Polarization of thermal molecular lines in the envelope of IK Tauri

Vlemmings, Wouter; Ramstedt, S.; Rao, Ramprasad; Maercker, M.

doi:10.1051/0004-6361/201218897

Cited by 34 publications

(29 citation statements)

References 24 publications

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“…A striking case is provided by the carbon star IRC+10216, where more than 70 molecular species have been detected Agúndez et al 2011;Neufeld et al 2011a;Decin et al 2010b,c;Cernicharo et al 2010a,b;Mauron & Huggins 2010;Pulliam et al 2010), while the dust-condensation zone is being resolved and probed thoroughly (Fonfría et al 2014;Cernicharo et al 2013Cernicharo et al , 2011Decin et al 2010b). Other examples of wellstudied stars which several chemical analyses have focused on are the oxygen star IK Tau (De Beck et al 2013;Vlemmings et al 2012;Decin et al 2010a,d;Kim et al 2010;Duari, Cherchneff, & Willacy 1999), and the S-type star χ Cig (Schöier et al 2011;Justtanont et al 2010;Cotton et al 2010;Duari & Hatchell 2000).…”

Section: Introductionmentioning

confidence: 99%

Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Marigo

Ripamonti

Nanni

et al. 2015

Mon. Not. R. Astron. Soc.

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We investigate the formation of hydrogen cyanide (HCN) in the inner circumstellar envelopes of thermally pulsing asymptotic giant branch (TP-AGB) stars. A dynamic model for periodically shocked atmospheres, which includes an extended chemo-kinetic network, is for the first time coupled to detailed evolutionary tracks for the TP-AGB phase computed with the COLIBRI code. We carried out a calibration of the main shock parameters (the shock formation radius r s,0 , and the effective adiabatic index γ eff ad ) using the circumstellar HCN abundances recently measured for a populous sample of pulsating TP-AGB stars. Our models recover the range of the observed HCN concentrations as a function of the mass-loss rates, and successfully reproduce the systematic increase of HCN moving along the M-S-C chemical sequence of TP-AGB stars, that traces the increase of the surface C/O ratio. The chemical calibration brings along two important implications for the physical properties of the pulsation-induced shocks: i) the first shock should emerge very close to the photosphere (r s,0 ≃ 1 R), and ii) shocks are expected to have a dominant isothermal character (γ eff ad ≃ 1) in the denser region close to the star (within ∼ 3 − 4 R), implying that radiative processes should be quite efficient. Our analysis also suggests that the HCN concentrations in the inner circumstellar envelopes are critically affected by the H-H 2 chemistry during the post-shock relaxation stages. Given the notable sensitiveness of the results to stellar parameters, this paper shows that such chemo-dynamic analyses may indeed provide a significant contribution to the broader goal of attaining a comprehensive calibration of the TP-AGB evolutionary phase.

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Section: Introductionmentioning

confidence: 99%

Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Marigo

Ripamonti

Nanni

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Moreover, recent observations Table 7 is available in electronic form at http://www.aanda.org support the presence of magnetic fields around AGB and post-AGB stars (e.g., Amiri et al 2011;Pérez-Sánchez et al 2011;Leal-Ferreira et al 2012;Vlemmings et al 2012). However, the sample of low and intermediate mass evolved stars around which magnetic fields have been measured is still small.…”

Section: Introductionmentioning

confidence: 99%

Magnetic fields around evolved stars: further observations of H₂O maser polarization

