Submillimeter narrow emission lines from the inner envelope of IRC+10216

TL;DR

This study presents a spectral-line survey of IRC+10216 revealing narrow molecular emission lines within 60 AU of the star, providing insights into the dust-formation region and stellar wind acceleration.

Contribution

It reports the detection and mapping of narrow vibrationally excited molecular lines close to the star, highlighting a region of dust formation and wind acceleration.

Findings

Narrow lines indicate expansion velocities of ~4 km/s.

Emission confined within ~60 AU of the star.

Detection of vibrationally excited molecular lines.

Abstract

A spectral-line survey of IRC+10216 in the 345 GHz band has been undertaken with the Submillimeter Array. Although not yet completed, it has already yielded a fairly large sample of narrow molecular emission lines with line-widths indicating expansion velocities of ~4 km/s, less than 3 times the well-known value of the terminal expansion velocity (14.5 km/s) of the outer envelope. Five of these narrow lines have now been identified as rotational transitions in vibrationally excited states of previously detected molecules: the v=1, J=17--16 and J=19--18 lines of Si34S and 29SiS and the v=2, J=7--6 line of CS. Maps of these lines show that the emission is confined to a region within ~60 AU of the star, indicating that the narrow-line emission is probing the region of dust-formation where the stellar wind is still being accelerated.