Evidence of tidal debris from Cen in the Kapteyn moving group

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Evidence of tidal debris from ? Cen in the
Kapteyn moving group?

• Grand-daughter Elizabeth Wylie de Boer
• RSAA, ANU

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• ACT I
• Set the scene
• ACT II
• Introduce the protagonists
• ACT III
• Insert some dynamic and chemistry
• ACT IV
• Tragic end with plenty of suspense ..

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Objective

• Major goal of Galactic Archaeology is to identify
  importance of mergers and accretion events in
  building up the Galactic disks, bulge, halo (et
  al.)

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Why moving groups?

• Long-lived kinematic substructure
• Can be associated with
• Dynamical resonances or spiral structure
  (Hercules, Bensby et al. 2007)
• Dispersed star-forming aggregates (HR1614, De
  Silva et al. 2007)
• Debris of infalling objects (Arcturus moving
  group, Williams et al. 2009)

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Hercules (Bensby et al. 2007)

• Abundances can not be distinguished from field
  stars
• This is a DYNAMICAL group, NOT the relic of a
  star-forming event
• Associated with local kinematic disturbances by
  the inner bar

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HR 1614 (De Silva et al. 2007, incl. Bessell)

• Tightly confined in abundance space
• Chemically homogeneous
• Dispersed relic of star-forming event
• Remember Marys talk

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Why moving groups?

• Some debris from these events will be phase-mixed
• Unrecognizable kinematically
• Retains common chemical signature --gt Chemical
  Tagging --gt Galactic Archaeology

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Introducing Kapteyn Group

• First identified by Eggen (1965) as a potential
  star-forming remnant that had dispersed
• Detailed kinematic and chemical study of 17 stars
  of the Kapteyn moving group
• Ascertain status as moving group
• Common origin, chemical homogeneity etc
• Or something else

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Re-Introducing Omega Cen

• Long thought that Omega Cen is surviving nucleus
  of dwarf galaxy that had outer stellar envelope
  removed via tidal stripping (Freeman 1993)
• Metallicity distribution, multiple populations
  and abundance anomalies support this theory
  (Norris and da Costa, 1995)

The Spaghetti Survey (Morrison et al)
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Remnants of the past

• Omega Cen remnants prominent in kinematic space
• Vrot in metal-poor sample of Beers et al. 2000
• Jz in metal-poor sample of Gratton et al. 2003

From Meza et al. 2005
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Remnants of the past

• Dinescu (2002) searched for kinematic signature
  left by parent galaxy (with NGC 362, NGC 6779 -
  proper motions and Cu abundances)
• Provided a theoretical prediction of where
  remnants would be found in kinematic space
• Lz -200 to -600 km/s over range of energies

From Dinescu 2002
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Kinematic Analysis of Kapteyn

• Candidates taken from Eggen (1996)
• U, V, W space velocities calculated
• E, Jz found using same potential as Dinescu
  (modified Paczynski (1990) model) in order to
  compare with her theoretical region
• Lindblad diagram (E vs Jz) to determine any
  overlap between theoretical Omega Cen and Kapteyn
• 1000 point Monte Carlo simulation to follow
  uncertainties through calculation

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Space motions

• All stars lie within range of V -115 to -368
  km/s (consistent with Eggen 96 but larger range)
• All U values well within range suggested by Meza
  05 of U -300 to 300 km/s

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• Points of Note
• Dinescu region uncertainty on LSR
• Eggens original Lz estimate for Kapteyn star
• Beers thick disk population
• Gratton, Kapteyn fall within suggested region
• Cluster at (-200, -95,000)

B00 with Fe/H filter G03 with Lz
filter Kapteyn (this study) Omega Cen
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• Points of Note
• Monte Carlo simulations using uncertainties on
  variables - highly correlated (major contributor
  is distance)
• Banded structure seen (errors add emphasis but
  are not suggestive)
• Within 1? then 13 of Kapteyn stars fall within
  potential Omega Cen remnant region
• 2 stars right on end of 1? tail

G03 with Lz filter Kapteyn (this study) Omega
Cen
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Kinematic Summary

• Considering U, V, W and Lindblad position.
• Of 17 stars, 13 look to be kinematically related
  to Omega, 2 which may be
• 2 remaining stars show doubtful link to Omega
  kinematics

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Observations

• July 2006 to August 2007
• 2.3m, SSO, echelle
• Coverage 4120 - 6920 Å
• Resolution of R25,000
• S/N p.r.e 70

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Atmospheres Abundances

• Phot. and spec. methods
• Standard Fe analysis
• Agreement between both methods to within ?T
  200K, ?log g 0.3 (with 2 exceptions)
• Kurucz model grid
• MOOG spectrum synthesis

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Sanity check - Me vs Gratton Sample of 1

