Jump to: navigation, search

Astrophysics Seminars From 2018 - 2019


Fall 2018

September 26, 2018

 "Imaging Protoplanets with Adaptive Optics and Interferometry"

Steph Sallum
Chancellor's Postdoctoral Fellow & NSF Postdoctoral Fellow
UC Santa Cruz

 Understanding the details of planet formation requires direct observations of protoplanets themselves. Transition disks, protoplanetary disks with inner clearings in dust, are the most promising targets for these studies. Their inner clearings and relatively low stellar accretion rates may be caused by forming planets sweeping up material that would have otherwise fallen onto the star. While protoplanets are expected to have low infrared contrasts compared to mature exoplanets, the large distances to transition disks necessitate novel imaging techniques beyond adaptive optics and coronagraphy to make these detections. Non-redundant masking (NRM), which transforms a conventional telescope into an interferometric array, is well suited for imaging protoplanets directly. I will present the results of NRM observations of transition disks, as well as strategies for disentangling accretion signals from light scattered by disk material. I will also discuss the potential for protoplanet characterization using interferometric techniques, and applications of these techniques on next generation facilities such as the Thirty Meter Telescope and James Webb Space Telescope.

October 3, 2018

 "Probing the Large-Scale Environments of Local AGN"

Meredith Powell
Graduate Student
Yale University

 I present the clustering analysis of local AGN in the Swift-BAT Spectroscopic Survey (BASS). With 548 AGN in the redshift range 0.01<z<0.1 over the full sky, BASS provides the largest and least biased sample of local AGN to date due to its hard X-ray selection (14-195 keV) and rich multiwavelength/ancillary data. By measuring the projected cross-correlation function between the AGN and 2MASS galaxies, and interpreting it via HOD and subhalo-based models, we constrain the halo occupation of the full AGN sample as well as in bins of column density an black hole mass. We find that AGN tend to reside in galaxy group environments, and that on average they occupy their dark matter halos similar to inactive galaxies of the same stellar mass distribution. We also find evidence that obscured AGN tend to reside in denser environments than unobscured AGN, even when samples were matched in luminosity, redshift, stellar mass, and Eddington ratio. I show that this can be explained either by significantly different halo occupation distributions or statistically different host halo assembly histories.

October 10, 2018

 "The Miniature X-ray Solar Spectrometer (MinXSS) CubeSats: instrument capabilities and early science analysis on the quiet Sun, active regions, and flares"

Chris Moore
Postdoctoral Fellow
Harvard-Smithsonian CfA

 Detection of soft X-rays (sxr) from the Sun provide direct information on coronal plasma at temperatures in excess of ~1 MK, but there have been relatively few solar spectrally resolved measurements from 0.5 – 10. keV. CubeSats can be a low-cost alternative to rapidly fill astrophysical observations gaps, that large missions are currently missing. The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is the first solar science oriented CubeSat mission flown for the NASA Science Mission Directorate, and has provided measurements from 0.8 -12 keV, with resolving power ~40 at 5.9 keV, at a nominal ~10 second time cadence. MinXSS design and development has involved over 40 graduate students supervised by professors and professionals at the University of Colorado at Boulder. Instrument radiometric calibration was performed at the National Institute for Standard and Technology (NIST) Synchrotron Ultraviolet Radiation Facility (SURF) and spectral resolution determined from radioactive X-ray sources. The MinXSS spectra allow for determining coronal abundance variations for Fe, Mg, Ni, Ca, Si, S, and Ar in active regions and during flares.

Measurements from the first of the twin CubeSats, MinXSS-1, have proven to be consistent with the Geostationary Operational Environmental Satellite (GOES) 0.1 – 0.8 nm energy flux. Simultaneous MinXSS-1 and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations have provided the most complete sxr spectral coverage of flares in recent years. These combined measurements are vital in estimating the heating flare loops by non-thermal accelerated electrons. MinXSS-1 measurements have been combined with the Hinode X-ray Telescope (XRT) and Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO-AIA) to further constrain the coronal temperature distribution during quiescent times. The structure of the temperature distribution (especially for T > 5 MK) is important for deducing heating processes in the solar atmosphere. MinXSS-1 observations yield some of the tightest constraints on the high temperature component of the coronal plasma, in the absence of the intermittent solar observations from the Focusing Optic X-ray Solar Imager (FOXSI) sounding rocket and the Nuclear Spectroscopic Telescope Array (NuSTAR). MinXSS-2 is scheduled to launch in late 2018 for improved solar observations for at least a four year mission.

