High-resolution spectroscopic observations of two s-process-enriched and carbon-poor post-AGB stars: GLMP 334 and IRAS 15482−5741

C. B. Pereira; R. Gallino; S. Bisterzo

doi:10.1051/0004-6361/201117398

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Volume 538 (February 2012)

A&A, 538 (2012) A48

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Issue		A&A Volume 538, February 2012


Article Number		A48
Number of page(s)		15
Section		Stellar structure and evolution
DOI		https://doi.org/10.1051/0004-6361/201117398
Published online		31 January 2012

Online material

Table 2

Observed Fe i and Fe ii lines.

Table 4

Other lines studied.

Appendix A: Supplementary material

A.1. GLMP 334 and IRAS 15482–5741

We provide an additional set of figures for both post-AGB stars in this section. We aim to shown the behavior of theoretical predictions by changing the AGB initial mass and ¹³C-pocket efficiency. The discrepancy between predicted and observed [C, N/Fe] may be improved by increasing the metallicity by 0.2 dex in both stars. This would reduce the predicted [C/Fe] by 0.3 dex with respect to Figs. 3 and 4, while leaving [ls/Fe] and [hs/Fe] unchanged. Indeed, ¹²C is primarily produced during partial He burning in the convective thermal pulse (independently of the metallicity) and is then dredged-up in the envelope after each TDU. In Figs. A.13 and A.14 we present two special cases modelled for both post-AGB stars. We present a summary of the theoretical interpretations of the two post-AGB stars discussed here compared with other post-AGB stars found in the literature in Sect. A.2.

	Fig. A.1 GLMP 334: the same as Fig. 3, but showing an additional ¹³C-pocket (case ST, thin solid line). This figure shows as by further decreasing the s-process efficiency, the observed [hs/Fe] is underestimated by the theoretical prediction.
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	Fig. A.2 GLMP 334: the same as Fig. 3, but for = 3 M_⊙ models. Three ¹³C-pocket efficiencies are shown: cases ST × 2 (solid line), ST × 1.3 (dotted thin line) and ST (dotted thick line). The first two ¹³C-pockets provide solutions similar to = 2 M_⊙ models.
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	Fig. A.3 GLMP 334: the same as Fig. A.2, but for = 1.5 M_⊙ models. Owing to the lower number of thermal pulses with TDU (19th), none of the ¹³C-pockets reach the observed [ls/Fe] value. These solutions were discarded.
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	Fig. A.4 GLMP 334: the same as Fig. A.2, but for = 1.4 M_⊙ models (11 TDUs). None of the ¹³C-pockets reach the observed ls and hs peaks. These solutions were discarded.
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	Fig. A.5 GLMP 334: the same as Fig. A.2, but for = 1.3 M_⊙ models (5 TDUs). Even if these solutions perfectly agree with the observed [C/Fe], the low s-process distribution strongly underestimates the observed ls and hs peaks.
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Fig. A.6

Theoretical interpretation of the post-AGB stars GLMP 334 ([Fe/H] = − 0.4; T_eff = 7400 K; log g = 1.4) with = 5 M_⊙ models. Three ¹³C-pocket efficiencies are shown: cases ST-IMS × 4 (solid line), ST-IMS × 2 (dotted thin line) and ST-IMS (dotted thick line). Note that a different ¹³C-pocket notation is adopted for IMS stars, because they have a smaller He-intershell than low-mass AGBs, with a smaller ¹³C-pocket (see Bisterzo et al. 2010). None of these solutions agrees with the observations.

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	Fig. A.7 IRAS 15482–5741: the same as Fig. 4, but showing a different range of ¹³C-pockets: cases ST × 2 (solid line), ST (dotted thin line) and ST/3 (dotted thick line). This figure shows the behavior of the s-process elements if the ¹³C-pocket is changed.
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	Fig. A.8 IRAS 15482–5741: the same as Fig. 4, but for = 1.3 M_⊙ models. The theoretical [ls/Fe] is about 0.6 dex lower than observed. Even if the predicted [C/Fe] is closer to the low observed value, we discarded this solution.
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Fig. A.9

IRAS 15482–5741: the same as Fig. 4, but for = 1.5 M_⊙ models. These models do not provide good theoretical interpretations for two reasons: first of all, with respect to Fig. 4, a further increase of about 0.2 dex is predicted for [C/Fe], because higher initial masses more TDUs (specifically, 19 instead of 11). Second, no good match is obtained of both ls and hs peaks: [ls/Fe] is perfectly interpreted by a case ST × 2, but [hs/Fe] is too high with respect the observed value. But, case ST/1.3 predicts a [ls/Fe] slightly higher than observed, even if the theoretical [hs/Fe] still lies within the errorbars.

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	Fig. A.10 IRAS 15482–5741: the same as Fig. A.9, but for = 2 M_⊙ models. Owing to [C/Fe], [ls/Fe] and [hs/Fe], these solutions were discarded.
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	Fig. A.11 IRAS 15482–5741: the same as Fig. A.9, but for = 3 M_⊙ models. Owing to [C/Fe], [ls/Fe] and [hs/Fe], these solutions were discarded.
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	Fig. A.12 Theoretical interpretation of the post-AGB star IRAS 15482–5741 ([Fe/H] = − 0.5; T_eff = 7400 K; log g = 1.1) with = 5 M_⊙ models. Three ¹³C-pocket efficiencies are shown: cases ST-IMS × 4 (solid line), ST-IMS × 2 (dotted thin line) and ST-IMS (dotted thick line). None of these solutions agree with the observations.
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Fig. A.13

Theoretical interpretation of the post-AGB star GLMP 334 ([Fe/H] = − 0.4; T_eff = 7400 K; log g = 1.4) by assuming a metallicity 0.2 dex higher than that observed. AGB models of initial mass of 1.5 M_⊙ (19 TDUs), cases ST × 2 (solid line), ST × 1.7 (dotted thin line) and ST × 1.3 (dotted thick line) are shown. Note that the mass of the pocket was multiplied by a plausible factor of two to obtain 0.2 dex higher abundances in both [ls/Fe] and [hs/Fe]. We modelled these special cases to decrease [C/Fe] predictions with respect to Fig. 3, leaving [ls/Fe] and [hs/Fe] unchanged.

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Fig. A.14

Theoretical interpretation of the post-AGB star IRAS 154825741 ([Fe/H] = − 0.5; T_eff = 7400 K; log g = 1.1) by assuming a metallicity 0.2 dex higher than that observed. AGB models of initial mass of 1.4 M_⊙ (10 TDU), cases ST × 2 (solid line), ST × 1.7 (dotted thin line) and ST × 1.3 (dotted thick line) are shown. Note that the mass of the pocket was multiplied by a plausible factor of two to obtain 0.2 dex higher abundances in both [ls/Fe] and [hs/Fe]. We modelled these special cases to decrease the [C/Fe] predictions with respect to Fig. 4, leaving [ls/Fe] and [hs/Fe] unchanged.

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A.2. Comparison with other post-AGB stars presented in the literature.

We provide in Table A.1 a summary of the theoretical interpretations of the post-AGB stars discussed in the literature. Solutions are found within the mass range = 1.4 to 3 M_⊙. The choice of the ¹³C-pocket efficiency is peaked at ST/1.5, with a spread between ST/3 and ST × 2 (see also Gallino et al. 2008).

Table A.1

Summary of the stellar parameters, metallicities, [ls/Fe], [hs/Fe] and theoretical interpretations of the two post-AGB stars studied in this paper compared with the post-AGB stars discussed in the literature.

© ESO, 2012

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