Characterizing non-thermal equilibrium contact binaries

Abstract

Formation and evolution of marginal contact binaries with larger temperature difference between their two components remain inexplicable to date. To get a better understanding of the nature of such population we investigate on an individual, NSVS 7358116, by analysing observational data obtained from ground-based and space-based telescopes. It is found that NSVS 7358116 is a marginal contact totally eclipsing binary with a small fill-out factor by 3 per cent but large temperature difference by 2000 K or t-ratio by 0.3. This suggests that the two components are only geometrically contact but not in thermal contact. By collecting all available targets in literature, we compiled a table of 80 non-thermal equilibrium contact binaries (nTCBs) including 53 STRONG t-ratio samples and 27 WEAK t-ratio samples. We performed statistical distribution analysis on physical parameters which reveals that STRONG t-ratio samples will evolve to WEAK t-ratio samples through heat and mass transfer along with angular momentum loss, meanwhile thickening their common envelop. This current investigation is acted as only an appetizer, because more exploration on nTCBs and its evolutionary connection with related populations will follow.

Five Massive Contact Binaries with Twin Components in LMC

“…To find the third body for these five massive binaries, the LTTE was adopted. In this process, the observed minima are needed for these binaries; then, the theoretical minima are subtracted from the observed minima, resulting in the quantities referred to as O − C (Qian et al 2013;Wang et al 2022). The periodic oscillations in the O − C values indicate the possible presence of a third body influencing the binary system.…”

1SWASP J010313.78+352903.7: A Totally Eclipsing Binary with Components in Poor Thermal Contact

“…We collected samples of deep low mass ratio (DLMR) over-contact binaries from Yang & Qian (2015), where the gray dots and gray crosses represent the primary and secondary components respectively. The orange and cyan crosses stand for secondary components of STRONG t-ratio and WEAK t-ratio non-thermal equilibrium contact binaries (nTCBs) are taken from Wang et al (2022), which pointed that the STRONG t-ratio samples will evolve to WEAK t-ratio samples through heat and mass transfer along with angular momentum loss, meanwhile thickening their common envelop. Also we find in Figure 4 that there is a tendency that WEAK t-ratio nTCBs are evolving toward DLMR over-contact binaries if thermal equilibrium is continuously establishing.…”

“…As investigated by Li & Zhang (2006), Yang & Qian (2015), Kim et al (2019), Li et al (2021a) and Christopoulou et al (2022), low mass ratio deep contact binaries have a relationship between J spin /J orb and q. To better understand the character of samples with large temperature difference between two components, we also revisited samples of nTCBs from Wang et al (2022) and figured out their J spin /J orb at k 2 = 0.05. We constructed the q − J spin /J orb diagram and discriminated the unstable region and stable region of contact binaries by the Bressan et al (2012).…”

“…The blue and red dots with err bars are the primary and secondary component of J0103. The background gray dots and gray crosses represent the primary and secondary components of deep low mass ratio (DLMR) over-contact binaries taken from Yang & Qian (2015); the orange and cyan crosses stand for secondary components of STRONG t-ratio and WEAK t-ratio non-thermal contact binaries (nTCBs) are taken from Table A2 in Wang et al (2022), where the STRONG t-ratio samples to those with relative temperature difference (t-ratio), (T 1 − T 2 )/T 1 > 0.2 and the WEAK t-ratio samples to those 0.05 < t-ratio = (T 1 − T 2 )/T 1 < 0.2. boundary of J orb = 3J spin (blue dashed line in Figure 5). From the figure we can find that STRONG t-ratio samples are mostly distributed between the q value of 0.25 and 0.6, whereas the WEAK t-ratio samples are located mostly in both sides.…”

“…They are non-thermal contact binaries (nTCBs) where the components are in poor thermal contact (Rucinski & Duerbeck 1997). Based on a statistical work of 80 nTCBs, Wang et al (2022) noticed an evolutionary channel from strong t-ratio samples to weak t-ratio samples, during which process their common envelop will thicken. This evolutionary status has been predicted by the thermal relaxation oscillation (TRO, Lucy 1976;Flannery 1976;Robertson & Eggleton 1977) theory, whereas more issues remain obscure.…”