Speaker: Dr. Nancy S. Brickhouse, 2022 Distinguished Alumni Awardee, Senior Science Advisor Center for Astrophysics, Harvard University & Smithsonian
Abstract: Observations of cool star atmospheres show a broad range of physical conditions, with some stars having peak electron temperatures around a few MK like the Sun, while others show peaks above 20 MK. The X-ray luminosities of some quiescent coronae are as much as five orders of magnitude larger than the Sun’s. For the past three decades we have used ultraviolet and X-ray spectrometers to determine the physical conditions ---electron temperature, electron density, elemental abundances --- for a relatively small sample of cool stars (mostly the brightest). The youngest stars show a hot accretion shock in addition to an active corona, although the resolving powers of instruments to date are not sufficient to cleanly separate the two components. We are proposing Arcus, a NASA medium-scale explorer mission (MIDEX), to study structure and evolution in the Universe. Arcus will host a grating spectrometer of sufficient spectral resolution to go beyond the measurement of physical conditions to the exploration of the physical processes that produce the high energy emission.