Dr. Alan Alves-BritoARC Super Science Fellow
Red giant stars as tracers of the chemical evolution of the
Galactic bulge
Astounding Stories of Super Science - Hobart, April 18-20. 2
Main Collaborators
Dr. Jorge Meléndez (IAG/USP, Brazil)
Prof. Martin Asplund (RSAA, Australia)
Dr. Thomas Bensby (Lund Observatory, Sweden)
Astounding Stories of Super Science - Hobart, April 18-20. 3
Scientific Motivation
age kinematics dynamics chemical enrichment
DIRBE@COBEDwek et al. 1995
OPTICAL IMAGEAxel Mallenhoff 2001
Astounding Stories of Super Science - Hobart, April 18-20. 4
Tracers of the Galactic bulge
K and M giant stars in the field(e.g. Mcwillian & Rich 1994; Fulbright et al. 2006,2007; Zoccali et al. 2006; Lecureur et al. 2007; Zoccali et al. 2008; Meléndez et al. 2008; Ryde et al. 2009; Alves-Brito et al. 2010; Bensby et al. 2010; Alves-Brito et al. 2012b, in preparation)
Giant stars in globular clusters(e.g. Alves-Brito et al. 2006; Barbuy et al. 2006; Barbuy et al. 2009)
Dwarf, sub-giant and giant stars in gravitational microlenses(e.g. Cohen et al. 2008;2009; Bensby et al. 2008;2009; Alves-Brito et al. 2012c, in preparation)
Astounding Stories of Super Science - Hobart, April 18-20. 5
When and how the Galactic bulge was
formed?
Credit: University of Texas, MacDonald Observatory
stellar content
(classical) vs.
morphology(pseudobulg
e)
Kormendy & Kennicutti 2004
see also Elmegreen et al. 2008
Astounding Stories of Super Science - Hobart, April 18-20. 6
Main goal: Galactic genealogy
Big Bang
Fe-peak
Light elements
Neutroncapture
Grevesse & Sauval 1998
Solar Abundance Pattern
Astounding Stories of Super Science - Hobart, April 18-20. 7
Chemical enrichment: [X/Fe] ~ SF
[O/Fe] ---> SNII/SNIa
Tinsley 1979; Chiappini 2004
Astounding Stories of Super Science - Hobart, April 18-20. 8
Bulge (giants) vs. Disks (dwarves)
The bulge chemical enrichment is dominated by SNII (massive stars). It must have formed faster than both the thick and thin disks
Ballero et al. (2007): MDF and [Mg/Fe] imply different IMFs for the bulge and the thick disk.
Lecureur et al. 2007 and previous works
FLAMES:UVES@VLT: R = 20,000 - 40,000[Fe/H] = log(Fe/H)_star - log(Fe/H)_sun
Astounding Stories of Super Science - Hobart, April 18-20. 9
Concerns Giants (bulge) vs. dwarves (disks): Teff
Zero points on stellar parameters
Line list (different lines, atomic data)
Solar abundances
Methods of analysis
Astounding Stories of Super Science - Hobart, April 18-20. 10
High resolution spectra
PHOENIX@GeminiMIKE@MagellanUVES@VLTELODIE@OHP2dcoude@McDonaldHIRES@Keck
R = / ≥ 60,000
[Fe/H] = log(Fe/H)_star - log(Fe/H)_sun-1.5 < [Fe/H] < +0.5
Astounding Stories of Super Science - Hobart, April 18-20. 11
data reduction
heliocentric radial velocity
continuum normalization
EWs, T, logg, vt, [Fe/ H]
atomic data: loggf, damping ctes spectr um synthesis
MARCS and Kurucz models
spectr a @ optical and I R wavelength s
Methods
Astounding Stories of Super Science - Hobart, April 18-20. 12
Alves-Brito, Meléndez, Asplund et al. 2010, A&A, 513, 35Meléndez, Asplund, Alves-Brito et al. 2008 : CNO
Optical data: R = 60,000 : S/N = 200
thick thin
same knee (thick disk)
The bulge and the (local) thick disk are indistinguishable
Astounding Stories of Super Science - Hobart, April 18-20. 13
Bensby, Alves-Brito, Oye et al. 2010, A&A Bensby, Alves-Brito, Oye et al. 2011, ApJ (outer
disk)
Optical data: MIKE@Magellan R = 55,000 : S/N = 100
Inner Disk (44 giants : 3-7 kpc)
inner disk
, local thick and thin disks; * bulge
The metal poor bulge and the (inner) thick disk are indistinguishable
Astounding Stories of Super Science - Hobart, April 18-20. 14
Alves-Brito, Johnson, Bensby et al. 2012, in preparation
The bulge (normal giants and microlensed ones) and the thick disk are indistinguishable
Astounding Stories of Super Science - Hobart, April 18-20. 15
Gonzalez, Rejkuba, Zoccali et al. 2011, A&A; also using Alves-Brito et al. 2010’s data
Different techniques and independent methods ¡confirm our results! The bulge and the thick disk
are indistinguishable
Optical data: FLAMES@VLT R = 30,000 : S/N = 100 474 giants in 4 different fields
Astounding Stories of Super Science - Hobart, April 18-20. 16
Similar chemical evolution: genetic link
Short timescale, similar SFR and IMF
Classical bulge vs. secular/dynamical
Bulge vs. local and inner thick-disk:
Conclusions
Astounding Stories of Super Science - Hobart, April 18-20. 17
What about the heavy elements?
