11. The galactic nucleus and central bulge 11.1 Infrared observations (cont.)
THE GALACTIC BULGE
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Transcript of THE GALACTIC BULGE
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THE GALACTIC BULGETHE GALACTIC BULGE
B. BarbuyB. Barbuy
IAG - Universidade de SIAG - Universidade de São Pauloo Paulo
S. Ortolani, E. Bica, M. Zoccali,V. Hill, D.Minniti, A. Renzini, A. Gomez, C. Babusiaux
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Galactic bulge:Galactic bulge:
Template for stellar populations in EllipticalsTemplate for stellar populations in Ellipticals
and bulge of spirals and bulge of spirals Spectra provide metallicity, kinematicsSpectra provide metallicity, kinematics
- field and globular clusters- field and globular clusters Formation of the bulge: secular evolution orFormation of the bulge: secular evolution or
classical scenario, or satellite accretionclassical scenario, or satellite accretion More recent evidence:More recent evidence:
X-shape bulge; He-enrichmentX-shape bulge; He-enrichment
Chemical enrichment by massive spinstarsChemical enrichment by massive spinstars
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Outline:Outline:
Interest of studies on Galactic bulge Interest of studies on Galactic bulge Data available on metallicity, kinematicsData available on metallicity, kinematics
in field bulge starsin field bulge stars More recent evidence: X-shape bulge; He-rich?More recent evidence: X-shape bulge; He-rich? Metal-poor globular clusters in the inner bulgeMetal-poor globular clusters in the inner bulge
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VVV: 84 million stars (Saito+ 2012)
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FLAMES:
7 stars with UVES – R = 45,000130 fibers with Giraffe – R = 22,000
Many programs:Bulge fieldGlobular clusters
Multi-object high-res spectroscopy needed – not logical to do stars one by one
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800 bulge field *sZoccali+2008
l(°) b(°)BW 1.14 -4.2-6° 0.2 -6-1 0 -126553 5.2 -3
METALLICITY(from high-res)
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Babusiaux+ 2010Baade’s Window:Metal-rich stars = bar
Metal-poor stars = spheroid or thick disk b>-4o =Spheroid’s
b<4o mix pops masks non-gradient
KINEMATICS
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Gonzalez et al. 2011Gonzalez et al. 2011
GIRAFFE spectra650 stars
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Cescutti & Matteucci Cescutti & Matteucci 2011,A&A,525,1262011,A&A,525,126
Intense 10xSFR Intense 10xSFR and short and short timescale of timescale of formation, formation, 0.1-0.1-0.3Gyr0.3Gyr
O and Mg: O and Mg: (Zoccali+06; (Zoccali+06; Fulbright+06; Fulbright+06; Lecureur+07)Lecureur+07)
Si,S (Alves-Si,S (Alves-Brito+10;Ryde+09Brito+10;Ryde+09;Bensby+10);Bensby+10)
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Clarkson+2008
SagittariusWindow: l=1.25° b=-2.65°
proper motion cleaned
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More recent evidence:More recent evidence:
X-shape bulgeX-shape bulge Microlensed metal-rich dwarfs: Helium-Microlensed metal-rich dwarfs: Helium-
rich rich
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Saito et al. 2012
2 red clumps at ǂ distances
ΔKs clump best seen in #8
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FLAMES: Vazquez, Zoccali et al. 2012
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CONCLUSIONS BULGE FIELD
If X-shape is an indication of a pseudobulge, there remains to explain:
•Kinematic difference between metal-poor and metal-rich stars but metal-poor is a tiny fraction, and could be very old
•alpha-element enhancement but all the structure could be very oldX-shape could have formed in the 1st 1Gyr
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Formation of inner bulge metal-poor Globular Clusters:
First generation of massive fast-evolving stars: redshifts z~35 (Gao et al. 2010).
Second generation of low-mass stars: forming in inner parts of galaxies.
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Metal-poor globular clusters in the Galactic Bulge
Marin-Franch+09
added:NGC 6522: oldest so far
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Metal-poor GCs:Padova, Y=0.30, ages = 10, 13 Gyr
BHB:Old
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Padova 13 Gyr Z=0.002, Y=0.23, 0.30
or
He-Rich?
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CONCLUSIONS ON METAL-POOR GCs:
Oldest objects in the Galaxy?
Younger if He-enhanced: counts on blue extended HB needed
Metal-rich inner bulge GC NGC 6553: RGBB/RC~0.3 – He not enhanced
Field and GCs: further evidence on enrichment by fast rotating massive *s: Ba, Y, He
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SCIENCE ONLY FEASIBLE SCIENCE ONLY FEASIBLE WITH MULTI-OBJECT HIGH-WITH MULTI-OBJECT HIGH-
RES IN >8m CLASSRES IN >8m CLASS
E-ELT Turn-off stars
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Microlensed dwarfs: high He
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Turn-off stars of bulge clusters:Age, metallicity, element abundance spread
Oldest in the Galaxy, more subject to gravitational disruption, etc.
Multiple populations in many of them?
And clearly: multiple populations in the Galactic bulge, to be disentangled
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The End
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Chiappini+ 2011Nature472, 454
Excess Yconfirms
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[Ba/Eu]=+0.5
s-fraction r-fractionBa: 0.853 0.147Eu: 0.027 0.973
From r-process only, Ba could not be moreabundant than Eu There is a significant s-production of Ba
Excess Ba, Y predicted in massive spinstars
(Barbuy+09)
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Evidence of enrichment by Massive spinstars
Rotational mixing transports:12C from He-burning core into H-rich layers 14N and 13C
This primary 14N is transported back to He core converted to 22Ne = main neutron source
s-process occurs in hydrostatic He-coreburning primary s-process Ba is produced
r-process in the explosion: Eu + some Ba
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SCIENCE ONLY FEASIBLE SCIENCE ONLY FEASIBLE WITH MULTI-OBJECT HIGH-WITH MULTI-OBJECT HIGH-
RES IN >8m CLASSRES IN >8m CLASS
PRESENTLY: PRESENTLY: FLAMES/VLTFLAMES/VLT
MIKE/MAGELLANMIKE/MAGELLAN
M2FS/MAGELLAN – 2013M2FS/MAGELLAN – 2013
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E-ELTE-ELT
TURN-OFF STARSTURN-OFF STARS