Abundance analysis for long-period variables

Lebzelter, T.; Nowotny, W.; Hinkle, Kenneth H.; Höfner, Susanne; Aringer, B.

doi:10.1051/0004-6361/201424078

Cited by 24 publications

(29 citation statements)

References 44 publications

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“…As the temperature in Figure B2 are computed with static atmospheres under the assumption of LTE and no dust, tem-peratures below 4000 K may be less trustworthy. A more refined treatment by Lebzelter et al (2014) suggests that the brightest, pulsating stars may have temperatures slightly (∼100 K) lower than predicted, although there are considerable systematic uncertainties preventing us stating this with certainty.…”

Section: B1 Existing Stellar Evolution Modelsmentioning

confidence: 93%

Mass-loss on the red giant branch: the value and metallicity dependence of Reimers’ η in globular clusters

McDonald

2015

Monthly Notices of the Royal Astronomical Society

113

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The impact of metallicity on the mass-loss rate from red giant branch (RGB) stars is studied through its effect on the parameters of horizontal branch (HB) stars. The scaling factors from Reimers (1975) and Schröder & Cuntz (2005) are used to measure the efficiency of RGB mass loss for typical stars in 56 well-studied Galactic globular clusters (GCs). The median values among clusters are, respectively, η R = 0.477 ± 0.070 +0.050 −0.062 and η SC = 0.172 ± 0.024 +0.018 −0.023 (standard deviation and systematic uncertainties, respectively). Over a factor of 200 in iron abundance, η varies by < ∼ 30 per cent, thus mass-loss mechanisms on the RGB have very little metallicity dependence. Any remaining dependence is within the current systematic uncertainties on cluster ages and evolution models. The low standard deviation of η among clusters (≈14 per cent) contrasts with the variety of HB morphologies. Since η incorporates cluster age, this suggests that age accounts for the majority of the "second parameter problem", and that a Reimers-like law provides a good mass-loss model. The remaining spread in η correlates with cluster mass and density, suggesting helium enrichment provides the third parameter explaining HB morphology of GCs. We close by discussing asymptotic giant branch (AGB) mass loss, finding the AGB tip luminosity is better reproduced and η has less metallicity dependence if globular clusters are more co-eval than generally thought.terised by a scaling factor, η, which determines the constant of proportionality in these scaling laws.Calibrating η is important in understanding the post-RGB stages of low-mass stellar evolution, particularly if η varies with other stellar parameters, such as stellar metallicity. No direct variation of metallicity is included in the Reimers and SC05 relations, however metallicity indirectly affects the parameterised mass-loss rate through the consequent variation of stellar radius and the speed at which the star evolves. Mass loss from RGB stars is thought to occur via (magneto-)acoustic processes, hence it should be largely independent of metallicity. If a parameterisation like those of Reimers (1975) and SC05 provides is an accurate representation of the mass-loss rates of RGB stars, we can expect η to be independent of metallicity too.RGB mass loss is notoriously difficult to measure, relying mainly on three tracers. Blueshifted components in optical and near-IR lines trace mass motions close to the stellar surface, but this does not necessarily translate into the rate at which mass is ejected from the star (e.g. McDonald & van Loon 2007; Mészáros et al. 2009). Submm CO line strengths trace material far from the star, but c 9999 RAS 1 The unpublished documentation for this edition can be found at http://arxiv.org/abs/1012.3224. c 9999 RAS, MNRAS 000, 1-22

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Section: B1 Existing Stellar Evolution Modelsmentioning

confidence: 93%

Mass-loss on the red giant branch: the value and metallicity dependence of Reimers’ η in globular clusters

McDonald

2015

Monthly Notices of the Royal Astronomical Society

113

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“…The stellar sample discussed here consists entirely of large amplitude AGB variables, Miras and SRa variables. As mentioned above spectrum synthesis for these objects continues to be beyond the grasp of model atmospheres and line modeling techniques (Lebzelter et al 2014). To undertake a first analysis of isotopic ratios in these stars we have turned to a largely empirical technique.…”

Section: Curve Of Growth Analysismentioning

confidence: 99%

“…The photospheric lines, which can be detected only in the infrared, undergo large temperature and velocity variations (Hinkle et al 1982). Model atmospheres and spectrum synthesis techniques are clearly limited in dealing with these spectra (McSaveney et al 2007;Lebzelter et al 2014). Here we employ an empirical technique that utilizes broad-band near-IR spectra and is best suited for the analysis of isotopomers.…”