Leal-Ferreira¹,

Vlemmings²,

Kemball³

et al. 2013

A&A

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Context.A low-or intermediate-mass star is believed to maintain a spherical shape throughout the evolution from the main sequence to the asymptotic giant branch (AGB) phase. However, many post-AGB objects and planetary nebulae exhibit non-spherical symmetry. Several candidates have been suggested as factors that can play a role in this change of morphology, but the problem is still not well understood. Magnetic fields are one of these possible agents. Aims. We aim to detect the magnetic field and infer its properties around four AGB stars using H 2 O maser observations. The sample we observed consists of the following sources: the semi-regular variable RT Vir, and the Mira variables AP Lyn, IK Tau, and IRC+60370. Methods. We observed the 6 1,6 −5 2,3 H 2 O maser rotational transition in full-polarization mode to determine its linear and circular polarization. Based on the Zeeman effect, one can infer the properties of the magnetic field from the maser polarization analysis. Results. We detected a total of 238 maser features in three of the four observed sources. No masers were found toward AP Lyn. The observed masers are all located between 2.4 and 53.0 AU from the stars. Linear and circular polarization was found in 18 and 11 maser features, respectively. Conclusions. We more than doubled the number of AGB stars in which a magnetic field has been detected from H 2 O maser polarization. Our results confirm the presence of fields around IK Tau, RT Vir, and IRC+60370. The strength of the field along the line of sight is found to be between 47 and 331 mG in the H 2 O maser region. Extrapolating this result to the surface of the stars, assuming a toroidal field (∝r −1 ), we find magnetic fields of 0.3−6.9 G on the stellar surfaces. If, instead of a toroidal field, we assume a poloidal field (∝r −2 ), then the extrapolated magnetic field strength on the stellar surfaces are in the range between 2.2 and ∼115 G. Finally, if a dipole field (∝r −3 ) is assumed, the field strength on the surface of the star is found to be between 15.8 and ∼1945 G. The magnetic energy of our sources is higher than the thermal and kinetic energy in the H 2 O maser region of this class of objects. This leads us to conclude that, indeed, magnetic fields probably play an important role in shaping the outflows of evolved stars.

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“…Circular polarization due to magnetic-field-induced Zeeman splitting has been measured using maser polarization observations (e.g., Herpin et al 2006;Vlemmings et al 2005;Bains et al 2003). For C-type (C/O > 1) stars, Zeeman splitting of the paramagnetic molecule CN has been used to estimate the magnetic field (Herpin et al 2009), and recently, the first estimate of a magnetic field around an evolved star using polarized CO emission was published (Vlemmings et al 2012). The current measurements are consistent with either an R −1 (toroidal) or an R −2 (poloidal) dependence, indicating field strengths of order several tens of Gauss at the stellar surface (Vlemmings 2011).…”

Section: Introductionmentioning

confidence: 99%

Searching for X-ray emission from AGB stars

Ramstedt¹,

Montez²,

Kastner³

et al. 2012

A&A

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Context. Magnetic fields have been measured around asymptotic giant branch (AGB) stars of all chemical types using maser polarization observations. If present, a large-scale magnetic field would lead to X-ray emission, which should be observable using current X-ray observatories. Aims. The aim is to search the archival data for AGB stars that are intrinsic X-ray emitters. Methods. We have searched the ROSAT, CXO, and XMM-Newton archives for serendipitous X-ray observations of a sample of ∼500 AGB stars. We specifically searched for the AGB stars detected with GALEX. The data is calibrated, analyzed and the X-ray luminosities and temperatures are estimated as functions of the circumstellar absorption. Results. We identify 13 AGB stars as having either serendipitous or targeted observations in the X-ray data archives, however for a majority of the sources the detailed analysis show that the detections are questionable. Two new sources are detected by ROSAT: T Dra and R UMa. The spectral analysis suggests that the emission associated with these sources could be due to coronal activity or interaction across a binary system. Conclusions. Further observations of the detected sources are necessary to clearly determine the origin of the X-ray emission. Moreover, additional objects should be subject to targeted X-ray observations in order to achieve better constraints for the magnetic fields around AGB stars.

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Polarization of thermal molecular lines in the envelope of IK Tauri

Cited by 34 publications

References 24 publications

Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Magnetic fields around evolved stars: further observations of H₂O maser polarization

Searching for X-ray emission from AGB stars

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Polarization of thermal molecular lines in the envelope of IK Tauri

Cited by 34 publications

References 24 publications

Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes – I. Hydrogen cyanide

Magnetic fields around evolved stars: further observations of H2O maser polarization

Searching for X-ray emission from AGB stars

Contact Info

Product

Resources

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Magnetic fields around evolved stars: further observations of H₂O maser polarization