The radius inflation problem in short-period low-mass binaries: a large sample analysis

Abstract

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...

Recovering variable stars in large surveys: EAup Algol-type class in the Catalina Survey

“…For instance, the Gaia distance for CSS J162549.3+102124 is recovered if we assume a temperature ∼250 K higher than that used by us. Garrido et al (2019) characterized a sample of 230 detached closeorbiting eclipsing binaries with low-mass main-sequence components (M < 1 M ), orbital periods shorter than 2 d, and temperatures below 5720 K. They suggest a trend according to which low-mass stars would have inflated radii. Besides, they found that around 61 per cent of the sample has the secondary star more inflated in radius than the primary.…”

“…Fig. 7 presents a mass-radius diagram for low-mass stars in binaries, where the objects found in this work are shown in red and blue, and the sample from Garrido et al (2019) in black and grey. The lines represent theoretical models from Baraffe et al (1998) with isochrones of 1, 5, and 8 Gyr for solar metallicity and helium abundance Y = 0.275.…”

“…Another important feature of EA systems is that they may contain low-mass stars whose radii and masses can be known to better than 5 per cent accuracy (often better than 3 per cent; see Feiden 2015). There is a suggestion that radii of low-mass stars are inflated by more than 10 per cent in comparison with theoretical models for isolated stars (Kraus et al 2011;Birkby et al 2012;Feiden & Chaboyer 2012;Garrido et al 2019). This may be associated with non-solar metallicity (Berger et al 2006;López-Morales 2007), increased magnetic activity (Chabrier, Gallardo & Baraffe 2007;Kraus et al 2011), or be an observational effect related to distortions in the light curves caused by spots or flares (Morales, Ribas & Jordi 2008;Morales et al 2010).…”

“…This may be associated with non-solar metallicity (Berger et al 2006;López-Morales 2007), increased magnetic activity (Chabrier, Gallardo & Baraffe 2007;Kraus et al 2011), or be an observational effect related to distortions in the light curves caused by spots or flares (Morales, Ribas & Jordi 2008;Morales et al 2010). Only a small number of low-mass binaries that are detached EBs with components of late-K or M types present accurate radii determinations in the literature (Garrido et al 2019).…”

The Quest for Pulsating M Dwarf Stars

“…However, the physical parameters of M dwarfs are not easy to obtain and there are persistent discrepancies in theoretical estimations from stellar evolution models and observations regarding fundamental parameters, such as mass, radius and effective temperature in eclipsing binary systems, as well as in interferometry of single stars. The radius anomaly (see e.g., Tognelli et al, 2018) has been related to the effects of enhanced magnetic activity, a spotted stellar surface, or metallicity, which have been invoked to explain the observational-theoretical disagreement (see e.g., Higl and Weiss, 2017;Garrido et al, 2019;Kochukhov and Shulyak, 2019, and references therein).…”