Letter to the Editor

Disappearance of N_2H^+ from the gas phase in the class 0 protostar IRAM 04191^*

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² LERMA/LRA, École Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France
³ Service d'Astrophysique, CEA/DSM/DAPNIA, C.E. Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: pandre@cea.fr

Corresponding author: A. Belloche, belloche@mpifr-bonn.mpg.de

Received: 23 February 2004
Accepted: 10 April 2004

Abstract

We present a high-resolution millimeter study of the very young class 0 protostar IRAM 04191+1522 in the Taurus molecular cloud. N₂H⁺(1-0) observations with the IRAM Plateau de Bure Interferometer and 30 m telescope demonstrate that the molecular ion N₂H⁺ disappears from the gas phase in the inner part of the protostellar envelope ( AU, ₂ cm^-3). This result departs from the predictions of current chemical models. It suggests either that N₂ is more depleted than the models predict, owing to a higher binding energy on polar ice or an enhanced grain chemistry transforming N₂ to less volatile species, or that strong deuterium fractionation enhances N₂D⁺ to the detriment of N₂H⁺.