According to Gaia, ASAS J082841-2735.0 has a Right Ascension of -7.248 +/- 0.506 mas/y and Declination of 1.915 +/- 1.054 mas/y. The star was previously studied by G.Pojmanski, Acta Astronomica (2002) and afterwards, there has not been any research paper on the target. With further research from VSO, I found out that the star was categorized as an EC type eclipsing binary  or low mass contact binary according to its variable star index on AAVSO. 

I then went to Gaia to enter the coordinates of the stars and compare the target star’s brightness with other nearby stars to ensure that its magnitude was not affected by nearby brighter stars. From the step above, I concluded that the star has no light contamination from nearby stars. Afterwards, I downloaded the data from ASAS-SN and ASAS-3 to create a periodogram. Using the CoLab script provided by Dr. Janzen, I ran a periodogram analysis on the data downloaded from ASAS-SN and ASAS-3. Below is the periodogram of the star for single oscillator and double oscillator:

From the diagram, the period presented is 0.873259 for single oscillation and 1.7465198 days for double oscillation, from which I belive the double oscillation is the best fit period for this star. However, what was interesting for me was that the light curve peaks are asymmetric (there are two peaks and one is higher than the other), which should not occur in a normal eclipsing binary. Because the two peaks correspond to the two times when both stars are both visible. Hence, the system should have the same magnitude at both peaks instead of having one taller than the other.

With further investigation with the TAs, we came to the conclusion that this is the result of O’Connell effect, which has previously been observed in multiple EW type eclipsing binaries. Unfortunately, the O’Connell effect does not have a consensus explanation but its effect is well-observed by astronomers. Following Wikipedia, I also found out that the star has a positive O’Connell effect which is the maximum following the primary minimum is nearly always brighter than the preceding one. Hence, taking into the phenomenon, I concluded that the star is an EB eclipsing binary with the O’Connell effect.

Having discovered the O’Connell effect, I feel quite accomplished and find myself lucky to find such a phenomenon within the 10 stars that I observed. It’s definitely not uncommon in the eclipsing binary system but it is still very special for me at least. I enjoy this lab the most and learned a lot about eclipsing binary as well as sampling their periodogram 🙂

 

Reference:

G.Pojmanski, Acta Astronomica (2002)

O’Connell effect (https://en.wikipedia.org/wiki/O%27Connell_effect)