Detection of SiC 6 in IRC +10216 through Q -band lines

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 3 σ detection limit. Among them is a new, harmonically related series with integer quantum numbers ranging from J up = 26 to 40, which has allowed it to be assigned to SiC 6 . 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 T A * 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 SiC 6 , providing a column density of ∼8 × 10 11 cm −2 and a rotational temperature around 19 K. A similar analysis was done for SiC 4 , 29 SiC 4 , and 30 SiC 4 . Together, these insights offer the first view at the chemistry of linear silicon carbides in IRC+10216.