SIMBAD references

We present a comprehensive analysis of the evolution of envelopes surrounding protostellar systems in the Perseus molecular cloud using data from the MASSES survey. We focus our attention to the C¹⁸O(2-1) spectral line, and we characterize the shape, size, and orientation of 54 envelopes and measure their fluxes, velocity gradients, and line widths. To look for evolutionary trends, we compare these parameters to the bolometric temperature T _bol, a tracer of protostellar age. We find evidence that the angular difference between the elongation angle of the C¹⁸O envelope and the outflow axis direction generally becomes increasingly perpendicular with increasing T _bol, suggesting the envelope evolution is directly affected by the outflow evolution. We show that this angular difference changes at T _bol = 53 ± 20 K, which includes the conventional delineation between Class 0 and I protostars of 70 K. We compare the C¹⁸O envelopes with larger gaseous structures in other molecular clouds and show that the velocity gradient increases with decreasing radius (| { \mathcal G }| ∼{R}^{-0.72±0.06}). From the velocity gradients we show that the specific angular momentum follows a power-law fit J/M ∝ R ^1.83±0.05 for scales from 1 pc down to ∼500 au, and we cannot rule out a possible flattening out at radii smaller than ∼1000 au.