Exploring the orbits of the stars from a blind chemical

tagging experiment

Borja AnguianoMacquarie University, Sydney, Australia

Siblings, siblings, siblings…everywhere !

Star formation• Stars form in molecular clouds (HII) when

denser parts core collapse under their on gravity

New second generation from massive stars

Presence of radioactive-isotopes in primitive meteorites, the Sun was polluted by a SN of star about 15-25 solar masses within a distance of 0.02-1.6 pc (Looney et al. 2006).

Open clusters: Chemical abundances

Chemical information remains preserved in an open cluster (De Silva et al. 2007, Sestito et al. 2007) -> RECALL D. Yong’s talk about inhomogeneities in Open Clusters

Chemical Tagging

“Spectroscopic survey of about a million stars, aimed at using chemical tagging techniques to reconstruct the star-forming aggregates that built up the disk, the bulge and halo of the Galaxy”

A blind chemical tagging experiment A. Mitschang PhD thesis, Macquarie Uni.

Goal: Using element abundance information from field stars to search for co-natal groups

- What is the probability that any two stars were born together ?

- Empirically- Define a difference metric

C = chemical speciesAc = [X/Fe]

See A. Mitschang et al. 2012 for more details

A blind chemical tagging experiment…Bensby, T.; Feltzing, S.; Oey, M. S. 2014

O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, and Ba for 714 nearby F and G dwarf stars.

Random errors ~0.05 dex

Using a principal component analysis on chemical abundances spaces Ting et al. 2012 concluded that the [X/Fe] chemical abundance space in the solar neighbourhood has about six independent dimensions

Why so many -in such a small volume- ?

Possible scenarios:– Groups are highly contaminated– Open clusters are not good representatives– Galactic mixing is weak– Groups are not co-natal stars, just co-eval-- ??

See A. Mitschang et al. 2014 for more details

A new way to get ages ?

age-metallicity relation

Mitschang et al. 2014

B. Anguiano PhD thesis 2012Edvardsson et al. 1993

OrbitsBensby et a. 2014 calculated the Galactic orbits using the GRINTON integrator (Bedin et al. 2006)

Output parameters:

- Minimum and maximum distances from the Galactic centre –peri and apocentric values (Rmin,Rmax)

- Maximum distance from the Galactic plane, Zmax

- Eccentricity, Etot, Lz

Chemical tagging + Galactic orbits

IDEA: Use coeval groups identified in Mitschang et al. 2014 using the data set from Bensby et al. 2014 to explore the evolution of the stellar orbits parameters with time

Coeval groups with more than 5 members -> A total of 45 groups to play with.

Age vs <Rmin, Rmax>

Dots: mean value for Rmax, Rmin for a given group, error bars: standard deviation of the group.

Rmin is more sensitive to the angular momentum than Rmax

Age vs <eccentricity>

Mean <e> of the coeval groups increase with age. The dispersions is significant. e > 0.3 range from 2 to 10 Gyr…

Age vs <Zmax>

We find an age relation with respect to the mean maximum distance from the Galactic plane for the computed orbits of the coeval groups. However note the scatter, there are old stars with low Zmax values

Age vs <Lz>

Age vs. σL

Final points

• Chemical Tagging is a promising tool for Galactic astronomy studies

• Gaia + ground base spectroscopy surveys will change our current views of Galaxy formation/evolution. Where astrometry finds the periodic table…

• Is chemical tagging a tool to get precise ages for field stars ?

• Are the orbits of the coeval groups fundamental for our understanding how the Galaxy was built ?