Category: Seminars

4/16 seminar: Christoph Baranec, U. Hawaii: The Palomar Robo-AO System

April 11th, 2014 in Seminars

Astrophysics Seminar Series

Scientific Highlights from the Palomar Robo-AO System and Plans for a Mauna Kea Robo-AO

Christoph Baranec
Institute for Astronomy, University of Hawaii

Wednesday, April 16, 2014
Refreshments at 3:15pm in CAS 500
Talk begins at 3:30pm in CAS 502

Abstract:

Robo-AO is the world’s first fully automated laser adaptive optics instrument. The prototype system, fielded at the Palomar Observatory 60-inch telescope, went live in June 2012 and has since executed ~10,000 observations at the ~0.1′′ visible diffraction limit. Among these observations are the largest diffraction limited surveys of stellar multiplicity in the local solar neighborhood and of nearby companions to Kepler exoplanet host candidates. The Palomar system will be augmented with two new infrared camera next summer which will both widen the spectral bandwidth of observations and enable deeper visible-light imaging using adaptive-optics-sharpened infrared tip-tilt guide sources – necessary for completion of the Kepler survey by the fall of 2014. I am planning on bringing an upgraded facility-class Robo-AO system to the University of Hawai’i’s 2.2-m telescope on Mauna Kea to exploit the excellent native seeing and enable imaging approaching that of HST. This new system will be used for high-cadence monitoring of solar-system weather, characterization of asteroids and supernovae discovered by Pan-STARRS and ATLAS, and for validating the potentially tens of thousands of exoplanet host candidates discovered by the future Transiting Exoplanet Survey Satellite.

4/10 seminar: Tony Case, CfA: The Solar Wind

April 10th, 2014 in Seminars

Space Physics Seminar

The Solar Wind and Development of Solar Probe Plus

Tony Case
Harvard–Smithsonian Center for Astrophysics

Thursday, April 10, 2014
725 Commonwealth Ave.
Refreshments at 3:30pm in CAS 500
Talk begins at 4:00pm in CAS 502

Abstract:

The supersonic flow of plasma outwards from the solar corona, known as the solar wind, was first observed at the dawn of the space age, yet the precise mechanisms leading to the heating and acceleration of the wind are still unknown. Through modeling and remote observations researchers have been able to discern that the heating and acceleration take place primarily below about 20 solar radii through any number of processes such as ion-cyclotron resonant heating or dissipation of turbulent fluctuations. The Solar Probe Plus (SPP) mission is designed to provide insight into this issue by directly measuring the plasma environment in the region of interest (specifically down to 10 solar radii). The SWEAP (Solar Wind Electrons, Alphas, and Protons) investigation is a suite of instruments on-board SPP designed to measure the thermal ions and electrons that make up the solar wind. The suite consists of two electrostatic analyzers (ESAs) that measure electrons, an ESA that measures ions, and a Faraday Cup that measures electrons, protons, and alphas. In order to address the primary objectives of the mission, the Faraday cup must be pointed directly at the Sun throughout the full solar encounter. The resulting extreme operating environment presents complex engineering challenges that must be overcome to meet the stringent measurement requirements of the mission. This presentation will review the outstanding scientific issues to be addressed by SPP, introduce the mission and spacecraft, and then discuss the novel approaches taken to design, build, and test a working prototype of the SPP Faraday cup.

4/3 seminar: David Hysell, Cornell University: Equatorial Spread F

April 3rd, 2014 in Seminars

Space Physics Seminar

Equatorial Spread F – A space weather problem finally resolved?

David Hysell
Cornell University

Thursday, April 3, 2014
725 Commonwealth Ave.
Refreshments at 3:30pm in CAS 500
Talk begins at 4:00pm in CAS 502

Abstract:

The forecastability of equatorial spread F (ESF), an important aspect of terrestrial space weather, is considered experimentally and theoretically. Ionospheric state parameters including plasma number density and vector drift profiles were measured at the Jicamarca Radio Observatory in campaigns in 2013. Neutral winds were measured by the red-line Fabry Perot interferometer at Jicamarca. Coherent radar backscatter from plasma irregularities associated with equatorial spread F (ESF) was also recorded. A numerical simulation of ionospheric irregularities, initialized and forced using parametrizations derived from a combination of measurements and empirical models, was used to model the ESF activity observed. Simulations were able to recover the salient features of the irregularities, thanks in part to the inclusion of important but often neglected physics (nonequipotential magnetic field lines and plasma shear flow). White noise was used to “seed” irregularities in the simulations, suggesting that atmospheric gravity waves did not play a central role in the phenomenology. The forecast problem appears to be one of forecasting the relevant background ionospheric state parameters.