October 17, 2018

 "Mapping the z~2 Cosmic Web with IGM Tomography with Keck, Subaru, and TMT"

Khee-Gan Lee
Assistant Professor
Kavli IPMU (University of Tokyo)

 In recent years, the CLAMATO survey on the Keck telescope, which observed high area densities of z~2-3 star-forming galaxies spectra. This created a closely-spaced grid of sightlines probing the Lyman-alpha forest in the intergalactic medium at z~2.0-2.5. I will discuss the observations which lead to the highest-redshift detection of cosmic voids and preliminary results for the cross-correlation with co-eval galaxies. Future applications include constrained realizations of the observed volume, constraining galaxy-cosmic web intrinsic alignments, and cosmological parameter measurement. In the final 15 minutes of the talk, I will talk about proposed fiber-based spectrographs for Keck (FOBOS) and TMT (*Please bring your smartphone to this talk for a virtual reality demonstration*)

October 24, 2018

 "The Precision Radial Velocity Landscape"

Arpita Roy
Millikan Postdoctoral Fellow

 The field of radial velocity (RV) exoplanet detection is entering a new era with the advent of next-generation instrumentation. Currently in build+commissioning phases are planet hunting optical Doppler spectrographs aiming at 10-30cm/s long-term RV precision in the quest for Earth analogs, and several major NIR facilities aiming for <1m/s that are providing a new level of scrutiny into M dwarf stars and their planets. These massive instruments leverage a range of technological advances, from high-homogeneity illumination delivery setups, to sophisticated wavelength calibration, and ultra stable environmental control. In this talk I will review the status of the field, and our readiness for TESS followup, focusing on the three extreme precision instruments I am helping develop (KPF, NEID, HPF) and including the latest updates shared from instrument teams across the world.

October 31, 2018

 "X-ray Reflection Spectroscopy of Accreting Black Holes"

Javier Garcia
Research Scientist

 In the region close to compact object such as black holes (or neutron stars), the extreme conditions created by the strong gravitational field produces copious amounts of energetic radiation (ultra-violet, X-rays, and Gamma-rays). The interaction of this radiation with the surrounding material results in observables that carry important physical information. X-ray spectral and timing techniques provide direct access to the accretion physics on these systems, such as the black hole spin, the location of the inner-edge of the accretion disk, its ionization stage and composition, among others. In this talk, I will discuss the development of modern relativistic reflection models and how they can be used for the interpretation of the X-ray spectrum from supermassive black holes in AGN and stellar-mass black holes in binary systems. I will show examples of the implementation of our new models to observational data from several X-ray observatories (e.g., RXTE, Swift, XMM-Newton, Suzaku, and NuSTAR), and discuss current outstanding issues, such as the large iron abundances frequently required to fit the reflection spectra, controversies on the disk truncation, the origin of the soft excess in AGN, and the effects of high density in the observed spectra.

November 7, 2018

 "BICEP/Keck: Constraining the primordial gravitational-wave signal with CMB polarization observations from the South Pole"

