On the Brγ line emission of the Herbig Ae/Be star MWC 120

Abstract

The origin of the Br γ line in Herbig Ae/Be stars is still an open question. It has been proposed that a fraction of the 2.166 µm Br γ emission might emerge from a disc wind, the magnetosphere, and other regions. Investigations of the Br γ line in young stellar objects are important to improve our understanding of the accretion-ejection process. Near-infrared long-baseline interferometry enables the investigation of the Br γ line emitting region with high spatial and high spectral resolution. We observed the Herbig Ae/Be star MWC 120 with the VLTI/AMBER instrument in different spectral channels across the Br γ line with a spectral resolution of R ∼ 1500. Comparison of the visibilities, differential, and closure phases in the continuum and the line-emitting region with geometric and radiative transfer disc-wind models lead to constraints on the origin and dynamics of the gas emitting the Br γ light. Geometric modelling of the visibilities reveals a line emission region about two times smaller than the K-band continuum region, which indicates a scenario where the Br γ emission is dominated by an extended disc wind rather than by a much more compact magnetospheric origin. To compare our data to a physical model, we applied a state-of-the-art radiative transfer disc-wind model. We find that all measured visibilities, differential and closure phases of MWC 120 can approximately be reproduced by a disc-wind model. A comparison with other Herbig stars indicates a correlation of the modelled inner disc-wind radii with the corresponding Alfvén radii for late spectral type stars.

Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

“…The base of disk winds is another potential source of Brγ emission but it would have to originate here within 5 R from the central object. Moreover, rotating disk winds and bipolar outflows alike, yield an S-shape signature in the spectrally dispersed differential interferometric phases across the line profile (e.g., Weigelt et al 2011;Kreplin et al 2018), which is not seen here (see Fig. 2).…”

The accretion rates and mechanisms of Herbig Ae/Be stars

“…find the line emission region consistent with a rotating disk. Similarly,Tambovtseva et al (2016) andKreplin et al (2018) find the diskwind a more likely explanation for the emitting region than the compact accretion channels. Even higher resolution Hα CHARA data discussed byMendigutía et al (2017) present a similar diversity.…”

First NIR interferometrically resolved high-order Brackett and forbidden Fe lines of a B[e] star: V921 Sco

“…Better S/R data and sophisticated radiative transfer modelling is required in order to determine whether the high order Brackett lines originate from a Keplerian disk or a disk wind (Tambovtseva et al, submitted;Kreplin et al 2018;Tambovtseva et al 2017). This is the first interferometric study in H-band emission lines and shows the great potential of interferometric H-band observations at a decent spectral resolution.…”

“…The model was constructed using our own developed modelling suite for interferometric data incorporating different fitting algorithms (Newville et al 2014) as used in former projects (e.g. Kreplin et al 2016Kreplin et al , 2018. The position of the companion was fitted using a Monte-Carlo Markov Chain algorithm (emcee) to a separation SEP=23.5 ± 0.1mas (corresponding to a projected separation on the sky of ∼26au at a distance of 1150pc) and a position angle PA=320.3 ± 0.3 • The best fit can approximately reproduce not only the visibilities but also the closure phase of the LR AMBER data (see Fig.…”

“…For interpretation of the individual spectral lines we employ a geometric modelling approach for young stellar objects (YSOs) used in earlier studies (e.g. Kreplin et al 2018).…”