Astrometry of 6.7 GHz Methanol Maser toward W 3(OH) with Japanese VLBI Network

摘要

WepresenttheresultsofmultiepochVLBIobservationsfora6.7GHzmethanolmasertowardtheUCHIIregionofW3(OH)withJapaneseVLBINetwork(JVN).Basedonphase-referencingVLBIastrometry,wederivedthetrigonometricannualparallaxtobe0.598$$pm$$0.067mas,correspondingtoadistanceof1.67$$^{+0.21}_{-0.17}$$kpc.Thisisthefirstdetectionofparallaxfora6.7GHzmethanolmaserwithJVN,anddemonstratesthatJVN/VERAiscapableofconductingVLBIastrometryfor6.7GHzmethanolmasersourceswithinfewkpcfromtheSun.Basedonin-beammappingoftheW3(OH)methanolmaser,wealsomeasuredtheinternalpropermotionsofits6.7GHzmethanolmaserforthefirsttime.Theinternalpropermotionsbasicallyshownortha€“southexpansionwithavelocityoffewkms$$^{-1}$$,beingsimilartoOHmasers.Thespatialdistributionandtheinternalpropermotionsof6.7GHzmethanolmaserssuggestarotatingandexpandingtorusstructuresurroundingtheUCHIIregion.