Trigonometric Distance and Proper Motion of Iras 20056+3350: A Massive Star-forming Region on the solar Circle

Abstract

We report our measurement of the trigonometric distance and proper motion of IRAS 20056+3350, obtained from the annual parallax of H₂O masers. Our distance of D = 4.69^+0.65_-0.51 kpc, which is 2.8 times larger than the near kinematic distance adopted in the literature, places IRAS 20056+3350 at the leading tip of the Local arm and proximal to the solar circle. Using our distance, we reevaluate past observations to reveal IRAS 20056+3350 as a site of massive star formation at a young stage of evolution. This result is consistent with the spectral energy distribution of the source evaluated with published photometric data from UKIDSS, WISE, AKARI, IRAS, and the submillimeter continuum. Both analytical approaches reveal the luminosity of the region to be 2.4 × 10⁴ L _⊙, and suggest that IRAS 20056+3350 is forming an embedded star of >=16 M _⊙. We estimated the proper motion of IRAS 20056+3350 to be (μ_αcos δ, μ_δ) = (-2.62 ± 0.33, -5.65 ± 0.52) mas yr^-1 from the group motion of H₂O masers, and use our results to estimate the angular velocity of Galactic rotation at the Galactocentric distance of the Sun, Ω₀ = 29.75 ± 2.29 km s^-1 kpc^-1, which is consistent with the values obtained for other tangent point and solar circle objects.