Spectral features of the gaseous envelope of the Ae/Be Herbig Star HD 37806

Abstract

We analyze spectra of the Herbig Ae/Be star HD 37806 obtained from 2009 to 2019 in the region of the Hα, Hβ, He i λ 5876, Fe ii λ 4923, and DNa i lines. Observations were carried out at two observatories: Crimean Astrophysical Observatory and OAN SPM (Mexico). Over 11 years we obtained 280 high-resolution spectra during 48 observational nights. From the whole variety of observed spectral variability, in this report we will focus on its three types:

1. Changes in the ratio of the maximum intensity of the violet (V) and red (R) emission peaks of the Hα profile on the time scale months—years. An interpretation of this variability is proposed within a model of changes in the latitudinal wind distribution on both sides of the equatorial accretion disk.

2. Appearance of local absorption features on the violet emission component of the H_α line profile, shifting toward zero radial velocity with a characteristic time of a day. It is shown that such variability can be explained within the frame of a kinematic model of an outflowing stream rotating in the wind zone. We estimated the distance at which such a stream should cross the line of sight on various dates. They are in good agreement with the disk wind model in a region far from the star, where the outflow of matter forms in the decelerating disk wind.

3. Observation on certain dates of the so-called accretion episodes, when red absorption components appeared on the profiles of the H_β, He i λ 5876 and Fe ii λ 4923 lines, which are characteristic of accretion flows with velocities reaching 300—400 km/s. The duration of such episodes was several days, which exceeds the expected period of rotation of the star together with its hypothetical magnetosphere (about 1.5 days) and rules out rotational profile modulation as a possible cause of their changes. It is concluded that the observed phenomenon may be associated with local short-term changes of the accretion rate in the disk.