Apertures for measuring the mass associated with bubble N107. The pixels lying within the apertures contribute to the measured masses. The dashed circles mark bubble N107 as was identified in the 8 μm emission by Churchwell et al. (2006). Left: H i line emission at 42.8 km s^-1. The innermost circle (BG) is the region we used to derive the background emission. Right: ¹³CO line emission at 42.8 km s^-1. We used two apertures to measure the molecular mass. Aperture 1 is the same as that for measuring the H i mass, while aperture 2 is smaller and covers only the immediate vicinity of the bubble.