Patricia Cruz
We have searched for detached low-mass eclipsing binaries (LMEBs) in the Catalina Sky Survey to determine their orbital and physical parameters and study the radius anomaly problem found in such systems. Here we present our results, where we have identified and photometrically characterised a sample of 230 detached close-orbiting LMEB systems, with main-sequence components only. These low-mass stars have effective temperatures of less than 5720 K and orbital periods shorter than 2 days. We adopted a purely photometric method to derive stellar parameters, such as the effective temperature, photometric mass, and fractional radius, by using the available light curves and photometric colours obtained from 2MASS and SDSS magnitudes. We modelled all light curves with the JKTEBOP code (suitable for detached systems), associated with an asexual genetic algorithm, to derive the best solution for orbital parameters and the radius of each component. The adopted method allowed an unprecedented analysis of such a homogeneous set of parameters for low-mass stars in short-period binary systems, despite large individual uncertainties. The distribution of the studied components in the mass-radius diagram not only confirms the radius inflation in low-mass main-sequence stars but also shows a relative increase of inflation towards lower masses. The distribution also suggests that the secondary components of these short-period systems are more inflated than the primary components, as they present larger radii than primaries of the same mass, when compared to stellar evolutionary models.
The second slide describes the motivation of the work, where the text is presented on the left. Why are detached eclipsing binaries interesting? Close-orbiting low-mass systems present stellar radii 5 to 20% bigger than expected. The text also contains possible explanations for the radius anomaly problem. Example: high magnetic activity would suppress convection, making the star to inflate. On the top right, a plot of the mass-radius diagram is shown, which is a modified version of figure 5 presented in Cruz et al. (2018). The graphic shows detached systems with orbital period of less than 2 days, which components have mass of less than 70% of the mass of the Sun. It also shows a comparison to stellar models and the inflated model by Knigge et al. (2011).
On the left of the third slide, a white box contains the text which explains the methodology used to obtain temperatures and photometric masses of the analysed detached systems. In the upper central part, the light curve modelling is briefly mentioned, where an example of a plot of a phase-folded light curve with the obtained best-fit model is shown. In the upper right part of the slide, the new mass-radius diagram described, explaining the results obtained for the 230 new detached systems. In total, there are 460 individual stars and they were separated in two plots, for primary and secondary components. An intriguing and new found is that secondaries seem more inflated than primary components! The plot of the mass-radius diagram is shown at the bottom of the slide (at the centre and the right), showing the distribution for primary and secondary components separately. Below the plot, the slide ends with two questions: Are secondaries really more inflated than primaries? Why do they behave differently?
The fourth and last slide begins with the analysis of Kolmogorov-Smirnov test, showing on the left the distributions obtained from this analysis (central left) and a table with the results (bottom left). The distribution plots are divided in 6 plots, where the upper three plots are the distributions obtained from the KS test for the primary components and the lower three are those from the secondaries. The panels on the left (in the same figure) have stars within a bin of mass ranging from 0.7 and 1.0 solar mass, the middle panels have a mass range from 0.56 to 0.7 solar mass, and the panels on the right go from 0.56 to 0.2 solar mass. The part on the right of the slide describes the results obtained from the KS test and present. The distributions change the pattern when we compare primaries to secondaries, reaching larger radii for a same range of mass, and presenting even a bimodal behaviour for the secondary components. A very succinct discussion is presented to conclude the poster, emphasising the importance to investigate the causes of the radius anomaly.