Pen portraits of Presidents — Charles Greaves

Walker, Malcolm

doi:10.1002/j.1477-8696.2001.tb06600.x

Cited by 1 publication

(2 citation statements)

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“…However, the characteristics of R Cen are very similar to other stars with known or suspected double maxima, and all of these stars have long periods (Lebzelter et al 2005;Templeton & Willson 2005). Walker & Greaves (2001) noted that the two maxima have different (B − V ) colors, indicating that the physical causes of each maximum are different, and that the time between two maxima having the same color is the true period.…”

Section: R Cenmentioning

confidence: 81%

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Secular Evolution in Mira Variable Pulsations

Templeton

Mattei

Willson

2005

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Stellar evolution theory predicts that asymptotic giant branch (AGB) stars undergo a series of short thermal pulses that significantly change their luminosity and mass on timescales of hundreds to thousands of years. These pulses are confirmed observationally by the existence of the short-lived radioisotope technetium in the spectra of some of these stars, but other observational consequences of thermal pulses are subtle and may only be detected over many years of observations. Secular changes in these stars resulting from thermal pulses can be detected as measurable changes in period if the star is undergoing Mira pulsations. It is known that a small fraction of Mira variables exhibit large secular period changes, and the detection of these changes among a larger sample of stars could therefore be useful in evolutionary studies of these stars. The American Association of Variable Star Observers (AAVSO) International Database currently contains visual data for over 1500 Mira variables. Light curves for these stars span nearly a century in some cases, making it possible to study the secular evolution of the pulsation behavior on these timescales. In this paper we present the results of our study of period change in 547 Mira variables using data from the AAVSO. We use wavelet analysis to measure the period changes in individual Mira stars over the span of available data. By making linear fits to the period versus time measurements, we determine the average rates of period change, d ln P/dt, for each of these stars. We find nonzero d ln P/dt at the 2 significance level in 57 of the 547 stars, at the 3 level in 21 stars, and at the level of 6 or greater in eight stars. The latter eight stars have been previously noted in the literature, and our derived rates of period change largely agree with published values. The largest and most statistically significant d ln P/dt are consistent with the rates of period change expected during thermal pulses on the AGB. A number of other stars exhibit nonmonotonic period change on decades-long timescales, the cause of which is not yet known. In the majority of stars, the period variations are smaller than our detection threshold, meaning the available data are not sufficient to unambiguously measure slow evolutionary changes in the pulsation period. It is unlikely that more stars with large period changes will be found among heretofore well-observed Mira stars in the short term, but continued monitoring of these and other Mira stars may reveal new and serendipitous candidates in the future.

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Section: R Cenmentioning

confidence: 81%

“…The general behavior of the period variation was discussed by Walker & Greaves (2001), and the AAVSO visual data for R Cen between 1950 and 2000 were analyzed in detail by Hawkins et al (2001). The latter derived a rate of period change of about -1 day per year, yielding d ln P/dt of −1.9 × 10 −3 y −1 .…”

Section: R Cenmentioning

confidence: 99%

Secular Evolution in Mira Variable Pulsations

Templeton

Mattei

Willson

2005

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Pen portraits of Presidents — Charles Greaves

Cited by 1 publication

References 2 publications

Secular Evolution in Mira Variable Pulsations

Secular Evolution in Mira Variable Pulsations

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