New Light Elements for the High Amplitude delta Scuti Star RS Gruis

Volume 42 number 1 (2014)

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Roy Andrew Axelsen

P.O. Box 706, Kenmore, Queensland 4069, Australia; reaxelsen@gmail.com

Abstract

Photoelectric and DSLR photometry of the monoperiodic high amplitude delta Scuti star RS Gruis yielded 16 times of maximum determined by the author from 2007 to 2013.These data are combined with historical observations obtained from 1952 to 1988 and more recent observations by others from 2003 to 2010. This combined dataset, comprising 50 times of maximum spanning 61years, was subjected to O–C analysis, which revealed an obvious change in the period of the star between 1988 and 2003. Separate O–C analysis of the data from 2003 to 2013, comprising 28 times of maximum, yielded a quadratic fit, with the pulsational period increasing at the rate of dP/Pdt = 84.95 (15.74) × 10–8 yr–1. To our knowledge, this rate of increase in period is the highest ever reported for a Population I high amplitude δ Scuti star with radial pulsation. From a quadratic (second order polynomial) ephemeris, the period was calculated to be 0.14701118 (0.00000011) d at HJD 2452920 (in October 2003) and 0.14701241 (0.00000012) d at HJD 2456497 (in July 2013).