Optically visible post-AGB stars, post-RGB stars and young stellar objects in the Large Magellanic Cloud

Kamath, D.; Wood, P. R.; Winckel, H. Van

doi:10.1093/mnras/stv1202

Cited by 89 publications

(134 citation statements)

References 109 publications

(173 reference statements)

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“…The objects were carefully selected from our low-resolution surveys (van Aarle et al 2011;Kamath et al 2015). Our high-resolution spectral data reveal very rich spectra, literally swamped with atomic lines of s-process elements.…”

Section: Discussionmentioning

confidence: 99%

“…The effective temperatures of both stars could be determined accurately. Kamath et al (2015) estimate stellar parameter for J051848, based on lowresolution spectra. We find that the derived stellar parameters of our study and those of Kamath et al (2015) agree well within the estimated errors.…”

Section: Atmospheric Parametersmentioning

confidence: 99%

“…van Aarle et al (2011) and Kamath et al (2015), provide catalogues of spectroscopically verified optically visible post-AGB candidates in the Large Magellanic Cloud (LMC) and Kamath et al (2014) provides a catalogue of spectroscopically verified optically visible post-AGB candidates in the Small Magellanic Cloud (SMC).…”

Section: Introductionmentioning

confidence: 99%

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

Smedt

Winckel

Kamath

et al. 2015

A&A

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Context. This paper is part of a larger project in which we systematically study the chemical abundances of extra-galactic postasymptotic 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. Aims. 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. Methods. 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. Results. We obtained accurate atmospheric parameters for J051213.81-693537.1 (T eff = 5875 ± 125 K, log g = 1.00 ± 0.25 dex, [Fe/H] = −0.56 ± 0.16 dex) and J051848.86-700246.9 (T eff = 6000 ± 125 K, log g = 0.50 ± 0.25 dex, [Fe/H] = −1.06 ± 0.17 dex). 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 1.5 M . Conclusions. 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, th...

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Section: Discussionmentioning

confidence: 99%

Section: Atmospheric Parametersmentioning

confidence: 99%

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

Smedt

Winckel

Kamath

et al. 2015

A&A

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“…In our recent studies of post-AGB stars in the Magellanic Clouds (van Aarle et al 2011;Kamath et al 2014Kamath et al , 2015, we focused on the intrinsic s-process enriched post-AGB star J004441. 04-732136.4 (J004441) in the Small Magellanic Cloud (SMC;De Smedt et al 2012.…”

Section: Introductionmentioning

confidence: 99%

Detailed homogeneous abundance studies of 14 Galactics-process enriched post-AGB stars: In search of lead (Pb)

Smedt

Winckel

Kamath

et al. 2016

A&A

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Context. This paper is part of a larger project in which we systematically study the chemical abundances of Galactic and extragalactic post-asymptotic giant branch (post-AGB) stars. The goal at large is to provide improved observational constraints to the models of the complex interplay between the AGB s-process nucleosynthesis and the associated mixing processes. Aims. Lead (Pb) is the final product of the s-process nucleosynthesis and is predicted to have large overabundances with respect to other s-process elements in AGB stars of low metallicities. However, Pb abundance studies of s-process enriched post-AGB stars in the Magellanic Clouds show a discrepancy between observed and predicted Pb abundances. The determined upper limits based on spectral studies are much lower than what is predicted. In this paper, we focus specifically on the Pb abundance of 14 Galactic s-process enhanced post-AGB stars to check whether the same discrepancy is present in the Galaxy as well. Among these 14 objects, two were not yet subject to a detailed abundance study in the literature. We apply the same method to obtain accurate abundances for the 12 others. Our homogeneous abundance results provide the input of detailed spectral synthesis computations in the spectral regions where Pb lines are located. Methods. We used high-resolution UVES and HERMES spectra for detailed spectral abundance studies of our sample of Galactic post-AGB stars. None of the sample stars display clear Pb lines, and we only deduced upper limits of the Pb abundance by using spectrum synthesis in the spectral ranges of the strongest Pb lines. Results. We do not find any clear evidence of Pb overabundances in our sample. The derived upper limits are strongly correlated with the effective temperature of the stars with increasing upper limits for increasing effective temperatures. We obtain stronger Pb constraints on the cooler objects. Moreover, we confirm the s-process enrichment and carbon enhancement of two unstudied 21 µm sources IRAS 13245-6428 and IRAS 14429-4539. The mildly s-process enhanced post-AGB star IRAS 17279-1119 is part of a binary system and may be the long sought precursor of extrinsic Ba stars. Conclusions. Stars with T eff > 7500 K do not provide strong constraints on the Pb abundance as the strongest line in the optical spectrum is only detectable at unrealistically high Pb atmospheric abundances. Combining the Pb abundance results from this study with abundances from our previous studies, we conclude that the discrepancy between theory and observation increases towards lower metallicities. The model predictions are consistent with the deduced upper limits on the Pb abundances for all stars with [Fe/H] > −0.7 dex. For stars with [Fe/H] < −0.7 dex, however, the model predictions overestimate the Pb abundances with respect to the other s-process elements. All objects, except IRAS 17279-1119, confirm the relation between neutron exposure [hs/ls] and third dredge-up efficiency [s/Fe], whereas no relation between metallicity and neut...

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“…What was surprising is the detection of IR excess among the WVir stars below luminosities predicted by single star evolutionary tracks. This IR excess was independently found by [7][8][9] to be dusty post-RGB stars and possibly related to binary evolution.…”

Section: The Ir Excessmentioning

confidence: 59%

Properties of Anomalous and Type II Cepheids in the Small and Large Magellanic Clouds

Jurković

Groenewegen

2017

EPJ Web Conf.

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Abstract. The Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC) give us the possibility to study individual variable star types in a new way. Literature data provide us with photometric information about objects from the ultraviolet to the infrared. Here we would like to show the results of our study of 335 Anomalous and Type II Cepheids in the SMC and LMC detected by OGLE. Using the code More of DUSTY (MoD), a modified version of the DUSTY radiative transfer code, and the assumption that our objects are at a known distance, luminosity and effective temperature were determined. From these data the Hertzsprung-Russell diagram of these objects was compared with the theoretical models. The radius and masses of the examined stars was estimated, too. In the end, we have given the period-luminosity relations for the Anomalous and Type II Cepheids.

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Optically visible post-AGB stars, post-RGB stars and young stellar objects in the Large Magellanic Cloud

Cited by 89 publications

References 109 publications

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

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

Detailed homogeneous abundance studies of 14 Galactics-process enriched post-AGB stars: In search of lead (Pb)

Properties of Anomalous and Type II Cepheids in the Small and Large Magellanic Clouds

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