2005ApJ...628L..61M

We present the discovery of the first molecular hot core associated with an intermediate-mass protostar in the Cep A HW2 region. The hot condensation was detected from single-dish and interferometric observations of several high-excitation rotational lines (from 100 to 880 K above the ground state) of SO₂ in the ground vibrational state and of HC₃N in the vibrationally excited states v₇=1 and v₇=2. The kinetic temperature derived from both molecules is ∼160 K. The high angular resolution observations (1".25x0".99) of the SO₂J=28_7,21⟶29_6,24 line (488 K above the ground state) show that the hot gas is concentrated in a compact condensation with a size of ∼0".6 (∼430 AU), located 0".4 (300 AU) east from the radio jet HW2. The total SO₂ column density in the hot condensation is ∼10¹⁸/cm2, with an H₂ column density ranging from ∼10²³ to 6x10²⁴/cm2. The H₂ density and the SO₂ fractional abundance must be larger than 10⁷/cm3 and 2x10^–7, respectively. The most likely alternatives for the nature of the hot and very dense condensation are discussed. From the large column densities of hot gas, the detection of the HC₃N vibrationally excited lines, and the large SO₂ abundance, we favor the interpretation of a hot core heated by an intermediate-mass protostar of 10³ L_☉. This indicates that the Cep A HW2 region contains a cluster of very young stars.