Detection of SiC

Ongoing Q-band (31–50 GHz) integrations on IRC +10216 with the Yebes 40m telescope have now reached the level of sub-mK noise, with hundreds of new lines arising above the 3σ detection limit. Among them is a new, harmonically related series with integer quantum numbers ranging from Jup = 26 to 40, which has allowed it to be assigned to SiC6. We clearly detected a total of nine isolated (or otherwise not critically blended) spectral features, with peak intensities around or slightly below 1 mK in the TA* scale, thanks to the extremely low noise in the spectra. Five additional lines were seen to be partially blended with lines from other species, but could still be relatively well modeled due to the uniformity of the characteristic U-shaped line profiles emerge from the envelope of IRC+10216. As a result, we built a rotation diagram for SiC6, providing a column density of ∼8 × 1011 cm−2 and a rotational temperature around 19 K. A similar analysis was done for SiC4, 29SiC4, and 30SiC4. Together, these insights offer the first view at the chemistry of linear silicon carbides in IRC+10216.