Due to the recent increase in the availability of photometric time-series databases, the characterisation of low-mass eclipsing binaries for the study of their orbital and physical parameters is now possible in large samples and with good precision. We have identified and photometrically characterised a sample of 230 detached close-orbiting eclipsing binaries with low-mass main-sequence components in the Catalina Sky Survey. These low-mass stars have masses of M ≤ 1.0 M and orbital periods shorter than 2 days. The adopted method provided a robust estimate of stellar parameters (as mass and fractional radius) by using only light curves and photometric colours, since no spectroscopic information was available for these objects. A SDSS-2MASS ten-colour grid of composite synthetic and observed colours and the K-Nearest Neighbours method were employed to identify main-sequence stars and to estimate their effective temperatures, typically of T eff ≤ 5720 K. Each light curve was modelled with the JKTEBOP code together with an asexual genetic algorithm to obtain the most coherent values for the fitted parameters. The present work provides an unprecedented number of homogeneous estimates of main stellar parameters in short-period low-mass binary systems. The distribution of the components of the investigated detached eclipsing binaries in the mass-radius diagram supports a trend of radius inflation on low-mass main-sequence stars. A relative increase of inflation for lower masses is also found and our results suggest that the secondaries are more inflated, i.e. they present larger radii than the primary components of same mass, when compared to stellar evolutionary models. 2 H. E. Garrido et al. therein). For instance, Southworth (2015) maintain an on-line catalogue of detached EB systems with mass and radius derived with high accuracy (of ∼2%), with around 40 systems where the most massive component (primary) has a mass of M ≤ 1 M . If only close systems are considered, with orbital period of less than 2 days, this number is smaller, less 20 short-period DEBs are well characterised. Eker et al. (2014) also have published a catalogue of detached double-lined EBs, but gathering from the literature systems with physical parameters determined with larger uncertainties. Among them, over 60 DEBs have primaries with mass of M ≤ 1 M , but only 35 of them have periods shorter than 2 days.Given the availability of extensive photometric time-series databases, the characterisation of low-mass eclipsing binary systems (LMEBs) has become possible in large samples, where trends can be seen despite the large individual uncertainties. Deriving masses and radii in statistically significant samples may allow the investigation of the correlation between radius inflation and other basic stellar parameters.Knowing that the number of known detached short-period systems in the literature is limited, this work is then dedicated to identify and photometrically characterise short-period detached eclipsing binaries, with low-mass main-sequence star...
We analyze multicolor light curves and high resolution optical spectroscopy of the eclipsing binary and Double Periodic Variable OGLE 05155332-6925581. According to Mennickent et al., this system shows a significant change in the long non-orbital photometric cycle, a loop in the color-magnitude diagram during this cycle and discrete spectral absorption components that were interpreted as evidence of systemic mass loss. We find that the best fit to the multiband light curves requires a circumprimary optically thick disc with a radius about twice the radius of the more massive star. The spectroscopy indicates a mass ratio of 0.21 ± 0.02 and masses for the hot and cool stars of 9.1 ± 0.5 and 1.9 ± 0.2 M , respectively. A comparison with synthetic binary-star evolutionary models indicates that the system has an age of 4.76 × 10 7 years, is in the phase of rapid mass transfer, the second one in the life of this binary, in a Case-B mass-exchange stage. Donor-subtracted Hα profiles show the presence of double emission formed probably in an optically thin circumstellar medium, while the variable He I profile and the Hβ absorption wings are probably formed in the optically thick circumprimary disc. The model that best fit the observations shows the system with a relatively large mass transfer rate ofṀ = 3.1 × 10 −6 M /yr. However, the orbital period remains relatively stable during almost 15 years. This observation suggests that the hot-spot mass-loss model proposed by other authors is not adequate in this case, and that some other mechanism is efficiently removing angular momentum from the binary. Furthermore, our observations suggest that the DPV phenomenon could have an important effect in the balance of mass and angular momentum in the system.
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