On the frequency of NH+ and ND*
LERMA & UMR8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France e-mail: [laurent.pagani;marie-lise.dubernet]@obspm.fr
2 Department of Molecular and Infrared Astrophysics (DAMIR), Consejo Superior de Investigaciones Científicas (CSIC), C/ Serrano 121, 28006 Madrid, Spain e-mail: email@example.com
Accepted: 10 November 2008
Context. Dynamical studies of prestellar cores search for small velocity differences between different tracers. The highest radiation frequency precision is therefore required for each of these species.
Aims. We want to adjust the frequency of the first three rotational transitions of N2H+ and N2D+ and extrapolate to the next three transitions.
Methods. We compare N2H+ and N2D+ to NH3, the frequency of which is more accurately known and which has the advantage of being spatially coexistent with N2H+ and N2D+ in dark cloud cores. With lines among the narrowest, and the N2H+ and NH3 emitting region among the largest, L183 is a good candidate for comparing these species.
Results. A correction of ~10 kHz for the N2H+ (J: 1-0) transition is found (~0.03 km s-1). Similar corrections from a few m s-1 up to ~0.05 km s-1 compared to previous astronomical determinations are reported for the other transitions (N2H+ (J: 3-2) and N2D+(J: 1-0), (J: 2-1), and (J: 3-2)). Einstein spontaneous-decay coefficients (Aul) are included.
Key words: molecular data / ISM: kinematics and dynamics / radio lines: ISM
Based on observations made with the IRAM 30-m and the GBT 100-m. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). GBT is run by the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
© ESO, 2009