Lorenzo Moncelsi
Staff Scientist

 The inflationary scenario generically predicts the existence of primordial gravitational waves (GW), though over a wide range of amplitudes from slow-roll to multi-field models. Currently the most promising method for constraining, and potentially detecting, an inflationary GW background is to search for the imprint that these tensor perturbations would leave on the cosmic microwave background (CMB) polarization as a parity-odd “B-mode” pattern. The BICEP/Keck experiments (BK) target this primordial signature by observing the polarized microwave sky at degree-scale resolution from the South Pole. Attempting to observe the very faint primordial B-mode signal requires a telescope with exquisite sensitivity and tight control of systematics. The presence of bright Galactic emission, along with the distortion of the CMB polarization field due to gravitational lensing, make this measurement extremely challenging. In order to disentangle the primordial signal from these “foregrounds”, a wide frequency coverage is necessary. I will present the latest BK constraints on the tensor-to-scalar ratio “r” using data taken from 2010 to 2015 at 90, 150, 220 GHz (BK15), in combination with data from the Planck and WMAP satellites. Upcoming observations with the “Stage-3” BICEP Array experiment will extend this frequency range to 30-270 GHz, ultimately improving our sensitivity to r by an order of magnitude with respect to BK15, thus constraining natural inflation and all single-field models.

November 14, 2018

 "Cold Gas Giant Exoplanets: From Detection to Characterization"

Paul Dalba
Postdoctoral Scholar
UC Riverside

 It is now common knowledge within the astrophysics community that the Galaxy is teeming with exoplanets. With an ever-growing sample of known exoplanets to draw from, the focus of many investigations has begun to shift from detection to characterization. However, this transition is shaped by observational biases. Limited observational baselines and detection efficiencies have so far restricted the majority of characterization efforts to exoplanets with short-period orbits that are strikingly different than the Solar System planets. Yet, the fundamental questions surrounding exoplanetary science—ones of formation, evolution, and even habitability—cannot be addressed without probing the outer reaches of planetary systems as well as the inner regions. In this talk, I will discuss the challenges facing the detection-characterization transition for cold giant exoplanets akin to Jupiter and Saturn. I will present observations dedicated to recovering long-period exoplanets originally discovered in transit and radial velocity surveys. Although somewhat risky, these efforts are necessary to prevent us from "losing track" of known exoplanets. Moving into characterization, I will present research that utilizes Solar System data sets to simulate atmospheric observations of cold giant exoplanets. This work identifies a new method of exoplanet atmospheric characterization and emphasizes the amenability of cold giant exoplanets to characterization.

November 28, 2018

 "Star Forming Clumps in Local Luminous Infrared Galaxies"

Kirsten Larson
Postdoctoral Scholar

 Local luminous infrared galaxies (LIRGS) are a mixture of single disk galaxies, interacting systems, and advanced mergers, exhibiting enhanced star formation rates and AGN activity. This makes them an ideal laboratory of studying resolved star formation in the local Universe. A number of studies have found that high redshift star forming galaxies tend to have turbulent, clumpy disks with extreme star forming clumps that are not seen in normal local galaxies. I will present the results from our HST narrow-band Paα and Paβ imaging study of 48 local LIRGs from the Great Observatories All-Sky LIRG Survey (GOALS). These data allow us to measure the star formation rates, sizes, ages, and masses of 810 spatially resolved star forming regions, and directly compare their properties to those found in both local and high-redshift star forming galaxies. I will show how the star formation rates of the clumps in local LIRGs nicely span the range of star formation rates found in normal local star forming galaxies to the clumps found in high-redshift star forming galaxies at z = 1–3. By comparing star formation in LIRGs to normal low redshift galaxies, high redshift galaxies, and sophisticated hydrodynamical simulations, we can better understand how global galaxy properties and environment influence star formation on smaller scales.

December 5, 2018

 "Update on NASA Exoplanet Exploration Program (ExEP) and Science"

Eric Mamajek
Deputy Program Scientist, Exoplanet Exploration Program

 I'll provide an update on the NASA Exoplanet Exploration Program (ExEP), the Astrophysics Division's program responsible for implementing NASA's plans for discovering and characterizing exoplanets and searching for potentially habitable worlds. One of the key recommendations of the recent NAS Exoplanet Science Strategy (ESS) report, which is providing input to the Astro2020 Decadal Survey, is for NASA to "lead a large strategic direct imaging mission capable of measuring the reflected-light spectra of temperate terrestrial planets orbiting Sun-like stars." I'll summarize some recent NASA ExEP-supported activities (since the 2010 Decadal Survey) which have made critical progress towards informing the design of mission(s) for implementing this recommendation, including 1) exoplanetary occurrence rates (Kepler/K2), 2) observational constraints on levels of exozodiacal dust around nearby stars (LBTI/HOSTS survey), and 3) advances in starlight suppression technology including coronagraphs and starshades. Time permitting - I'll discuss some research results related to the transits of young planets and searches for circumplanetary matter and the ages of exoplanetary systems.

