Dr. Sean Robert Brannon, Ph.D
Postdoctoral Research Associate
Sean Robert Brannon
Barnard Hall – 242
Department of Physics
Montana State University
Bozeman, MT 59717
Flat field & FUV background calibrations for the Interface Region Imaging Spectrograph (IRIS)
I am an active member of the IRIS calibration team. My responsibilities include processing the monthly SJI/SG flat field and SG FUV background calibrations each month, maintaining an archive of past calibrations, and tracking long-term trends in the calibration parameters.
The complete set of calibrations is located here, and the calibration trends are located here.
Imaging and spectroscopic analysis of accelerating jet substructure suggesting origin in reconnection region
Coronal jets typically appear as thin, collimated structures in EUV and X-ray wavelengths, and are understood to be initiated by magnetic reconnection in the lower corona or upper chromosphere. Plasma that is heated and accelerated upward into coronal jets may therefore carry indirect information on conditions in the reconnection region and current sheet located at the jet base.
On 2017 October 14, the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory / Atmospheric Imaging Assembly (SDO/AIA) observed a series of jet eruptions originating from NOAA AR 12599. The jet structure has a length-to-width ratio that exceeds 50, and remains remarkably straight throughout its evolution. Several times during the observation bright blobs of plasma are seen to erupt upward, ascending and subsequently descending along the structure. These blobs are cotemporal with footpoint and arcade brightenings, which we believe indicates multiple episodes of reconnection at the structure base.
Through imaging and spectroscopic analysis of jet and footpoint plasma we determine a number of properties, including the line-of-sight inclination, the temperature and density structure, and lift-off velocities and accelerations of jet eruptions. We use these properties to constrain the geometry of the jet structure and conditions in reconnection region.
Measuring optical thickness and geometric effects in flare ribbon plasma with Si IV spectral lines as observed by IRIS
It is well-established that the Si IV spectral line pair at 1394 and 1403 Å exist in a 2:1 intensity ratio in optically thin plasma, and that deviations from this ratio arise as an effect of optical thickness and/or geometric effects in the emitting plasma. These effects are expected to be particularly prevalent in the bright, dense chromospheric plasma that forms the ribbons during a flare, and the Si IV line pair therefore provides a diagnostic of the plasma conditions at the flare loop footpoints. The Interface Region Imaging Spectrograph (IRIS) contains spectral windows that observe both the Si IV 1394 and 1403 Å spectral lines with a spatial resolution of up to 0".33, spectral resolution up to 26 mÅ, and temporal resolution up to 1 s, which is ideal for detailed observations of flare ribbon plasma.
We select IRIS observations of flares that record both Si IV lines with an 8-step or fewer raster, and identify 26 potential observations for which the flare ribbon is covered by the spectrograph slit. We establish criteria for identifying spectra that capture flare ribbon emission, and for eliminating spectra that contain defects (e.g. saturated pixels). We calculate absolute intensities, Doppler shifts, line widths, and the intensity ratio for the Si IV line pair for all selected spectra in each event, and conduct a statistical analysis of these quantities across our selected flares. The statistical results for the line ratio are then correlated to the results for the individual spectral lines, as well as to properties of the flare and active region, such as GOES class, ribbon geometry, LOS angle, and magnetic field complexity.
VUV Spectroscopy of the Sun-as-a-Star
I am a team member for a new sounding rocket mission to obtain the first high resolution, high quality VUV (100-200 nm) spectrum of the Sun-as-a-star. Our immediate science goal is to understand better the processes of chromospheric and coronal heating. HST data exist for a dozen or so Sun-like stars of a quality already beyond our ability to construct a comparable sun-as-a-star UV spectrum. The solar spectrum we obtain will enable us to understand the nature of magnetic energy dissipation as a Sun-like star evolves, and the dependence of magnetic activity on stellar mass and metallicity.
I am currently working on aspects of the instrument design, specifically on a testbed optical layout.
ASTR 110 — Introduction to Astronomy: Mysteries of the Sky
An introduction to contemporary astronomy that explores the nature, methods, and limitations of scientific inquiry within the context of our struggle to understand the structure and evolution of the Universe. Topics include the history of astronomy, motions of the night sky, the solar system, stellar evolution, galaxies, and cosmology.
Semesters taught: SP 2018, FA 2018, SP 2019
PHSX 207 — College Physics II
Second semester of introductory algebra-based physics sequence. Topics include simple harmonic motion, electric forces and fields, DC electric circuits, magnetic forces and fields, and magnetic induction and motors.
Semesters taught: SU 2010
Last updated: March 1, 2019