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
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 species
Ac = [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
B. Anguiano PhD thesis 2012
Edvardsson et al. 1993
Mitschang et al. 2014
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
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 ?