New H2O masers in the NGC 7538 region

Abstract

H2O maser emission in the NGC 7538 molecular cloud has been mapped with the Nobeyama Millimeter Array with absolute and relative positional accuracies of 0.5 arcsec and 0.2 arcsec, respectively. Five new masers have been found within an 8 arcmin x 8 arcmin area. One is associated with IRS 9, and the other four are not associated with any known infrared or optical sources. The brightest H2O maser spot is 3 arcmin southwest from IRS 11 with a flux density of 156 Jy. These masers may be related to premain-sequence objects and/or protostars in the NGC 7538 molecular cloud. Two previously known H2O masers associated with IRS 1-3 and IRS 11 are resolved into 11 and 12 maser spots, respectively. The H2O maser spots associated with IRS 1-3 seem to be separated into two groups: one of which is very close to the ultracompact H II region at IRS 1, and the other far from IRS 1.