Wind mass transfer in S-type symbiotic binaries

Abstract

Context. The structure of the wind from the cool giants in symbiotic binaries carries important information for understanding the wind mass transfer to their white dwarf companions, its fuelling, and thus the path towards different phases of symbiotic-star evolution. Aims. In this paper, we indicate a non-spherical distribution of the neutral wind zone around the red giant (RG) in the symbiotic binary star, EG And. We concentrate in particular on the wind focusing towards the orbital plane and its asymmetry alongside the orbital motion of the RG. Methods. We achieved this aim by analysing the periodic orbital variations of fluxes and radial velocities of individual components of the Hα and [O III] λ5007 lines observed on our high-cadence medium (R ∼ 11 000) and high-resolution (R ∼ 38 000) spectra. Results. The asymmetric shaping of the neutral wind zone at the near-orbital-plane region is indicated by: (i) the asymmetric course of the Hα core emission fluxes along the orbit; (ii) the presence of their secondary maximum around the orbital phase φ = 0.1, which is possibly caused by the refraction effect; and (iii) the properties of the Hα broad wing emission originating by Raman scattering on H0 atoms. The wind is substantially compressed from polar directions to the orbital plane as constrained by the location of the [O III] λ5007 line emission zones in the vicinity of the RG at/around its poles. The corresponding mass-loss rate from the polar regions of ≲10−8 M⊙ yr−1 is a factor of ≳10 lower than the average rate of ≈10−7 M⊙ yr−1 derived from nebular emission of the ionised wind from the RG. Furthermore, it is two orders of magnitude lower than that measured in the near-orbital-plane region from Rayleigh scattering. Conclusions. The startling properties of the nebular [O III] λ5007 line in EG And provides an independent indication of the wind focusing towards the orbital plane – the key to understanding the efficient wind mass transfer in symbiotic binary stars.

THA 15-31: Discovery with VLT/X-Shooter and Swift/UVOT of a new symbiotic star of the accreting-only variety

“…The latter results in a strong density enhancement on the orbital plane at the expense of the polar directions: the higher density favors a higher accretion by the companion compared to the case of an unfocussed, spherically symmetric wind outflowing from the RG. The presence of a strong density enhancement on the equatorial plane of SySts is expected theoretically (Mohamed & Podsiadlowski 2007, Booth et al 2016, and was confirmed by the marked bipolar shape observed for the spatially resolved nova ejecta of RS Oph (Ribeiro et al 2009) and V407 Cyg (Giroletti et al 2020), and inferred by modeling of line profiles in high-inclination systems like EG And by Shagatova et al (2016Shagatova et al ( , 2021.…”

Photometry and spectroscopy of the new symbiotic star 2SXPS J173508.4-292958

“…One thing about the narrow absorption seems however well established: its velocity is positive with respect to the K4III giant, so it seems unlikely it may form in the gentle wind out-flowing from it and engulfing the whole binary system. A typical shift ∆vel ≈−10/−20 km s −1 is generally observed in symbiotic stars for the narrow absorption superimposed to the Hα emission, matching the typical wind velocity of field cool giants (Munari et al 2020b, Shagatova et al 2020. This leaves open the possibility that the narrow absorption component seen in 2SXPS may form elsewhere in the binary system (as the accretion disk itself or an atmosphere engulfing it), or in alternative its appearance is spurious and the Hα profile is actually composed by two separate emission components.…”

SRGA J181414.6-225604: A New Galactic Symbiotic X-Ray Binary Outburst Triggered by an Intense Mass-loss Episode of a Heavily Obscured Mira Variable

“…Assuming that a fraction ò of the rest-mass energy of this material is emitted by the compact object during the X-ray flare peak (L X ≈ 2.5 × 10 36 erg s −1 ), we estimate ò ≈ 0.3, similar to the expected conversion efficiency for accretion onto an NS (ò ∼ 0.2). A lower conversion efficiency would be required if the ejected dust shell were focused by the Roche potential into the plane of the binary system (Shagatova et al 2021). If we assume that the wind velocity prior to dust formation was close to that estimated by DUSTY prior to the onset of dust formation (E1; 2010-11) for a steady-state wind (Table 9), the ≈4× lower mass-loss rate would both reduce the mass-transfer rate onto the NS as well as reduce the accretion efficiency, due to the larger magnetospheric radius at low accretion rates (Kuranov et al 2015).…”