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


Query : 2015A&A...583A..56D

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

goto Full paper

goto View the references in ADS

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 - 2023
#notes
1 OGLE SMC-LPV-4910 pA* 00 44 41.1035011488 -73 21 36.123508332   17.06 15.61 15.44 14.515 G:I 26 0
2 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10848 1
3 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6829 1
4 IRAS 04296+3429 pA* 04 32 56.9743899192 +34 36 12.459816288   16.13 14.09 13.64 11.64 G0Ia 143 0
5 2MASS J05063210-7142298 pA* 05 06 32.1295674936 -71 42 29.924779896 14.801 14.717 14.298 13.950 13.780 A3Iab/F0Ibpe 15 0
6 2MASS J05121381-6935371 LP* 05 12 13.8252355152 -69 35 37.130193780   17.47 15.72 14.204 14.226 K2: 8 0
7 2MASS J05184886-7002469 LP* 05 18 48.8624065560 -70 02 47.086220796 18.692 17.142 15.429 14.31 13.852 F4Ib-II(e) 14 0
8 IRAS S05211-6926 pA* 05 20 43.8870629914 -69 23 41.139112840 17.618 16.515 15.075 13.92 13.887 F5Ib(e) 22 0
9 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 16987 1
10 2MASS J05325071-7139257 LP* 05 32 50.7147024408 -71 39 25.723947636 17.985 16.533 15.069 14.029 13.803 F6Ia 17 0
11 IRAS 05341+0852 pA* 05 36 55.0511076432 +08 54 08.656315452   15.37 13.45 12.95 11.43 F5I 113 0
12 IRAS 06530-0213 pA* 06 55 31.8205478808 -02 17 28.243142520   16.38 13.99 13.26   F5Ia 76 0
13 HD 56126 pA* 07 16 10.2590823192 +09 59 47.954735376   9.20 8.32     F0/5Ia 314 0
14 IRAS 08143-4406 pA* 08 16 03.0217187040 -44 16 04.640255580           F8I 28 0
15 HD 187885 pA* 19 52 52.7033593752 -17 01 50.289441096   9.25 8.68 8.32   F2/6Ia 176 0
16 V* V448 Lac pA* 22 24 31.4283564864 +43 43 10.978781916 11.22 10.61 9.69     F7I 108 0
17 IRAS 23304+6147 pA* 23 32 44.7858431592 +62 03 49.090372272   15.36 12.99 12.23 10.50 G2Ia 114 0

To bookmark this query, right click on this link: simbad:objects in 2015A&A...583A..56D and select 'bookmark this link' or equivalent in the popup menu


2023.09.30-01:17:53

© Université de Strasbourg/CNRS

    • Contact