AAVSO: American Association of Variable Star Observers

Digital Single Lens Reflex Photometry in White Light: a New Concept Tested on Data from the High Amplitude δ Scuti Star V703 Scorpii

Volume 45 number 1 (2017)

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

Abstract

A novel method of digital single lens reflex (DSLR) photometry is described. It derives non-transformed instrumental magnitudes from white light (green, blue, and red channels of the DSLR sensor combined), and is assessed by comparing the results with non-transformed instrumental magnitudes from the green channel alone, and with green channel magnitudes transformed to the Johnson V standard. The white light data and the non-transformed green channel data allow differential photometry only; true magnitude values cannot be calculated. The same time series images of the high amplitude delta Scuti star V703 Scorpii were processed by all three methods. The light curves from the white light data were almost identical to those from the non-transformed green channel data and to those in V magnitude, but with a slightly greater amplitude for the variable star (from highest peak to lowest trough of the light curve on each night) in the white light curves. There was also an impression, in some areas, of slightly smoother curves from the white light data, implying improved precision. The check star data in white light showed slightly smaller ranges and standard deviations for most nights, and for all nights averaged, than those for the non-transformed green channel data, and for the transformed V magnitude data, implying that the best precision was achieved by using the data in white light. For most of the peaks in the light curve, the times of maximum in white light differed little from those in V magnitude. Fourier analysis using the Lomb-Scargle method revealed identical power spectra and identical discovered frequencies in white light and in V magnitude. DSLR photometry in white light is a valid procedure, at least in those cases where the color indices of the variable and comparison stars differ by only small values. It is considered promising for the timing of maxima and minima of light curves and for Fourier analysis of those stars with more than one period.