Probing the IRC +10° 216 Circumstellar Envelope Using Spectroscopic Observations of Background Stars

Abstract

A unique and novel set of observations has been undertaken to study the circumstellar envelope (CSE) of the nearby (130pc) carbon star IRC +10° 216 using optical absorption spectroscopy towards two background stars lying beyond the envelope. The primary aim of the observations is to search for diffuse band (DIB) carriers in the CSE. The circumstellar H+2H₂ column density expected along the line of sight towards the targets is large compared to that derived from the small interstellar reddening in this region, E _B–V < 0.03 mag. We summarise our main findings, already reported in (2002): The 6284 Å DIB is detected in the VLT/UVES spectrum of one target, but clearly arises in the foreground ISM. No other DIB is seen. Hence the DIB carriers, if present in the CSE, have a low abundance relative to H in the C-rich envelope of IRC +10° 216, in comparison with this ratio in the ISM. An important new result, previously unreported, concerns the detection of circumstellar C ₂ via absorption of the Phillips band near 8760Å.

Based on observations made with the ESO-VLT, WHT, and OHP 1.2 m telescopes.