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Astrophysics Seminars From 2014 - 2015


Summer 2014

July 17, 2014

NOTE: Special Astro Seminar @ 4:00 - SERF 383
 "Characterization of Hot Jupiters and a Disintegrating Rocky Planet with the SpeX Spectrograph"

Everett Schlawin
PhD Student, Department of Astronomy
Cornell University

 Transiting exoplanets are amenable to characterization because they absorb and scatter light from their host star on a periodic basis. The wavelength dependence of the transit constrains the composition of the atmosphere. This in turn can be used to understand a planet’s temperature profile and for evaporating atmospheres, the possible launching mechanisms. To enable high precision transmission spectrum measurements, a target star and simultaneous reference star are acquired in the low-resolution mode of the SpeX spectrograph on the ground-based Infrared Telescope Facility (IRTF). This observational setup was used to test the TiO/VO hypothesis in CoRoT-1b (that TiO and VO create a temperature inversion) and constrain the particle size of the debris escaping from the disintegrating rocky planet KIC 12557548b. The TiO/VO hypothesis is disfavored by best-fit models to CoRoT-1b’s spectrum. For the disintegrating planet KIC 12557548b, the transmission spectrum is inconsistent with the prediction for dust particles, suggesting either a systematic noise source or an additional non-dusty component in KIC 12557548b’s escaping debris.

Fall 2014

October 8, 2014

 "There's Government in Your Science"

Joshua Shiode
John Bahcall Public Policy Fellow
American Astronomical Society (AAS)

 Nearly all basic science research in the United States — including that in the astronomical sciences — is funded by the federal government. This is both good and bad. Good because there are a lot of resources available, despite the fact that it represents a small fraction of the total federal budget. Bad because individual scientific projects, and the careers of the scientists involved, can be affected by political winds they would otherwise never feel. In this talk, I’ll try to convey a sense of those winds. I’ll discuss recent government action (or inaction) and long-term policy trends relevant to the scientific enterprise, and we’ll explore how individual scientists and science advocates can play a role in the political and policymaking process.

October 22, 2014

 "Microlensing: Understanding Planets Beyond the Snow Line"

Jennifer Yee
Sagan Fellow
Harvard-Smithsonian Center for Astrophysics (CfA)

 Microlensing uses the gravitational bending of light to detect exoplanets. New upgrades and new surveys have made the discovery and followup of microlensing events more efficient, transitioning the field from discovering individual planets to detecting planets en masse. I will use recent microlensing discoveries to demonstrate how microlensing complements other planet detection techniques. In addition, I will show how higher-order effects enable us to more fully characterize these planetary systems. These techniques expand the scope of microlensing to include brown dwarfs, stellar remnants, and the mass function of the inner galaxy.

October 29, 2014

 "Insights into Galaxy Formation from z=15 to the Present Day"

Peter Behroozi
Giacconi Postdoctoral Fellow
STScI (Space Telescope Science Institute)

 We show that the ratio of galaxies' specific star formation rates to their host halos' specific mass accretion rates strongly constrains how the galaxies' stellar masses, specific star formation rates, and host halo masses evolve over cosmic time. This evolutionary constraint provides a simple way to probe z>8 galaxy populations without direct observations, and predicts that JWST should see galaxies above 10^8 Msun even to z=15. We also discuss using close galaxy pairs as a probe for major halo mergers at very low redshifts (z<0.05). We find no evidence that the recent halo formation history influences the quenched fraction of L* galaxies at z=0, though we do find intriguing SFR enhancement signatures for star-forming hosts.

