SPECTRAL AND PHOTOMETRICAL PECULIARITIES OF THE UNUSUAL HERBIG AE STAR HD 179218
Abstract and keywords
Abstract (English):
We present the results of the spectroscopic monitoring of the Herbig Ae star HD 179218 carried out at the Shamakha Astronomical Observatory from 2015 to 2021 and the $UBVRI$ photometry at the Crimean Astronomical Observatory, covering the period 2007–2021. This object has a unique orientation of its rotation axis close to ``pole-on". The H$\beta$ line profiles are a single emission profile overlapped by blue and red absorption features living about several days. The 17 dates of 77 the H$\beta$ and the He I $\lambda$5876 line profiles demonstrated the inverse P Cyg-type profile with the variable velocity of the red edge of the absorption component up to 400 km/s. The period of the variations $P = 1.341 \pm 0.002$ days determined by Lafler–Kinman method is in accordance with the expected rotation period of the star. This observational fact can be a signature of the magnetospheric character of accretion in HD 179218. The inclination angle of the rotation axis is estimated as $i = 23^{\circ} \pm 3^{\circ}$. The observed phenomena can be connected with a specificity of stellar magnetism of HD 179218. Additionally, it has been shown that equivalent widths of the H$\alpha$ and H$\beta$ lines as well as the photometric $UBVRI$ parameters of HD 179218 demonstrate cyclic variability with several periods falling in the range from 19 days to 737 days. A possible interpretation of these phenomena can be a result of presence near HD 179218 of a low-mass binary component or exoplanets. A sudden drop of circumstellar extinction took place in October of 2011, possible interpretations of this phenomenon are considered.

Keywords:
stars: variables: Herbig Ae/Be, circumstellar matter; accretion; individual: HD 179218
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