A Model of the Dust Envelope of the Carbon Mira Star V CrB from Photometry, Infrared Spectroscopy, and Speckle Polarimet
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del of the Dust Envelope of the Carbon Mira Star V CrB from Photometry, Infrared Spectroscopy, and Speckle Polarimetry A. A. Fedoteva1, 2* , A. M. Tatarnikov2 , B. S. Safonov2 , V. I. Shenavrin2 , and G. V. Komissarova2 1
2
Faculty of Physics, Moscow State University, Moscow, 119991 Russia Sternberg Astronomical Institute, Moscow State University, Universitetskii pr. 13, Moscow, 119992 Russia Received October 18, 2019; revised November 21, 2019; accepted December 5, 2019
Abstract—U BV JHKLM photometry for the carbon Mira star V CrB are presented. The infrared observations were carried out in the time interval 1989–2018, while the U , B, and V data were obtained in 2001–2014. The light and color curves are analyzed. The pulsation period of V CrB has been found to be 355d.2 in the infrared JHKLM bands and 352d for the optical BV band. In the JHK bands, apart from periodic pulsations, there are distinct sinusoidal variations in the average brightness level with a characteristic period of ∼8300 days. Color–magnitude relationships have been revealed for the infrared and optical bands. The phase curves exhibit the wavelength dependence of the brightness variability amplitude. The light curves for various bands and colors are discussed. We have constructed the model of a spherically symmetric circumstellar dust envelope that allows the observed spectral energy distribution at both maximum and minimum light to be reproduced equally well (within the model assumptions) and is consistent with the observations of V CrB by differential speckle polarimetry. The model is characterized by the following parameters: the optical depth is τK = 0.33, the inner and outer radii of the envelope are 8 and 40 000 AU, respectively. The envelope contains spherical carbon dust grains (3/4 by mass) and silicon carbide dust grains. Dust grains with a radius of 0.5 μm account for 90% of the envelope mass. The remaining 10% of the mass is accounted for by finer dust with a grain radius of 0.1 μm. Based on the observational data, we have estimated the bolometric flux from V CrB: 2.6 × 10−7 and 5.1 × 10−7 erg cm−2 s−1 at minimum and maximum light, respectively. The effective temperature of the star is Tmax = 3000 K at maximum light and Tmin = 2400 K at minimum light. DOI: 10.1134/S1063773720010016 Keywords: carbon stars, AGB stars, speckle interferometry, polarimetry, dust envelopes.
1. INTRODUCTION
mean J−H, K−L, and L−M colors and the J light and J−H, K−L, and L−M color curves over 1998– 2003, corresponding to approximately five pulsation periods. The infrared light curves over 3.5 periods are also presented in Price et al. (2010). In this paper the pulsation periods were estimated in the 1.25, 2.2, 3.5, and 4.8 μm bands to be from 350 to 391 days. Besides, the authors point to the presence of a noticeable (∼1/6 of the period) phase lag between the optical and infrared light curves.
The star V CrB is a long-period Mira Ceti-type variable, a Mira star. The stars of this type are in the upper part of the asymptotic giant branch (AGB stars) on the Her
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