boxes in Figure \[fig4\]a). The selected region “p3" covering larger area and the small circle in Figure \[fig4\]b are very close, where one may expect similar molecular profiles. In the $^{12}$CO spectrum, two peaks (around $-$20 and $-$17 km s$^{-1}$) are clearly seen in the direction of the region p3, while the peak of the corresponding $^{13}$CO spectrum (around $-$18.5 km s$^{-1}$) is found toward a dip between two peaks seen in the $^{12}$CO spectrum (see also Figure \[fig4\]c). In the direction of other small regions (or away from the central part of the filamentary feature), the peak in the $^{12}$CO spectrum nearly matches with the peak in the $^{13}$CO profile. Hence, in the direction of the region p3, the shift of velocity in the $^{12}$CO and $^{13}$CO could be due to the presence of self-absorption of $^{12}$CO line around $-$18.5 km s$^{-1}$. It can be treated as an example of a blue-asymmetric self-absorption profile. Based on a relatively low ratio value ($<$ 2.5) of $^{12}$CO/$^{13}$CO at $-$18.5 km s$^{-1}$, the $^{12}$CO self-absorption feature is found toward the elongated filamentary feature (see a summary figure in this Section and also Section \[sec:disc\] for more details). If we use the ratio 