4/7 seminar: Fabian Hatch, UNC at Chapel Hill: Molecular Cloud and Star Formation

April 3rd, 2014 in Seminars


Astrophysics Seminar Series

Molecular Cloud and Star Formation: Why Accretion Matters

Fabian Heitch
University of North Carolina at Chapel Hill

Monday, April 7, 2014
Refreshments at 3:15pm in CAS 500
Talk begins at 3:30pm in CAS 502

Abstract:

“Molecular clouds are filamentary” – with this statement one certainly cannot go wrong, especially given the recent- abundant – observational evidence for filamentary molecular cloud structure. While filament formation, structure, and
fragmentation has been explored abundantly, the role of the ambient gas reservoir on a filament’s evolution is less clear. I will discuss observational and theoretical attempts to quantify the role of accretion for the evolution of filamentary molecular clouds.

3/27 Seminar: Matthew Zettergren, ERAU: Modeling ionospheric density structures

March 24th, 2014 in Seminars

Space Physics Seminar

Modeling ionospheric density structures generated by magnetospheric and lower atmospheric interactions

Matthew Zettergren
ERAU

Thursday, March 27, 2014
725 Commonwealth Ave.
Refreshments at 3:30pm in CAS 500
Talk begins at 4:00pm in CAS 502

Abstract:

Plasma densities in the ionosphere are influenced, through a wide range of processes, by energy exchange with the magnetosphere and atmosphere. At high latitudes energetic particle precipitation produces impact ionization and heating of the ambient ionospheric electrons, as well as auroral light. Intense auroral electric fields and associated field-aligned currents dissipate energy in the ionosphere, resulting in frictional heating, compositional changes, and density depletions. These heating processes also produce expansion and upwelling which facilitates the escape of terrestrial plasma via other energization processes. Atmospheric acoustic and gravity waves can achieve significant amplitudes in the ionosphere and are also important drivers of plasma density structure. These waves influence the ions through both ion-neutral drag and the generation of dynamo electric fields and currents. This talk will review some details of these processes and present recent modeling results relevant to ionospheric plasma density structuring and outflow to the magnetosphere. In particular, we focus on simulations elucidating details of the formation of F-region plasma density depletions in auroral current systems. Chemical alterations due to frictional heating are shown to be an important feature of the ionospheric response to strong electric fields. Furthermore, ionospheric responses to heating are shown to be highly transient and the propagation of these disturbances to higher altitudes implies a significant hysteresis effect in the amount and types of particles escaping to the magnetosphere. Finally, we present some initial results from studies of ionospheric responses to upward propagating acoustic waves generated from seismic, volcanic, and weather sources. Electron density and dynamo electric field perturbations driven by the interaction of these waves with the ionosphere are strongly influenced by local geomagnetic field geometry and wave source characteristics.

Tues 3/25: Kathy Reeves (CfA): Energy Transport and Conversion in Solar Eruptions

March 24th, 2014 in Seminars

Tuesday Lunch

Energy Transport and Conversion in Solar Eruptions

Dr. Kathy Reeves
Harvard/Smithsonian Center for Astrophysics

Tuesday, March 25, 2014
12:10pm CAS 500

Abstract:

Eruptions on the Sun convert an immense amount of energy from magnetic fields into other forms of energy.  In this talk, I will examine the types of energy that are produced during coronal mass ejections and solar flares, and talk about how this energy is transported out into the heliosphere and also into the lower layers of the Sun’s atmosphere.  I will also examine the “current sheet” region of these eruption, where much of the energy conversion takes place.  Observations of this region show hot plasma, as well as turbulent motions, which give clues about the physical processes taking place in this energy conversion region.  MHD models are also useful for understanding the energy partition in this region.