Section: Introductionmentioning

confidence: 99%

Carbon and Oxygen Isotopic Ratios for Nearby Miras

Hinkle

Lebzelter

Straniero

2016

ApJ

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Carbon and oxygen isotopic ratios are reported for a sample of 46 Mira and SRatype variable AGB stars. Vibration-rotation first and second overtone CO lines in 1.5 to 2.5 µm spectra were measured to derive isotopic ratios for 12 C/ 13 C, 16 O/ 17 O, and 16 O/ 18 O. Comparisons with previous measurements for individual stars and with various samples of evolved stars, as available in the extant literature, are discussed. Models for solar composition AGB stars of different initial masses are used to interpret our results. We find that the majority of the M stars had main sequence masses ≤ 2 M ⊙ and have not experienced sizable third dredge-up episodes. The progenitors of the four S-type stars in our sample are slightly more massive. Of the six C stars in the sample three have clear evidence relating their origin to the occurrence of the third dredge-up. Comparisons with O-rich presolar grains from AGB stars that lived before the formation of the solar system reveal variations in the interstellar medium chemical composition. The present generation of low-mass AGB stars, as represented by our sample of Long Period Variables, show a large spread of 16 O/ 17 O ratios, similar to that of group 1 presolar grains and in agreement with theoretical expectations for the composition of mass 1.2 to 2 M ⊙ stars after the first dredge up. On the contrary, the 16 O/ 18 O ratios of present-day Long Period Variables are definitely smaller than those of group 1 grains. This occurrence is most probably a consequence of the the decrease with time of the 16 O/ 18 O ratio in the interstellar medium due to the chemical evolution of the Milky Way.One star in our sample has an O composition similar to that of group 2 presolar grains originating in an AGB star undergoing extramixing. This occurrence may indicate that the extramixing process is hampered at high metallicity or, equivalently, favored at low metallicity. Similar to O-rich grains no star in our sample shows evidence of hot bottom burning, expected for massive AGB stars.

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“…This cluster was chosen partly because its stars show a relatively small spread in chemical abundances compared to other clusters of similar size (Worley et al 2010;Gratton et al 2013;Cordero et al 2014;Černiauskas et al 2014;Dobrovolskas et al 2014;Lebzelter et al 2014;Thygesen et al 2014;Johnson et al 2014), and partly because it contains a well-studied set of luminous, dusty AGB stars.…”

Section: Target Selectionmentioning

confidence: 99%

“…Although initially faster, this wind slows to ∼10 km s −1 at the luminosity of the RGB tip (McDonald & van Loon 2007;Groenewegen 2014). Later, κ- Cutri et al (2003, 2MASS); (2) 2MASS offset from cluster core (00 24 05.67, -72 04 52.6); (3) average and semi-amplitude of radial velocities from ; with a -8.7 km s −1 correction from heliocentric velocity, plus V -band magnitude pulsation amplitudes (full range) and periods; (4) McDonald et al (2011a), based on multi-wavelength literature photometry; (5) Lebzelter et al (2014), based on instantaneous measurements at the given pulsation phase. mechanism pulsations can levitate material from the star, enhancing the mass-loss rate (Wood 1979;Bowen 1988).…”

Section: Introductionmentioning

confidence: 99%

ALMA reveals sunburn: CO dissociation around AGB stars in the globular cluster 47 Tucanae

McDonald

Zijlstra

Lagadec

et al. 2015

Mon. Not. R. Astron. Soc.

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ALMA observations show a non-detection of carbon monoxide around the four most luminous asymptotic giant branch (AGB) stars in the globular cluster 47 Tucanae. Stellar evolution models and star counts show that the mass-loss rates from these stars should be ∼1.2-3.5 × 10 −7 M ⊙ yr −1 . We would naïvely expect such stars to be detectable at this distance (4.5 kpc). By modelling the ultraviolet radiation field from post-AGB stars and white dwarfs in 47 Tuc, we conclude CO should be dissociated abnormally close to the stars. We estimate that the CO envelopes will be truncated at a few hundred stellar radii from their host stars and that the line intensities are about two orders of magnitude below our current detection limits. The truncation of CO envelopes should be important for AGB stars in dense clusters. Observing the CO (3-2) and higher transitions and targeting stars far from the centres of clusters should result in the detections needed to measure the outflow velocities from these stars.

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Abundance analysis for long-period variables

Cited by 24 publications

References 44 publications

Mass-loss on the red giant branch: the value and metallicity dependence of Reimers’ η in globular clusters

Mass-loss on the red giant branch: the value and metallicity dependence of Reimers’ η in globular clusters

Carbon and Oxygen Isotopic Ratios for Nearby Miras

ALMA reveals sunburn: CO dissociation around AGB stars in the globular cluster 47 Tucanae

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