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C.R. Cowley (Department of Astron. Univ. Michigan), F. Castelli (Osserv. Astron. Trieste)
We describe attempts to evaluate several aspects of the calculation of Balmer profiles from theoretical models using LTE codes. Only the most recent work on the Balmer lines has included the new Stark profiles of Stehlé and her coworkers (cf. Stehlé and Hutcheon AAS, 140, 93, 1999). Much work on stellar atmospheres makes use of the routines (BALMER9) provided by Kurucz (cf. Kurucz 2001, http://cfaku5.harvard.edU), with Stark profiles by Vidal, Cooper, and Smith (ApJS, 25, 37, 1973). These routines make no provision for the inclusion of microturbulence in the line profiles, and resonance or self broadening is included in an approximate way rather than by means of a convolution. We have made test calculations for solar abundance models with effective temperatures ranging from 4500K to 12000K, with log(g) from 4.4 to 1.5. We find no significant difference between the resulting stellar profiles using the Kurucz programs and those we can make with the most recent profiles and correct convolutions in almost all cases. Only when the microturbulence approaches the sound speed do significant differences appear, in the line cores, and this is because there is no explicit provision to include microturbulence for the Balmer lines in the BALMER9 code. We obtain good, though not perfect fits to the lowest four Balmer lines for the center of the solar disk, using the neutral broadening from Barklem, Piskunov, and O'Mara (A&Ap, L5, 2000), and scaled for H-gamma and H-delta.
We see no way to fit H-alpha in Arcturus with an LTE code. We can match the observed width with a microturbulence of the order of 12 km/sec, but the calculated depth is far too small.
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The author(s) of this abstract have provided an email address for comments about the abstract: cowley@umich.edu