Mathematics – Spectral Theory
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...289..185h&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 289, no. 1, p. 185-201
Mathematics
Spectral Theory
36
Chromosphere, H Lines, Main Sequence Stars, Spectral Theory, Stellar Models, Balmer Series, Continuous Spectra, Electron Density (Concentration), Line Spectra, Photoionization, Radiative Transfer
Scientific paper
We present the first successful attempt in modeling simulta- neously the H-alpha and H-beta high resolution profiles and the H-alpha to Ly-alpha flux ratio for a dMe star (AU Mic, dM2.5e). We show that a very high transition region pressure and a thin transition region are simultaneously required to reproduce our observations. We give evidence that lower pressure model chromospheres can also reproduce the Balmer line profiles, but give Lyman surface fluxes overestimated by more than an order of magnitude. Our model also reproduces the Balmer decrements, the Ly-alpha full width half maximum (upper limit) and the Balmer jump which is weak. Discrepancies in the profiles between observations and our model point to possible systematic upward flows in active stellar chromospheres. We obtain the Paschen lines in emission and Paschen decrements as large as 41 for Pabeta. For our model, we obtain a transition region column mass of 1.26 10-3 g/sq cm (log(M) approximately = -2.9) which should be a lower limit (with the present modeling approximations). This large pressure chromosphere yields too large equivalent widths by a factor of 3.3. The electron density at the top of the chromosphere is in the 1012-5 1012/cu cm range, in agreement with previous estimates based on the Balmer decrements. The pressure is 6.3 Pa, of the same order as the current estimates for coronal pressures (approximately 10 Pa). We compare our model to other dMe, dKe and solar model chromospheres. It shares common physical properties with solar flare models, thus implying a large and continuous chromospheric heating rate. The temperature break at 8200 K is very close to values obtained for the quiet Sun, plages, flares and other stellar models. The total radiative cooling in the Hydrogen lines and continua is about 1.22 108 erg/sq cm/s, of which 66% arise from the Balmer series and continuum. The radiative cooling is dominated by the Balmer series respectively in the transition region and the chromosphere. Cooling is dominated by the Paschen lines in the lower chromosphere. The short penetration of the Lyman radiation field produces a net backwarming in the upper chromosphere, while other series penetrate deeper and backwarm the lower chromosphere and the temperature minimum.
Doyle Gerry J.
Houdebine E. R.
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