November 12, 2014

 "Search for Sterile Neutrinos in Tritium Beta Decay"

Susanne Mertens
Post Doctoral Fellow, Feodor Lynen Fellow (Alexander von Humboldt Foundation)
Institute for Nuclear & Particle Astrophysics
Lawrence Berkeley National Laboratory (LBNL)

 A minimal extension of the Standard Model suggests the existence of right-handed partners to the known left-handed neutrino states. These would not interact with other particles in the Standard Model, and are therefore called sterile neutrinos. However, sterile neutrinos can mix with the active neutrinos and thereby form additional neutrino mass eigenstates, which leads to very exciting physics implications. Sterile Neutrinos in the eV mass range can resolve several anomalies in reactor and short-baseline experiments, while sterile neutrinos in the keV mass range are a prime candidate for dark matter. In particular, this form of dark matter, as opposed to weakly interacting massive particles (WIMPS), can act as warm dark matter, the existence of which would reconcile recent structure observations from sub-galactic to larger scales. This talk focuses on the perspectives of the Karlsruhe Tritium Neutrino (KATRIN) Experiment to search for sterile neutrinos in the eV to keV range.

December 10, 2014

 "A critical phase in galaxy formation"

Greg Stinson
Postdoc Researcher

 As galaxies grow and evolve, they go through a violent phase of their evolution where intense star formation drives outflows. I will examine this phase using cosmological galaxy formation simulations. The simulations show that starbursts and outflows have implications for many observed properties of galaxies including their gaseous halos, morphology, potential, and star formation history.

Winter 2015

January 7, 2015

Dr. Simmonds & Sam's Title: "Quantum Statistics: Affects on Human Dancers
and the Observer"

Raymond Simmonds
Experimental Physicist / Lecturer
NIST / University of Colorado Boulder, Department of Physics
Sam Mitchell
Graduate Student, Department of Theatre & Dance

Dr. Simmonds & Sam's Abstract: The Arts and Sciences may seem to be immiscible fields of study, even at odds with each other. In Leonardo Da Vinci’s time these two fields were not polarized, in fact, they coexisted naturally. Despite the appearance of being far distant cousins, both artists and scientists share a creative gene, a passion for their work, and a brave curiosity that pushes them past current boundaries to explore the unknown. In this lecture, we will present some recent examples of those mixing these two worlds and our own attempts to do so with Dance Theater and Quantum Physics. While quantum mechanics is a well-established theory, proven true overwhelmingly by experiments, it is still confounding to most people, even those in science. At its heart, it describes nature in terms of possible realities with probable outcomes, with almost no predictable certainty. Experts still struggle to interpret its philosophical consequences and the notion that there may be no “objective reality”. Even Albert Einstein, one of its co-creators, disapproved of its bazaar properties, saying that "God does not play dice with the universe".
In the creation of this work, “Dunamis Novem”, we have taken some of the probabilistic rules that govern quantum systems and integrated them into a creative process. The results are then born from an artistic aesthetic and an algorithmic code that produces dynamics that embody in some way randomness, concepts of “quantum entanglement”, and the effects of observation or “measurement”. Our work shows that “Science” can inspire and direct new forms of “Art”, and we hope that the liminal world of “Art” can be an effective medium to transmit the sometimes counterintuitive results of empirical “Science” to a broader audience, also generating a dialogue between the two. We will describe the scientific concepts that currently inspire us, the process by which we convert quantum principles into movements, and the challenges of distilling this into a theatrical setting. We encourage everyone to attend the three concerts at the Mandell Weiss Forum Theater from January 23-25, 2015 at 7:30 pm.
For more information go to:

January 14, 2015

 "Putting the Neutron Star Jigsaw Puzzle together”

Matthias Kuehnel
PhD Student
Remeis Observatory & Erlangen Center for Astroparticle Physics (Bamberg, Germany)

 Mass accretion is one of the most powerful processes in the Universe. In X-ray binaries (XRBs), the largest fraction of accretion power is converted into X-rays. The central engine is a compact object, e.g., a neutron star. Although these objects have been discovered 40 years ago, a self- consistent model of the extreme physical conditions around, on, and inside neutron stars is still lacking.
To improve our understanding of neutron stars we need to understand the extreme physical conditions above magnetic poles, such as the strong gravitational field, velocities up to the speed of light, and magnetic fields in the order of 10^12 Gauss.
Certain observables help us to answer these questions. From cyclotron lines in the X-ray spectra of accreting neutron stars, we can measure the magnetic field strength. The shape of the X-ray pulse profile is an imprint of the emission geometry at the magnetic poles. The spectral behavior of the mass accretion depends on the accretion geometry and the properties of the material. All these observables are pieces of the neutron star puzzle, but we have only started to investigate them.

