AAS 201st Meeting, January, 2003
Session 117. Delta Scuti and Pulsating Friends
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

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[117.11] ``But I am constant as the North Star*'' - The Return of Polaris as a Low Amplitude Classical Cepheid

J.J. Davis, J.C. Tracey, S.G. Engle, E.F. Guinan (Villanova University)

* Julius Caesar, William Shakespeare

Polaris (<V> \approx +2.0 mag; B-V = +0.60; F7 Ib) is a low amplitude Classical Cepheid with a pulsation period of P = 3.97 days. Polaris is one of the nearest (dHipparcos = 132 ± 8 pc) and brightest Cepheid. This Cepheid (Polaris A) is the luminous member of the multiple star system (ADS 1477). Over the last century amazing changing have been occurring for this famous star. The pulsation period has been increasing a rate of dP/dt = +3.2 sec/yr while the light amplitude has decreased from ~0.12 mag (1900s) to ~0.02 mag (early1990s). A recent summary and thorough discussion of Polaris's interesting properties are given by Evans et al. (2002, ApJ, 567, 1121).

We have been carrying out photoelectric photometry of Polaris starting in early 2002. This photometry is a continuation of the work done on Polaris by Kamper and Fernie. Our observations were made to obtain new epochal light curves and accurate times of maximum light. We secured well defined 450 nm and 550 nm light curves from which we extracted accurate measures of light amplitudes of 0.033 ± 0.004 mag and 0.028 ± 0.003 mag, respectively. These light amplitudes are slightly larger than those observed during the early 1990s. So it appears that the century long decrease in the light amplitude has halted (or paused). Our time of maximum light was combined with previous timings and reaffirms the increase in period of +3.2 sec/yr. These observations lend strong support to overtone nature of Polaris's pulsations, whose transition from moderate to low amplitude pulsator will be discussed in more detail in this poster. In addition to the long-term secular increase in the Polaris's pulsation period, an analysis of the O-Cs indicates ±0.25 day cyclic oscillations in the apparent period with time scale of 11-12 years. The nature of these period oscillations is being investigated and will be discussed.

We gratefully acknowledge the support for this research from NSF/RUI Grant AST 00-71260 and by the Undergraduate Summer Research Assistance Program Grant from Delaware Space Grant Consortium.

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