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

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.

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 ?

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

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 ?

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.

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)-

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)

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

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

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 !

Rocha-Pinto et al. 2000

Feltzing et al. 2001

different results using different isochrones

Large errors in age estimations

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

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.

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

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

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

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.

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).

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

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)

Exploring the Fourier Quotient...

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

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.