort (https://arxiv.org/abs/2006.02448), using four different calibrations: stellar isochrones, RR Lyrae stars, Cepheids, and the SFD extinction maps. The resulting error is decreased to <~ 0.04 mag.

28 September

D'Arcy Kenworthy (JHU)

Next-Generation Standardization of Type Ia Supernovae for Cosmology
Type Ia supernova luminosities, after standardization using a light curve model, are an excellent probe of the luminosity distance - redshift relation. This allows measurement of cosmological parameters of interest such as the equation of state of dark energy and the Hubble constant. Meeting the science goals of next generation projects such as the Vera Rubin Observatory and the Roman Space Telescope requires improvements in systematic uncertainties in type Ia light curve modeling. In contrast, measurement of the Hubble constant is statistics-limited by the small number of nearby type Ia SNe, whose precision can be improved by the use of near-infrared data. I will present an overview of a new Python-based code to train supernova light curve models to achieve better standardization across these domains.

Sihao Cheng (JHU)

A New Vocabulary for Patterns and its Cosmological Application
I will present a new tool to characterize patterns in datasets, called the "scattering transform”. It borrows ideas from convolutional neural nets, but it is much more interpretable and controllable. I will also show its application to weak lensing data for constraining cosmological parameters, and compare its performance with classic statistical estimators and neural nets.

Cyril Creque-Sarbinowski (JHU)

TBD

5 October

Ben Mazin (UCSB)

Large Satellite Constellations and their Impact on Astronomy
I will discuss recent work to quantify the impact of large satellite constellations, such as SpaceX Starlink and OneWeb constellations that are currently in construction, on astronomical observations across the electromagnetic spectrum. In the process, I will also discuss the economics and other potential issues raised by these constellations.

12 October

Philip Kaaret (U Iowa)

A Clumpy Disc-Dominated Circumgalactic Medium of the Milky Way Seen in X-ray Emission
The Milky Way galaxy is surrounded by a circumgalactic medium (CGM) that may play a key role in galaxy evolution as the source of gas for star formation and a repository of metals and energy produced by star formation and nuclear activity. The CGM may also be a repository for baryons seen in the early universe, but undetected locally. The CGM has an ionized component at temperatures near 2 MK studied primarily in the soft X-ray band. Here we report a survey of the southern Galactic sky with a CubeSat-based soft X-ray spectrometer optimized to study diffuse soft X-ray emission. The X-ray emission is best fit with a disc-like model based on the radial profile of the surface density of molecular hydrogen, a tracer of star formation, suggesting that the X-ray emission is predominantly from hot plasma produced via stellar feedback. Strong variations in the X-ray emission on angular scales of 10° indicate that the CGM is clumpy. Addition of an extended, and possibly massive, halo component is needed to match the halo density inferred from other observations.

19 October

Brian Healy (JHU)

The Orientation of Stellar Spins in Open Clusters
Measuring the distribution of stellar spin axis orientations in a coeval group of stars probes the physical processes underlying the stars' formation. Combining spectroscopic and photometric observations of open cluster members allows us to determine their degree of spin alignment. An isotropic distribution of spins implies a star-forming environment in which turbulence dominated ordered motion, while an aligned distribution suggests a more substantial contribution from rotation. In this talk, I will present our orientation results for the open cluster NGC 2516 and describe how they motivate a larger study of stellar spin in additional clusters.

Cyril Creque-Sarbinowski (JHU)

Resonant Neutrino Self-Interactions
If neutrinos have self-interactions, these will induce scatterings between astrophysical and cosmic neutrinos. Prior work proposed to look for possible resulting resonance features in astrophysical neutrino spectra in order to seek a neutrino self-interaction which can be either diagonal in the neutrino flavor space or couple different neutrino flavors. The calculation of the astrophysical spectra involves either a Monte Carlo simulation or a computationally intensive numerical integration of an integro-partial-differential equation. As a result only limited regions of the neutrino self-interaction parameter space have been explored, and only flavor-diagonal self-interactions have been considered. Here, we present a fully analytic form for the astrophysical neutrino spectra for arbitrary neutrino number and arbitrary self-coupling matrix that accurately obtains the resonance features in the observable neutrino spectra. The results can be applied to calculations of the diffuse supernova neutrino background and of the spectrum from high-energy astrophysical neutrino sources. We illustrate with a few examples.

