A Search for Acoustic Heating in the Chromospheres of Low Activity Dwarfs

Details A Search for Acoustic Heating in the Chromospheres of Low Activity Dwarfs A Search for Acoustic Heating in the Chromospheres of Low Activity Dwarfs

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8143s&link_type=abstract

HST Proposal ID #8143

Computer Science

Hst Proposal Id #8143 Cool Stars

Scientific paper

Recent observations cast doubt on the importance of acoustic waves for chromospheric heating, at least in inactive giant stars, and have set small upper limits to their contribution to upper layers of the Solar chromosphere. These findings contradict the widely accepted picture that acoustic heating accounts for a significant fraction, the ``basal component'', of chromospheric heating in inactive stars across the HR diagram. To help resolve this issue, we propose to observe an extremely inactive {basal} dwarf star {Tau Ceti} to search for specific signatures of upward propagating acoustic waves: blue-shifts and enhanced blue wings in chromospheric lines. Solar data show that the strength of blue-shift can be used to estimate the acoustic contribution to chromospheric heating. We will also analyze archival HST data of an active dwarf of the same spectral type, and solar spectra from the SUMER instrument on SOHO, for comparison with the new data. Lack of a significant acoustic signature in Tau Ceti would indicate that magnetic heating generated by a local {turbulent, non- cycling} dynamo is responsible for the basal component of chromospheric heating in main sequence stars. Tau Cet may be in a phase analogous to the solar Maunder minimum, and HST spectra might serve as a proxy for the solar spectrum in this state. The spectra will also be used for emission measure analysis differentially between the Sun and solar-like stars.

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