W Hya through the eye of Odin

Justtanont, K.; Bergman, P.; Larsson, Bengt; Olofsson, H.; Schöier, F. L.; Frisk, U.; Hasegawa, T.; Kwok, Sun; Olberg, M.; Sandqvist, Aa.; Volk, Kevin; Elitzur, Moshe

doi:10.1051/0004-6361:20052969

Cited by 39 publications

(78 citation statements)

References 37 publications

(48 reference statements)

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“…The upper limit implied by the cosmic abundances of carbon and oxygen is no more than 1 × 10 −3 , assuming that all carbon is locked in CO and the remaining oxygen goes into H 2 O (Anders & Grevesse 1989). Vaporization of icy bodies (Justtanont et al 2005) or grain surface reactions via Fischer-Tropsch catalysis (Willacy 2004) will also result in a higher water abundance. Considering the agreement between the derived and the TE abundance, the effects of the other processes seem negligible for IK Tau.…”

Section: Resultsmentioning

confidence: 99%

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

Decin

Justtanont

Beck

et al. 2010

A&A

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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 highresolution HIFI spectrometer onboard Herschel. We report on the first detection of H 16 2 O and the rarer isotopologues H 17 2 O and H 18 2 O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10 −5 , and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H 2 O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12 CO, 13 CO, 28 SiO, 29 SiO, 30 SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.

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Section: Resultsmentioning

confidence: 99%

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

Decin

Justtanont

Beck

et al. 2010

A&A

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“…For the molecular line excitation analysis well-tested, non-LTE and non-local, spectral line radiative transfer codes (based on the Monte Carlo and ALI methods), as presented in Schöier & Olofsson (2001), Justtanont et al (2005) and Maercker et al (2008Maercker et al ( , 2009) are used. The codes have also been benchmarked to high accuracy against other non-LTE radiative line transfer codes (van Zadelhoff et al 2002;Maercker et al 2008).…”

Section: Radiative Transfer Analysismentioning

confidence: 99%

“…In the detailed modelling of circumstellar H 2 O line emission for a number of M-type AGB stars, observed using the ISO and Odin satellites, the derived ortho-H 2 O abundances are ∼10 −4 (Justtanont et al 2005;Maercker et al 2008Maercker et al , 2009). The recent analysis of Herschel data of the M-type AGB star IK Tau confirms this (Decin et al 2010c).…”

Section: Introductionmentioning

confidence: 99%

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

Schöier

Maercker

Justtanont

et al. 2011

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Context. S-type AGB stars (C/O ≈ 1) are thought to be transition objects from M-type (O-rich) AGB stars to carbon stars and as such are interesting objects in themselves. Of particular interest is to determine accurate circumstellar properties and molecular abundances, due to their predicted sensitivity to the photospheric C/O-ratio. Aims. Presented here are new sensitive sub-millimetre line observations of molecules towards the S-type AGB star χ Cyg, using the HIFI instrument on-board the Herschel Space Observatory. The observed lines predominantly probe warm gas relatively close to the central star. Methods. Detailed, non-LTE, radiative transfer modelling has been used in order to interpret the circumstellar molecular line observations performed using HIFI, assuming a spherically symmetric, smooth, accelerating wind. Results. Lines from common molecules such as H 2 O, CO and SiO, which are expected to be abundant in an S-type AGB star, are clearly detected (as well as some of their isotopologues) in the HIFI spectra. In addition, we detect lines from carbon-bearing molecules such as HCN and CN. The CO line modelling indicates that the mass-loss rate has not undergone any significant modulations during the past ≈1000 yr. The derived o-H 2 O fractional abundance is ≈7 × 10 −6 , i.e., lower than those obtained for a small sample of M-type AGB stars but higher than what has been derived for a few carbon stars. We further obtain a p-H 2 O fractional abundance of ≈5 × 10 −6 giving an o/p-ratio of ≈1.4. Molecular line cooling is dominated by H 2 O only in a region close to the star ( 6 × 10 14 cm). The SiO abundance is estimated to be ≈1 × 10 −5 . The 12 CO/ 13 CO ratio is 43 ± 6. The high-excitation rotational lines clearly probe the acceleration region of the stellar wind ( 2 × 10 15 cm) and put constraints on dynamical wind models. We are unable to fit consistently the combined ground-based and HIFI data for HCN and CN. Conclusions. The derived H 2 O abundance is reasonably consistent with recent chemical model predictions and so is the SiO abundance. The o/p-ratio of ≈1.4 supports a chemical formation under non-LTE conditions for the H 2 O molecules, and the presence of carbon-bearing molecules at relatively large abundances is also indicative of the importance of non-LTE chemical processes in regulating the circumstellar chemistry. The velocity field derived from the molecular line modelling is consistent with that obtained from solving for the wind dynamics through the coupled momentum equations of the dust and gas particles.

