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Register a new userSPHERE / ZIMPOL observations of the symbiotic system R Aqr. I. Imaging of the stellar binary and the innermost jet clouds
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R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We determine from the Halpha emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region (<2) of R Aqr and determine Halpha emissivities mean density, mass, recombination time scale, and other cloud parameters. Our data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 46+/-1 mas West of the mira. The central jet source is the strongest Halpha component. North east and south west from the central source there are many clouds with very diverse structures. We see in the SW a string of bright clouds arranged in a zig-zag pattern and, further out, more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure and faint perpendicular wisps further out. Some jet clouds are also detected in the ZIMPOL [OI] and He I filters, as well as in the HST line filters for Halpha, [OIII], [NII], and [OI]. We determine jet cloud parameters and find a very well defined anti-correlation between cloud density and distance to the central binary. Future Halpha observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion.
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We have observed the symbiotic stellar system R Aqr, aiming to describe the gravitational interaction between the white dwarf (WD) and the wind from the Mira star, the key phenomenon driving the symbiotic activity and the formation of nebulae in such systems. We present high-resolution ALMA maps of the 12CO and 13CO J=3-2 lines, the 0.9 mm continuum distribution, and some high-excitation molecular lines in R Aqr. The maps, which have resolutions ranging between 40 milliarcsecond (mas) and less than 20 mas, probe the circumstellar regions at suborbital scales as the distance between the stars is ~ 40 mas. Our observations show the gravitational effects of the secondary on the stellar wind. The AGB star was identified in our maps from the continuum and molecular line data, and we estimated the probable position of the secondary from a new estimation of the orbital parameters. The (preliminary) comparison of our maps with theoretical predictions is surprisingly satisfactory and the main expected gravitational effects are directly mapped for the first time. We find a strong focusing in the equatorial plane of the resulting wind, which shows two plumes in opposite directions that have different velocities and very probably correspond to the expected double spiral due to the interaction. Our continuum maps show the very inner regions of the nascent bipolar jets, at scales of some AU. Continuum maps obtained with the highest resolution show the presence of a clump that very probably corresponds to the emission of the ionized surroundings of the WD and of a bridge of material joining both stars, which is likely material flowing from the AGB primary to the accretion disk around the WD secondary.
We investigate the structure, dynamics, and chemistry of the molecule-rich nebula around the stellar symbiotic system R Aqr, which is significantly affected by the presence of a white dwarf (WD) companion. We study the effects of the strong dynamical interaction between the AGB wind and the WD and of photodissociation by the WD UV radiation on the circumstellar shells. We obtained high-quality ALMA maps of the 12CO J=2-1, J=3-2, and J=6-5 lines and of 13CO J=3-2. The maps were analyzed by means of a heuristic 3D model that is able to reproduce the observations. In order to interpret this description of the molecule-rich nebula, we performed sophisticated calculations of hydrodynamical interaction and photoinduced chemistry. We find that the CO-emitting gas is distributed within a relatively small region <~ 1.5. Its structure consists of a central dense component plus strongly disrupted outer regions, which seem to be parts of spiral arms that are highly focused on the orbital plane. The structure and dynamics of these spiral arms are compatible with our hydrodynamical calculations. We argue that the observed nebula is the result of the dynamical interaction between the wind and the gravitational attraction of the WD. We also find that UV emission from the hot companion efficiently photodissociates molecules except in the densest and best-shielded regions, that is, in the close surroundings of the AGB star and some shreds of the spiral arms from which the detected lines come. We can offer a faithful description of the distribution of nebular gas in this prototypical source, which will be a useful template for studying material around other tight binary systems.
We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study the photosphere, the warm molecular layer, and the inner wind of the close-by oxygen-rich AGB star R Doradus. We present observations in filters V, cntH$alpha$, and cnt820 and investigate the surface brightness distribution of the star and of the polarised light produced in the inner envelope. Thanks to second-epoch observations in cntH$alpha$, we are able to see variability on the stellar photosphere. We find that in the first epoch the surface brightness of R Dor is asymmetric in V and cntH$alpha$, the filters where molecular opacity is stronger, while in cnt820 the surface brightness is closer to being axisymmetric. The second-epoch observations in cntH$alpha$ show that the morphology of R Dor changes completely in a timespan of 48 days to a more axisymmetric and compact configuration. The polarised intensity is asymmetric in all epochs and varies by between a factor of 2.3 and 3.7 with azimuth for the different images. We fit the radial profile of the polarised intensity using a spherically symmetric model and a parametric description of the dust density profile, $rho(r)=rho_circ r^{-n}$. On average, we find exponents of $- 4.5 pm 0.5$ that correspond to a much steeper density profile than that of a wind expanding at constant velocity. The dust densities we derive imply an upper limit for the dust-to-gas ratio of $sim 2times10^{-4}$ at 5.0 $R_star$. Given the uncertainties in observations and models, this value is consistent with the minimum values required by wind-driving models for the onset of a wind, of $sim 3.3times10^{-4}$. However, if the steep density profile we find extends to larger distances from the star, the dust-to-gas ratio will quickly become too small for the wind of R Dor to be driven by the grains that produce the scattered light.
Two Chandra observations of the R Aqr symbiotic binary system taken 3.3 years apart show dramatic changes in the X-ray morphology and spectral characteristics in the inner 500 AU of this system. The morphology of the soft X-ray emission has evolved from a nearly circular region centered on the binary system to an hourglass shape that indicates the formation of a new southwest jet. Synchrotron radiation from the new jet in contemporaneous VLA radio spectra implies the physical conditions in the early stages of jet development are different from those in the more extended outer thermal jets known to exist for decades in this system. The central binary source has two X-ray spectral components in each of the two epochs, a soft component and a highly absorbed hard component characterized by T ~ 10^8 K if fit with a thermal plasma model. The spectrum hardened considerably between 2000.7 and 2004.0, primarily due to increased flux above 5 keV, suggesting a change in the accretion activity of the white dwarf on a timescale of a few years or less. Point-source Fe K emission is detected at the position of the central binary system in both observations. While the earlier observation shows evidence of only a single emission peak near Fe K alpha at 6.4 keV, the later observation shows a more complex emission structure between 6 and 7 keV. Finally, we have discovered a modulation in the hard X-ray flux with a period of 1734 s at a 95% confidence level in the 2004 observation only. The modulation potentially arises from standing shocks in an accretion column and we have explored the possibility that the white dwarf in R Aqr is analogous to the magnetic white dwarfs in Intermediate Polar.
In this proceeding, we present a short review of the fascinating nebulosities of symbiotic binary R Aquarii. The R Aquarii system, comprising the central binary and surrounding nebular material, has been the subject of near-continuous study since its discovery, with a few hundred papers listed in ADS. As such, it is impossible to provide here the comprehensive review that R Aquarii deserves, instead we chose to focus on the nebulosities -- covering both our own research and other relevant results from the literature.
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