---
author:
- 'M. Agúndez, J. Cernicharo, G. Quintana-Lacaci, A. Castro-Carrizo, L. Velilla Prieto, N. Marcelino, M. Guélin, C. Joblin, J. A. Martín-Gago, C. A. Gottlieb, N. A. Patel, and M. C. McCarthy'
date: 'Received; accepted'
title: 'The growth of carbon chains in IRC+10216 mapped with ALMA[^1]'
---

[Linear carbon chains are common in various types of astronomical molecular sources. Possible formation mechanisms involve both bottom-up and top-down routes. We have carried out a combined observational and modeling study of the formation of carbon chains in the C-star envelope IRC+10216, where the polymerization of acetylene and hydrogen cyanide induced by ultraviolet photons can drive the formation of linear carbon chains of increasing length. We have used ALMA to map the emission of $\lambda$ 3 mm rotational lines of the hydrocarbon radicals C$_2$H, C$_4$H, and C$_6$H, and the CN-containing species CN, C$_3$N, HC$_3$N, and HC$_5$N with an angular resolution of $\sim$1$''$. The spatial distribution of all these species is a hollow, 5-10$''$ wide, spherical shell located at a radius of 10-20$''$ from the star, with no appreciable emission close to the star. Our observations resolve the broad shell of carbon chains into thinner sub-shells which are 1-2$''$ wide and not fully 