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New Distance and Revised Natures of High Mass Star Formation in G5.89-0.39

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DOI: 10.1093/pasj/63.1.31
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We report on the astrometric observations of the 22 GHz H2O masers in the high mass star-forming region G5.89-0.39 with VERA (VLBI Exploration of Radio Astrometry). Newly derived distance of 1.28^{+0.09}_{-0.08} kpc is the most precise and significantly nearer than previous values. We revised physical parameters and reconsidered nature of G5.89-0.39 based on the new distance as follows. (1) The ionizing star of the ultra compact (UC) HII region is a late O-type (O8 - 8.5) zero age main sequence (ZAMS) star, consistent with previously established limits based on its infrared spectral line emission. (2) Crescent-like maser alignment at the position of the O type ZAMS star may trace accretion disk (or its remnant), which suggests that the star is still young and before complete evaporation of circumstellar materials. (3) Although the revised mass for the east-west outflow has been reduced, it still quite large (100 Msun) which indicates that a significant fraction of the mass is entrained material and that the dynamical age significantly underestimates the actual outflow age. Our newly-derived distance emphasizes that G5.89-0.39 is one of the nearest targets to investigate ongoing high-mass star formation and evolution in a compact cluster containing a young O-type star.


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