GO Cancri / GO Cnc
Observations and light curves of this under-observed EA type eclipsing binary GO Cancri / GO Cnc.
Photometry from 144 unfiltered images taken with the Bradford Robotic Telescope Cluster Camera (BRT) from 2012 November 24 to 2016 January 16.
Photometry from 144 unfiltered images taken with the Bradford Robotic Telescope Cluster Camera (BRT) from 2012 November 24 to 2016 January 16.
For a discussion on the phase of the secondary minimum, see the bottom of this page. Here, inspection using Peranso suggests that the secondary minimum is at approximately phase 0.45.
A series of follow up observations were made with the Open University COAST telescope; 209 images were taken through a V filter between 2019 January 5 and 2022 June 17. The light curve and phase diagram are below.
The catalogue period is 3.649969d (GCVS, AAVSO VSX, Kreiner, accessed 2022 February 24.) The above phase diagram is plotted with this period.
For these observations, the phase of the secondary minimum appears to be approximately 0.43. For a discussion on the phase of the secondary minimum, see the bottom of this page.
For these observations, the phase of the secondary minimum appears to be approximately 0.43. For a discussion on the phase of the secondary minimum, see the bottom of this page.
A primary minimum was observed from Somerby Observatory using the 2" Titan on 2022 February 22. The unfiltered observations were started as soon as the sky became dark enough and, although not ideal, a time of minimum was determined. This was HJD 2459633.365014 +- 0.000262
This time of minimum is more than an hour later than that published in the current AAVSO VSX ephemeris (accessed 2022 February 22)
Discussion of period of this system
When combining all of the above data into a light curve and phase diagram, it became evident that my observations did not agree with the catalogued period of 3.649969d (GCVS, AAVSO VSX, Kreiner, accessed 2022 September 4.)
In the following light curve, the BRT results are in red (and have been reduced in brightness by 0.1 mag to bring them into the same range as the other sets of data), the COAST results are in blue and the Somerby results are in black.
Using the catalogue period of 3.6499d generated the following light curve. It will be seen that the primary minima obtained from the three sets of data do not coincide. See below.
Enlargements of the primary minimum follow, each plotted with slightly different periods.
The 'best fit' from this - not rigorous - graphical method was found to be a period of 3.65001 days, as below.
The complete phase diagram for the period of 3.65001 days is
For the above observations alone, it will be seen that a period of approximately 3.65001 days fits the data better than the catalogued period of 3.649969 days. It should be noted that this is an informal graphical method, not a rigorous statistical analysis, but by themselves these results do appear inconsistent with the catalogued period.
As ever, more observations will be made in due course. However, these will be from Somerby only, as the ever increasing aperture of the COAST telescope [currently 17 inches / 42 cm] requires exposures which are too short for serious photometry of this system.
As ever, more observations will be made in due course. However, these will be from Somerby only, as the ever increasing aperture of the COAST telescope [currently 17 inches / 42 cm] requires exposures which are too short for serious photometry of this system.
The phase of the secondary minimum
The current (2022 September 4) AAVSO VSX value for the phase of the secondary minimum is 0.475, which is consistent with ASAS3 data for the period 2002 and 2009. Taking approximate mid-points of the three sets of data and plotting the associated phase of the secondary minimum results in the following.
The current (2022 September 4) AAVSO VSX value for the phase of the secondary minimum is 0.475, which is consistent with ASAS3 data for the period 2002 and 2009. Taking approximate mid-points of the three sets of data and plotting the associated phase of the secondary minimum results in the following.
This suggests apsidal precession of the eccentric orbits of the system, but three data points are not sufficient to draw any firm conclusions. I hope to observe primary and secondary minima from Somerby to obtain accurate timings to test this conclusion.
[Page updated 2022 September 4]