Detection of a hot core in the intermediate - mass Class 0 protostar NGC 7129 – FIRS 2

the date of receipt and acceptance should be inserted later Abstract. We report high angular resolution (HPBW∼ 0.6 ′′ × 0.5 ′′ at 1.3mm) observations of the Class 0 intermediate-mass (IM) protostar NGC 7129–FIRS 2 using the Plateau de Bure Interferometer. Our observations show the existence of an intense unresolved source in the continuum at 1.3mm and 3mm at the position of the Class 0 object. In addition, compact CH3CN emission is detected at this position. The high rotational temperature derived from the CH3CN lines (Trot≈50 K) as well as the enhanced CH3CN fractional abundance (X(CH3CN)∼7.0 10 −9) show the existence of a hot core in this IM young stellar object. This is, up to our knowledge , the first IM hot core detected so far. Interferometric maps of the region in the CH3OH 5 kk ′ →4 kk ′ , and D2CO 404→303 lines are also presented in this paper. The methanol emission presents two condensations, one associated with the hot core which is very intense in the high upper state energy lines (Eu>100 K) and other associated with the bipolar outflow which dominates the emission in the low excitation lines. Enhanced CH3OH abundances (X(CH3OH) ∼ 3 10 −8 – a few 10 −7) are measured in both components. While intense D2CO 404→303 emission is detected towards the hot core, the N2D + 3→2 line has not been detected in our interferometric observations. The different behaviors of D2CO and N2D + emissions suggest different formation mechanisms for the two species and different deuteration processes for H2CO and N2H + (surface and gas-phase chemistry, respectively). Finally, the spectrum of the large bandwidth correlator show a forest of lines at the hot core position reavealing that this object is extraordinarily rich in complex molecules. To have a deeper insight into the chemistry of complex molecules, we have compared the fractional abundances of the complex O-and N-bearing species in FIRS 2 with those in hot corinos and massive hot cores. Within the large uncertainty involved in fractional abundance estimates towards hot cores, we do not detect any variation of the relative abundances of O-and N-bearing molecules ([CH3CN]/[CH3OH]) with the hot core luminosity. However, the O-bearing species H2CO and HCOOH seem to be more abundant in low and intermediate mass stars than in massive star forming regions. We propose that this could be the consequence of a different grain mantle composition in low …