Remarks on the Determination of Velocity Gradients in Moving Atmospheres.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Remarks on the Determination of Velocity Gradients in Moving Atmospheres. Teske, R. G. Abstract Theoretical line profiles and curves of growth have been constructed for atmospheres in uniform and in nonuniform motion; they are based on a pure absorption mechanism in a Milne-Eddington model. The purpose of this study is to describe methods for the detection and measurement of atmospheric velocity gradients such as those which may arise during Cepheid pulsation. The positions of cores of absorption lines which are formed in a unifrrmly expanding (contracting) atmosphere will be a function of the central intensity of the line; the relation is such that strong lines are less displaced by the effects of expansion than are weak lines. This relative position line strength relation depends upon the velocity of expansion and is further complicated by the smearing effect of the spectrographic app aratus. Thus, if one relates measured radial velocity to a parameter which is proportional to line strength, it is possible to infer the presence of velocity gradients where none in fact exist. An analysis of theoretical absorption lines formed in a velocity-gradient atmosphere shows that the relation between the displacement of the line cores and their mean depth of formation r, measured in the continuum, does not yield the input velocity field. Recourse is had to high-precision spectropho tometry; a spectrophotome tric method is described which allows quantitative determination of differential atmospheric motions independent of radial velocity data. The method is limited to a velocity function that is linear with optical depth in the continuum. Some of the calculations upon which this investigation is based were performed with the IBM 704 computer at the Massachusetts Institute of Technology; others were done with the IBM 704 at the Smithsonian Astrophysical Observatory's Computations and Analysis Division. Publication: The Astronomical Journal Pub Date: 1960 DOI: 10.1086/108065 Bibcode: 1960AJ.....65Q..57T full text sources ADS |