A New Intermediate-Mass Protostar in the Cepheus A HW2 Region

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 SO sub(2) in the ground vibrational state and of HC sub(3)N in the vibrationally excited states u sub(7) = 1 and u sub(7) = 2. The kinetic temperature derived from both molecules is 6160 K. The high angular resolution observations (1."25 x 0."99) of the SO sub(2) J = 28 sub(7,21) 1 29 sub(6,24) line (488 K above the ground state) show that the hot gas is concentrated in a compact condensation with a size of 60."6 (6430 AU), located 0."4 (300 AU) east from the radio jet HW2. The total SO sub(2) column density in the hot condensation is 610 super(18) cm super(-2), with an H sub(2) column density ranging from 610 super(23) to 6 x 10 super(24) cm super(-2). The H sub(2) density and the SO sub(2) fractional abundance must be larger than 10 super(7) cm super(-3) and 2 x 10 super(-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 HC sub(3)N vibrationally excited lines, and the large SO sub(2) abundance, we favor the interpretation of a hot core heated by an intermediate-mass protostar of 10 super(3) L sub( ). This indicates that the Cep A HW2 region contains a cluster of very young stars.