Disk in the circumstellar envelope of carbon Mira V Cygni

Abstract

AGB stars are the primary source of dust and complex molecules in the interstellar medium. The determination of outflow parameters is often hindered by the unknown geometry of the circumstellar environment, creating a demand for high-angular resolution observations. We use our NIR spectra and photometry of the carbon AGB star V Cyg, along with literature data, to construct its SED over a wide range of wavelengths. The dust envelope responsible for the IR excess was also resolved in scattered polarized light at angular scales of 50-80 mas using differential speckle polarimetry. We present an interpretation of the thermal and scattered radiation of the dust using models of a spherical dusty outflow (Mdust = 5.3e-7 M_sun) and an inclined equatorial density enhancement, either in the form of a disk (Mdust = 7.6e-3 M_earth) or a torus (Mdust = 5.7e-3 M_earth), which material is concentrated at stellocentric distances less than 25 AU. The dust material consists of amorphous carbon and SiC, with 84% of the dust being amorphous carbon. Dust particle radii range from 5 to 950 nm and follow a power law with an exponent of -3.5. Modeling of the envelope allowed us to improve the accuracy of stellar luminosity estimations: 21000 L_sun and 8300 L_sun at maximum and minimum brightness, respectively. The relation between the disk and the high water content in the envelope is also discussed.