Spectral and photometrical peculiarities of the unusual Herbig Ae star HD 179218

Le résumé fourni par la source

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.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.