Newborn jet in the symbiotic system R Aquarii

Abstract

R Aquarii (R Aqr) is a well-known symbiotic binary that has attracted renewed interest during its recent periastron passage, an event that occurs only once every about 40 years. This passage marks the first to be observed with modern, state-of-the-art instruments. We investigate the inner, sub-arcsecond active region of R Aqr during this recent periastron passage, with the goal of gaining insight into the jet-launching mechanisms at work in this system. We analyse Ha speckle interferometric images obtained one month apart using Fourier techniques. These are complemented by high-resolution optical spectra in the same emission line. Our speckle imaging reveals a newborn two-sided jet orientated in the north-south direction. Its proper motion, 66 +- 19 mas per year, confirms that it was launched around 2020 Jan 7, at the onset of the periastron passage. Further analysis of the elongated central structure reveals a knot in the southern counterpart of the jet, moving away from the binary with a 27 +- 17 mas per year at a position angle of 187 degrees, and an ejection time around 2019 Oct 28. This interpretation is further supported by our high-resolution spectroscopic data. In addition, we update the expansion parallax distance of R Aqr to 260 pc.

Figures (6)

• Figure 1: Light curve of R Aqr. Black lines mark Zorro observations, blue and red lines indicate the ejection of the newborn jet and the knot, respectively. Shaded regions indicate uncertainties.
• Figure 2: Left: Zorro H$\alpha$ image with identified features marked. Right: Zoom in to the central area with contours added. Dashed line shows the PA 186.9$^{\circ}$. The origin of the axes represents the geometric centre of R Aqr. Contours are drawn at relative flux levels $F=0.03\times2^{n}$, where n=0,1,2,3,4. North is up, east is left.
• Figure 3: Profile cuts along the major (red) and minor (blue) axes of the central elongated area for both Zorro dates. Profile cuts are centred at the Gaussian fit and flux normalized.
• Figure 4: Latest orbital solution of R Aqr. Small black dots trace the WD orbit around the Mira variable (gray circle) in 0.1-phase steps, with corresponding dates in black. Zorro observing epochs (2020.82 and 2020.91) are marked by yellow hexagons. The green segment marks the recent periastron passage (2018.9–2023.3); the blue dot indicates the time of two-sided jet, and the red one time of the knot ejection. The two-sided jet is schematically drawn in blue. The black star marks the system’s geometric centre, and black circles show the knot positions at two epochs, Oct 31 and Nov 27, respectively. North is up, east is left.
• Figure 5: H$\alpha$ line profiles of the Asiago spectra. Zero point represents the average systemic velocity of R Aqr, $-24.9$ ^-1 km s$^{-1}$.