The evolutionary state of Miras with changing pulsation periods

Uttenthaler, S.; Stiphout, K. van; Voet, K.; Winckel, H. Van; Eck, S. Van; Jorissen, A.; Kerschbaum, F.; Raskin, Gert; Prins, S.; Pessemier, Wim; Waelkens, Christoffel; Frémat, Y.; Hensberge, H.; Dumortier, L.; Lehmann, H.

doi:10.1051/0004-6361/201116463

Cited by 41 publications

(68 citation statements)

References 56 publications

(95 reference statements)

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“…Thanks to is proximity (∼78 pc; Knapp et al 2003) and its brightness, R Dor is also well studied with various observational techniques from the visible to the radio. This semi-regular variable has a light curve showing a clear periodicity with period of 389 days (Uttenthaler et al 2011). The molecular abundance stratification in its circumstellar envelope was studied in detail by Khouri et al (2014a,b).…”

Section: Target Selectionmentioning

confidence: 99%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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Context. The condensation of inorganic dust grains in the winds of evolved stars is poorly understood. As of today, it is not yet known which molecular clusters form the first dust grains in oxygen-rich (C/O < 1) asymptotic giant branch (AGB) winds. Aluminium oxides and iron-free silicates are often put forward as promising candidates for the first dust seeds. Aims. We aim to constrain the dust formation histories in the winds of oxygen-rich AGB stars. Methods. We obtained Atacama Large Millimeter/sub-millimeter array (ALMA) observations with a spatial resolution of 120 × 150 mas tracing the dust formation region of the low mass-loss rate AGB star, R Dor, and the high mass-loss rate AGB star, IK Tau. We detected emission line profiles of AlO, AlOH, and AlCl in the ALMA data and used these line profiles to derive a lower limit of atomic aluminium incorporated in molecules. This constrains the aluminium budget that can condense into grains. Results. Radiative transfer models constrain the fractional abundances of AlO, AlOH, and AlCl in IK Tau and R Dor. We show that the gas-phase aluminium chemistry is completely different in both stars with a remarkable difference in the AlO and AlOH abundance stratification. The amount of aluminium locked up in these three molecules is small, ≤1.1 × 10 −7 w.r.t. H 2 , for both stars, i.e. only ≤2% of the total aluminium budget. An important result is that AlO and AlOH, which are the direct precursors of alumina (Al 2 O 3 ) grains, are detected well beyond the onset of the dust condensation, which proves that the aluminium oxide condensation cycle is not fully efficient. The ALMA observations allow us to quantitatively assess the current generation of theoretical dynamical-chemical models for AGB winds. We discuss how the current proposed scenario of aluminium dust condensation for low mass-loss rate AGB stars within a few stellar radii from the star, in particular for R Dor and W Hya, poses a challenge if one wishes to explain both the dust spectral features in the spectral energy distribution (SED) in interferometric data and in the polarized light signal. In particular, the estimated grain temperature of Al 2 O 3 is too high for the grains to retain their amorphous structure. We advocate that large gas-phase (Al 2 O 3 ) n clusters (n > 34) can be the potential agents of the broad 11 µm feature in the SED and in the interferometric data and we propose potential formation mechanisms for these large clusters.

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Section: Target Selectionmentioning

confidence: 99%

Study of the aluminium content in AGB winds using ALMA

Decin

Richards

Waters

et al. 2017

A&A

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“…Instead of the flux derived with the SPHERE-ZIMPOL filter, we used the high-resolution visible spectrum presented by Uttenthaler et al (2011) with our absolute flux calibration described in Paper I. For the near-IR domain, we scaled the spectrum obtained at phase 0.79 by Woodruff et al (2009, see their Fig.…”

