2015A&A...583A..56D


C.D.S. - SIMBAD4 rel 1.7 - 2020.07.03CEST21:28:27

2015A&A...583A..56D - Astronomy and Astrophysics, volume 583A, 56-56 (2015/11-1)

Chemical abundance study of two strongly s-process enriched post-AGB stars in the LMC: J051213.81-693537.1 and J051848.86-700246.9.

DE SMEDT K., VAN WINCKEL H., KAMATH D. and WOOD P.R.

Abstract (from CDS):

This paper is part of a larger project in which we systematically study the chemical abundances of extra-galactic post-asymptotic giant branch (post-AGB) stars. The aim of our programme is to derive chemical abundances of stars covering a large range in luminosity and metallicity with the ultimate goal of testing, constraining, and improving our knowledge of the poorly understood AGB phase, especially the third dredge-up mixing processes and associated s-process nucleosynthesis. Post-AGB photospheres are dominated by atomic lines and indicate the effects of internal chemical enrichment processes over the entire stellar lifetime. In this paper, we study two carefully selected post-AGB stars: J051213.81-693537.1 and J051848.86-700246.9 in the Large Magellanic Cloud (LMC). Both objects show signs of s-process enhancement. The combination of favourable atmospheric parameters for detailed abundance studies and their known distances (and hence luminosities and initial masses) make these objects ideal probes of the AGB third dredge-up and s-process nucleosynthesis in that they provide observational constraints for theoretical AGB models. We use high-resolution optical UVES spectra to determine accurate stellar parameters and subsequently perform detailed elemental abundance studies of post-AGB stars. Additionally, we use available photometric data covering optical and IR bands to construct spectral energy distributions for reddening and luminosity determinations. We then estimate initial masses from theoretical post-AGB tracks. We obtained accurate atmospheric parameters for J051213.81-693537.1 (Teff=5875±125K, logg=1.00±0.25dex, [Fe/H]=-0.56±0.16dex) and J051848.86-700246.9 (Teff=6000±125K, logg=0.50±0.25dex, [Fe/H]=-1.06±0.17dex). Both stars show extreme s-process enrichment associated with relatively low C/O ratios of 1.26±0.40 and 1.29±0.30 for J051213-693537.1 and J051848-700246.9, respectively. We could only derive upper limits of the lead (Pb) abundance. These upper limits show a possible very slight Pb overabundance with respect to heavy s-elements for J051213-693537.1, while J051848-700246.9 shows an upper limit of the Pb abundance similar to [hs/Fe]. A comparison with theoretical post-AGB evolutionary tracks in the HR-diagram reveals that both stars have low initial masses between 1.0 and 1.5M. This study adds to the results obtained so far on a very limited number of s-process enriched stars in the Magellanic Clouds. With the addition of the two stars in this study, we find an increasing discrepancy between observed and predicted Pb abundances towards lower metallicities of the studied s-process rich post-AGB stars in the Magellanic Clouds. The more metal-rich J051213-693537.1 fits the theoretical Pb abundance predictions well, while the five other objects with [Fe/H]<1, including J051848-700246.9, have much lower Pb overabundances than predicted. In all objects found so far, including the objects in this study, the C/O ratio is very moderate because of the enhancement of O as well as C. We find that all s-process rich stars in the LMC and SMC studied so far, cluster in the same region of the HR-diagram and are associated with low-mass stars with a low metallicity on average. We corroborate the published lack of correlation between the metallicity and the neutron irradiation, while the neutron exposure ([hs/ls]) is strongly correlated with the third dredge-up efficiency ([s/Fe]). These correlations seem to hold in our Galaxy as well as in the Magellanic Clouds.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - stars: abundances - stars: evolution - Magellanic Clouds

VizieR on-line data: <Available at CDS (J/A+A/583/A56): j051213.dat j051848.dat>

Simbad objects: 17

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Number of rows : 17

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 OGLE SMC-LPV-4910 pA* 00 44 41.1033737346 -73 21 36.127700113   17.06 15.61 15.44 14.515 G:I 19 0
2 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9440 1
3 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 5665 1
4 IRAS 04296+3429 pA* 04 32 56.9768181234 +34 36 12.505781495   16.13 14.09 13.64 11.64 G0Ia 135 0
5 2MASS J05063210-7142298 pA? 05 06 32.1298124432 -71 42 29.926032757 14.801 14.717 14.298 13.950 13.780 A3Iab/F0Ibpe 12 0
6 2MASS J05121381-6935371 LP* 05 12 13.8249526805 -69 35 37.129848019   17.47 15.72 14.204 14.226 K2: 8 0
7 2MASS J05184886-7002469 LP* 05 18 48.8620022034 -70 02 47.086511947 18.692 17.142 15.429 14.31 13.852 F4Ib-II(e) 10 0
8 IRAS S05211-6926 LP* 05 20 43.858 -69 23 40.31 17.618 16.515 15.075 13.92 13.887 F5Ib(e) 17 0
9 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 14826 1
10 2MASS J05325071-7139257 LP* 05 32 50.7148448136 -71 39 25.725291413 17.985 16.533 15.069 14.029 13.803 F6Ia 14 0
11 IRAS 05341+0852 pA* 05 36 55.0500719686 +08 54 08.646055747   15.37 13.45 12.95 11.43 F6I 105 0
12 IRAS 06530-0213 pA* 06 55 31.8196049619 -02 17 28.245201716   16.38 13.99 13.26   F5Ia 68 0
13 HD 56126 pA* 07 16 10.2589670319 +09 59 47.953674864   9.20 8.32     F0/5Ia 303 0
14 IRAS 08143-4406 pA* 08 16 03.0216081249 -44 16 04.636233725           F8I 23 0
15 HD 187885 pA* 19 52 52.7031438648 -17 01 50.293465852   9.25 8.68 8.32   F2/6Ia 170 0
16 V* V448 Lac pA* 22 24 31.4284207830 +43 43 10.975183855 11.22 10.61 9.69     F7I 101 0
17 IRAS 23304+6147 pA* 23 32 44.7854376478 +62 03 49.083515796   15.36 12.99 12.23 10.50 G2Ia 107 0

    Equat.    Gal    SGal    Ecl

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2020.07.03-21:28:27

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