3/24 Seminar: Meredith Hughes, Wesleyan University: Planet Formation

March 24th, 2014 in Seminars

Astrophysics Seminar Series

Planet Formation through Radio Eyes

Meredith Hughes
Wesleyan University

Monday, March 24, 2014
Refreshments at 3:15pm in CAS 500
Talk begins at 3:30pm in CAS 502

Abstract:

Circumstellar disks provide the raw material and initial conditions for planet formation. Millimeter-wavelength interferometry is a powerful tool for studying gas and dust in planet-forming regions, and it is undergoing a multiple-order-of-magnitude leap in sophistication with the advent of the ALMA interferometer that is now in the late stages of construction. I will discuss some ways in which millimeter-wavelength interferometry is being used to study the process of planet formation in circumstellar disks, with particular emphasis on the kinematics of turbulence in protoplanetary disks and the degree to which debris disk structure reflects the dynamics of embedded planetary systems.

3/20 Seminar: T. T. Koskinen (U. of Arizona): Sunsets on Saturn

March 17th, 2014 in Seminars

Space Physics Seminar

T. T. Koskinen
University of Arizona

Sunsets on Saturn –
a new perspective on the upper atmosphere from Cassini UVIS occultations

Thursday, March 20, 2014
725 Commonwealth Ave.
Refreshments at 3:30pm in CAS 500
Talk begins at 4:00pm in CAS 502

Abstract:

Despite significant advances in our understanding of Saturn’s upper atmosphere since the Pioneer and Voyager missions, many important questions remain. For example, the observed temperatures in the thermosphere are much higher than expected from solar heating only and the missing energy source is still unknown. This problem is common to all of the giant planets in the solar system, and the solution could also be relevant to many extrasolar giant planets. Past studies indicate that breaking gravity waves, redistribution of auroral energy by circulation, and electrodynamics may help to explain the high temperatures. There are, however, almost no observations available to directly study such dynamics in the upper atmosphere and only a few observations of even the density and temperature profiles above the stratosphere. In this sense, solar and stellar occultations observed by Cassini UVIS that probe the atmosphere from the stratosphere to the exobase provide much needed constraints on the photochemical and dynamical models. In particular, the spatial and temporal coverage of the data potentially allows for the identification of trends indicative of dynamics and energy deposition. The analysis of these observations, however, poses unique challenges that can lead to significant confusion over their interpretation. I will review some of these challenges and present results from more than 20 occultations that map the temperature and density structure in Saturn’s upper atmosphere.

3/17 Seminar: Joan Najita (NOAO and CfA): From Planetesimals to Giant Planets

March 17th, 2014 in Seminars

Astrophysics Seminar Series

Joan Najita
NOAO and CfA

“From Planetesimals to Giant Planets:
Chemical and Dynamical Probes of Planet Formation”

Monday, March 17, 2014
Refreshments at 3:15pm in CAS 500
Talk begins at 3:30pm in CAS 502

Abstract:

Work with the Spitzer Space Telescope revealed that emission from water and organic molecules is commonly present in the mid-infrared spectra of disks surrounding young stars. I will describe how these features might be used to help lift the veil on a very early stage of planet formation, the formation of planetesimals, those theoretically fundamental but observationally elusive building blocks of planets in core accretion theory. I will also describe some results from high resolution spectroscopy that suggest that forming high-mass giant planets may reveal themselves through non-axisymmetric signatures of their presence, e.g., circumplanetary disks and eccentric inner rims.

Wed 3/5: Jennifer Yee (CfA): Microlensing: Beyond Planet Detection

March 4th, 2014 in Seminars

Wednesday Lunch

“Microlensing: Beyond Planet Detection”

Jennifer Yee
Sagan Fellow, Harvard/Smithsonian Center for Astrophysics

Wednesday, March 5, 2014
12:10 pm, 500 CAS

Abstract:

Microlensing uses the gravitational bending of light to detect exoplanets. Because the typical timescale of the events is ~20 days and the individual events are not repeated, microlensing is generally thought of as giving only an instantaneous snapshot of the planetary system. In the context of recent microlensing discoveries, I will show how additional data and the inclusion of higher order effects in the analysis enables us to more fully characterize these planetary systems. These techniques expand the scope of microlensing beyond planet detection and toward a better understanding of brown dwarfs, stellar remnants, and the mass function of the inner galaxy.