A compact NH₂D source without NH₃ counterpart in the S187 high-mass star-forming region

Our goal is to investigate a so far only tentatively detected compact NH₂D source devoid of a notable NH₃ counterpart, located rather close to the luminous IRAS 01202+6133 source (the projected distance is 0.3 pc) in the S187 high-mass star-forming region. A high ammonia deuteration in such an environment is unusual. We performed observations of this area with the 20-m OSO radio telescope in several frequency ranges from ~72 to ~112 GHz. The area was mapped at the lower frequencies while at the higher frequencies only the position of the NH₂D emission peak was observed. The data were analyzed using non-LTE modeling. The data confirm a compact NH₂D source with a size of 0.2 pc. In addition, emission from about 20 molecules was detected, but only the DCO⁺(1-0) peak coincides with the NH₂D clump. The clump is not associated with any known astronomical source or an NH₃ emission peak but the dust continuum map shows an enhancement at approximately the same position. The gas kinetic temperature derived from various indicators is ~20-30 K, which possibly characterizes the surrounding material. The intrinsic NH₂D line width (~0.4 km/s) implies a clump with subsonic or transonic turbulence. The ortho/para NH₂D line intensity ratio is consistent with an abundance ratio of 3, expected from the spin statistics. The NH₂D/NH₃ abundance ratio may be ~1. In general, the data hint at a compact cold gravitationally stable dense core within the warm environment, which may represent pristine material. However this picture still needs a verification with observations at a higher angular resolution.