title: Hints of a rotating spiral structure in the innermost regions around IRC +10216.
abstract: The Atacama Large Millimeter/submillimeter Array (ALMA) is allowing us to study the innermost regions of the circumstellar envelopes of evolved stars withun-precedentedprecision and sensitivity. Key processes in the ejection of matter and dust from these objects occur in their inner zones. In this work, we present sub-arcsecond interferometric maps of transitions of metal-bearing molecules towards the prototypical C-rich evolved star IRC +10216. While Al-bearing molecules seem to be present as a roughly spherical shell, the molecular emission from the salts NaCl and KCl presents an elongation in the inner regions, with a central minimum. In order to accurately analyze the emissionfromthe NaCl rotational lines, we present new calculations of the collisional rates for this molecule based on new spectroscopic constants. The most plausible interpretation for the spatial distribution of the salts is a spiral with a NaCl mass of 0.08M☉. Alternatively, a torus of gas and dust would result in similar structures as those observed.From the torus scenario we derive a mass of~ 1.1 × 10-4M☉.In both cases, the spiral and the torus, the NaCl structure presents an inner minimum of 27 AU. In the case of the torus, the outer radius is 73 AU. The kinematics of both the spiral and the torus suggests that they are slowly expanding and rotating. Alternative explanations for the presence of the elongation are explored. The presence ofthese featuresonly in KCl and NaCl might be a result of their comparatively high dipole moment with respect to the Al-bearing species.
authors.affiliation: Group of Molecular Astrophysics. ICMM, CSIC. C/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain.
authors.forename: G
authors.initials: G
authors.lastname: Quintana-Lacaci
authors.affiliation: Group of Molecular Astrophysics. ICMM, CSIC. C/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Cernicharo
authors.affiliation: Group of Molecular Astrophysics. ICMM, CSIC. C/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Agúndez
authors.affiliation: Group of Molecular Astrophysics. ICMM, CSIC. C/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain ; Centro de Astrobiología, INTA-CSIC. E-28691 Villanueva de la Cañada, Madrid, Spain.
authors.forename: L Velilla
authors.initials: LV
authors.lastname: Prieto
authors.affiliation: Institut de Radioastronomie Millimétrique. 300 rue de la la Piscine, F-38406, Saint Martin d'Hères, France.
authors.forename: A
authors.initials: A
authors.lastname: Castro-Carrizo
authors.affiliation: INAF, Istituto di Radioastronomia, via P. Gobetti 101, 40129, Bologna, Italy.
authors.forename: N
authors.initials: N
authors.lastname: Marcelino
authors.affiliation: Grupo de Espectroscopía Molecular, Edificio Quifima, Laboratorios de Espectroscopía y Bioe-spectroscopía. Unidad asociada CSIC, Parque científico Uva, Universidad de Valladolid, Paseo de Belén 5, E-47011, Valladolid, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Cabezas
authors.affiliation: Grupo de Espectroscopía Molecular, Edificio Quifima, Laboratorios de Espectroscopía y Bioe-spectroscopía. Unidad asociada CSIC, Parque científico Uva, Universidad de Valladolid, Paseo de Belén 5, E-47011, Valladolid, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Peña
authors.affiliation: Grupo de Espectroscopía Molecular, Edificio Quifima, Laboratorios de Espectroscopía y Bioe-spectroscopía. Unidad asociada CSIC, Parque científico Uva, Universidad de Valladolid, Paseo de Belén 5, E-47011, Valladolid, Spain.
authors.forename: J L
authors.initials: JL
authors.lastname: Alonso
authors.affiliation: Universidad de Murcia. Faculdad de Química. Dpto. de Química-Física. Campus Espinardo E-30100, Murcia, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Zúñiga
authors.affiliation: Universidad de Murcia. Faculdad de Química. Dpto. de Química-Física. Campus Espinardo E-30100, Murcia, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Requena
authors.affiliation: Universidad de Murcia. Faculdad de Química. Dpto. de Química-Física. Campus Espinardo E-30100, Murcia, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Bastida
authors.affiliation: LOMC-UMR 6294, CNRS-Université du Havre, 25 rue Philippe Lebon, BP. 1123, 76063 Le Havre cedex, France ; Department of Optics and Spectroscopy, Tomsk State University, 36 Lenin av., Tomsk 634050, Russia.
authors.forename: Y
authors.initials: Y
authors.lastname: Kalugina
authors.affiliation: LOMC-UMR 6294, CNRS-Université du Havre, 25 rue Philippe Lebon, BP. 1123, 76063 Le Havre cedex, France.
authors.forename: F
authors.initials: F
authors.lastname: Lique
authors.affiliation: Institut de Radioastronomie Millimétrique. 300 rue de la la Piscine, F-38406, Saint Martin d'Hères, France ; LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR 8112, F-75014, Paris, France.
authors.forename: M
authors.initials: M
authors.lastname: Guélin
keywords: astrochemistry; circumstellar matter; stars: AGB and post-AGB; stars: individual (IRC +10216)