Contributed Talk - Splinter Stellar

Thursday, 24 September 2020, 15:35   (virtual room M)

The new orbital paramaters of the R Aqr symbiotic system

J. Alcolea 1; J. Mikolajeswka 2; M. Gómez-Garrido 1; V. bujarrabal 1; K. Ilkiewicz 2; et al.
1) OAN (IGN/CNIG, MITMA, Spain); 2) CANK-­PAN (Pland); 3) IRAM (France)

R Aqr, a D-type symbiotic system, is the interacting binary closest to us. Despite that, the orbital parameters were poorly known until a few years ago. This was due to the nature of the system, consisting of a Mira variable and a WD secondary. The large size primary, bigger than the expected parallax, poses some doubts on the Tycho/Gaia distance measurements; the large luminosity contrast between the two components makes the direct measurement of the relative position of the stars very difficult too. This situation was greatly improved in 2018 when the first images reliably resolving the system became available. Since then, our group has continued working on the system. We have largely improved the determination of the radial velocity curve of the Mira component, by adding new observations and using a new method for estimating the systemic velocity of the star from the observations of SiO masers. Besides, we have obtained a third determination of the relative position of the stars. Altogether, we have been able, for the first time, to determine all seven orbital parameters independently, being the distance to the system the main source of error. The resulting orbit agrees very well with all kinds of observation of the system: previous attempts to resolve the two stars; changes in the optical variability of the Mira, etc. From the obtained parameters we have also determined the mass of the two components as a function of the distance to the system, concluding that the values derived from period-luminosity and period-diameter relationships for the Mira (265 pc) are yet the most reliable. Another important result is that the eccentricity of the system is much larger than previously assumed, e=0.57, so the distance between the stars at periastron passage (which happened at BY 2019.7) was just 6.8 AU, with the Mira component almost filling its Roche lobe. Here we present all these new results and discuss their implications on the status and evolution of the system.