The compact H$\alpha$ emitting regions of the Herbig Ae/Be stars HD 179218 and HD 141569 from CHARA spectro-interferometry

TL;DR

This study uses high-resolution spectro-interferometry to analyze the spatial extent of Hα emission in two Herbig Ae/Be stars, revealing very compact emission regions and exploring different models to explain their origins.

Contribution

It provides new interferometric measurements of Hα regions in HD 179218 and HD 141569, doubling the sample size and testing models like hot blackbody discs and magnetospheric accretion.

Findings

Hα emission regions are smaller than 0.21 and 0.12 au.

Magnetospheric accretion explains HD 179218's Hα emission.

Different scenarios are needed to explain Hα in various HAeBe stars.

Abstract

This work presents CHARA/VEGA H$\alpha$ spectro-interferometry (R ~ 6000, and $\lambda$/2B ~ 1 mas) of HD 179218 and HD 141569, doubling the sample of Herbig Ae/Be (HAeBe) stars for which this type of observations is available so far. The observed H$\alpha$ emission is spatially unresolved, indicating that the size of the H$\alpha$ emitting region is smaller than ~ 0.21 and 0.12 au for HD 179218 and HD 141529 (~ 15 and 16 R*, respectively). This is smaller than for the two other HAeBes previously observed with the same instrumentation. Two different scenarios have been explored in order to explain the compact line emitting regions. A hot, several thousand K, blackbody disc is consistent with the observations of HD 179218 and HD 141569. Magnetospheric accretion (MA) is able to reproduce the bulk of the H$\alpha$ emission shown by HD 179218, confirming previous estimates from MA shock modelling with a mass accretion rate of 10^-8 Msun/yr, and an inclination to the line of sight between 30 and 50 degr. The H$\alpha$ profile of HD 141569 cannot be fitted from MA due to the high rotational velocity of this object. Putting the CHARA sample together, a variety of scenarios is required to explain the H$\alpha$ emission in HAeBe stars -compact or extended, discs, accretion, and winds-, in agreement with previous Br$\gamma$ spectro-interferometric observations.