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Two new eJAAVSO preprints: O-C Methods; EQ Eri

ejaavso281

Methods for O–C (Observed Minus Computed) Diagrams and for the Determination of Light Elements of Variable Stars with Linear and Second Order Polynomial Ephemerides

   pdf

Roy Andrew Axelsen
P.O. Box 706, Kenmore, Queensland 4069, Australia

Received July 24, 2014; accepted July 28, 2014

Abstract

Methods are described for the construction and analysis of O–C (observed minus computed) diagrams and for the determination of light elements (ephemerides) of variable stars and the standard errors of the elements. The methods described are those that apply: (1) when the period of the star is constant, and (2) when the period of the star is changing continuously, and the light elements can be represented by a second order polynomial function.

ejaavso280

EQ Eridani, a Multiperiodic delta Scuti Star

   pdf

Roy Andrew Axelsen
P.O. Box 706, Kenmore, Queensland 4069, Australia

Received May 24, 2014; revised August 8, 2014; accepted August 11, 2014

Abstract

DSLR photometry of the delta Scuti star EQ Eridani (HD 28665) was undertaken on six nights between 2 November and 8 December 2013. Comparison and check stars were HD 28508 and HD 28901, respectively. Inspection of the light curves revealed an irregular pattern and variation in amplitude that signified the presence of two or more periods. Fourier analysis using the software period04 yielded at least three pulsation frequencies of 14.3663, 11.6862, and 7.2128 cycles per day, corresponding to periods of 0.0696, 0.0856, and 0.1386 day, respectively. The first of these frequencies is very close to the period of 0.0700 day listed in a catalogue of d Scuti stars published in 2000. This is the first report of multiperiodicity in EQ Eri. None of the period ratios fall within the range of 0.74–0.78 expected for the ratio of the first overtone to the fundamental mode of delta Scuti stars pulsating in the radial mode.

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