We report the detection of the ground-state rotational transition of the methylidyne cation
CH+ and its isotopologue 13 CH+ toward the remote massive star-forming regions W33A,
W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen
only in absorption against the dust continuum emission of the star-forming regions. The CH+
absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight
that include gas associated with the star-forming regions (SFR) and Galactic foreground�…

We present initial results from the Herschel GT key program: Herschel observations of EXtra-
Ordinary Sources (HEXOS) and outline the promise and potential of spectral surveys with
Herschel/HIFI. The HIFI instrument offers unprecedented sensitivity, as well as continuous
spectral coverage across the gaps imposed by the atmosphere, opening up a largely
unexplored wavelength regime to high-resolution spectroscopy. We show the spectrum of
Orion KL between 480 and 560 GHz and from 1.06 to 1.115 THz. From these data, we�…

High resolution line spectra of star-forming regions are mines of information: they provide
unique clues to reconstruct the chemical, dynamical, and physical structure of the observed
source. We present the first results from the Herschel key project “Chemical HErschel
Surveys of Star forming regions”, CHESS. We report and discuss observations towards five
CHESS targets, one outflow shock spot and four protostars with luminosities bewteen 20
and 2� 10 5: L1157-B1, IRAS 16293-2422, OMC2-FIR4, AFGL 2591, and NGC 6334I. The�…

We report the detection of absorption by interstellar hydroxyl cations and water cations,
along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI
instrument, in dual beam switch mode, to observe the 972 GHz N= 1–0 transition of OH+ and
the 1115 GHz 1 11–0 00 transition of ortho-H 2 O+. The resultant spectra show absorption
by ortho-H 2 O+, and strong absorption by OH+, in foreground material at velocities in the
range 0 to 70 km s-1 with respect to the local standard of rest. The inferred OH+/H 2 O+�…

We report the first detection of chloronium, H 2 Cl+, in the interstellar medium, using the HIFI
instrument aboard the Herschel Space Observatory. The 2 12–1 01 lines of ortho-HCl+ and
ortho-HCl+ are detected in absorption towards NGC 6334I, and the 1 11–0 00 transition of
para-HCl+ is detected in absorption towards NGC 6334I and Sgr B2 (S). The H 2 Cl+ column
densities are compared to those of the chemically-related species HCl. The derived HCl/H 2
Cl+ column density ratios,~ 1–10, are within the range predicted by models of diffuse and�…

We performed a sensitive search for the ground-state emission lines of ortho-and para-water
vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines
are detected down to 3σ levels in 0.5 km s-1 channels of 4.2 mK for the 1 10–1 01 line and
12.6 mK for the 1 11–0 00 line. We report a very tentative detection, however, of the 1 10–1
01 line in the wide band spectrometer, with a strength of T mb= 2.7 mK, a width of 5.6 km s-1
and an integrated intensity of 16.0 mK km s-1. The latter constitutes a 6σ detection�…

Context. Hydrides of the most abundant heavier elements are fundamental molecules in
cosmic chemistry. Some of them trace gas irradiated by UV or X-rays. Aims. We explore the
abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation.
Methods. W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep
integration (2500 s) in 8 spectral regions. Results. The target lines including CH, NH, H 3
O+, and the new molecules SH+, H 2 O+, and OH+ are detected. The H 2 O+ and OH+ J= 1�…

We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight
line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI
instrument in dual beam switch mode to observe the 1232.4762 GHz J= 1–0 HF transition in
the upper sideband of the band 5a receiver. We detected foreground absorption by HF
toward both sources over a wide range of velocities. Optically thin absorption components
were detected on both sight lines, allowing us to measure–as opposed to obtain a lower limit�…

We report the detection of the ground state N, J= 1, 3/2 1, 1/2 doublet of the methylidyne
radical CH at~ 532 GHz and~ 536 GHz with the Herschel/HIFI instrument along the sight-line
to the massive star-forming regions G10. 6–0.4 (W31C), W49N, and W51. While the
molecular cores associated with these massive star-forming regions show emission lines,
clouds in the diffuse interstellar medium are detected in absorption against the strong
submillimeter background. The combination of hyperfine structure with emission and�…

During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of
their mass through an intense wind, enriching the interstellar medium with products of
nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau
using the high-resolution HIFI spectrometer onboard Herschel. We report on the first
detection of H $ _2^{16} $ O and the rarer isotopologues H $ _2^{17} $ O and H $ _2^{18} $
O in both the ortho and para states. We deduce a total water content (relative to molecular�…