Other
Scientific paper
Jun 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...246..502g&link_type=abstract
Astrophysical Journal, Part 1, vol. 246, June 1, 1981, p. 502-514.
Other
39
Atmospheric Models, Calcium, Chromosphere, Emission Spectra, Late Stars, M Stars, Stellar Spectra, Atmospheric Heating, Dwarf Stars, Energy Dissipation, Flare Stars, H Lines, K Lines, Line Spectra, Radiative Heat Transfer, Resonance Lines, Spectral Line Width, Stellar Radiation, Stellar Temperature
Scientific paper
We present 142 mÅ resolution spectra of the cores and wings of the Ca II H and K lines in three dMe and four comparison dwarf M stars, obtained with the KPNO 4 m echelle spectrograph and blue image tube. The narrow-band photometry of Willstrop and the Barnes and Evans relations for stellar angular diameters convert the observed relative flux to absolute surface flux units with an estimated uncertainty of ± 15 %. We derive chromospheric radiative loss rates in the H and K lines and discuss trends in these loss rates with effective temperature. Monochromatic surface fluxes are tabulated for different features in the H and K lines, and radiation temperatures are derived from the mean surface fluxes at K1 and H1, respectively. We find TR(H1) > TR(K1), consistent with partial redistribution theory. The TR(K1)/Teff ratio is higher in these M dwarfs than the giants studied in Paper X, and it is anomalously high for the dMe flare star YZ CMi. If TR(K1)/Teff is an empirical age indicator, then the result for YZ CMi implies that flare activity and youth are directly correlated, as has been suggested by other investigators. Moreover, the result implies that a high degree of nonradiative heating is present in the upper photospheres of dMe stars. Measurements of line widths at H1 and K1 are presented together with FWHM data for the H and K lines. We find that the scaling law proposed by Ayres generally agrees with the observed trend exhibited by the K1 widths. We also discuss chromospheric radiative loss rates in the Hɛ line compared with loss rates in the H and K lines, and present corrected FWHM(K) widths and compare them to the widths predicted by the Wilson-Bappu relation as calibrated by Lutz.
Cram Lawrence E.
Giampapa Mark S.
Schneeberger Timothy J.
Worden Simon P.
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