January 28, 2015

 "Implications of the Candidate Dark Matter Decay Line at 3.5 keV"

Kevork "Kev" Abazajian
Associate Professor, Department of Physics & Astronomy
UC Irvine

 Two independent groups have detected an unidentified X-ray line at 3.5 keV that is consistent with the dark matter density in the field of view of the observations toward the Perseus Cluster, stacked X-ray clusters, Andromeda, and the Milky Way Galactic Center. I will discuss the sterile neutrino dark matter decay interpretation of the line, including its production mechanisms and its potentially alleviating effects on persistent problems in structure in the Local Group of Galaxies.

February 4, 2015

 "Architecture and Timing of Planetary Systems"

Daniel Fabrycky
Assistant Professor, Department of Astronomy and Astrophysics
University of Chicago

 The Kepler mission represents a breakthrough in the dynamics of exoplanetary systems. Over 500 systems with multiple transiting planets have been found. By comparing transit durations of planets in the same system, we can see that inclinations of planets relative to each other are on the order of 2 degrees, just like in the Solar System. The number of systems with detectably perturbed orbits is now over 100. Models of the systems with high signal-to-noise transit timing variations (TTVs) can uniquely determine the mass and orbital parameters of the perturbing planet. With continued monitoring, the TTVs in these systems will result in mass-radius measurements for cool exoplanets and inferences on the formation and evolution of exoplanetary systems.

February 11, 2015

 "Can we detect keV-mass ‘sterile’ neutrinos in the laboratory?"

Peter F. Smith
UCLA and Rutherford Appleton Laboratory, UK

 During the past 25 years considerable effort and funding has been devoted to underground experiments for direct detection of heavy supersymmetric particles as an explanation of the 90% unidentified dark matter component of our galaxy, so far without observing any signal. During the past 10 years, a new explanation of dark matter has been proposed by neutrino theorists – a quasi-sterile neutrino with mass in the range 2-10 keV. Because of its low mixing with standard neutrinos, this would be nearly stable, but occasionally decay with emission of an X-ray photon. Recent X-ray observations from galaxy clusters and the galactic center hint at such a signal which would corresponding to a mass 7.1 keV and a coupling ~ 7,10-11.
This would not be observable in existing dark matter detectors or with any other proposed direct detection ideas. However, a quasi-sterile neutrino of this mass would, despite its very low coupling, be observable in principle in the laboratory as a rare component of the neutrino emission in nuclear beta decay or K-capture. The basic idea has been suggested previously, but no design with sufficient sensitivity has yet been proposed. This talk will describe some of the problems of doing this in practice, with studies currently in progress at UCLA. It is suggested that such an experiment, though challenging, may be feasible with sufficient sensitivity to reach the mass and coupling levels corresponding to the astronomical X-ray signal.

February 18, 2015

 "The Relativistic Inverse Stellar Structure Problem"

Lee Lindblom
Research Scientist

 The observable macroscopic properties of relativistic stars (whose equations of state are known) can be predicted by solving the stellar structure equations that follow from Einstein’s equation. For neutron stars, however, our knowledge of the equation of state is poor, so the direct stellar structure problem can not be solved without modeling the highest density part of the equation of state in some way. This talk will describe recent work on developing a model independent approach to determining the high-density neutron-star equation of state by solving an inverse stellar structure problem. This method uses the fact that Einstein’s equation provides a deterministic relationship between the equation of state and the macroscopic observables of the stars which are composed of that material. This talk illustrates how this method will be able to determine the high-density part of the neutron-star equation of state with few percent accuracy when high quality measurements of the masses and radii of just two or three neutron stars become available. This talk will also show that this method can be used with measurements of other macroscopic observables, like the masses and tidal deformabilities, which can (in principle) be measured by gravitational wave observations of binary neutron-star mergers.

