The Distribution of Ortho–H 2 D + (1 1,0 –1 1,1 ) in L1544: Tracing the Deuteration Factory in Prestellar Cores

Abstract

Prestellar cores are unique laboratories for studying the chemical and physical conditions preceding star formation. We observed the prestellarcore L1544 in the fundamental transition ofortho-H2D+ (11,0-11,1) atdifferent positions over 100" and found a strong correlation between itsabundance and the CO depletion factor. We also present a tentativedetection of the fundamental transition ofpara-D2H+ (11,0-10,1) at thedust emission peak. Maps in N2H+,N2D+, HCO+, and DCO+ areused and interpreted with the aid of a spherically symmetric chemicalmodel that predicts the column densities and abundances of these speciesas a function of radius. The correlation between the observed deuteriumfractionation of H+3, N2H+,and HCO+ and the observed integrated CO depletion factoracross the core can be reproduced by this chemical model. In addition, asimpler model is used to study the H2D+ortho-to-para ratio. We conclude that, in order to reproduce theobserved ortho-H2D+ observations, the grain radiusshould be larger than 0.3 μm.