• HD 181743
• Gratton This study
• Teff 5968 (50) 6050 (150)
• Log g 4.40 (0.10) 4.25 (0.25)
• Fe/H -1.77 (0.3) -1.67 (0.15)
• Na/H 0.05 (0.05) 0.25 (0.10)
• Mg/H 0.49 (0.06) 0.60 (0.29)
• Ca/H 0.29 (0.03) 0.28 (0.17)

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Fe/H sampling

• 3 populations of Omega Cen (Norris et al. 1996)
• Fe/H -1.7, -1.2, -0.6
• Histogram of Kapteyn group sample
• Falls at upper end of MDF but within cluster MDF

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Light elements

• OC vs FH
• Clear distinction in Na
• Separation not so obvious in Mg
• Ca distinct until Fe/H lt -1.5, where both
  populations overlap

Omega Cen Field Halo
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s-process elements

• OC vs FH
• Clear sep. in ls, with OC showing enhanced ls
• Large distinction in Ba, until Fe/H lt -1.7
  where two populations overlap

Omega Cen Field Halo
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Light elements

• OC vs KG
• KG distinct from halo in Na, more overlapped with
  OC
• Mg, Ca inconclusive

Omega Cen Kapteyn Group
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s-process elements

• OC vs KG
• KG overlaps with OC in ls, distinct from halo
• KG shows Ba enhancements, as do OC stars

Omega Cen Kapteyn Group
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Abundance distributions
?

• (Kapteyn Omega)?Halo
• Na, Mg (?), ls, hs
• Inconclusive
• Ca
• STOP PRESS
• Johnson et al. 09
• Na/Fe 0.03 to 0.2
• Ca/Fe 0.36 constant
• La/Fe -0.4 to 2.0

?
?
?
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Abundance statistics

• Both parametric t-test and non-parametric KS test
• If P value is small (lt0.05) then two samples
  from different populations. If P value is
  larger, no conclusion can be drawn
• Results from both tests identical
• Kapteyn and Halo are from different populations
  in Na, ls, hs
• Omega and Halo different in Na, Mg, Ca, ls, hs

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A quick word on copper

• Determined Cu abundances in 4 stars
• (Fe/H -1.1 to -1.65)
• ALL four depleted
• Cu/Fe -0.47 to -0.60
• Consistent with Smith et al. 2000
• Cu in Omega Cen, constant at Cu/Fe -0.60
• In field stars Cu increases with metallicity
  (Sneden et al. 1991, Castro et al. 1999)

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Abundance Summary

• Kapteyn is not chemically homogeneous
• Kapteyn/Omega different population from halo in
  Na, Mg(?), ls, hs
• All three populations overlap in Ca --gt
  inconclusive
• 4 of the sample show Omega Cen Cu signature

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The story, so far what we DO know

• Omega Cen is weird with complex formation history
• Kapteyn is not a chemically homogeneous moving
  group

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The story, so far what we THINK we know

• Omega Cen may be a remnant of dwarf spheroidal
  merger
• Omegas elevated alpha- and solar scaled Fe-peak
  suggest Type II SNe dominate, almost no Type Ia
  SNe contribution (Johnson et al. 2009)
• Additional source of light elements to account
  for enhanced Na (greater than expected from Type
  II Sne)

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The story, so far what we THINK we know

• Kapteyn seems to show kinematic relation to Omega
  Cen, along with other stars in same region of L.
  diagram
• Kapteyn abundances show distributions/patterns
  similar to those seen in Omega Cen

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The story, so far what we THINK we know

• Stars in Kapteyn group are remnants of tidal
  debris from same merger event that created
  Omega Cen

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The story, so far what were guessing

• Banded structure seen in Lindblad diagram
• Perhaps indicative of different energies from
  different wraps/orbits (Meza et al. 2005)

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The story, so far what were guessing

• Banded structure
• Omega Cens existence at present radius
• gt
• Parent galaxy must have been dense
• Needs to be 108 Msun before DF will have any
  effect

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The story, so far what we dont know yet

• Mass of parent galaxy
• Fornax-esque dwarf ?
• Merger details
• When? 10Gyr (BF03)
• How many orbits?
• Chances of finding stars from a parent galaxy?
• If event happened a long time ago then chances
  would be slim due to thorough mixing
• Maybe not mixed very much, then OK
• How many more GC are in similar predicament?
  (Yong, da Costa)

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Conclusion

• 15 stars in Kapteyn appear both kinematically and
  chemically linked to Omega Cen
• Further investigation needed into detail of
  merger/tidal disruption/debris
• Watch this space
• Wylie de Boer et al., 2009
• Wylie de Boer and Freeman

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• Two households, both alike in dignity
• In fair Verona, where we lay our scene,
• From ancient grudge break to
• new mutiny,
• Where civil blood makes civil hands unclean.
• For never was a story of more woe
• Than this of Juliet and her Romeo.

dynamics and chemistry
objects
The Milky Way
problems
still the same old problems
post-doc
stellar
Centauri, O
Kapteyn
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• HAPPY BIRTHDAY
• to
• John and Mike