TitleRadial abundance gradients in the outer Galactic disk as traced by main-sequence OB stars
Publication TypeJournal Article
Year of Publication2019
AuthorsBragança, GA, Daflon, S, Lanz, T, Cunha, K, Bensby, T, McMillan, PJ, Garmany, CD, Glaspey, JW, M. Fernandes, B, Oey, MS, Hubeny, I
JournalAstronomy & Astrophysics
Volume625
PaginationA120
Date Published05/2019
ISSN0004-6361
KeywordsAstrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics; parker solar probe; Solar Probe Plus; stars: abundances; stars: early-type
Abstract

Context. Elemental abundance gradients in galactic disks are important constraints for models of how spiral galaxies form and evolve. However, the abundance structure of the outer disk region of the Milky Way is poorly known, which hampers our understanding of the spiral galaxy that is closest to us and that can be studied in greatest detail. Young OB stars are good tracers of the present-day chemical abundance distribution of a stellar population and because of their high luminosities they can easily be observed at large distances, making them suitable to explore and map the abundance structure and gradients in the outer regions of the Galactic disk.
Aims: Using a sample of 31 main-sequence OB stars located between galactocentric distances 8.4-15.6 kpc, we aim to probe the present-day radial abundance gradients of the Galactic disk.
Methods: The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m telescope on Las Campanas. We used a non-NLTE analysis in a self-consistent semi-automatic routine based on TLUSTY and SYNSPEC to determine atmospheric parameters and chemical abundances.
Results: Stellar parameters (effective temperature, surface gravity, projected rotational velocity, microturbulence, and macroturbulence) and silicon and oxygen abundances are presented for 28 stars located beyond 9 kpc from the Galactic center plus three stars in the solar neighborhood. The stars of our sample are mostly on the main-sequence, with effective temperatures between 20 800-31 300 K, and surface gravities between 3.23-4.45 dex. The radial oxygen and silicon abundance gradients are negative and have slopes of -0.07 dex kpc-1 and -0.09 dex kpc-1, respectively, in the region 8.4 ≤ RG ≤ 15.6 kpc.
Conclusions: The obtained gradients are compatible with the present-day oxygen and silicon abundances measured in the solar neighborhood and are consistent with radial metallicity gradients predicted by chemodynamical models of Galaxy Evolution for a subsample of young stars located close to the Galactic plane. Based on data obtained with the Magellan Clay telescope at the Las Campanas observatory and the ESO/MPI telescope at La Silla under the ESO-ON agreement.

URLhttps://www.aanda.org/10.1051/0004-6361/201834554https://www.aanda.org/10.1051/0004-6361/201834554/pdf
DOI10.1051/0004-6361/201834554
Short TitleA&A


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