Letter to the Editor

Abundant HD in the pre–stellar core L1544

¹ Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: caselli@arcetri.astro.it
² Max–Planck–Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: vdtak@mpifr-bonn.mpg.de
³ Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex, France e-mail: cecilia.ceccarelli@obs.ujf-grenoble.fr
⁴ European Southern Observatory, Karl–Schwarzschild–Str. 2, 85748 Garching bei München, Germany e-mail: abacmann@eso.org

Corresponding author: P. Caselli, caselli@arcetri.astro.it

Received: 19 February 2003
Accepted: 5 April 2003

Abstract

We have detected the 372 GHz line of ortho– towards the pre–stellar core L1544. The strongest emission (1 K) occurs at the peak of the millimeter continuum emission, while measurements at offset positions indicate that  is confined within ~20´´, where CO is highly depleted. The derived abundance of ~10^-9 is comparable with previous estimates of the electron abundance in the core, which suggests that  is the main molecular ion in the central 20´´ (2800 AU) of L1544. This confirms the expectations that  is dramatically enhanced in gas depleted of molecules other than . The measured abundance even exceeds the present model predictions by about a factor ten. One possibility is that all CNO–bearing neutral species, including atomic oxygen, are almost completely (98%) frozen within a radius of ~2800 AU.