CD Andromedae / CD And
Light curves and phase diagrams of the EA type eclipsing binary CD Andromedae / CD And. These were constructed from 384 images taken between 2017 July 6 and 2023 March 18 with the Open University COAST telescope using a V filter.
Due to changes to the available instruments, the light curve was constructed from photometry of images taken with several different systems. However, the comparisons used remained the same, and the checkstar showed no deviation between instruments.
Due to changes to the available instruments, the light curve was constructed from photometry of images taken with several different systems. However, the comparisons used remained the same, and the checkstar showed no deviation between instruments.
The catalogue value for the period of this star is 68.8832 days (GCVS, AAVSO VSX, Kreiner.) (Accessed 2023 April 13)
This period generated the following phase diagram.
According to the GCVS, the primary and secondary minima should both have a depth of 0.5 mag.
From these observations there is indeed a primary minimum of approximately 0.5 mag depth, but a secondary minimum is not conspicuous in this data although there are a few data points suggesting one. The following investigation was carried out.
Investigation
74 observations had previously been obtained with COAST's precursor, The Bradford Robotic Telescope Cluster Camera (BRT), between 2013 September 30 and 2016 October 1. Although different comparisons were used (due to different fields of view) and different filters were used ('green' instead of V), they were included in the light curve below. The BRT results are in red and the COAST results are in black.
Again, a 'conspicuous' primary minimum but little strong evidence of a secondary minimum. Enlargements of the phases of the primary and secondary minima appear below.
The presence of a secondary minimum at phase 0.5 appears possibly inconsistent with the primary minimum in terms of its width, but the data is 'gappy' here and is inconclusive.
However, doubling the period to 137.77d resulted in the following phase diagram.
However, doubling the period to 137.77d resulted in the following phase diagram.
Enlargements of the primary and secondary minima appear below.
Here, the depths of the primary and secondary minima are consistent with the GCVS data, and their widths are superficially consistent with each other.
However, this period is inconsistent with radial velocity data obtained by Imbert, M. (2002), which does indeed indicate that the 68.8832d period is the correct one.
This system needs more observations to resolve this apparent discrepancy with the secondary minimum and it remains in my observing program.
However, this period is inconsistent with radial velocity data obtained by Imbert, M. (2002), which does indeed indicate that the 68.8832d period is the correct one.
This system needs more observations to resolve this apparent discrepancy with the secondary minimum and it remains in my observing program.
[This page updated 2023 April 13]