2010A&A...512A..41B


Query : 2010A&A...512A..41B

2010A&A...512A..41B - Astronomy and Astrophysics, volume 512, A41-41 (2010/3-1)

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. II. Ages, metallicities, detailed elemental abundances, and connections to the Galactic thick disc.

BENSBY T., FELTZING S., JOHNSON J.A., GOULD A., ADEN D., ASPLUND M., MELENDEZ J., GAL-YAM A., LUCATELLO S., SANA H., SUMI T., MIYAKE N., SUZUKI D., HAN C., BOND I. and UDALSKI A.

Abstract (from CDS):

The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars, and accurately trace the chemical evolution of a stellar population, is under debate. In particular, recent observations of a few microlensed dwarf stars give a very different picture of the evolution of the Bulge from that given by the giant stars. We aim to resolve the apparent discrepancy between Bulge metallicity distributions derived from microlensed dwarf stars and giant stars. Additionally, we aim to put observational constraints on the elemental abundance trends and chemical evolution of the Bulge. We perform a detailed elemental abundance analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra that were obtained while the stars were optically magnified during gravitational microlensing events. The analysis method is the same as for a large sample of F and G dwarf stars in the Solar neighbourhood, enabling a fully differential comparison between the Bulge and the local stellar populations in the Galactic disc. We present detailed elemental abundances and stellar ages for six new dwarf stars in the Galactic bulge. Combining these with previous events, here re-analysed with the same methods, we study a homogeneous sample of 15 stars, which constitute the largest sample to date of microlensed dwarf stars in the Galactic bulge. We find that the stars span the full range of metallicities from [Fe/H]=-0.72 to +0.54, and an average metallicity of <[Fe/H]≥-0.08±0.47, close to the average metallicity based on giant stars in the Bulge. Furthermore, the stars follow well-defined abundance trends, that for [Fe/H]<0 are very similar to those of the local Galactic thick disc. This suggests that the Bulge and the thick disc have had, at least partially, comparable chemical histories. At sub-solar metallicities we find the Bulge dwarf stars to have consistently old ages, while at super-solar metallicities we find a wide range of ages. Using the new age and abundance results from the microlensed dwarf stars we investigate possible formation scenarios for the Bulge.

Abstract Copyright:

Journal keyword(s): gravitational lensing: micro - Galaxy: bulge - Galaxy: formation - Galaxy: evolution - Galaxy: disk - stars: abundances

VizieR on-line data: <Available at CDS (J/A+A/512/A41): table1.dat table4.dat table5.dat>

Simbad objects: 25

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Number of rows : 25
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 * mu. Leo PM* 09 52 45.8170136628 +26 00 25.024269924 6.50 5.10 3.88 2.97 2.39 K2IIIbCN1Ca1 446 0
2 * i Sco * 16 30 12.4751393 -25 06 54.804270 3.93 4.72 4.79 4.85 4.99 B3V 304 1
3 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 14383 0
4 MOA 2009-BLG-456 * 17 48 56.40 -34 13 29.7           ~ 9 0
5 MOA 2006-BUL-99 * 17 54 10.99 -35 13 38.0           G 15 0
6 MOA 2009-BLG-493 * 17 55 46.13 -28 48 25.5           ~ 10 0
7 MOA 2008-BLG-311 * 17 56 53.65 -31 23 49.9           ~ 17 0
8 MACHO 98-BLG-6 * 17 57 32.8 -28 42 45     19.5     G5IV 20 0
9 MACHO 99-BLG-6 * 17 57 42.9 -28 01 03     18.7     ~ 2 0
10 MOA 2009-BLG-489 * 17 57 46.7236172064 -28 38 57.070782024           ~ 10 0
11 MOA 2009-BLG-259 * 17 57 57.51 -29 11 39.4           ~ 9 0
12 OGLE-2007-BUL-514 * 17 58 03.09 -27 31 05.7           ~ 15 0
13 OGLE-2009-BLG-076 * 17 58 31.93 -29 12 17.9           ~ 14 0
14 MOA 2009-BLG-475 * 18 02 27.46 -27 26 49.4           ~ 10 0
15 NAME Baade Window reg 18 03.5 -30 01           ~ 612 3
16 OGLE-2008-BUL-209 * 18 04 49.8347028546 -29 42 33.675924320           ~ 14 0
17 OGLE BUL-SC33 164492 * 18 05 05.28 -28 34 41.7           ~ 36 0
18 MOA 2007-BLG-379 ** 18 05 24.43 -26 25 18.8           ~ 52 1
19 MOA 2009-BLG-133 * 18 06 32.85 -31 30 11.4           ~ 10 0
20 OGLE-2006-BUL-265 * 18 07 18.88 -27 47 42.7           G 17 0
21 MACHO 99-BLG-1 * 18 08 50.0 -30 31 56           G2V 6 0
22 MACHO 97-BLG-45 * 18 21 01.80 -28 46 45.0     19.8     ~ 11 0
23 NGC 6791 OpC 19 20 53.0 +37 46 41   10.52 9.5     ~ 1038 0
24 * mu. PsA PM* 22 08 23.0113421424 -32 59 18.491668224 4.60 4.55 4.50 4.43 4.38 A1.5IVn 125 0
25 NAME Galactic Bulge reg ~ ~           ~ 4290 0

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