Eclipsing binaries allow the study of physical stellar parameters in a model-independent way, when photometric and spectroscopic data are combined. However, when spectroscopic data are not available, purely photometric methods can be adopted to first estimate stellar properties, especially for large samples. Cruz et al. have then characterized components of detached EB systems from photometric colors and light curves from the literature, with the purpose of estimating trends from statistical values. An inflation trend of around 20% was estimated, which is in agreement with several results from the literature. As a response to MacDonald & Mullan, the obtained values for individual systems should not be analyzed separately, since they could mislead the results. We encourage further spectroscopic measurements to verify the values estimated from the photometric method.

The characterisation of detached eclipsing binaries with low mass components has become important when verifying the role of convection in stellar evolutionary models, which requires model-independent measurements of stellar parameters with great precision. However, spectroscopic characterisation depends on single-target radial velocity observations and only a few tens of well-studied low-mass systems have been diagnosed in this way. We characterise eclipsing detached systems from the Kepler field with low mass components by adopting a purely-photometric method. Based on an extensive multi-colour dataset, we derive effective temperatures and photometric masses of individual components using clustering techniques. We also estimate the stellar radii from additional modelling of the available Kepler light curves. Our measurements confirm the presence of an inflation trend in the mass-radius diagram against theoretical stellar models in the low-mass regime.

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 $M \leq 1.0\ M_{\odot}$ 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 $T_{\rm eff}\leq 5720$ 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.

We present a photometric and spectroscopic study of AzV322, an emission line object located in the Small Magellanic Cloud previously classified between O9 and B0. We analyse 17.5 yr of I-and V-band OGLE-II, -III and -IV light curves and find four significant frequencies, viz. f(1) = 0.386 549 +/- 0.000 003, f(2) = 0.101 177 +/- 0.000 005, f(3) = 0.487 726 +/- 0.000 015 and f(4) = 0.874 302 +/- 0.000 020 cycles d(-1). The f(1) frequency (period 2.587 00 +/- 0.000 02 d) provides the stronger periodogram peak and gives a single wave light curve of full amplitude 0.066 mag in the I band. High-resolution optical spectroscopy confirms the early B-type spectral type and reveals prominent double peak Balmer, Paschen, OI 8446 and He I 5875 emissions. The spectral energy distribution shows significant colour excess towards long wavelengths possibly attributed to free-free emission in a disc -like envelope. Our analysis yields T-eff = 23 000 +/- 1500 K, log g = 3.0 +/- 0.5, M = 16 +/- 1 M-circle dot, R = 31.0 +/- 1.1 R-circle dot and L-bol = 10(4.87 +/- 0.06) L-circle dot. AzV322 might be a member of the new class of slowly pulsating B supergiants introduced by Saio et al. and documented by Lefever, Puls & Aerts; however its circumstellar disc makes it an hither to unique object. Furthermore, we notice that an O-C analysis for f(1) reveals quasi-cyclic changes for the times of maximum in a time-scale of 20 yr, which might indicate a light-travel time effect in a very wide orbit binary with an undetected stellar component.

We investigate the luminous star ELHC 10 located in the bar of the Large Magellanic Cloud (LMC), concluding that it is a SB1 long-period eclipsing binary where the main eclipse is produced by an opaque structure hiding the secondary star. For the more luminous component we determine an effective temperature of 6500 +/- 250 K, log g = 1.0 +/- 0.5 and luminosity 5970 L-aS (TM). From the radial velocities of their photospheric lines, we calculate a mass function of 7.37 +/- 0.55 M-aS (TM). Besides Balmer and forbidden N ii emission, we find splitting of metallic lines, characterized by strong discrete absorption components, alternatively seen at the blue and red side of the photospheric spectrum. These observations hardly can be interpreted in terms of an structured atmosphere but might reflect mass streams in an interacting binary. The primary shows signatures of s-process nucleosynthesis and might be a low-mass post-asymptotic giant branch star with a rare evolutionary past if the binary is semidetached. The peak separation and constancy of radial velocity in H alpha suggest that most of the Balmer emission comes from a circumbinary disc.

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 multi-band 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_sun, respectively. A comparison with synthetic binary-star evolutionary models indicates that the system has an age of 4.76E7 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 H_alpha profiles show the presence of double emission formed probably in an optically thin circumstellar medium, while the variable HeI profile and the H_beta 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 of dM/dt = 3.1E-6 M_sun/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.