NS(J = 5∕2–3/2) spectra, in the temperature scale (in K), toward L1521E, L1521B, L1498, and L1544 (from left to right). In each panel, the hf set of lines (identified by their quantum number F) is split into the Π⁺ (top) and Π⁻ (bottom) (see Table C.1). For the sake of clarity, hf transitions are shown individually. The position number (see Fig. 2) and the offsets (in arcsec), with respect to the reference position given in Table 1, are indicated on the left of each spectrum. The vertical dotted lines indicate the adopted systemic velocity. The horizontal and vertical scales are indicated in bold face.