Detection of OH⁺and H₂O⁺towards Orion KL

Abstract

We report observations of the reactive molecular ions OH + , H 2 O + , and H 3 O + towards Orion KL with Herschel/HIFI. All three N = 1−0 finestructure transitions of OH + at 909, 971, and 1033 GHz and both fine-structure components of the doublet ortho-H 2 O + 1 11 −0 00 transition at 1115 and 1139 GHz were detected; an upper limit was obtained for H 3 O + . OH + and H 2 O + are observed purely in absorption, showing a narrow component at the source velocity of 9 km s −1 , and a broad blueshifted absorption similar to that reported recently for HF and para-H 18 2 O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH + and H 2 O + for the 9 km s −1 component of 9±3×10 12 cm −2 and 7± 2× 10 12 cm −2 , and those in the outflow of 1.9± 0.7× 10 13 cm −2 and 1.0± 0.3× 10 13 cm −2 . Upper limits of 2.4× 10 12 cm −2 and 8.7× 10 12 cm −2 were derived for the column densities of ortho and para-H 3 O + from transitions near 985 and 1657 GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate.

Chemistry in cosmic ray dominated regions

“…Recent results indicate that higher cosmic ray ionization rates might be present in diffuse clouds throughout the Galaxy and in the Orion bar (e.g. Indriolo et al 2007;Shaw et al 2008;Indriolo, Fields & McCall 2009 and even more recent results from Herschel/HIFI such as Gupta et al 2010;Neufeld et al 2010). More precisely, Indriolo et al (2007) presents H + 3 column densities varying between 0.2-2.1 × 10 14 cm −2 depending on the diffuse cloud observed (see their Tables 3 and 4).…”

Hot, metastable hydronium ion in the Galactic centre: formation pumping in X-ray-irradiated gas?

“…The differences between the H + 3 and H 3 O + absorption patterns may be partly due to the limited signal-to-noise ratio of the high-frequency HIFI spectra. However, it appears that H 3 O + is strongly enhanced only in some of the H [15] is interesting. On this line of sight, the column densities of the three oxygen-bearing ions are up to an order of magnitude lower than those towards W31C and W49N.…”

Principles and promise of Fabry–Perot resonators at terahertz frequencies

“…Equation (8) assumes that the system consists of two equivalent mirrors and cavity quality is thus a reflection of the amount of power lost as the photons travel down one length of the cavity. Since this condition holds for most cavities used in ring-down instruments this equation correctly calculates the theoretical Q factor.…”

“…Conditions in the interstellar medium, for example, allow for the existence and survival of species that can be difficult to create in the gas phase on Earth; for example, transient species such as complex ions or radicals, 7,8 or molecules that are difficult to volatilize such as large organic acids. Various laser or high temperature induced reactions/vaporization techniques combined with supersonic molecular beam expansions that decrease the reaction or interaction opportunities do, in some cases, allow such difficult targets to be studied.…”