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tokens: to be around 2.5 throughout the whole envelope in good agreement with previous measures. All these conclusions lead us to think that Y CVn is a quite active star that could have developed structure in its envelope. Due to the physical mechanisms that are producing the suggested asymmetries close to the star, the high temperatures, gas densities below ~ 10 8 –10 10 cm −3 , the influence of the Galactic UV radiation field in the chemistry at different distances from the star, and its proximity, Y CVn is a good candidate to better understand the physical and chemical evolution of the envelopes of low mass-loss rate C-rich stars. Appendix A Brief description of HCN Hydrogen cyanide is a linear triatomic molecule that belongs to the C ∞ group and displays a permanent dipole moment of 2.985 D ( Ebenstein Muenter 1984 ). The vibration of its atoms can be described with the aid of four normal modes, two of which are degenerate and are combined into the bending mode ν 2 ( π ). These two degenerate normal modes involve atomic oscillations out of the molecular axis that allow the molecule to spin around it. This results in the creation of a vibrational angular momentum that splits the rotational levels in sublevels with different e − f parity ( Brown et al. 1975 ). The other two normal modes, ν 1 ( σ + ) and ν 3 ( σ + ), are stretching modes that can be essentially described as the HC–N and H–C vibrations along the molecular axis, respectively (e.g., Herzberg 1956 ). Fig. A.1 Vibrational energy diagram of HCN below 5000 K. The lines that connect the vibrational states represent the strongest allowed vibrational transitions. The transitions in blue lie around 13.5 μm, in red around 7.5 μm, and in orange at other wavelengths (3.0, 3.6, 4.8, and 8.2 μm, depending on the transition). Those plotted with ticker lines are detected in the spectra presented in the current work ( Figs. 1 and 2 ). In the current work, we adopted two different notations commonly used in Molecular Spectroscopy and Astrophysics to label a vibrational state: v 1 ν 1 + v 2 ν 2 + v 3 ν 3 ( l ± ) and , where i = 1, 2, 3. The v i is the vibrational quantum number related to the i -th normal mode, l the quantum number for the vibrational angular momentum, which can be expressed with the Greek letters σ , π , δ , φ , γ , ... for l = 0, 1, 2, 3, 4, ..., ± is the total parity of the molecule in this vibrational state (usually given only for the σ states), and p is the e − f parity. The v = 0 means the vibrational ground state (G.S.). The change of the rotational number in a transition is given by B p ( J l ) for the ro-vibrational lines, where J u and J l are the upper and lower rotational levels, respectively, B is the branch (P: Δ J = J u − J l = −1, Q: Δ J = 0, and R: Δ J = +1), and J = J u − J l for the pure rotational ones. More information about the selection rules and the line intensities of linear molecules can be found, for example, in Fonfría et al. (2008) . Figure A.1