Letter to the Editor

First detection of the HSO radical in space^⋆

¹ Observatorio Astronómico Nacional (IGN), C/ Alfonso XII 3, 28014 Madrid, Spain
e-mail: n.marcelino@oan.es
² Observatorio de Yebes (IGN), Cerro de la Palera s/n, 19141 Yebes, Guadalajara, Spain
³ Dipartimento di Chimica “Giacomo Ciamician”, Universitá di Bologna, Via F. Selmi 2, 40126 Bologna, Italy
⁴ Grupo de Astrofísica Molecular, Instituto de Física Fundamental, CSIC, C/ Serrano 123, 28006 Madrid, Spain

Received: 18 May 2023
Accepted: 5 June 2023

Abstract

We report the discovery of HSO towards several cold dark clouds. The detection is confirmed by the observation of the fine and hyperfine components of two rotational transitions in the protostellar core B1-b, using the Yebes 40 m and IRAM 30 m telescopes. Furthermore, all the fine and hyperfine components of its fundamental transition 1_0, 1 − 0_0, 0 at 39 GHz were also detected toward the cyanopolyyne peak of TMC-1. The measured frequencies were used to improve the molecular constants and predict more accurate line frequencies. We also detected the strongest hyperfine component of the 1_0, 1 − 0_0, 0 transition of HSO toward the cold dark clouds L183, L483, L1495B, L1527, and Lupus-1A. The HSO column densities were obtained using LTE models that reproduce the observed spectra. The rotational temperature was constrained to 4.5 K in B1-b and TMC-1 using the available Yebes 40 m and IRAM 30 m data. The obtained column densities range between 7.0×10¹⁰ cm⁻² and 2.9×10¹¹ cm⁻², resulting in abundances in the range of (1.4–7.0) × 10⁻¹² relative to H₂. Our observations show that HSO is widespread in cold dense cores. However, more observations, together with a detailed comparison with other S-bearing species, are needed to constrain the chemical production mechanisms of HSO, which are not considered in current models.