Bulge vs Thin/Thick disk in the Galactic center
The critical -0.3 < [Fe/H] < +0.0 range
Gaia mission (from 2011-2020): ~1 billion of stars to V=20. 3D map of our Galaxy
Australian GMT, HERMES
SIMPLE@E-Extremely Large Telescopes: high R of dwarf stars in the bulge!
More info: bulge vs. inner disks
Age spread, kinematics and chemical abundances can constrain different models of bulge formation
Perspectives
Astounding Stories of Super Science - Hobart, April 18-20. 18
Thank you very much
Astounding Stories of Super Science - Hobart, April 18-20. 19
Bulge MDF
Astounding Stories of Super Science - Hobart, April 18-20. 20
~245,000 starsl,b = 10.25,-20.65
CMD @HST
t = 10Gyr ([Fe/H] = 0) Unevolved MS t = 10Gyr ([Fe/H] =0.5)
t = GC +- 2.5 Gyr (Ortolani et al. 1995; Zoccali et al. 2003)
Sahu et al. 2006
Astounding Stories of Super Science - Hobart, April 18-20. 21
# 19 gigantes do bojo + 49 gigantes de comparação
Meléndez, Asplund, Alves-Brito et al. 2008, A&A : IR: Phoenix@Gemini-S
bulgethick diskthin diskhalo
[O/Fe] vs. [Fe/H]
[(C+N)/Fe] vs. [Fe/H]
[(C+N)/Fe] = cte
[O/Fe] = 0.41 - 0.02*[Fe/H]
[O/Fe] = 0.39 - 0.01*[Fe/H]
[O/Fe] = 0.03 0.09 dexThe bulge and the (local) thick disk are indistinguishable
Astounding Stories of Super Science - Hobart, April 18-20. 22
# 11 giants in the bulge
X Meléndez et al. 2008
Ryde, Gustafson, Edvardson et al. 2009, A&A
IR: CRIRES@VLT : CNO, R = 70,000 : S/N = 40-110
[O/Fe] @ IR : Phoenix and CRIRES results are consistent
Astounding Stories of Super Science - Hobart, April 18-20. 23
Thick disk formationMichelle et al. 2011
Accretion
Heating via a minor merger
Intense SF in a gas turbulent environment
Radial migration
Astounding Stories of Super Science - Hobart, April 18-20. 24
Ages of Disk Stars
Thick disk: ~10 Gyr Thin disk: <8 Gyr
Bensby et al. (2007)
Astounding Stories of Super Science - Hobart, April 18-20. 25
Inner disk stars
Astounding Stories of Super Science - Hobart, April 18-20. 26
Inner disk: Toomre Diagram
Bensby et al. (2010)
Astounding Stories of Super Science - Hobart, April 18-20. 27
Uncertainties
∆T = ±100K : ∆logg = ±0.30 dex : ∆v = ±0.20 Km/s
Fe: 0.03 dex Mg: 0.07 dex
C: 0.11 dex Si: 0.12 dex
N: 0.11 dex Ca: 0.10 dex
O: 0.14 dex Ti: 0.17 dex
Astounding Stories of Super Science - Hobart, April 18-20. 28
Uncertainties
Continuum level Line fitting (?) Damping parameters Stellar atmospheres : 1D models Non-LTE effects