Abundance of HOCO⁺ and CO₂ in the outer layers of the L1544 prestellar core

¹ Université de Toulouse, UPS-OMP, IRAP, 31013 Toulouse, France
e-mail: charlotte.vastel@irap.omp.eu
² CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
³ Université de Grenoble Alpes, IPAG, 38000 Grenoble, France
⁴ CNRS, IPAG, 38000 Grenoble, France
⁵ Observatorio Astronómico Nacional (OAN, IGN), Calle Alfonso XII, 3, 28014 Madrid, Spain

Received: 3 March 2016
Accepted: 18 May 2016

Abstract

The L1544 prestellar core has been observed as part of the ASAI IRAM Large Program at 3 mm. These observations led to the detection of many complex molecules. In this Letter, we report the detection of two lines, at 85.5 GHz (4_0,4–3_0,3) and 106.9 GHz (5_0,5–4_0,4), respectively, of the protonated carbon dioxide ion, HOCO⁺. We also report the tentative detection of the line at 100.4 GHz (5_0,5–4_0,4) of DOCO⁺. The non-LTE analysis of the detected lines shows that the HOCO⁺ emission originates in the external layer where non-thermal desorption of other species has previously been observed. Its abundance is (5 ± 2) × 10^-11. Modelling of the chemistry involved in the formation and destruction of HOCO⁺ provides a gaseous CO₂ abundance of 2 × 10^-7 (with respect to H₂) with an upper limit of 2 × 10^-6.