We report high angular resolution ( HPBW \sim 0.6 ^ { \prime \prime } \times 0.5 ^ { \prime \prime } 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 CH _ { 3 } CN emission is detected at this position .
The high rotational temperature derived from the CH _ { 3 } CN lines ( T _ { rot } \approx 50 K ) as well as the enhanced CH _ { 3 } CN fractional abundance ( X ( CH _ { 3 } CN ) \sim 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 CH _ { 3 } OH 5 _ { kk ^ { \prime } } \rightarrow 4 _ { kk ^ { \prime } } , and D _ { 2 } CO 4 _ { 04 } \rightarrow 3 _ { 03 } 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 ( E _ { u } > 100 K ) and other associated with the bipolar outflow which dominates the emission in the low excitation lines .
Enhanced CH _ { 3 } OH abundances ( X ( CH _ { 3 } OH ) \sim 3 10 ^ { -8 } – a few 10 ^ { -7 } ) are measured in both components .
While intense D _ { 2 } CO 4 _ { 04 } \rightarrow 3 _ { 03 } emission is detected towards the hot core , the N _ { 2 } D ^ { + } 3 \rightarrow 2 line has not been detected in our interferometric observations .
The different behaviors of D _ { 2 } CO and N _ { 2 } D ^ { + } emissions suggest different formation mechanisms for the two species and different deuteration processes for H _ { 2 } CO and N _ { 2 } H ^ { + } ( 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 ( [ CH _ { 3 } CN ] / [ CH _ { 3 } OH ] ) with the hot core luminosity .
However , the O-bearing species H _ { 2 } CO 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 and massive star forming regions .