March 3, 2015

NOTE: Special Astro Seminar @ 3:00 - SERF 383
 "Future of Radio Telescopes"

Sander Weinreb
Senior Faculty Associate, Electrical Engineering Department

 Radio Astronomy grew from an accidental discovery in 1932, virtually ignored for years, to a prolific window to a previously invisible universe, producing four Nobel Prizes. A major new international instrument, the Square Kilometer Array, is now in the detailed design phase and next steps for complementary instruments in the US are being explored. A theme of the lecture will be lessons-learned from past history and application to the future. Some of the gems of history leading to the start of radio astronomy at Caltech and NRAO will be recalled in the contributions of Jansky, Reber, Greenstein, and Heeschen. The current state-of-the-art and future directions of receivers will be briefly presented. The evolution of the VLA will be described along with the status of the SKA and plans for a next generation of the VLA. Finally, I will present my views concerning some of the vital global policies relevant to astronomy.

March 4, 2015

 "Flat Spacetime Cosmology in a Scalar-Tensor Theory of Gravity”

Meir Shimon
Research Associate
Tel Aviv University

 A scalar-tensor theory of gravity, linear in the scalar curvature, is formulated in which $G$, particle masses, and a cosmological constant are allowed to vary. The theory yields a flat and static cosmological model with time-independent densities and angular scales. No flatness and horizon `problems' arise in this model; consequently, there is no need for an inflationary expansion phase. Lack of (global) evolutionary timescales implies that there are no cosmological coincidences, including the near equality of the energy densities of dark energy and dark matter. Irrespective of the specifics of the model it can be shown that the energy densities of dark energy ($\rho_{DE}$), dark matter ($\rho_{DM}$), and non relativistic baryons ($\rho_{b}$), are related by $\rho_{DE}=2\rho_{DM}+\rho_{b}/2$, in good agreement with current observations, if dark energy and dark matter are associated with the kinetic and potential energy densities of the scalar fields.

March 11, 2015

 "Turbulent Frontiers in Massive Stellar Death"

Sean Couch
Senior Postdoctoral Scholar at TAPIR

 Core-collapse supernovae are the luminous explosions that herald the death of massive stars. Neutron stars, pulsars, magnetars, and black holes are all born in these explosions. Supernovae are the drivers of galactic chemical evolution, being responsible for the synthesis of most of the heavy elements throughout the universe. Additionally, a Galactic supernova should be detectable by neutrino and gravitational wave detectors, opening entirely new windows on the observable universe. Despite the importance of CCSNe to our understanding of many aspects of astrophysics, the mechanism that reverses stellar core collapse and drives these explosions is not fully understood. I will discuss the revolution underway in supernova theory made possible by high-fidelity 3D simulations. In particular, I will focus on my work revealing the paradigm-shifting importance of turbulence in aiding neutrino-driven supernova explosions, and how this turbulence is influenced by realistic 3D progenitor structure as well as magnetic fields. These new developments at the frontier of core-collapse supernova theory may lead to a solution for the long-standing problem of how massive stars explode.

Spring 2015

April 15, 2015

 "The NuSTAR view of AGN: the case of NGC 1365"

Elizabeth Rivers
NuSTAR Postdoctoral Scholar

 The Nuclear Spectroscopic Telescope Array, the first focusing high-energy X-ray (3 - 79 keV) telescope in orbit, extends sensitive X-ray observations above the band pass where Chandra and XMM-Newton operate. With an unprecedented combination of sensitivity, spectral and imaging resolution above 10 keV, NuSTAR is advancing our understanding of black holes, neutron stars, and supernova remnants. I will give an overview of the mission and then present detailed results from the joint campaign with XMM-Newton on the Seyfert 1.8, NGC 1365, which has provided a wealth of information on its accretion disk, outflow, and variable multi-layered absorption geometry.

April 22, 2015

 "Magnetic Fields at Low Temperatures: Cool Stars, Brown Dwarfs,
and (Eventually) Exoplanets"

Peter Williams
Postdoctoral Fellow
Harvard College Observatory

 The magnetic field of Earth protects its surface from cosmic rays and the solar wind, while that of Jupiter enables powerful aurorae that can be brighter than the Sun at long radio wavelengths. What are the magnetic fields of extrasolar planets like? While direct observational probes are not yet feasible, the groundwork for answering this question is being laid, with the ultimate goal of characterizing magnetic properties across the spectrum of exoplanet types and peering “inside" rocky planets to identify which ones may be geologically active. I will discuss my recent work in this direction, including the detection of periodic auroral radio bursts from a 900-Kelvin T6.5 dwarf, and prospects for the future.

