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Issue A&A
Volume 403, Number 3, June I 2003
Page(s) L37 - L41
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20030526



A&A 403, L37-L41 (2003)
DOI: 10.1051/0004-6361:20030526

Letter

Abundant H $\mathsf{_{2}}$D $\mathsf{^{+}}$ in the pre-stellar core L1544

P. Caselli1, F. F. S. van der Tak2, C. Ceccarelli3 and A. Bacmann4

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

(Received 19 February 2003 / Accepted 5 April 2003)

Abstract
We have detected the 372 GHz line of ortho- ${\rm H}_{2}{\rm D}^{+}$ towards the pre-stellar core L1544. The strongest emission ( $T_{\rm mb} \sim$1 K) occurs at the peak of the millimeter continuum emission, while measurements at offset positions indicate that  ${\rm H}_{2}{\rm D}^{+}$ is confined within ~20´´, where CO is highly depleted. The derived  ${\rm H}_{2}{\rm D}^{+}$abundance of ~10 -9 is comparable with previous estimates of the electron abundance in the core, which suggests that  ${\rm H}_{2}{\rm D}^{+}$ is the main molecular ion in the central 20´´ (2800 AU) of L1544. This confirms the expectations that  ${\rm H}_{2}{\rm D}^{+}$ is dramatically enhanced in gas depleted of molecules other than  ${\rm H}_2$. 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 ( $\ga$98%) frozen within a radius of ~2800 AU.


Key words: ISM: individual: L1544 -- ISM: molecules -- radio lines: ISM

Offprint request: P. Caselli, caselli@arcetri.astro.it

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