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Astrophysics Seminars

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The CASS Astrophysics Seminar features world-class astrophysicists from around the world speaking on current topics of research. Presentations are aimed at the graduate and post-graduate level, but are open to the general public. CASS seminars take place on Wednesdays from 4:00 - 5:00 p.m. in 383 SERF (Marlar Seminar Room), unless otherwise noted. You can watch a live stream of the talk or prior talks at the CASS Seminar YouTube Channel. The organizers are Prof. Quinn Konopacky and Dr. Alexei Kritsuk.


Upcoming Seminars

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

Meredith Powell
Graduate Student
Yale University



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

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



October 24, 2018

Arpita Roy
Millikan Postdoctoral Fellow
Caltech



November 7, 2018

Lorenzo Moncelsi
Staff Scientist
Caltech



November 14, 2018

Paul Dalba
Postdoctoral Scholar
UC Riverside



December 5, 2018

Eric Mamajek
Deputy Program Scientist, Exoplanet Exploration Program
JPL



December 12, 2018

Eva Schinnerer
Staff Scientist
Max Planck Institute for Astronomy


Winter 2019


February 13, 2019

Gwen Rudie
Staff Astronomer
Carnegie Observatories