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Abundance structure and chemical Abundance structure and chemical evolution of the Galactic discevolution of the Galactic disc
Thomas BensbyThomas BensbyEuropean Southern ObservatoryEuropean Southern Observatory
Sofa Feltzing - Lund ObservatorySofa Feltzing - Lund ObservatorySally Oey – University of MichiganSally Oey – University of MichiganBengt Gustafsson – Uppsala UniversityBengt Gustafsson – Uppsala University
CollaboratorsCollaborators
Milky Way panoramaMilky Way panorama
The Lund Milky Way panorama (hand painted 1x2 m)
NGC 891NGC 891
NGC 891NGC 891
Thin disc
NGC 891NGC 891
Thick discThin disc
NGC 891NGC 891
Thin disc Thick disc Bulge
NGC 891NGC 891
Thin disc Thick disc Bulge
Milky Way look-alike?
The dichotomy of the Galactic discThe dichotomy of the Galactic disc
Scale heights:
Thick disk: ~1000 pc (1450) Thin disk: ~300 pc
Local densities:
Thick disk: ~10% (2%)Thin disk: ~90% (98%)c
Galactic stellar populationsGalactic stellar populations
Solar neighbourhood (Hipparcos, i.e. ~200pc radius),heavily dominated by disk stars ~90% thin disk stars
~10% thick disk stars~0.1% halo stars
All populations have their highest concentrations in the plane!
Thin diskdominates
Thick diskdominates
Thick diskdominates
Halodominates
Halodominates
The dichotomy of the Galactic discThe dichotomy of the Galactic disc
Bensby et al., 2004, A&A, 415, 155
Filled symbols represent kinematically hot thick disc stars
Open symbols representkinematically cold thin disc stars
Uncomplete sample, stars were selected basedon their kinematic propertiesto be possible members of eitherof the two discs.
Still, the two samples clearlyshow different abundance trends
However, two extreme samples,What about stars with less extremekinematic properties?
The dichotomy of the Galactic discThe dichotomy of the Galactic disc
Fuhrmann, 2008, MNRAS, 3384, 173
Volume limitedsample of nearby starsshow divided abundance trends.
Teff>5300K
Size of points proportionalto age of the stars.
Substructure in velocity spaceSubstructure in velocity space
Navarro et al. (2004)
Beers et al. (2000) catalogue, kinematically un-biased sample of 2106 star with -4.0<[Fe/H]<0.0.
Decomposed into three Gaussiandistributions; halo, thick disk, thin disk
Excess of stars at V
rot≈170 km/s (V
LSR≈-50 km/s)
attributed to the Hercules stream
Rotates as the thick disk!
Arcturus moving group – remnantstars of the “last major merger”?
Substructure in velocity spaceSubstructure in velocity space
Bensby et al. (2007, ApJL, 655, L89)
Contour plot of ~14000 stars from the Geneva-Copenhagen survey(Nordstrom et al 2004).
Thin disc
Thick disc
v_pec is the total space velocity, i.e.U
LSR, V
LSR, and W
LSR combined
A new stellar sampleA new stellar sample
899 kinematically selectedF and G dwarf stars
R > 60000S/N > 200complete 400 – 980 nm
MIKE @ MagellanUVES @ VLTFEROS @ ESO 1.5m & 2.2mSOFIN @ NOT
A new stellar sampleA new stellar sample
283 stars with thick disckinematics
A new stellar sampleA new stellar sample
283 stars with thick disckinematics
428 stars with thin disckinematics
A new stellar sampleA new stellar sample
283 stars with thick disckinematics
428 stars with thin disckinematics
87 stars with Herculesstream kinematics
A new stellar sampleA new stellar sample
283 stars with thick disckinematics
428 stars with thin disckinematics
87 stars with Herculesstream kinematics
63 stars with “in between”kinematics
A new stellar sampleA new stellar sample
283 stars with thick disckinematics
428 stars with thin disckinematics
87 stars with Herculesstream kinematics
63 stars with “in between”kinematics
38 stars with halo kinematics
A new stellar sample - questions?A new stellar sample - questions?
How metal-rich is thethick disc?
?
A new stellar sample - questions?A new stellar sample - questions?
How metal-rich is thethick disc?
How metal-poor is thethin disc?
?
A new stellar sample - questions?A new stellar sample - questions?
How metal-rich is thethick disc?
How metal-poor is thethin disc?
“In between” stars – thin or thick, or a population of their own?
?
A new stellar sample - questions?A new stellar sample - questions?
How metal-rich is thethick disc?
How metal-poor is thethin disc?
“In between” stars – thin or thick, or a population of their own?
The interface between the metal-rich haloand metal-poor thickdisc?
?
Abundances - TitaniumAbundances - TitaniumStars with thick disc kinematics
Stars with thin disc kinematics
red line = running median of the thick disc blue line = running median of the thin disc
Abundances - TitaniumAbundances - Titanium
Abundances - TitaniumAbundances - Titanium
Abundances - TitaniumAbundances - Titanium
Kinematic confusion...Kinematic confusion...
Stars selected purely on kinematics
Stars selected purely on theirages
Toomre diagram forthe age selected samples
Many young stars havehot kinematics!!
Hercules-stream starsHercules-stream stars
A wide spread in ageand metallicity
Abundance ratiosnot seen in dSph inthe Local Group
==>
Most likely the resultof a phenomenon originating inside theMilky Way, possiblythe bar
Either inner disk stars,or due to the bar'souter Lindblad resonance
A bulge-thick disc connection?A bulge-thick disc connection?
In situ Bulge dwarf stars,observed while being optically magnified duringmicrolensing events.
Abundance trend in theBulge is essentiallyidentical to what we seein the nearby thick disc!
(poster 106 at IAUS265)
* What is the Bulge? * What is the thick disc?* Are they the same?* Is the bar responsible for the kinematic heating of the thick disc?
Abundance trends in the inner disc?Abundance trends in the inner disc?
A sample of giants starsthat we just observed.
Will trace the abundance trends in the Galactic discat approximately 4, 8, and12 kpc from the Galacticcentre.
(short) Summary(short) Summary
● Galactic disc consists of two distinctly different disc systems Galactic disc consists of two distinctly different disc systems (ages, abundances, and (ages, abundances, and kinematicskinematics), indicating a complex ), indicating a complex history for the Milky Way – how did two so different disc history for the Milky Way – how did two so different disc systems form?systems form?
● Kinematic confusion, maybe age criteria is better?Kinematic confusion, maybe age criteria is better?
● Hercules stream is likely a dynamic effect, (and not of extra-Hercules stream is likely a dynamic effect, (and not of extra-galactic origin.....)galactic origin.....)
● Bulge trend is very similar to what is seen in the nearby thick Bulge trend is very similar to what is seen in the nearby thick disc...disc...
.....see also tomorrow's talk(s) at IAUS 265.....see also tomorrow's talk(s) at IAUS 265
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