The Gaia-ESO Survey: characterisation of the [α/Fe] sequences in the Milky Way discs

被引：68

作者：

Kordopatis, G. ^{[1
]}

Wyse, R. F. G. ^{[2
]}

Gilmore, G. ^{[3
]}

Recio-Blanco, A. ^{[4
]}

de Laverny, P. ^{[4
]}

Hill, V. ^{[4
]}

Adibekyan, V. ^{[5
]}

Heiter, U. ^{[6
]}

Minchev, I. ^{[1
]}

Famaey, B. ^{[7
]}

Bensby, T. ^{[8
]}

Feltzing, S. ^{[8
]}

Guiglion, G. ^{[4
]}

Korn, A. J. ^{[6
]}

Mikolaitis, S. ^{[4
,9
]}

Schultheis, M. ^{[4
]}

Vallenari, A. ^{[10
]}

Bayo, A. ^{[11
]}

Carraro, G. ^{[12
]}

Flaccomio, E. ^{[13
]}

Franciosini, E. ^{[16
]}

Hourihane, A. ^{[3
]}

Jofre, P. ^{[3
]}

Koposov, S. E. ^{[3
,14
]}

Lardo, C. ^{[15
]}

Lewis, J. ^{[3
]}

Lind, K. ^{[6
]}

Magrini, L. ^{[16
]}

Morbidelli, L. ^{[16
]}

Pancino, E. ^{[17
,18
]}

Randich, S. ^{[16
]}

Sacco, G. G. ^{[16
]}

Worley, C. C. ^{[3
]}

Zaggia, S. ^{[10
]}

机构：

[1] Leibniz Inst Astrophys Potsdam AIP, D-14482 Potsdam, Germany

[2] Johns Hopkins Univ, Baltimore, MD 21218 USA

[3] Univ Cambridge, Inst Astron, Cambridge CB3 0HA, England

[4] Univ Nice Sophia Antipolis, CNRS, Observ Cote Azur, Lab Lagrange,UMR 7293, F-06304 Nice 4, France

[5] Univ Porto, CAUP, Inst Astrofis & Ciencia Espaco, P-4150762 Oporto, Portugal

[6] Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden

[7] Univ Strasbourg, CNRS, UMR 7550, Observ Astron Strasbourg, F-67000 Strasbourg, France

[8] Lund Observ, Dept Astron & Theoret Phys, S-22100 Lund, Sweden

[9] Vilnius State Univ, Inst Theoret Phys & Astron, LT-01108 Vilnius, Lithuania

[10] Padova Observ, INAF, I-35122 Padua, Italy

[11] Univ Valparaiso, Inst Fis & Astron, Valparaiso, Chile

[12] European So Observ, Santiago, Chile

[13] Osserv Astron Palermo, INAF, I-90134 Palermo, Italy

[14] Moscow MV Lomonosov State Univ, Sternberg Astron Inst, Moscow 119992, Russia

[15] Liverpool John Moores Univ, Astrophys Res Inst, Liverpool L3 5RF, Merseyside, England

[16] Osserv Astrofis Arcetri, INAF, I-50125 Florence, Italy

[17] Osservatorio Astron Bologna, INAF, I-40127 Bologna, Italy

[18] ASI Sci Data Ctr, I-00133 Rome, Italy

来源：

ASTRONOMY & ASTROPHYSICS | 2015年 / 582卷

基金：

瑞典研究理事会; 英国科学技术设施理事会;

关键词：

Galaxy: abundances; Galaxy: stellar content; Galaxy: evolution; Galaxy: kinematics and dynamics; Galaxy: disk; stars: abundances; VELOCITY EXPERIMENT RAVE; DIGITAL SKY SURVEY; DARK-MATTER UNIVERSE; GALACTIC THICK DISK; 3RD DATA RELEASE; SOLAR NEIGHBORHOOD; CHEMICAL EVOLUTION; STELLAR POPULATIONS; NEARBY STARS; GIANT STARS;

D O I：

10.1051/0004-6361/201526258

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

Context. High-resolution spectroscopic surveys of stars indicate that the Milky Way thin and thick discs follow different paths in the chemical space defined by [alpha/Fe] vs. [Fe/H], possibly suggesting different formation mechanisms for each of these structures. Aims. We investigate, using the Gaia-ESO Survey internal Data-Release 2, the properties of the double sequence of the Milky Way discs, which are defined chemically as the high-alpha and low-alpha populations. We discuss their compatibility with discs defined by other means, such as metallicity, kinematics, or positions. Methods. This investigation uses two different approaches: in velocity space, for stars located in the extended solar neighbourhood; and, in chemical space, for stars at different ranges of Galactocentric radii and heights from the Galactic mid-plane. The separation we find in velocity space allows us to investigate, using a novel approach, the extent of metallicity of each of the two chemical sequences, without making any assumption about the shape of their metallicity distribution functions. Then, using the separation in chemical space, adopting the magnesium abundance as a tracer of the alpha-elements, we characterise the spatial variation of the slopes of the [alpha/Fe] [Fe/H] sequences for the thick and thin discs and the way in which the relative proportions of the two discs change across the Galaxy. Results. We find that the thick disc, defined as the stars tracing the high-alpha sequence, extends up to super-solar metallicities ([Fe/H] approximate to + 0.2 dex), and the thin disc, defined as the stars tracing the low-alpha sequence, extends at least down to [Fe/H] approximate to 0.8 dex, with hints pointing towards even lower values. Radial and vertical gradients in alpha-abundances are found for the thin disc, with mild spatial variations in its [alpha/Fe] [Fe/H] paths, whereas for the thick disc we do not detect any spatial variations of this kind. This is in agreement with results obtained recently from other high-resolution spectroscopic surveys. Conclusions. The small variations in the spatial [alpha/Fe] [Fe/H] paths of the thin disc do not allow us to distinguish between formation models of this structure. On the other hand, the lack of radial gradients and [alpha/Fe] [Fe/H] variations for the thick disc indicate that the mechanism responsible for the mixing of metals in the young Galaxy (e.g. radial stellar migration or turbulent gaseous disc) was more efficient before the (present) thin disc started forming.

引用

页数：21

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