Tuesday Lunch Talk

Astrophysics Tuesday Lunch Talks will be held virtually via ZOOM for Fall 2020.

Coordinators:  Anna Ciurlo, Matt Hosek, Guido Roberts-Borsani

Fall 2020 Schedule

November 17 at 1:00 PM Pacific time

speaker name: Anna Rosen

institution: Harvard University
A (Massive) Star is Born: How Stellar Feedback Limits Accretion onto Massive Stars
Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium (ISM) with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Massive stars form from the gravitational collapse of magnetized, dense, and turbulent molecular gas in massive pre-stellar cores, which are located in highly embedded environments. During their formation, feedback from their intense radiation fields, magnetically launched collimated protostellar outflows, and fast, isotropic radiatively driven winds can limit their growth by accretion. In this talk, I will show a series of radiationmagnetohydrodynamic (RMHD) simulations of the collapse of massive pre-stellar cores into massive stellar systems that include these feedback processes to demonstrate how stellar feedback can limit accretion onto massive stars and disrupt their natal environments. In addition, I will also discuss how stellar feedback from massive stars, which are born in clustered environments, affects the dynamics of HII regions that surround these clusters and can drive ISM turbulence in young, star clusters.

November 10 at 1:00 PM Pacific time

speaker name: Lucas Grosset

institution: SOFIA Science Center

Mapping the dust distribution in the central region of nearby Active Galactic Nuclei through polarimetry
Dust plays a critical role in the formation and evolution of active galactic nuclei (AGN). Its distribution in the central tens of parsecs of AGNs is still debated. The main observational difficulties are due to the high angular resolution required to detect these small structures (smaller than 10 pc) at large distance (larger than 4 Mpc). Polarization is a powerful tool to investigate these dust structures as it allows to trace scattering events in the near IR, but also the magnetic fields in the far IR. I will present polarimetric observations of two iconic and nearby active nuclei (NGC 1068 and Circinus) obtained with SPHERE/VLT at ESO’s Paranal Observatory (0.8 to 2.3 μm), and with HAWC+ (53 to 214 μm) on board of SOFIA (NASA’s Stratospheric Observatory for Infrared Astronomy). Both these observations trace dust structures and magnetic fields at different scales and help constraining the existing models of AGNs environments. These models were first aimed at solving the apparent dichotomy in AGNs observed properties such as differences in line widths, and they are still currently evolving to better represent the high complexity of the flows of matter in these regions.

October 13 at 1:00 PM Pacific time

speaker name: Vince Estrada-Carpenter
institution: Texas A&M
Stellar Populations and Formation Histories of  Massive Galaxies Derived from Deep Hubble Space Telescope Grism Data


Understanding the correlations between mass, morphology, stellar populations, and formation history in galaxies is difficult, primarily due to the uncertainties in galaxy star-formation histories. Star-formation histories are better constrained for higher redshift galaxies, observed closer to their formation and quenching epochs. These properties in high redshift galaxies can be difficult to do from ground-based telescopes, as they are subject to higher backgrounds and a high density of telluric (night-sky) emission lines. The HST/WFC3 grism grants us access to (low-resolution) rest frame optical spectrum for galaxies at ~ 1 < z < 2. The age and metallicity features present at these wavelengths, along with the sample sizes provided by grism surveys, allow us to better constrain stellar populations and star-formation histories. In my talk, I will discuss research using a forward modeling technique to fit deep HST grism data from the CLEAR (CANDELS Lyα Emission at Reionization) survey. Work which includes studying the mass - stellar metallicity relationship, where we find that massive quiescent galaxies up to a redshift of ~ 1.8 have ~ solar stellar metallicities. As well as a study on the relationship between morphology and formation redshift (when the galaxy formed ~ 50% of their mass) using “non-parametric” star-formation histories, where we find that quiescent galaxies with the highest stellar-mass surface density, log(Σ1) > 10.25, show a minimum formation redshift. 


October 6 at 1:00 PM Pacific time

speaker name: Greg Gilbert
institution: The University of Chicago
The Architectures and Dynamics of Kepler’s Multiplanet Systems


Studying the present day architectures and dynamics of high-multiplicity (N ≥ 3) exoplanetary systems provides a unique avenue for probing the astrophysics of planet formation and for constraining exoplanet demographics. Here, I present a new framework for characterizing the arrangements of masses, periods, and mutual inclinations within such systems. I demonstrate that Kepler’s high multiplicity systems can be explained if most systems belong to a single intrinsic population, with a subset of systems hosting additional, undetected planets. I further demonstrate that planets within a system tend to be evenly spaced in log-period and roughly the same size, and that these trends are astrophysical in nature and not an artifact of observational biases. Conclusions regarding planetary inclinations and eccentricities are less clear and require improved transit lightcurve fits to allow for robust inferences. However, accurate transit modeling is confounded by both instrumental and asteroseismic noise, as well as by unresolved transit timing variations (TTVs) and transit duration variations (TDVs) which arise from gravitational interactions between neighboring planets. To remedy this problem, I am currently reprocessing all (~3300) Kepler lightcurves for stars known to host planet candidates. I employ all available short cadence data, using a technique that simultaneously models noise with a Gaussian Process (GP) regression and accounts for both TTVs and TDVs with an optimally flexible parametric model. These timing measurements can be inverted using dynamical models to produce a large statistical sample of planetary masses, filling out the mass-radius diagram. This project will yield the highest-fidelity measurements of TTVs and TDVs produced to date, as well as dramatically improved constraints on planetary inclinations and eccentricities. In the near future, I will extend these methods to every planetary candidate observed by Kepler, K2, and TESS, with an expected yield of nearly 100 previously undetected TTVs/TDVs. 


September 29 at 1:00 PM Pacific time

speaker name: Luke Bouma
institution: Princeton
Two Young Transiting Exoplanets: One Was, One Was Not

Over the first 100 million years of their lives, planetary systems undergo major changes.  Rocky planetesimals collide.  Atmospheres are accreted and lost.  Dynamical interactions shape and tilt planetary orbits.  After summarizing ongoing observational efforts aimed at discovering young exoplanets, I will motivate and discuss two specific questions.  First: what is the youngest hot Jupiter that exists?  I will present PTFO 8-8695b, a long-standing 10 Myr old candidate hot Jupiter that is probably a rare class of variable star.  Combined with other recent work, the story of PTFO 8-8695b suggests that approximately zero hot Jupiters younger than 100 Myr have been securely identified.  The second question is: what can observations teach us about how close-in Neptunian-mass planets form and evolve?  This topic will be explored through the discovery and validation of a 40 Myr old Saturn-sized planet, TOI 837b. The planet's host star is bright enough to enable measurements of the stellar obliquity, the planet's mass, and potentially the planet's atmospheric mass loss.  These avenues of characterization, broadly applied to the young planets being discovered with TESS and K2, will likely improve our understanding of the processes that produce the observed exoplanet population.


Archives: Winter 2020 Schedule

2/4: Xuheng Ding, UCLA 
2/11: Jason Wang, Caltech
2/18: Kristen Larson, Caltech/IPAC
2/25: Ylva Goetberg , Carnegie
3/3: Evan Bauer, UCSB