Modelling of dust around the symbiotic Mira RR Telescopii during obscuration epochs

Abstract

Context. Symbiotic Miras represent a class of peculiar binaries whose nature is still not well understood. Physical properties of the circumstellar dust and associated physical mechanisms play an important role in understanding the evolution of symbiotic binaries and the interaction between their components. We present a model of inner dust regions around the cool Mira component of the symbiotic nova RR Tel based on the near-IR terrestrial photometry and infrared ISO spectra. Aims. Our goal is to find a comprehensive and consistent model of the circumstellar inner dust regions around the Mira component that can explain the observed photometric and spectroscopic features in the near-and mid-infrared. Methods. Available JHKL photometric observations from South African Astronomical Observatory were collected and corrected for Mira pulsations as well as for interstellar reddening to follow temporal changes of the near-infrared colours. Spectral energy distributions (SEDs) from 1 to 13 μm during obscuration epoch were reconstructed with the simultaneously available ISO/SWS spectra and JHKL magnitudes. The dust properties were determined by modelling both the reconstructed SEDs and the near-IR colours using the DUSTY numerical code. This 1D code solves radiative transfer through the circumstellar dust by calculating the dust temperature profile assuming spherical symmetry. Results. The Mira pulsation period of 387 days was found and confirmed with two independent fitting methods. A long-term variation of ∼7000 days, which cannot be attributed to orbital motion, was obtained from the analysis of the near-IR magnitudes. Reconstructed infrared SEDs were modelled successfully by a single dust shell with dust distribution enhanced by radiatively driven stellar winds. Mira temperature, dust sublimation temperature, grain diameter, density distribution, and optical depth have been obtained. Our model shows a maximum dust grain diameter of 4 μm, which is larger than expected and can be explained by grain growth in conditions of increased mass loss during obscuration epochs. Obscurations in the near-IR can be understood as a result of change of the dust optical depth and of the mass loss rate of Mira component. Change of the dust temperature on the inner boundary of the dust shell with pulsation phase have been identified by SED modelling. Assuming a gas-to-dust ratio of 200, we found a variable mass loss rate between 2.3 and 9.0 × 10 −6 M /yr and estimated the distance to RR Tel to be 2.7 kpc. Our results suggest a relatively low influence of the hot component on circumstellar dust and strong shielding of dust from the UV flux.

A census of symbiotic stars in the 2MASS, WISE and Gaia surveys

“…RR Tel is a special case for which two BBs are required in order to fit the SED, and our dust temperature estimate agrees with the previous work from Jurkic & Kotnik-Karuza (2012). Moreover, the upper limit of the W2 magnitude makes this SySt quite more uncertain.…”

“…For instance, RR Tel is a known and well-studied variable SySt with maximum amplitudes up to 3.47 mag in J, 2.84 mag in H, 2.05 mag in K and 1.29 mag in L magnitudes (Gromadzki et al 2009). Nevertheless, our T dust =1258 K agrees with the temperature derived from a more detailed SED study between 1200 and 1350 K (Jurkic & Kotnik-Karuza 2012). The S-type SySt CH Cyg is another example for which our T eff =3063 K agrees with the value reported by Hinkle, Fekel & Joyce (2009).…”

“…Multi-epoch photometric studies have been carried out either in the optical wavelengths or the near-infrared regime(e.g. Lorenzetti et al 1985;Henden & Munari 2000Gromadzki et al 2009Gromadzki et al , 2013Jurkic & Kotnik-Karuza 2012). All of these studies have shown that flux variations can have a maximum amplitude up to 6-7 mag in the optical regime but significantly smaller at longer wavelengths.…”

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

“…The shallower optical-NIR extinction law uniquely constrains the grain size distribution, requiring it to extend to a larger size of a max ≈ 2.0 μm. Such large grain sizes were also inferred in DUSTY modeling of the sudden obscuration episodes of the symbiotic Mira RR Tel (Jurkic & Kotnik-Karuza 2012). The rising flux in the MIR up to the W2 band requires the dust to be cooler (≈750 K) than at earlier epochs, and located farther away from the star, at ≈40 au.…”

Raman-scattered O vi Features in the Symbiotic Nova RR Telescopii

“…The variation of the Raman O VI profiles implies that the density distribution of the accretion disk has been more asymmetric in the last two decades. The increasing asymmetry of the matter distribution could be related to the dust obscuration episode that occurred between 1996 and 2000, which is associated with the enhancement of the mass-loss rate (Kotnik-Karuza et al 2006;Jurkic & Kotnik-Karuza 2012).…”