tokens: sources, while the HCO + line is either undetected or detected at a very weak level ( T mb 0.1 K) in disk-dominated Class II/Stage II sources. Another notable feature is an axisymmetric profile observed in the HCO + line, which may be indicative of an infalling envelope. Typically, a blue-dominated infall asymmetry has been seen in the HCO + profile of some low-mass protostars, while a red-dominated axisymmetry is usually associated with disk-only objects or the presence of an outflow (e.g., Thi et al. 2004 ; Evans et al. 1999 ; van Kempen et al. 2009 ). However, this is not always the case, since red-dominated asymmetry has been observed in embedded sources (D. Harsono et al. 2016, in preparation), an interpretation of which could be an expanding envelope that is due to an outflow. Among the bona fide detections in our present work, J182902.12, J182855.78, and J182956.67 have previously been categorized as Stage 0/I systems by Heiderman Evans ( 2015 ), based on the criteria of HCO + (3-2) integrated line intensity of ≥0.68 K km s −1 , while J182841.87 has been categorized as a Stage II system. We note that the Heiderman Evans ( 2015 ) criteria is solely based on a HCO + detection within 14′′ of the Spitzer c2d source position. As can be seen in Figure 6 , J182902.12 show a broad HCO + profile centered at the cloud velocity. The line model fit shows a typical Gaussian, which implies that there is no infalling envelope in this case. We have shown through SED modeling that J182902.12 is a Class Flat system and may possess a tenuous envelope. Using the “Stage” classification scheme also places J182902.12 in the Stage I-T category. Therefore, the Stage 0/I classification based on the HCO + detection is inconsistent with other schemes. For the case of J182855.78, results from line modeling indicate that the observed HCO + asymmetry can be explained by an infalling envelope model (Figure 6 ). The SED modeling results and the Stage classification also indicate that this is a genuine case of a Class 0/I or Stage 0/I system. For the case of J182956.67, the HCO + profile shows a hint of a blueshifted asymmetry and self-absorption at higher velocities (Figure 6 ). The results from line modeling for J182956.67 suggest that there may be blue-dominated infall asymmetry due to a weak envelope component with velocities between 0.5 and 1 km s −1 and a mass infall rate of 10 −7 M yr −1 . However, both the SED model fit and the Stage classification indicate that this is a Class II edge-on disk system or a Stage II source, rather than embedded Stage 0/I systems (Table 1 ; column 9). On the contrary, J182841.87 can be placed in the Stage I-T category and shows signatures of a tenuous envelope (Section 3.2 ), unlike the Stage II classification based on HCO + nondetection. The envelope mass in this system is too low to produce any detectable emission in a high-density tracer such as the HCO + (3-2) line. The submillimeter emission observed toward this source likely
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