Origin of the ionized wind in MWC 349A

TL;DR

This study uses high-resolution spectral observations and modeling to pinpoint the origin of the ionized wind in MWC 349A, revealing it is launched from about 24 AU from the star, supporting magnetohydrodynamic wind theories.

Contribution

It provides the first detection of spectral features from the wind launching region and estimates its radius using Herschel observations and advanced radiative transfer modeling.

Findings

Wind ejected at approximately 24 AU from the star

Detection of new blueshifted spectral components

Supports magnetohydrodynamic wind models

Abstract

The UC-HII region of MWC 349A is the prototype of an ionized wind driven by a massive star surrounded by a disk. Recent high angular resolution observations of the millimeter recombination lines have shown that the disk rotates with a Keplerian law in its outer parts. However, the kinematics of innermost regions in the UC-HII region of MWC 349A is still unknown, in particular the radius where the wind is launched from the disk. We performed hydrogen recombination line observations with the Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory to study the kinematics of its innermost regions by studying their spectral features. In addition to the two laser peaks, we report the first detection of two new components that are blueshifted with respect to the laser peaks for all the recombination lines with principal quantum number n<22. These new spectral features originate from the region where the wind is ejected from the disk. We used our 3D non-LTE radiative transfer model for recombination lines (MORELI) to show that these features are consistent with the wind being ejected at a radius of about 24 AU from the star, which supports magnetohydrodynamic wind models.