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The VLT-FLAMES Tarantula Survey XXXII. Low-luminosity late O-type stars: classification, main physical parameters, and silicon abundances

Markova, Nevena and Puls, Joachim and Dufton, Phillip and Lennon, Danny and Evans, Chris and de Koter, Alex and Ramirez Agudelo, Oscar Hernan and Sana, Hugues and Vink, Jorick (2020) The VLT-FLAMES Tarantula Survey XXXII. Low-luminosity late O-type stars: classification, main physical parameters, and silicon abundances. Astronomy and Astrophysics, 634 (A16). EDP Sciences. doi: 10.1051/0004-6361/201937082. ISSN 0004-6361.

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Official URL: https://www.aanda.org/articles/aa/pdf/2020/02/aa37082-19.pdf

Abstract

Analysis of late O-type stars observed in the Large Magellanic Cloud (LMC) by the VLT-FLAMES Tarantula Survey revealed a discrepancy between the physical properties estimated from model-atmosphere analysis and those expected from their morphological classifications. Here we revisit the analysis of 32 of these puzzling objects using new hydrogen-helium-silicon FASTWIND models and a different fitting approach to re-evaluate their physical properties. Our new analysis confirms that these stars indeed have properties that are typical of late O-type dwarfs. We also present the first estimates of silicon abundances for O-type stars in the 30 Dor clusters NGC 2060 and NGC 2070, with a weighted mean abundance for our sample of Epsilon(Si) = 7.05 +/- 0.03. Our values are ~0.20 dex lower than those previously derived for B-type stars in the LMC clusters N 11 and NGC 2004 using TLUSTY models. Various possibilities (e.g. differences in the analysis methods, effects of microturbulence, and real differences between stars in different clusters) were considered to account for these results. We also used our grid of FASTWIND models to reassess the impact of using the Galactic classification criteria for late O-type stars in the LMC by scrutinising their sensitivity to different stellar properties. At the cool edge of the O star regime the He II 4686/He I 4713 ratio used to assign luminosity class for Galactic stars can mimic giants or bright giants in the LMC, even for objects with high gravities (log g > 4.0 dex). We argue that this line ratio is not a reliable luminosity diagnostic for late O-type stars in the LMC, and that the Si IV 4089/He I 4026 ratio is more robust for these types.

Item URL in elib:https://elib.dlr.de/140542/
Document Type:Article
Title:The VLT-FLAMES Tarantula Survey XXXII. Low-luminosity late O-type stars: classification, main physical parameters, and silicon abundances
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Markova, NevenaInstitute of Astronomy, National Astronomical Observatory, Bulgarina Academy of SciencesUNSPECIFIED
Puls, JoachimLMU München, Universitäts-StenwarteUNSPECIFIED
Dufton, PhillipARC, School of Mathematics and Physics, The Queen's University of BelfastUNSPECIFIED
Lennon, DannyInstituto de Astrofisica de CanariasUNSPECIFIED
Evans, ChrisUK Astronomy Technology CentreUNSPECIFIED
de Koter, AlexAstronomical Institute Anton PannekoekUNSPECIFIED
Ramirez Agudelo, Oscar HernanOscar.RamirezAgudelo (at) dlr.dehttps://orcid.org/0000-0002-9379-5409
Sana, HuguesInstitute voor Sterrenkunde, KU LeuvenUNSPECIFIED
Vink, JorickArmagh Observatory and PlanetariumUNSPECIFIED
Date:February 2020
Journal or Publication Title:Astronomy and Astrophysics
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:634
DOI :10.1051/0004-6361/201937082
Publisher:EDP Sciences
Series Name:Astronomy and Astrophysics
ISSN:0004-6361
Status:Published
Keywords:stars: abundances, stars: early-type, stars: fundamental parameters, stars: mass-loss, Magellanic Clouds
HGF - Research field:other
HGF - Program:other
HGF - Program Themes:other
DLR - Research area:no assignment
DLR - Program:no assignment
DLR - Research theme (Project):no assignment
Location: other
Institutes and Institutions:Institute for the Protection of Terrestrial Infrastructures
Deposited By: Ramirez Agudelo, Oscar Hernan
Deposited On:28 Jan 2021 15:03
Last Modified:28 Jan 2021 15:03

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