REEXAMINING THE BEAT CEPHEID TU CAS - NO 2ND OVERTONE, NO MODE SWITCHING
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1992
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Abstract
Simultaneous photometry and radial-velocity measurements of the double-mode Cepheid TU Cas were obtained in 1987, to check on the mode behavior of this star after a decade-long gap in the observing record. We have performed least-squares fits of these data to isolate the primary (2.14 d) and secondary (1.52 d) variations. The residuals of our solution rule out the existence of any tertiary mode with V and velocity amplitudes greater than 0.004 mag and 0.7 km s-1, respectively, contradicting Faulkner's [ApJ, 218, 209 (1977)] report of such a mode with amplitude 0.05 mag. We also do not detect a significant change in the relative amplitudes of the modes compared to previous data, cited as evidence for mode switching in this star by earlier investigators. In addition, we use the components of our fit to the fundamental and first-overtone pulsations in TU Cas as a rigorous test of various Fourier parameters which have been proposed as mode discriminants.