Classical Rotational Broadening of Spectral Lines

Details Classical Rotational Broadening of Spectral Lines Classical Rotational Broadening of Spectral Lines

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.3701c&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #37.01; Bulletin of the American Astronomical Society, Vol. 24, p.786

Astronomy and Astrophysics

Astronomy

Scientific paper

In this paper we re-examine the classical problem of rotational line broadening with the view to clarifying the extent to which traditional rotational parameters may be expected to be determined from observation. We begin by investigating the role of limb-darkening in the classical rotational model of Struve and Unsold. Particular attention is paid to the effects of differing limb-darkening coefficients for the line and continuum. We focus on specific characteristics of the rotationally broadened profile, namely the half-width (FWHM) of the line, and the zeros of the Fourier Transform of the line profile. We compare the results obtained for the classical model with those obtained from models based on rotating non-gray atmospheres. By comparing the results of the classical Struve-Unsold model with those obtained from the more physically based models we find that the classical model provides an accurate (i.e. with in 10 percent) estimate of the projected rotational velocity within the parameters of the model for stars with intrinsic slow to moderate rates of rotation. However, when the rotation rates approach 90 percent of the critical velocity the classical model and derivatives of it tend to generally underestimate the actual rotational velocity by up to 50 percent regardless of whether the analysis employs half-widths or the zeros of the Fourier Transform. Thus line profiles provide a poor mechanism for the analysis of the rotational characteristics of the most rapidly rotating stars.

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