December 12, 2018

 "Star Formation and Galactic Environment"

Eva Schinnerer
Staff Scientist
Max Planck Institute for Astronomy

 High angular resolution observations of nearby galaxies allow us to sample the star formation process in different galactic environments.This provides insights on the importance and role of galactic components such as bulges, stellar bars, spiral arms and active galactic nuclei (AGN) in the conversion of cold (molecular) gas into stars. New instruments can now regularly image with high quality and sensitivity large field-of-views at the scale of individual star-forming units, namely Giant Molecular Clouds (GMCs) and HII region (complexes): ALMA is fundamental for imaging of the molecular gas properties in the star-forming disks, while the optical Integral Field Unit MUSE on the VLT is providing detailed information on the ionised gas and stellar population. I will highlight recent progress in the field and present new results from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey that studies a representative sample of nearby massive, normal star-forming galaxies.

Winter 2019

January 9, 2019

NOTE: Beginning this week, all Astrophysics Seminars will be held from
3:00-4:00pm unless otherwise noted

Rana Adhikari
Professor of Physics

January 16, 2019

 "Status of The Thirty Meter Telescope"

Ravinder Bhatia
Associate Project Manager
Thirty Meter Telescope

 The Thirty Meter Telescope (TMT) is one of the next generation of so-called Extremely Large Telescopes, and currently the only one that will be sited in the northern hemisphere.

In this talk, I will describe the broad range of scientific goals of TMT, which take advantage of its high sensitivity, high spectral resolution and high spatial resolution. Such goals span studying the early Universe through to galactic evolution, star formation and exoplanet characterization. These science goals are being established and refined by our International Science Development Teams.

The construction and operation of the observatory is funded through an international partnership, with each partner contributing to the development and production of the observatory sub-systems. I will describe the status of those different sub-systems, highlighting the technical challenges that we need to overcome. I will also give an update on the choice of the site for TMT, given recent developments in Hawaii and Spain.

In order to strengthen the scientific motivation even further, TMT is looking to collaborate with the Giant Magellan Telescope (GMT). GMT will be located in the southern hemisphere, and this collaboration would therefore allow for access to the full sky. This initiative also aims to secure further funding for each separate telescope project: TMT, GMT the National Optical Astronomy Observatory aim to submit a joint proposal to the National Science Foundation which, if successful, would provide observing access to US astronomers that are currently not affiliated with the existing partners of TMT or GMT. I will provide an update on this initiative, which is being pursued against the backdrop of the next Decadal Survey of Astronomy and Astrophysics.

I will end the talk with a brief commentary on three dimensions of working within a complex international partnership. First is Culture. Second is Governance. And third is the broader landscape of international relations within which the TMT project is embedded.

January 23, 2019

Katie Mack
Assistant Professor
North Carolina State University

January 30, 2019

Alison Coil
Professor of Physics

February 6, 2019

Nicole Vassh
Postdoctoral Research Associate, Department of Physics
Notre Dame University

February 13, 2019

Gwen Rudie
Staff Astronomer
Carnegie Observatories

February 20, 2019

Max Gronke
Postdoctoral Scholar
UC Santa Barbara

February 27, 2019

NOTE: Hans Suess Memorial Lecture 4:00-5:00pm in NSB Auditorium
(Reception in NSB Atrium from 3:00-4:00pm)

Victoria Meadows
University of Washington

March 13, 2019

Fridolin Weber
Distinguished Professor of Physics
San Diego State University

Spring 2019

March 27, 2019

NOTE: Spring Break - no seminar today

April 3, 2019

Dmitry Savranksy
Assistant Professor of Mechanical and Aerospace Engineering
Cornell University

June 5, 2019

Greg Mace
Research Associate
University of Texas, Austin