Physics & Astronomy Special Colloquium - Christopher S. Moore, Ph.D., Harvard-Smithsonian Center for Astrophysics
"Using CubeSats to Probe HOT Plasma in the Atmosphere of a COOL Star" by Christopher S. Moore, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
Abstract: The Sun is the closest star to Earth and hence provides a unique opportunity to study numerous stellar phenomena in detail unprecedented to other stars. One such phenomena, which is a longstanding mystery, is coronal heating of low mass stars. The solar corona contains plasma in excess of 1 MK at all times, strong concentrations of magnetic field called active region contain plasma at least up to 3 MK, and large flares heat plasma above 10 MK. The distribution of temperatures, elemental abundance, and time scales of each phenomena, provide unique insights on the various types of coronal heating processes. Currently, there are very few in-situ measurements of coronal plasma near the Sun (the solar wind provides an additional probe), thus radiative diagnostics are commonly used. Detection of soft X-rays (sxr) from the Sun provide direct information on coronal plasma of 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 observation gaps, that large missions are currently missing. The twin Miniature X-ray Solar Spectrometer (MinXSS) CubeSats are the first solar science oriented CubeSat missions flown for the NASA Science Mission Directorate. The first of the twins, MinXSS-1, 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 numerous solar observations, proving the scientific capability of CubeSats. MinXSS-2 is scheduled to launch in December 2018 for improved solar observations for at least a four year mission. Future improvements in solar soft x-ray spectroscopy can be achieved by combining Miniature X-ray Optics (MiXO) with high speed readout CMOS detectors for spectral imaging, improved dynamic range, and improved spectral resolution. These new prospects will also be discussed.