(AGENPARL) – LOW EARTH ORBIT, sab 23 maggio 2020
Stellar X-ray Cycles: the Shape of Things to Come
HST Proposal 15963
Thomas Ayres (publications @ ADS)
University of Colorado at Boulder
Proposal type: GO
Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are relevant for understanding the Sun’s analogous high-energy modulations, in turn crucial to Earth-impacting “Space Weather” (SW). Similarly, stellar SW counterparts can have eqivalent, or more severe, adverse effects on their exoplanets. The solar decadal oscillations are symptomatic of a deep-seated magnetic pump — the Dynamo — whose internal workings remain elusive. Key question: is Sun’s 11-year cycle normal, or instead a transition state? A 3-year continuation of previous long-term Chandra/HST programs will be carried out for Alpha Cen AB (G2V+K1V) and Procyon (F5IV), nearby bright stars that bracket the Sun in their fundamental stellar properties.
HST part of the program will measure FUV subcoronal (T~100,000 K) emission lines, like Si IV 140 nm and C IV 155 nm, as well as the important NUV chromospheric (T~10,000 K) emission doublet of Mg II at 280 nm, in all three stars, with one visit of STIS echelle spectroscopy per system each year. Non-standard wavecals provide better wavelength calibrations, so that subtle Doppler shifts of the high-excitation emissions can be assessed. Dynamical information also is encoded in distortions of the line shapes, captured using combinations of FUV medium- and high-resolution echelle settings.
Publications referencing this proposal
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