Page 514 - AWSAR 2.0

490 || AWSAR Awarded Popular Science Stories - 2019
these pools of collected data gave us the information we needed over a lengthy period of time, at least 10–50 years. We then had to make sure that the variability we observed was inherent in the contact systems we were studying and not due to other factors. For this, we used comparison stars in the same frame, a method known as differential photometry.
The technique we employed to study orbital period variation was to analyse the obtained O-C diagram, which showed the Observed minus Calculated time of arrival of light with respect to time. Period variation occurring in these eclipsing binaries due to mass transfer or any other changes in their orbital structure would lead to a shift in the time of arrival of light as measured by the observer, and the O-C diagram is a representation of this shift.
A mass transfer would reflect in the diagram as a secular increase or decrease in the O-C values. If this
secular variation is modelled
appropriately, it will yield the
period change rate and mass
transfer rate of the system.
This model is theoretically
predicted and is a function
of time. Once this model has
been removed from the overall
O-C variation, the residuals
would reveal variations caused
by the presence of a third-
body companion. As the inner
binary moves around the
common centre of mass of
the hierarchical triple system,
the time of arrival of light as
measured by us would be
slightly displaced. If that is the
case, this residual should be a
sinusoidal curve. If modelled accurately, it can even yield the orbital and physical parameters of the third body.
We have so far identified three contact binary systems with third-body companions. Monte Carlo simulations were used to verify all the solutions we obtained for these third-body parameters.
The first of these identified systems is an extremely low mass ratio (0.06) contact binary ASAS J083241+2332.4, which is one among the lowest mass ratio systems ever been reported. Based on the O-C diagram analysis, an orbital period change at the rate of 0.076 s per year was determined. The existence of such a system challenges theoretical models that predict a merger at a critical mass ratio limit of 0.06–0.07.
Interestingly, further inspection of the O-C diagram revealed that the residuals showed signatures of a third-body companion having 0.16–0.35 times the mass of the Sun and an orbital period of approximately 8.25 years. The second and third contact binaries similarly
constrained were the Kepler K2 EPIC 211957146 with a surface temperature very near to that of the dun at nearly 5900 K and EPIC 202073314. Modelling their O-C diagrams showed residuals exhibiting third-body signatures of components having 0.27–0.74 times the mass of the Sun with an orbital period of about 16.23 and 8.66 years. These third objects could be low-mass stars based on their derived mass and could be used to explore the mass– radius relationship between such stars, which still remains a mystery. There are hardly 50–60 low-mass stars whose mass and radii are known.
Furthermore, we also studied the correlation between the width of magnetically sensitive hydrogen spectral line and the orbital period
There are hardly 50–60 low-
mass stars whose mass and radii are known. Furthermore, we also studied the correlation between the width of magnetically sensitive hydrogen spectral line and the orbital period of contact binaries and found that there was a strong correlation between them, indicating that magnetic activity strongly depends on the orbital period.