We present Herschel/HIFI observations of the light hydride H$_{2}$S obtained from the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken as part of the HEXOS GT key program. In total, we observe 52, 24, and 8 unblended or slightly
blended features from H$_{2}$$^{32}$S, H$_{2}$$^{34}$S, and H$_{2}$$^{33}$S, respectively. We only analyze emission from the so called hot core, but emission from the plateau, extended ridge, and/or compact ridge are also detected. Rotation diagrams for ortho and para H$_{2}$S follow straight lines given the uncertainties and yield T$_{rm rot}$=141$pm$12 K. This indicates H$_{2}$S is in LTE and is well characterized by a single kinetic temperature or an intense far-IR radiation field is redistributing the population to produce the observed trend. We argue the latter scenario is more probable and find that the most highly excited states (E$_{rm up}$>1000 K) are likely populated primarily by radiation pumping. We derive an H$_{2}$$^{32}$S column density, N$_{rm tot}$(H$_{2}$$^{32}$S)=9.5$pm$1.9$times$10$^{17}$ cm$^{-2}$, gas kinetic temperature, T$_{rm kin}$=120$pm^{13}_{10}$ K, and constrain the H$_{2}$ volume density, n$_{H2}$>9$times$10$^{7}$ cm$^{-3}$, for the H$_{2}$S emitting gas. These results point to an H$_{2}$S origin in markedly dense, heavily embedded gas, possibly in close proximity to a hidden self-luminous source (or sources), which are conceivably responsible for Orion KLs high luminosity. We also derive an H$_{2}$S ortho/para ratio of 1.7$pm$0.8 and set an upper limit for HDS/H2S of <4.9$times$10$^{-3}$.
We have examined methanol emission from Orion KL with of the {em Herschel}/HIFI instrument, and detected two methanol bands centered at 524 GHz and 1061 GHz. The 524 GHz methanol band (observed in HIFI band 1a) is dominated by the isolated $Delta$J$=
$0, K$=-4rightarrow$-3, v$_t$$=$0 Q branch, and includes 25 E-type and 2 A-type transitions. The 1061 GHz methanol band (observed in HIFI band 4b) is dominated by the $Delta$J$=$0, K$=7rightarrow$6, v$_t$$=$0 Q branch transitions which are mostly blended. We have used the isolated E-type v$_t$$=$0 methanol transitions to explore the physical conditions in the molecular gas. With HIFIs high velocity resolution, the methanol emission contributed by different spatial components along the line of sight toward Orion KL (hot core, low velocity flow, and compact ridge) can be distinguished and studied separately. The isolated transitions detected in these bands cover a broad energy range (upper state energy ranging from 80 K to 900 K), which provides a unique probe of the thermal structure in each spatial component. The observations further show that the compact ridge is externally heated. These observations demonstrate the power of methanol lines as probes of the physical conditions in warm regions in close proximity to young stars.
We present the first high spectral resolution observations of Orion KL in the frequency ranges 1573.4 - 1702.8 GHz (band 6b) and 1788.4 - 1906.8 GHz (band 7b) obtained using the HIFI instrument on board the Herschel Space Observatory. We characterize
the main emission lines found in the spectrum, which primarily arise from a range of components associated with Orion KL including the hot core, but also see widespread emission from components associated with molecular outflows traced by H2O, SO2, and OH. We find that the density of observed emission lines is significantly diminished in these bands compared to lower frequency Herschel/HIFI bands.
