V725 Sagittarii: Real-Time Evolution of a Pulsating Star (Abstract)

Volume 34 number 2 (2006)

John R. Percy

Anna Molak

Hugh Lund

M. Danie Overbeek

Amelia Wehlau

Peter F. Williams

Abstract

(Abstract only) V725 Sgr is a unique pulsating variable star, first recognized by Henrietta Swope, which has increased its period by a factor of at least 5 in the past century. It has also changed its amplitude and its mean magnitude. It appears that, for the first few decades of the 20th century, its spectrum and variability were those of a Population II Cepheid. Now, they are those of a red semiregular (SRa or SRb) variable. We will review V725 Sgr’s past history. Unfortunately, it was largely neglected through the middle of the 20th century, though there was a key paper in 1973 by Serge Demers (J.Roy. Astron. Soc. Canada, 67, 19). We have now used visual (mostly Overbeek and Williams) and photoelectric CCD (Lund) photometry of V725 Sgr, from 1985 to 2004, to study V725 Sgr’s recent variability—period, amplitude, mean magnitude—using a variety of time-series analysis techniques (Fourier, least-squares, self-correlation), which we shall describe. We shall then discuss possible explanations; V725 Sgr’s behavior is consistent with the final stages of a thermal “flash” in its nuclear burning shells, from the asymptotic-giant branch and back.