Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Abstract

We report the detection in IRC +10216 of 63 rotational transitions of HCN, most of them with quantum numbers J = 3-2, pertaining to 28 different vibrational states with energies up to 10 700 K (ν 1 +3ν 2 +ν 3 ). Some of the transitions were also observed for the rare isotopologue H 13 CN. The observations were carried out with the IRAM 30-m telescope. The HCN lines with level energies above 5000 K arise within 1.5 stellar radius from the photosphere. Their intensities imply a vibrational temperature of T vib 2400 K and a fractional HCN abundance relative to H 2 , x(HCN) = 5-7 × 10 −5 . These high-energy levels are mainly populated by photospheric radiation, and their vibrational temperature yields a direct measurement of the stellar photospheric temperature. The lines with energy levels between 2000 and 5000 K yield T vib 1300 K and x(HCN) 0.8-2 × 10 −5 . They are radiatively excited and arise from a shell extending between 1.5 and 5 stellar radii. Finally, the lines from the low-energy vibrational states (<2000 K) trace a larger region of the envelope (5-28 stellar radii) with T vib = 400-600 K and x(HCN) = 4-6× 10 −6 . They are strongly affected by mid and near-infrared pumping. The line widths increase from 5 km s −1 near the 2400 K photosphere, to 19 km s −1 in the warm 400 K shell. This provides a unique insight into the physical conditions of the gas acceleration and dust formation region.

A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling

“…In particular, observations of CO emission lines have proven to be a useful tool to describe the mass loss (e.g., Schöier et al 2002;González Delgado et al 2003;Ramstedt et al 2008;De Beck et al 2010;Khouri et al 2014a). Observations of other molecules have led to important insights in the chemistry and structure of AGB CSEs (e.g., González Delgado et al 2003;Schöier et al 2007;Maercker et al 2008Maercker et al , 2009Decin et al 2010a;Cernicharo et al 2010Cernicharo et al , 2011De Beck et al 2012;Justtanont et al 2012;Khouri et al 2014b; Lombaert et al 2016).…”

“…It is one of the most abundant molecules in the winds of these stars, rivalled only by CO and H 2 (Cherchneff 2006;Maercker et al 2008Maercker et al , 2009Decin et al 2010a,c;Khouri et al 2014b). As an oxygen-bearing molecule it plays an important role in the oxygen chemistry and the formation of other molecules.…”

Molecular abundances in the inner layers of IRC +10216

“…We focus on the parent molecules CS, SiO, SiS, NaCl, KCl, AlCl, AlF, and NaCN. The cases of CO, HCN, and SiC 2 , also formed in the inner layers and reachable by the IRAM 30-m telescope, have been treated recently (De Beck et al 2012;Fonfría et al 2008;Cernicharo et al 2010Cernicharo et al , 2011. The observation of a large number of rotational transitions covering a wide range of excitation energies coupled to radiative transfer calculations allows us to derive accurate abundances throughout the envelope.…”

Laboratory and Astronomical Discovery of Hydromagnesium Isocyanide

“…The J=9-8 line is fully blended with a line of H 2 C 4 and it is not shown. The J=12-11 is partially blended with a narrow and weak transition of HCN coming from the dust formation zone (Cernicharo et al 2011). The J=13-12 line is also partially blended with a line of CCS but 80% of the frequency coverage of the HMgNC line is free of contamination and appears clearly detected.…”

“…Hence, we are confident that this feature is unknown previous to its assignment to HMgNC. The J=12-11 transition of HMgNC at 131534.4(5) MHz is slightly contaminated in its red part by a narrow, half power linewidth ≃3 MHz, and weak feature of HCN in its ν 1 + 3ν 2 + ν 3 vibrational mode (Cernicharo et al 2011). The CCS line in the high frequency part of the line profile is separated by 17 MHz from the J=12-11 transition of HMgNC and is not affecting the line profile.…”