Section: Determination Of Luminosity and Effective Temperature At Prementioning

confidence: 99%

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

Ohnaka

Weigelt

Hofmann

2016

A&A

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Aims. Our recent visible polarimetric images of the well-studied AGB star W Hya taken at pre-maximum light (phase 0.92) with VLT/SPHERE-ZIMPOL have revealed clumpy dust clouds close to the star at ∼2 R . We present second-epoch SPHERE-ZIMPOL observations of W Hya at minimum light (phase 0.54) as well as high-spectral resolution long-baseline interferometric observations with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Methods. We observed W Hya with VLT/SPHERE-ZIMPOL at three wavelengths in the continuum (645, 748, and 820 nm), in the Hα line at 656.3 nm, and in the TiO band at 717 nm. The VLTI/AMBER observations were carried out in the wavelength region of the CO first overtone lines near 2.3 µm with a spectral resolution of 12 000. Results. The high-spatial resolution polarimetric images obtained with SPHERE-ZIMPOL have allowed us to detect clear time variations in the clumpy dust clouds as close as 34-50 mas (1.4-2.0 R ) to the star. We detected the formation of a new dust cloud as well as the disappearance of one of the dust clouds detected at the first epoch. The Hα and TiO emission extends to ∼150 mas (∼6 R ), and the Hα images obtained at two epochs reveal time variations. The degree of linear polarization measured at minimum light, which ranges from 13 to 18%, is higher than that observed at pre-maximum light. The power-law-type limb-darkened disk fit to the AMBER data in the continuum results in a limb-darkened disk diameter of 49.1 ± 1.5 mas and a limb-darkening parameter of 1.16±0.49, indicating that the atmosphere is more extended with weaker limb-darkening compared to pre-maximum light. Our Monte Carlo radiative transfer modeling shows that the second-epoch SPHERE-ZIMPOL data can be explained by a shell of 0.1 µm grains of Al 2 O 3 , Mg 2 SiO 4 , and MgSiO 3 with a 550 nm optical depth of 0.6±0.2 and an inner and outer radii of 1.3 R and 10±2 R , respectively. Our modeling suggests the predominance of small (0.1 µm) grains at minimum light, in marked contrast to the predominance of large (0.5 µm) grains at pre-maximum light. Conclusions. The variability phase dependence of the characteristic grain size implies that small grains might just have started to form at minimum light in the wake of a shock, while the pre-maximum light phase might have corresponded to the phase of efficient grain growth.

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“…Information on the Tc content was compiled from the following sources: Little et al (1987), Smith & Lambert (1988), Vanture et al (1991), Lebzelter & Hron (1999, 2003, Van Eck & Jorissen (1999), Van Eck et al (2000), Uttenthaler et al (2007Uttenthaler et al ( , 2011 Uttenthaler & Lebzelter (2010), and Smolders et al (2012). Further data on the Tc content of carbon stars was taken from Abia et al (2002) and Barnbaum (priv.…”

Section: The Datamentioning

confidence: 99%

Period – mass-loss rate relation of Miras with and without technetium

Uttenthaler

2013

A&A

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Aims. We report the discovery that Mira variables with and without absorption lines of the element technetium (Tc) occupy two different regions in a diagram of near-to mid-IR colour versus pulsation period. Tc is an indicator of a recent or ongoing mixing event called the third dredge-up (3DUP), and the near-to mid-IR colour, such as the (K − [22]) colour where [22] is the the 22 μm band of the WISE space observatory, is an indicator of the dust mass-loss rate of a star. Methods. We collected data from the literature about the Tc content, pulsation period, and near-and mid-IR magnitudes of more than 190 variable stars on the asymptotic giant branch (AGB) to which Miras belong. The sample is naturally biased towards optical AGB stars, which have low to intermediate (dust) mass-loss rates. Results. We show that a clear relation between dust mass-loss rate and pulsation period exists if a distinction is made between Tc-poor and Tc-rich Miras. Surprisingly, at a given period, Tc-poor Miras are redder in (K − [22]) than are Tc-rich Miras; i.e., they have higher mass-loss rates than the Tc-rich Miras. A few stars deviate from this trend; physical explanations are given for these exceptions, such as binarity or high mass. Conclusions. We put forward two hypotheses to explain this dichotomy and conclude that the two sequences formed by Tc-poor and Tc-rich Miras are probably due to the different masses of the two groups. The pulsation period has a strong correlation with the dust-mass loss rate, indicating that the pulsations are indeed triggering a dust-driven wind. The location in the (K − [22]) vs. period diagram can be used to distinguish between pre-and post-3DUP Miras, which we apply to a sample of Galactic bulge AGB stars. We find that 3DUP is probably not common in AGB stars in the inner bulge.

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The evolutionary state of Miras with changing pulsation periods

Cited by 41 publications

References 56 publications

Study of the aluminium content in AGB winds using ALMA

Study of the aluminium content in AGB winds using ALMA

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

Period – mass-loss rate relation of Miras with and without technetium

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