Figure 1: Artist’s impression of a binary star system.
G. Zhou et al. (2015) present the discovery and characterisation of a binary system consisting of two low-mass red dwarf stars that periodically eclipse one another. The binary system is identified as HATS551-027. The more massive star is HATS551-027A and the less massive star is HATS551-027B, hereafter referred to as components A and B. HATS551-027 is also a double-lined binary system and this means that the spectral lines of both stars are visible. Double-lined eclipsing binary systems comprising of low-mass red dwarf stars serve as good natural laboratories for the precise measurements of fundamental stellar parameters (i.e. mass, radius, etc) of low-mass stars. These measurements can then be used to validate and improve models of low-mass stars.
The two components of HATS551-027 circle around one another ever ~4.1 days. Component A is estimated to have 0.24 times the mass and 0.26 times the radius of the Sun while component B is estimated to have 0.18 times the mass and 0.22 times the radius of the Sun. Compared to theoretical models, the radius of component A is consistent while the radius of component B is inflated by 9 percent at 2σ significance. Both components of HATS551-027 have masses low enough to support fully convective interiors. The estimated effective temperatures for components A and B are 3,190 ± 100 K and 2,990 ± 110 K, respectively. Both stars appear slightly cooler than predicted by theoretical models. HATS551-027 is the third well characterised double-lined eclipsing binary system with both components supporting fully convective interiors. The other two are CM Draconis and KOI-126.
Figure 2: Light curves of HATS551-027. The left panel corresponds to the primary eclipse (i.e. component B passing in front of component A) and the right panel corresponds to the secondary eclipse (i.e. component A passing in front of component B). G. Zhou et al. (2015).
Figure 3: Radial velocity curves of HATS551-027A (red) and B (black). As both components circle around one another, one component will appear to recede while the other component will appear to approach, and vice versa. The receding component will have its spectral lines red-shifted (i.e. positive radial velocity) while the approaching component will have its spectral lines blue-shifted (i.e. negative radial velocity). G. Zhou et al. (2015).
Figure 4: The measured masses, radii and temperatures of the well characterised double-line eclipsing binaries compared with theoretical models. G. Zhou et al. (2015).
G. Zhou et al. (2015), “A 0.24+0.18 Msun double-lined eclipsing binary from the HATSouth survey”, arXiv:1505.02860 [astro-ph.SR]