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BEGIN:VEVENT
DTSTART;TZID=Atlantic/Canary:20220614T123000
DTEND;TZID=Atlantic/Canary:20220614T133000
UID:iactalks-1578
X-WR-CALNAME: IAC Talks: Open Astronomy Seminars
X-ORIGINAL-URL: /iactalks/Talks/view/1578
CREATED:2022-06-14T12:30:00+01:00
X-WR-CALDESC: IAC Talks upcomming talks
SUMMARY:Why coronae disappear in cool giants and the role of the Athay poin
 t?
DESCRIPTION:Why coronae disappear in cool giants and the role of the Athay 
 point?\nDr. Klaus-Peter Schroder\n\n \nX-ray observations and non-det
 ections of cool giants suggested a picture of a division\nof warm solar-li
 ke giants with Coronae and cool inactive giants with cool winds instead,\n
 first suggested by Linsky and Haish 1979. But in the meantime, photospheri
 c magnetic field\nhas been detected in cool giants, and their chromospheri
 c emission mostly surpasses the\n"basal" flux, which is a minimum emission
  found in entirely inactive stars. Hence, the absence\nof coronae in cool 
 giants is not caused by a lack of magnetic activity! The real reason lies 
 in\nfundamental chromospheric physics, as we will show. Mayor evidence is 
 provided by the \nWilson Bappu effect: with lower gravity, density sc
 ale-heights increase. At the same time, \nchromospheric heating decre
 ases and the "Athay point", at which the solar corona begins,\nbecause chr
 omospheric radiative cooling collapses by reaching full Hydrogen ionizatio
 n, \nis not passed in giant chromospheres. A few case studies of ecli
 psing binaries with cool \ngiants, providing a direct account of thei
 r chromospheric extent and density profiles, \nare presented to illus
 trate this explanation.  
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