TY - JOUR
T1 - The unusual 3D distribution of NaCl around the asymptotic giant branch star IK Tau
AU - Coenegrachts, A.
AU - Danilovich, T.
AU - De Ceuster, F.
AU - Decin, L.
N1 - Funding Information:
The authors grateful to the anonymous referee for providing many constructive comments. We also thank Daniel Price for fruitful discussions regarding shocks. This paper makes use of the following ALMA data: ADS/JAO.ALMA2013.1.00166.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. Credit CASA: International consortium of scientists based at the National Radio Astronomical Observatory (NRAO), the European Southern Observatory (ESO), the National Astronomical Observatory of Japan (NAOJ), the CSIRO Australia Telescope National Facility (CSIRO/ATNF), and the Netherlands Institute for Radio Astronomy (ASTRON) under the guidance of NRAO. TD and FDC acknowledge support from the Research Foundation Flanders (FWO) through grants 12N9920N, and 1253223N, respectively. TD is supported in part by the Australian Research Council through a Discovery Early Career Researcher Award (DE230100183). LD thanks the support of the Fund of Scientific Research via the Senior Research Project G099720N.
Publisher Copyright:
© 2023 The Authors.
PY - 2023/10/10
Y1 - 2023/10/10
N2 - Context. Sodium chloride (NaCl) is a diatomic molecule with a large dipole moment, which allows for its detection even at relatively low abundances. It has been detected towards several evolved stars, including the asymptotic giant branch (AGB) star IK Tau, around which it is distributed in several clumps that lie off-centre from the star. Aims. We aim to study the 3D distribution of NaCl around the AGB star IK Tau and determine the abundance of NaCl relative to H2 for each of the clumps. Methods. First, a new value for the maximum expansion velocity was determined. The observed ALMA channel maps were then de-projected to create a 3D model of the distribution of NaCl. This model was then used as input for the radiative transfer modelling code Magritte. We determined the NaCl abundances of each of the clumps by comparing the observations with the results of the Magritte simulations. Results. We derive an updated value for the maximum expansion velocity of IK Tau: Ï exp = 28.4 ± 1.7 km s- 1. A spiral-like shape can be discerned in our 3D distribution model of NaCl. This spiral lies more or less in the plane of the sky, with the distribution flatter in the line-of-sight direction than in the plane of the sky. We find clump abundances of between 9- 10-9 and 5 - 10-8 relative to H2; the relative abundance is typically lower for clumps closer to the star. Conclusions. This is the first time de-projection has been used to understand the 3D environment of molecular emission around an AGB star and to calculate the fractional abundance of NaCl in clumps surrounding the star.
AB - Context. Sodium chloride (NaCl) is a diatomic molecule with a large dipole moment, which allows for its detection even at relatively low abundances. It has been detected towards several evolved stars, including the asymptotic giant branch (AGB) star IK Tau, around which it is distributed in several clumps that lie off-centre from the star. Aims. We aim to study the 3D distribution of NaCl around the AGB star IK Tau and determine the abundance of NaCl relative to H2 for each of the clumps. Methods. First, a new value for the maximum expansion velocity was determined. The observed ALMA channel maps were then de-projected to create a 3D model of the distribution of NaCl. This model was then used as input for the radiative transfer modelling code Magritte. We determined the NaCl abundances of each of the clumps by comparing the observations with the results of the Magritte simulations. Results. We derive an updated value for the maximum expansion velocity of IK Tau: Ï exp = 28.4 ± 1.7 km s- 1. A spiral-like shape can be discerned in our 3D distribution model of NaCl. This spiral lies more or less in the plane of the sky, with the distribution flatter in the line-of-sight direction than in the plane of the sky. We find clump abundances of between 9- 10-9 and 5 - 10-8 relative to H2; the relative abundance is typically lower for clumps closer to the star. Conclusions. This is the first time de-projection has been used to understand the 3D environment of molecular emission around an AGB star and to calculate the fractional abundance of NaCl in clumps surrounding the star.
KW - Circumstellar matter
KW - Stars: AGB and post-AGB
KW - Stars: individual: IK Tau
KW - Submillimeter: stars
UR - http://www.scopus.com/inward/record.url?scp=85175071434&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/202346116
DO - 10.1051/0004-6361/202346116
M3 - Article
AN - SCOPUS:85175071434
SN - 0004-6361
VL - 678
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
M1 - A85
ER -