Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...423..795s&link_type=abstract
Astrophysical Journal v.423, p.795
Astronomy and Astrophysics
Astronomy
19
Stars: Variables: Cepheids, Line: Formation, Radiative Transfer, Stars: Chromospheres
Scientific paper
We study the heating and dynamics of Cepheid chromospheres utilizing the He I λ10830 line, which due to its high excitation potential is not formed in the photospheres of such cool stars.
We construct time-dependent models of the chromospheres of the Cepheids by coupling hydrodynamics with non-LTE radiative line transfer calculations for H, He, Ca II, and Mg II. We conclude that Cepheids have chromospheres heated by acoustic (or magnetic) wave dissipation in addition to transient heating by the pulsation dynamics. Judging by the height of formation of the He I λ10830 line in Cepheid atmospheres, the existence of hot coronae around Cepheids seems unlikely. We use the Cepheid models to compute X-ray and EUV fluxes, and these are consistent with observed upper limits.
Lester John B.
Sasselov Dimitar D.
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