The metallicity of the intergalactic medium and its evolution
The Age-Metallicity-Velocity relation in the nearby disk
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Transcript of The Age-Metallicity-Velocity relation in the nearby disk
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The Age-Metallicity-Velocity relation in the nearby disk
Borja AnguianoAstrophysikalisches Institut Potsdam (AIP)
K. Freeman (ANU), E. Wylie de Boer (ANU), M. Steinmetz (AIP) & RAVE
collaboration
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Outline
Chemical & Kinematics evolution in the MW disk: Is there any Age-Metallicity-Velocity relation ?
Do we really know how old is a star ?
Comparison between observations and models/simulations -radial mixing, disk heating...-
RAVE: AMVR project.
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The Age-Metallicity Relation in the disk (AMR)
The AMR is a fundamental tool to understand the chemical evolution and enrichment history of the disk
Rocha-Pinto et al. (2000) / Edvardsson et al. (1993)
“Cosmic scatter” or observational ?
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Geneva-Copenhagen Survey ~16000 FGK dwarfs/subgiants accurate distances/kinematics, photometry metallicities. Stars ages suffer from considerabe uncertainties.
Holmberg et al. 2007
Different populations -- different AMRs ?
dwarf stars
subgiant stars
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From different selection in temperature we find different AMRs
Previous works present this kind of bias -Mayor (1974), Twarog (1980), Meusinger et al. (1991)-
Holmberg et al. 2007 derived new values for GCS. Have his corrections introduced systematic effects in the stellar parameters ?
GAP ?
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Different AMRs for different Mv
Garnett & Kobulnicky (2000) using Edvardsson et al. (1993)/Ng & Bertelli (1998) sample find a considerable scatter for stars with d < 30pc while stars with distance between 30 and 80 pc do not present the same amount of scatter.
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AMRs from the models of Galactic chemical evolutionModels taking into account
the chemical enrichment and the dynamical evolution of the system present a significant scatter in the AMR - Raiteri et al. (1996), Berzick et al. (1999) -Sellwood & Binney
(2002)Is the “Radial mixing” the missing piece of the AMR puzzle ? The stars can migrate over large radial distances -resonant interactions with spiral density waves-
Half of stars of the solar neighbourhood have come from large radial distances (>2 kpc) -Roskar et al. (2008b)- Most of the metal rich stars in the solar volume originate from the inner disk -Haywood (2008)-
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Age-Velocity Relation (AVR)
Kinematics properties -clues about the Galaxy evolution-
W-component (U,V components present similar properties)
youngest stars show a low velocity dispersion ~ 10 km/s
3-10 Gyr, the dispersion is around 20 km/s
For the oldest stars ~ 42 km/s
Edvardsson et al. (1993)/Freeman (1993)
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Continuous heating or with saturation at 4.5 - 6 Gyr (Seabroke & Gilmore 2007, Aumer & Binney 2009)
Are the age errors smoothing the kinemtatic groups ?
Heating mechanisms become inefficient at ~ 30 km/s -minor merger that created the thick disk 9 Gyr ago- (Quillen & Garnet 2001)
Nordstrom et al. 2004/Holmberg et al. 2007
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The semi-cosmological models and simulations fill the area between the two extreme observational results but these present a number of caveats, for example the cosmological disk were not chosen to be MW “clones”.
Gibson et al. 2008
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The Age of stars
The age of stars are crucial to place the observed chemical and kinematics properties of the stars in an evolutionary context
Chromospheric ages - Isochrones:
- chromospheric ages tends to be lower than the isochrones age for metal-poor stars (Rocha-Pinto & Maciel 1998). Is this method working for intermediate-old stars ?
- different ages using different isochrones and methods !
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Rocha-Pinto et al. 2000
Feltzing et al. 2001
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different results using different isochrones
Large errors in age estimations
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Holmberg et al. (2007) find a minimun around the solar age. Feltzing et al. (2001) find more stars in this age range.
Mistake in the legend: Black line: Holmberg et al. 2007Yellow line: Feltzing et al. 2001
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AMVR project
Different works with the same goal present different chemical and kinematical picture.
How the nearby disk stars have evolved with time over the past 10 Gyr remains a crucial open question.
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New derivation of the AMR and AVR using a selected sample of cooler subgiants (G stars) –ages 2-13 Gyr- from the Geneva-Copenhagen (Nordstrom et al. 2004/Holmberg et al. 2007) and RAVE surveys (Steinmetz et al. 2003/Zwitter et al. 2008).
Subgiants are suitable stars for dating the Galactic disk. Isochrones separate well for different ages, they run almost horizontally in the Mv-Teff diagram and also are 1-2 mag brighter than dwarfs which increases the volume for study.
Thoren et al. 2004
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From GCS (uvby-β photometry):
3.69 < log Teff < 3.76
Mv < 5.0
Mv = -31.25 * log Teff + 121.66 (avoid MS)
Sample definition
~ 450 stars, we know metallicity, rotation, ages, parallaxes, kinematics and Galactic orbits
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From RAVE (spectroscopy, R ~ 7000):
9.0 < I < 12.0 (input in RAVE survey)
3.5 < log g < 4.1
3.69 < log Teff < 3.75
~ 2000 stars with accurate RV and proper motions
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Contamination from dwarfs and giants, further observations are needed to improve [Fe/H], Teff and log g in order to select the cool subgiants and get accurate ages.
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Kinematics studies
GCS –mean error in the total proper motion is ~ 1.8 mas/yr, error in the space velocity ~ 0.7 km/s. The mean error in RV is typically ~ 0.25 km/s (Nordstrom et al 2004).
RAVE –the typical error in proper motion is 5 mas/yr and more than 80% of RV measurements have an internal accuracy better than 3 km/s (Steinmetz et al. 2006).
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Observations
Data from ANU/2.3m telescope in SSO. Double Beam Spectrograph (DBS)
Low resolution -R = 400 and 1.9A/px- (3100-6200 A)
We have collected ~ 450 stars from GCS and ~ 700 RAVE stars with high S/N. In the end of the project we will have ~ 1000 subgiants.
We expect to have ± 0.2 dex in [Fe/H], ± 100K in Teff and ± 0.2 dex in log g
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Preliminary results
1260 spectra taken, reduced, extracted, cleaned and calibrated.
Derivation of T, [M/H] and log g via chi-squared statistic using synthetic model atmospheres (Munari et al. 2005)
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Exploring the Fourier Quotient...
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We will use isochrone methods, Mv-Teff plane for GCS stars and logg-Teff plane for RAVE stars
10% error in parallax or 0.1 dex in log g correpond to about 2 Gyr in age uncertaint. The errors in age estimates may well sum up to 3-4 Gyr, at least for the older stars (Thoren et al. 2004)
Ages
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Conclusions
New derivation of the AMR and AVR in the nearby disk: Work out in a reliable picture of the Chemical and Kinematical picture of the Galaxy.
Subgiants: Good stars for dating the MW -good oportunity to test different grid of isochrones-
Low resolution/medium telescopes: Deriving a method of wide applie to deriving stellar parameters.