Recently Determined Light Elements for the delta Scuti Star ZZ Microscopii

Volume 43 number 1 (2015)

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Roy Andrew Axelsen

P.O. Box 706, Kenmore, Queensland 4069, Australia; address email correspondence to R. Axelsen, reaxelsen@gmail.com

Tim Napier-Munn

49 Limosa Street, Bellbowrie, Queensland 4070, Australia

Abstract

The delta Scuti star ZZ Microscopii (HD 199757) was studied by photoelectric photometry (PEP) on three nights in 2008 and by DSLR photometry on three nights in 2014. PEP yielded 51 magnitude measurements in V, including 4 peaks of the light curve, and DSLR photometry yielded 622 measurements, including 14 peaks of the light curve. Fourier analysis of the DSLR photometric data found a principle frequency F1 of 14.8853 (0.0001) c/d, and a harmonic frequency 2F1 of 29.7706 (0.0007) c/d, similar to the results of others. Another frequency F2 of 22.2049 (0.0025) c/d, of much lower amplitude than F1, was identified. F2 is higher than the frequency (19.15 c/d) previously reported in the literature, and its accuracy is regarded as uncertain as the semi-amplitude of F2 is low. Regression analysis of an O–C diagram, plotted from 33 historical times of maximum from 1960 to 2003, 4 times of maximum from our PEP in 2008, and 14 times of maximum light from our DSLR photometry in 2014 indicated that a cubic regression provided the best fit. The fitted curve confirms conclusions of others that the period of ZZ Mic was increasing at a constant rate during the years 1960 to 2003, and indicates that the period has decreased during more recent years. The following cubic ephemeris was derived, with zero epoch defined as the first peak of the DSLR photometry light curve on 19 July 2014: Tmax (HJD) = 2456858.0131 (0.0002) – 7.644 (2.532) × 10–19 E3 – 2.646 (0.973) × 10–13 E2 + 0.06717917 (0.00000001) E.