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A Carbon Rich Mira VariableIn a Globular Cluster:
A Stellar Merger
MW Feast JW Menzies PA WhitelockSAAO and UCT
Published onlineMNRAS Letters
29 Oct 2012
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N Matsunga (Thesis: Tokyo) 2006Intensive survey of globular clusters
with the IRSFfor variables
Lynga 7 V1
Mira variablePeriod = 551 days
Amplitude ΔK = 1.22 magJ-K
s =4.1 mag
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Mira variables are;Large amplitude, pulsating AGB stars.
Useful properties;1. They obey
a period- bolometric magnitude relation.2. Their initial (and probably final)
Mass increases with period.3. Their age decrease with period.
551 day Mira expected to be intermediateage objects
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Next SurpriseSPITZER spectra show
Lynga V1 is a carbon star
Carbon Miras with ~500 day periodAnd very red colours (due to dust shells)Are found in intermediate age clusters
Not globular clustersAnd have initial masses of ~1.5 solar masses
An ages of ~1-2 Gyr
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Cluster velocity (Saviane et al. 2012) +22±3 km/s V1 +27±5 km/s
Predicted velocity if in field –81 km/s
Bolometric Mag. from PL –5.2 magBolometric Mag. If cluster member –5.0 mag
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FR Ferraro et al. Nature 462, 1028-1031 (2009) doi:10.1038/nature08607
Comparison with collisional and binary-evolution models.
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Which sequence is most likelyFor the Lynga 7 Mira?
If matter transferred has changes composition(H/He)
It will affect later evolution
Possibly direct collision most likely?
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Are merged stars important in other contexts?
Does Galactic Bulge contain youngAnd intermediate age stars?