The light variations of nonradial pulsators - Theory and application to the line profile variable 53 Persei

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view Abstract Citations (113) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The light variations of nonradial pulsators: theory and application to the line profile variable 53 Persei. Buta, R. J. ; Smith, M. A. Abstract The nonradial pulsator 53 Persei (B4.5 V) has been observed during 13 nights in late 1977 to determine whether its photometric variations are reminiscent of its spectral line profile changes. Inspection of the resulting light curve shows a variable amplitude with an estimated time scale of 1.9 days. Simultaneous photographic spectroscopy confirms this behavior. The light variations can be modeled successfully with a pair of sinusoidal oscillations having closely spaced periods near 1.7 and 2.1 days and amplitudes of 0.03-0.04 mag. The theory of linear, adiabatic nonradial oscillations is developed for low-order modes and applied to 53 Per. In general, sinusoidal light variations are produced by two geometric distortions of the star (the projected surface area and distorted surface normal effects) and a local compression of the gas. For the long periods observed in 53 Per, compression caused by horizontal motions in traveling waves is predicted to be the primary source of light variations. However, our predicted light amplitudes are about an order of magnitude larger than those observed. The source of the disagreement can be traced to our assumption of adiabaticity. Moreover, our observed color curve is half a cycle out of phase with the predicted light curve arising from this compression (temperature) effect. This suggests again substantial departures from adiabaticity in this long- period object. Nonradial theory also predicts that a star's rotation will split a nonradial mode into several closely spaced frequencies. An analysis of the two close frequencies in our photometric data leads to a rotational velocity which agrees to within 17% of the spectroscopic value. Our solution precludes stellar models with rapidly rotating cores. It also places a condition on the two rn-mode indices: Am = 1. We are able to place firm constraints on the physical identifications of the observed rn-mode pair, namely, m = - I, - I + 1, where 1 = 2 or 3, only. There is some difficulty in interpreting the great length of the 1.9 day period. In linear theory a single overtone of very high order (k 20) would be required. However, if one drops linearity it becomes possible to understand the long periods in terms of nonlinear coupling with a subharmonic or "stray" high-overtone mode. 53 Persei has now become the first star to show both photometric and spectroscopic variations that can best be explained in the framework of nonradial pulsation. Subject headings: stars: individual - stars: pulsation Publication: The Astrophysical Journal Pub Date: August 1979 DOI: 10.1086/157281 Bibcode: 1979ApJ...232..213B Keywords: B Stars; Light Curve; Stellar Spectrophotometry; Variable Stars; Adiabatic Conditions; Least Squares Method; Line Spectra; Sine Waves; Stellar Rotation; Astrophysics; Light Curves:Pulsating Stars; Line Profiles:Pulsating Stars; Photometry:Pulsating Stars; Pulsating Stars:Models; Pulsating Stars:Spectroscopy full text sources ADS | data products SIMBAD (4)