BB Cephei / BB Cep
Light curves and phase diagrams of the EA type eclipsing binary BB Cephei / BB Cep. Data was obtained from photometry of 141nimages take with the Open University COAST Telescope, between 2017 July 6 and 2019 September 7, using a V filter. All measurements were made using the same comparison stars.
The light curve superficially appears inconsistent over time. To reduce the possibility that this was due to observational errors of some type the following diagram includes the light curve of a comparison star. For further discussion on this see here on this website.
The light curve of BB Cep has two interesting features; the general reduction in magnitude at about JD 2458025 (2017 September 28), and the change in shape of the maxima from around JD 2458601 (2019 April 28). These are discussed .below.
Overall reduction in magnitude.
Changing shape of the light curve at maxima.
The catalogued period for this star is 30.1851d (GCVS) and 30.1856d (AAVSO VSX) (accessed 2020 January 6). The following phase diagram was plotted using the latter period. The 'doubling' of the curve for the maxima is a consequence of the changing magnitude at the maxima over time. The red data points are discussed below.
There is a suggestion of a secondary minimum at phase 0.5, which is consistent with the following light curve and phase diagram (p=30.1856d) constructed from data from the Northern Sky Variability Survey (NSVS) for object ID 1457693 during the period May1999 to February 2000.
The difference in shape between the maxima between phase 0 and phase 0.5, and the maxima between phase 0.5 and phase 1, are an example of the O'Connell effect. This is possibly caused by the presence of star-spots and/or some form of interstellar material in the system. In the later COAST results, there appears to be a change in the shape of the maximum from phase 0.5 to phase 1, levelling out to more closely match that between phase 0 and phase 0.5. The red data points in the following enlargement of the phase diagram near maximum show this change.
These changes are possibly due to changes in the (presumed) star spots, and will be the subject of future modelling with Binary Maker 3. In the meantime, this system is still under observation by COAST and future results will be presented when available.
[This page updated 2020 January 6.]