EMBEDDED PROTOSTARS IN THE DUST, ICE, AND GAS IN TIME (DIGIT) HERSCHEL KEY PROGRAM: CONTINUUM SEDs, AND AN INVENTORY OF CHARACTERISTIC FAR-INFRARED LINES FROM PACS SPECTROSCOPY.

We present 50-210μm spectral scans of 30 Class 0/I protostellar sources, obtained with Herschel-PACS, and 0.5-1000μm spectral energy distributions, as part of the Dust, Ice, and Gas in Time Key Program. Some sources exhibit up to 75 H₂O lines ranging in excitation energy from 100 to 2000 K, 12 transitions of OH, and CO rotational lines ranging from J = 14 → 13 up to J = 40 → 39. [O I] is detected in all but one source in the entire sample; among the sources with detectable [O I] are two very low luminosity objects. The mean 63/145μm [O I] flux ratio is 17.2 ± 9.2. The [O I] 63μm line correlates with L_bol, but not with the time-averaged outflow rate derived from low-J CO maps. [C II] emission is in general not local to the source. The sample Lbol increased by 1.25 (1.06) and T_bol decreased to 0.96 (0.96) of mean (median) values with the inclusion of the Herschel data. Most CO rotational diagrams are characterized by two optically thin components (〈N〉 = (0.70 ± 1.12) × 10⁴⁹ total particles). NCO correlates strongly with L_bol, but neither T_rot nor N_CO(warm)/N_CO(hot) correlates with L_bol, suggesting that the total excited gas is related to the current source luminosity, but that the excitation is primarily determined by the physics of the interaction (e.g., UV-heating/shocks). Rotational temperatures for H₂O (〈T_rot〉 = 194 ± 85 K) and OH (〈T_rot〉 = 183 ± 117 K) are generally lower than for CO, and much of the scatter in the observations about the best fit is attributed to differences in excitation conditions and optical depths among the detected lines. [ABSTRACT FROM AUTHOR]