Qinan Wang (JHU)

Revealing progenitor system of Type Ia Supernovae with Kepler & TESS
Despite its crucial role as standard candle in cosmological measurement, the progenitor system of Type Ia supernovae is still unclear. One of the most direct ways to studying progenitors of supernovae is to look into the very early time of explosion for subtle signatures. The 30-min cadence of Kepler & TESS Full-Frame Images provide adequate time resolution to reveal these features that are hard to be seen from ground-based observations. In this talk I'm going to present recent results from Kepler SNe Ia sample, especially SN2018oh and SN2018agk, and current progress of TESS Supernovae study.

26 October

Vicky Kalogera (Northwestern)

Gravitational-Wave Astronomy Five Years Since the First Detection
Five years after the first gravitational-wave detection of a binary black-hole merger, we consider such detections routine and we are focusing on extracting population astrophysical information from a rapidly growing sample of black hole mergers. In parallel, gravitational-wave observations continue to surprise us with discoveries of mergers with unexpected properties, revealing novel aspects of compact object formation and evolution. In this talk I will summarize where our understanding stands at present, focus on the exceptional sources announced so far, and discuss what we anticipate for the future.

2 November

J. Xavier Prochaska (UC Santa Cruz)

Disentangling the Cosmic Web with Fast Radio Bursts
I will report on a set of new, well-localized (<1”) fast radio bursts (FRBs) discovered primarily by the ASKAP telescope. Nearly each of these events is coincident with a luminous galaxy which we designate as the host. Spectra of the galaxies establish the FRB redshifts and offer a first assessment of the dispersion measure vs. redshift (aka The Maquart Relation). This yields a new estimate of the cosmic baryon density for the low-z universe, consistent with measurements from BBN and the CMB, i.e. the so-called “missing baryons problem” has been resolved! Last (time permitting), we analyze the rotation measure and pulse width of one FRB to study the magnetic field and density of gas in a foreground galaxy halo.

16 November

Lingyuan Ji (JHU)

Standard Model Prediction for Cosmological 21cm Circular Polarization
Before cosmic reionization, hydrogen atoms acquire a spin polarization quadrupole through interaction with the anisotropic 21-cm radiation field. The interaction of this quadrupole with anisotropies in the cosmic microwave background (CMB) radiation field gives a net spin orientation to the hydrogen atoms. The 21-cm radiation emitted by these spin-oriented hydrogen atoms is circularly polarized. Here, we reformulate succinctly the derivation of the expression for this circular polarization in terms of Cartesian (rather than spherical) tensors. We then compute the angular power spectrum of the observed Stokes-V parameter in the standard ΛCDM cosmological model and show how it depends on redshift, or equivalently, the observed frequency.

Carolina Nunez (JHU)

The Cosmology Large Angular Scale Surveyor (CLASS): Instrument Overview and Internal Data Consistency Checks
The Cosmology Large Angular Scale Surveyor (CLASS) is a polarization-sensitive telescope array located at an altitude of 5,200 m in the Chilean Atacama Desert. CLASS is designed to characterize primordial gravitational waves and constrain the optical depth to reionization, through detection of "B-mode" (curl component) and "E-mode" (divergence component) polarization patterns in the Cosmic Microwave Background (CMB) over large angular scales. Currently, all four CLASS frequencies are fielded across three telescopes: the 40 GHz (Q-band) focal plane achieved first light in June 2016; the first of two 90 GHz (W-band) focal planes achieved first light in May 2018; and the high frequency (HF) dichroic 150/220 GHz focal plane achieved first light in September 2019. The detection of B-mode polarization over large angular scales is a particularly challenging measurement, requiring both high sensitivity and control of systematics. I will provide a brief overview of the CLASS science goals, the instrument design required to achieve them, and finally I will discuss the statistical tools used to confirm internal consistency of the data.