April 29, 2015

 "Letting the Data Speak for Themselves: What Observations Tell Us
About Galaxy Formation"

Neal Katz
Professor, Department of Astronomy
University of Massachusetts

 We infer the star formation rates in dark matter halos at different redshifts from halo merger histories expected in a Lambda CDM cosmology constrained to match the observed stellar mass/luminosity functions of galaxies at different redshifts and the local cluster galaxy luminosity function, which has a steeper faint end than that of field galaxies. The only other assumptions that we make are that the star formation rate of central galaxies depends on the halo mass and redshift and that when a galaxy becomes a satellite its star formation rate is quenched exponentially and it can eventually merge with the central galaxy on a dynamical friction timescale.

We find that 1) the star formation in the central galaxies of high mass halos (>10e12) has to be boosted at high redshift beyond what is expected from a simple scaling of the dynamical time; 2) below z=2 the star formation in halos below 1e11 must be quenched, which is not directly expected in standard stellar feedback models and is most easily explained by some form of preheating, and implies that there is a significant old stellar population in present-day dwarf galaxies with M_star < 10e8 and steep slopes for the high redshift stellar mass and star formation rate functions 3) the stellar mass of galaxies assembles in one of three ways depending on halo mass: > 1e12 the galaxies assemble through mergers and should hence have a spheroidal morphology and between 1e11 and 1e12 (e.g MW) it assembles slowly and at z>2 has less than 5% of its mass in place, which has extreme observational consequences.

May 6, 2015

 "Mergers and Outflows from Nearby Galaxies: A Sharper Image"

Claire Max
Interim Director, UC Observatories
Professor of Astronomy and Astrophysics, UC Santa Cruz
UCSC-UCO/Lick Observatory

 Abstract TBA

May 27, 2015

 "Constraining the Physics of Satellite Quenching"

Michael Cooper
Assistant Professor, Department of Physics & Astronomy
UC Irvine

 Despite remarkable success at modeling the evolution of massive galaxies over cosmic time, modern hydrodynamic and semi-analytic models of galaxy formation fail to reproduce the properties of low-mass galaxies. This shortcoming in our theoretical picture is largely driven by an inability to understand the physics of satellite (or "environmental") quenching. Using observations of satellite galaxies in the SDSS as well as detailed studies of dwarfs in the Local Volume, I will present recent work to constrain the timescale on which star formation is suppressed in low-mass satellites, focusing on the potential physical mechanisms that may be at play. As time allows, I’ll also discuss ongoing work to study the spatial anisotropy in satellite distributions as a test of the Lambda-CDM paradigm.

June 3, 2015

 "Neutrinos, Photons, and Nucleosynthesis from Newly Formed
Compact Objects"

Luke Roberts
NASA Einstein Fellow

 Hot dense neutron stars are formed in the inner most regions of massive stars during core collapse supernovae and during the merger of two neutron stars. Copious numbers of photons, neutrinos, and newly formed nuclei are produced during these events. In particular, the heavy r-process nuclei are likely produced in one or both of these scenarios. In these environments, nuclear physics, hydrodynamics, and gravity play paramount roles in determining the evolution of the dense object itself, what nuclei are synthesized, and the properties of the emitted radiation. I will first discuss the physics of the inner most regions core-collapse supernovae. This part of the talk will focus on my work studying neutrino emission from protoneutron stars, which has helped to constrain both the late time neutrino signal and possible modes of nucleosynthesis in these events. Second, I will discuss nucleosynthesis in material ejected during binary neutron star mergers and predictions of optical transients powered by the decay of ejected radioactive nuclei. I will highlight some of the uncertainties that exist in both of these scenarios, and how these uncertainties can be reduced with future theoretical and computational work with input from current and next generation observational and experimental facilities.