Circumstellar molecular composition of the oxygen-rich AGB star IK Tau: I. Observations and LTE chemical abundance analysis

Abstract

The aim of this paper is to study the molecular composition in the circumstellar envelope around the oxygen-rich star IK Tau. We observed IK Tau in several (sub)millimeter bands using the APEX telescope during three observing periods. To determine the spatial distribution of the ${}^{12}\mathrm{CO}(3-2)$ emission, mapping observations were performed. To constrain the physical conditions in the circumstellar envelope, multiple rotational CO emission lines were modeled using a non local thermodynamic equilibrium radiative transfer code. The rotational temperatures and the abundances of the other molecules were obtained assuming local thermodynamic equilibrium. An oxygen-rich Asymptotic Giant Branch star has been surveyed in the submillimeter wavelength range. Thirty four transitions of twelve molecular species, including maser lines, were detected. The kinetic temperature of the envelope was determined and the molecular abundance fractions of the molecules were estimated. The deduced molecular abundances were compared with observations and modeling from the literature and agree within a factor of 10, except for SO${}_2$, which is found to be almost a factor 100 stronger than predicted by chemical models. From this study, we found that IK Tau is a good laboratory to study the conditions in circumstellar envelopes around oxygen-rich stars with (sub)millimeter-wavelength molecular lines. We could also expect from this study that the molecules in the circumstellar envelope can be explained more faithful by non-LTE analysis with lower and higher transition lines than by simple LTE analysis with only lower transition lines. In particular, the observed CO line profiles could be well reproduced by a simple expanding envelope model with a power law structure.

13 pages, 14 figures, 8 tables *Accepted for publication in Astronomy and Astrophysics

Cited by in corpus (21)

• The millimeter IRAM-30m line survey toward IK Tau
• Tracing the phase transition of Al-bearing species from molecules to dust in AGB winds. Constraining the presence of gas-phase (Al2O3)n clusters
• Circumstellar molecular composition of the oxygen-rich AGB star IK~Tau: II. In-depth non-LTE chemical abundance analysis
• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• The Impact of Recent Advances in Laboratory Astrophysics on our Understanding of the Cosmos
• Sulphur molecules in the circumstellar envelopes of M-type AGB stars
• Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow
• The impact of stellar companion UV photons on the chemistry of the circumstellar environments of AGB stars
• Polarization of thermal molecular lines in the envelope of IK Tau
• An ALMA view of CS and SiS around oxygen-rich AGB stars
• Exploring the innermost dust formation region of the oxygen-rich AGB star IK~Tau with VLT/SPHERE-ZIMPOL and VLTI/AMBER
• An ALMA view of SO and SO${}_2$ around oxygen-rich AGB stars
• Silicon isotopic abundance toward evolved stars and its application for presolar grains
• Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes -- I. The case of hydrogen cyanide
• Vibrationally excited water emission at 658 GHz from evolved stars
• Chemistry in AGB stars: successes and challenges
• The unusual 3D distribution of NaCl around the AGB star IK Tau
• Molecules in the peculiar age-defying source IRAS 19312+1950
• PACS and SPIRE range spectroscopy of cool, evolved stars
• Molecules and Chemistry in Red Supergiants
• Exploring circumstellar chemistry in X-ray emitting AGB stars