Position-velocity plots of the ¹²CO(2–1) (gray scale) and CH₃CN(12–11) K = 4 line emission obtained with the SMA by Cesaroni et al. (2011). The offset is measured along the direction with PA = 68° passing through the HMC (see Fig. 3) and is measured from the phase center of the SMA observations (α(J2000) = 18^h47^m34315, δ(J2000) = –01°12′459), assumed positive toward NE. Contour levels increase from 0.2 in steps of 0.2 Jy beam^-1 for CH₃CN and from 0.24 in steps of 0.24 Jy beam^-1 for ¹²CO. The cross in the bottom left denotes the angular and spectral resolutions of the SMA data. The solid dots represent the 1665 MHz and 1667 MHz OH maser features detected in our VLBA observations. The black dashed line gives the best linear fit of the OH maser V_LSR versus corresponding positions.