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[6.09] The North Star Mysteries: The Remarkable Brightness Increase of Polaris from Historical and Modern Observations

S.G. Engle, E.F. Guinan (Villanova University), R.H. Koch (Univ. of Pennsylvania)

Polaris (alpha UMi A; ~+2.0 mag; F7Ib; P = 3.97d) has received special attention since precessing close to the North Celestial Pole. Polaris is a 2nd mag luminous member of a multiple star system (ADS 1477) and is a low-amplitude classical Cepheid with a pulsation period of P = 3.97d. Polaris is noteworthy among cepheids because its pulsation period and light amplitude are rapidly changing with time (Evans et al. 2002). From over 100 yrs. of observations, an increase in its apparent period of dP/dt = +3.51 sec/yr and a decrease in light amplitide have been found. Its light variation has decreased from ~0.15 mag (visual) in the 1900s to a minimum value of 0.020 mag during the mid-1990s. However, our recent photometry, from 2001-2004, indicates its light(V) amplitude is again increasing and is 0.038 mag during 2004.

In this paper we report on yet another remarkable characteristic of Polaris. Our analysis of all available 20th century photometry indicates that the mean brightness of Polaris has increased from about V ~ +2.12 mag, in the 1900s, to the current high value of = +1.95 mag. Motivated by this apparent luminosity increase, we have carefully investigated its brightness, starting with Ptolemy (Almagest 160 AD; m = +3 mag), and have examined all available historical sources. We have reconstructed its apparent visual magnitude by comparing its given magnitude at each epoch with a grid of nearby bright stars. The sources of historical data include Ptolemy, Al Sufi , Tycho, Uleg Beg, Tycho Brahe, Herschel, and many 19th century measures. Overall, when all of the data are combined and weighted, there is strong evidence that Polaris has increased in brightness by more, than 1 mag over the last two millennia. We discuss the results, as well ,as some possible scenarios to explain its luminosity changes along with changes in its pulsation properties over time. This research is supported by NSF/RUI grants to Villanova University that we gratefully acknowledge.

The author(s) of this abstract have provided an email address for comments about the abstract: edward.guinan@villanova.edu

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Bulletin of the American Astronomical Society, 36 #2
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