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摘要
We present astrometric VLBI observations of H2O masers associated with IRAS 22480+6002 (= IRC+60370, hereafter I22480) with the VLBI Exploration of Radio Astrometry (VERA). The stellar type of I22480 looks unusual in stellar maser sources, and has been debated since the 1970%26apos;s. We successfully determined that an annual parallax of a group of H2O maser spots is pi = 0.400 +/- 0.025 mas, corresponding to a distance to I22480 of D = 2.50(-0.15)(+0.17) kpc. This suggests that an estimated bolometric luminosity of I22480 should be revised to 35000 L-circle dot, preferring a K-type supergiant to an RV Tau-type variable star, previously suggested. Although its spectral type is unusual in stellar maser sources, internal motions of H2O maser features suggest that the H2O masers are associated with the circumstellar envelope of this star. We derived a secular proper motion of I22480, (mu(alpha), mu(delta)) = (-2.58 +/- 0.33, -1.91 +/- 0.17) [mas yr(-1)], from a possible stellar motion relative to the maser feature motion. The derived motion of I22480 in the Milky Way has a deviation of similar to -30 km s(-1) in the Galactic azimuthal direction from the circular motion, estimated from a galactocentric distance to I22480 and an assumption of a flat Galactic rotation curve. This peculiar motion is still comparable to those typically seen in H2O maser sources located in the Perseus Arm. Taking into account its peculiar motion and proximity to the Galactic midplane (z similar or equal to 60 pc), I22480 may be a member of the Galactic thin disk.
- 出版日期2012-12-25
- 单位中国科学院国家天文台
