title: The millimeter IRAM-30 m line survey toward IK Tau.
abstract: OBJECTIVE
  We aim to investigate the physical and chemical properties of the molecular envelope of the oxygen-rich AGB star IK Tau.
  
  
  METHODS
  We carried out a millimeter wavelength line survey between ~79 and 356 GHz with the IRAM-30 m telescope. We analysed the molecular lines detected in IK Tau using the population diagram technique to derive rotational temperatures and column densities. We conducted a radiative transfer analysis of the SO2lines, which also helped us to verify the validity of the approximated method of the population diagram for the rest of the molecules.
  
  
  RESULTS
  For the first time in this source we detected rotational lines in the ground vibrational state of HCO+, NS, NO, and H2CO, as well as several isotopologues of molecules previously identified, namely, C18O, Si17O, Si18O,29SiS,30SiS, Si34S, H13CN,13CS, C34S, H234S,34SO, and34SO2. We also detected several rotational lines in vibrationally excited states of SiS and SiO isotopologues, as well as rotational lines of H2O in the vibrationally excited stateν2=2. We have also increased the number of rotational lines detected of molecules that were previously identified toward IK Tau, including vibrationally excited states, enabling a detailed study of the molecular abundances and excitation temperatures. In particular, we highlight the detection of NS and H2CO with fractional abundances off(NS)~10-8andf(H2CO)~[10-7-10-8]. Most of the molecules display rotational temperatures between 15 and 40 K. NaCl and SiS isotopologues display rotational temperatures higher than the average (~65 K). In the case of SO2a warm component withTrot~290 K is also detected.
  
  
  CONCLUSIONS
  With a total of ~350 lines detected of 34 different molecular species (including different isotopologues), IK Tau displays a rich chemistry for an oxygen-rich circumstellar envelope. The detection of carbon bearing molecules like H2CO, as well as the discrepancies found between our derived abundances and the predictions from chemical models for some molecules, highlight the need for a revision of standard chemical models. We were able to identify at least two different emission components in terms of rotational temperatures. The warm component, which is mainly traced out by SO2, is probably arising from the inner regions of the envelope (at ≲8R∗) where SO2has a fractional abundance off(SO2)~10-6. This result should be considered for future investigation of the main formation channels of this, and other, parent species in the inner winds of O-rich AGB stars, which at present are not well reproduced by current chemistry models.
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, 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
authors.initials: L
authors.lastname: Velilla Prieto
authors.affiliation: Centro de Astrobiología, INTA-CSIC, E-28691 Villanueva de la Cañada, Madrid, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Sánchez Contreras
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, CSIC, c/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Cernicharo
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, CSIC, c/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Agúndez
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, 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: Observatorio Astronómico Nacional (IGN), Ap 112, 28803 Alcalá de Henares, Madrid, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Bujarrabal
authors.affiliation: Observatorio Astronómico Nacional (IGN), Alfonso XII No 3, 28014 Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Alcolea
authors.affiliation: LERMA, Observatoire de Paris, Sorbonne Université, UPMC, UMR 8112, F-92195 Meudon, France.
authors.forename: C
authors.initials: C
authors.lastname: Balança
authors.affiliation: Université de Bordeaux, LAB, UMR 5804, F-33270 Floirac, France; CNRS, LAB, UMR 5804, F-33270, Floirac, France.
authors.forename: F
authors.initials: F
authors.lastname: Herpin
authors.affiliation: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
authors.forename: K M
authors.initials: KM
authors.lastname: Menten
authors.affiliation: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Wyrowski
keywords: Astrochemistry; Circumstellar matter; Line: identification; Stars: AGB and post-AGB; Stars: abundances; Stars: individual: IK Tau