Abstract We report the internal proper motions of 12 GHz methanol masers in massive star-forming region G35.20–0.74 observed with the Very Long Baseline Array (VLBA) at four epochs spanning about 1.5 yr. Two groups of maser features were detected, groups A and B, and the latter that had a V-shaped spatial distribution is likely tracing the north outflow in G35.20–0.74. We present a three-dimensional model for the kinematics of these masers, by assuming the interstellar medium was blown by the stellar wind from the driving source (G35.2N) of the outflow. Adopting a position angle of ~81° for the main axis of the outflow from previous studies, we estimate an inclination of 35° ± 5.5°, a velocity of 8.1 ± 0.7 km s−1 for the stellar wind along the main axis and an expansion speed gradient of 0.05 ± 0.016 km s−1 AU−1 . From the model, we derive the age of the north outflow in G35.20–0.74 to be ~ 1.6 × 104 yr.

Keywords masers — ISM: molecules — stars: kinematics — stars: individual (G35.20–0.74) — stars: winds, outflows

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