HSO N = 1_0, 1 − 0_0, 0J = 3/2 − 1/2 F = 2 − 1 transition observed in five cold dense cores with the Yebes 40m telescope. The abscissa corresponds to the rest frequency assuming the local standard of rest velocity for each source (see Table 1). The ordinate is the antenna temperature corrected for atmospheric losses in mK. The red line shows the LTE synthetic spectrum obtained from a fit to the observed line profiles (see text). The green vertical dashed line indicates the new calculated frequency corresponding with this transition. Observed positions for each source are: L183: α_J2000 = 15^h54^m08.6^s and δ_J2000 = −02° 52′10.0″, L483: α_J2000 = 18^h17^m29.83^s and δ_J2000 = −04° 39′38.33″, L1495B: α_J2000 = 04^h15^m41.8^s and δ_J2000 = 28° 47′46.0″, L1527: α_J2000 = 04^h39^m53.88^s and δ_J2000 = 26° 03′11.0″, and Lupus-1A: α_J2000 = 15^h42^m52.4^s and δ_J2000 = −34° 07′53.5″.