2012ApJ...759...13K

We present an analysis of HCO⁺ (J = 3 ⟶ 2) and H¹³CO⁺ (J = 3 ⟶ 2) observations of the massive (M ∼ 20 M_☉) submillimeter/IR source IRAS 01202+6133 located on the periphery of the H II region KR 120 (Sh 2-187). The HCO⁺ line profile has a classic blue-asymmetric shape with the optically thin H¹³CO⁺ line peaking at the position expected if the HCO⁺ line arises from a combination of self-absorption and infall motion. We have modified existing analytic radiative transfer models to allow for the fitting of submillimeter/millimeter line profiles that have both self-absorption features and optically thin wings and applied these models to our HCO⁺ spectrum of IRAS 01202+6133. We conclude that it is a young Class I young stellar object with a substantial envelope undergoing slow infall and having some outflow motions. The young age of the H II region rules out a "collect and collapse" scenario. While we cannot eliminate the possibility that IRAS 01202+6133 formed spontaneously at its current location, considering its early evolutionary state and its proximity to the H II region, we think that the formation of IRAS 01202+6133 was triggered by the expansion of KR 120 (Sh 2-187).