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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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Thus~ 1.5 solar mass~ 1.5 Gyr oldMira variable

in a~ 13 Gyr old globular cluster

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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?

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FR Ferraro et al. Nature 462, 1028-1031 (2009) doi:10.1038/nature08607

The two blue straggler sequences of M30.