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“…We include these non-LTE effects by using an accelerated lambda iteration scheme (ALI, Rybicki & Hummer 1991) to solve the radiative transfer in a spherically symmetric model cloud. The ALI code we employed is the same as that used and tested by Justtanont et al (2005) and Maercker et al (2008). For the Sgr B2 cloud, we adopt the size, as well as gas and dust physical parameters for the envelope, provided by Zmuidzinas et al (1995), since those reproduce the observed continuum level around 557 GHz.…”

Section: Watermentioning

confidence: 99%

Ground-state ammonia and water in absorption towards Sgr B2

Wirström

Bergman

Black

et al. 2010

A&A

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Context. Observations of transitions to the ground-state of a molecule are essential to obtain a complete picture of its excitation and chemistry in the interstellar medium, especially in diffuse and/or cold environments. For the important interstellar molecules H 2 O and NH 3 , these ground-state transitions are heavily absorbed by the terrestrial atmosphere, hence not observable from the ground. Aims. We attempt to understand the chemistry of nitrogen, oxygen, and their important molecular forms, NH 3 and H 2 O in the interstellar medium of the Galaxy. Methods. We have used the Odin submillimetre-wave satellite telescope to observe the ground state transitions of ortho-ammonia and ortho-water, including their 15 N, 18 O, and 17 O isotopologues, towards Sgr B2. The extensive simultaneous velocity coverage of the observations, >500 km s −1 , ensures that we can probe the conditions of both the warm, dense gas of the molecular cloud Sgr B2 near the Galactic centre, and the more diffuse gas in the Galactic disk clouds along the line-of-sight.Results. We present ground-state NH 3 absorption in seven distinct velocity features along the line-of-sight towards Sgr B2. We find a nearly linear correlation between the column densities of NH 3 and CS, and a square-root relation to N 2 H + . The ammonia abundance in these diffuse Galactic disk clouds is estimated to be about 0.5-1 × 10 −8 , similar to that observed for diffuse clouds in the outer Galaxy. On the basis of the detection of H 18 2 O absorption in the 3 kpc arm, and the absence of such a feature in the H 17 2 O spectrum, we conclude that the water abundance is around 10 −7 , compared to ∼10 −8 for NH 3 . The Sgr B2 molecular cloud itself is seen in absorption in NH 3 , 15 NH 3 , H 2 O, H 18 2 O, and H 17 2 O, with emission superimposed on the absorption in the main isotopologues. The non-LTE excitation of NH 3 in the environment of Sgr B2 can be explained without invoking an unusually hot (500 K) molecular layer. A hot layer is similarly not required to explain the line profiles of the 1 1,0 ←1 0,1 transition from H 2 O and its isotopologues. The relatively weak 15 NH 3 absorption in the Sgr B2 molecular cloud indicates a high [ 14 N/ 15 N] isotopic ratio >600. The abundance ratio of H 18 2 O and H 17 2 O is found to be relatively low, 2.5-3. These results together indicate that the dominant nucleosynthesis process in the Galactic centre is CNO hydrogen burning.

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W Hya through the eye of Odin

Cited by 39 publications

References 37 publications

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen byHerschel/HIFI

A chemical inventory of the S-type AGB starχ Cygni based onHerschel/HIFI observations of circumstellar line emission

Ground-state ammonia and water in absorption towards Sgr B2

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