Exploring the orbits of the stars from a blind chemical tagging
experiment Borja Anguiano Macquarie University, Sydney,
Australia
Slide 2
Siblings, siblings, siblingseverywhere !
Slide 3
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).
Slide 4
Open clusters: Chemical abundances Chemical information remains
preserved in an open cluster (De Silva et al. 2007, Sestito et al.
2007) -> RECALL D. Yongs talk about inhomogeneities in Open
Clusters
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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
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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
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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
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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
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A new way to get ages ?
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age-metallicity relation Mitschang et al. 2014 B. Anguiano PhD
thesis 2012 Edvardsson et al. 1993
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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
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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.
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Age vs 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
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Age vs Mean of the coeval groups increase with age. The
dispersions is significant. e > 0.3 range from 2 to 10 Gyr
Slide 15
Age vs 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
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Age vs Age vs. L
Slide 17
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
?