Exploring the orbits of the stars from a blind chemical tagging experiment
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Exploring the orbits of the stars from a blind chemical tagging experiment. Borja Anguiano Macquarie University, Sydney, Australia. Siblings, siblings, siblings…everywhere !. Star formation. Stars form in molecular clouds (HII) when denser parts core collapse under their on gravity.

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Exploring the orbits of the stars from a blind chemical tagging experiment

Exploring the orbits of the stars from a blind chemical tagging experiment

Borja Anguiano

Macquarie University, Sydney, Australia


Siblings siblings siblings everywhere

Siblings, siblings, siblings…everywhere !


Star formation

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

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

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

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 species

    Ac = [X/Fe]

See A. Mitschang et al. 2012 for more details


A blind chemical tagging experiment

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


Exploring the orbits of the stars from a blind chemical tagging experiment

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

A new way to get ages ?


A ge metallicity relation

age-metallicity relation

B. Anguiano PhD thesis 2012

Edvardsson et al. 1993

Mitschang et al. 2014


Orbits

Orbits

Bensby 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

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

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

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

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


Exploring the orbits of the stars from a blind chemical tagging experiment

Age vs <Lz>

Age vs. σL


Final points

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 ?


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