Context : Studies of high-mass protostellar objects reveal important information regarding the formation process of massive stars .

Aims : We study the physical conditions in the dense core and molecular outflow associated with the high-mass protostellar candidate IRAS 18566+0408 at high angular resolution .

Methods : We performed interferometric observations in the { NH _ { 3 } } ( J , K ) = ( 1,1 ) , ( 2,2 ) and ( 3,3 ) inversion transitions , the SiO J=2-1 and HCN J=1-0 lines , and the 43 and 87 GHz continuum emission using the VLA and OVRO .

Results : The 87 GHz continuum emission reveals two continuum peaks MM-1 and MM-2 along a molecular ridge .
The dominant peak MM-1 coincides with a compact emission feature at 43 GHz , and arises mostly from the dust emission .
For dust emissivity index \beta of 1.3 , the masses in the dust peaks amount to 70 M _ { \odot } for MM-1 , and 27 M _ { \odot } for MM-2 .
Assuming internal heating , the central luminosities of MM-1 and MM-2 are 6 \times 10 ^ { 4 } and 8 \times 10 ^ { 3 } L _ { \odot } , respectively .

The SiO emission reveals a well collimated outflow emanating from MM-1 .
The jet-like outflow is also detected in { NH _ { 3 } } at velocities similar to the SiO emission .
The outflow , with a mass of 27 M _ { \odot } , causes significant heating in the gas to temperatures of 70 K , much higher than the temperature of \stackrel { \textstyle < } { \sim } 15 K in the extended core .
Compact ( < 3 ^ { \prime \prime } ) and narrow line ( < 1.5 km s ^ { -1 } ) { NH _ { 3 } } ( 3,3 ) emission features are found associated with the outflow .
They likely arise from weak population inversion in { NH _ { 3 } } similar to the maser emission .

Toward MM-1 , there is a compact { NH _ { 3 } } structure with a linewidth that increases from 5.5 km s ^ { -1 } FHWM measured at 3 ^ { \prime \prime } resolution to 8.7 km s ^ { -1 } measured at 1 ^ { \prime \prime } resolution .
This linewidth is much larger than the FWHM of < 2 km s ^ { -1 } in the entire core , and does not appear to originate from the outflow .
This large linewidth may arise from rotation/infall , or relative motions of unresolved protostellar cores .

Conclusions :