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.
September 26, 2018
- "Imaging Protoplanets with Adaptive Optics and Interferometry"
- 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"
- 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"
- 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
- Assistant Professor
- Kavli IPMU (University of Tokyo)
October 24, 2018
- Millikan Postdoctoral Fellow
November 7, 2018
- Staff Scientist
November 14, 2018
- Postdoctoral Scholar
- UC Riverside
December 5, 2018
- Deputy Program Scientist, Exoplanet Exploration Program
December 12, 2018
- Staff Scientist
- Max Planck Institute for Astronomy
February 13, 2019
- Staff Astronomer
- Carnegie Observatories