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A Carbon Rich Mira Variable In a Globular Cluster: A Stellar Merger MW Feast JW Menzies PA Whitelock SAAO and UCT Published online MNRAS Letters 29 Oct 2012. N Matsunga (Thesis: Tokyo) 2006 Intensive survey of globular clusters with the IRSF for variables Lynga 7 V1 Mira variable

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slide1

A Carbon Rich Mira Variable

In a Globular Cluster:

A Stellar Merger

MW Feast JW Menzies PA Whitelock

SAAO and UCT

Published online

MNRAS Letters

29 Oct 2012

slide2

N Matsunga (Thesis: Tokyo) 2006

Intensive survey of globular clusters

with the IRSF

for variables

Lynga 7 V1

Mira variable

Period = 551 days

Amplitude ΔK = 1.22 mag

J-Ks =4.1 mag

slide3

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 intermediate

age objects

slide4

Next Surprise

SPITZER spectra show

Lynga V1 is a carbon star

Carbon Miras with ~500 day period

And very red colours (due to dust shells)

Are found in intermediate age clusters

Not globular clusters

And have initial masses of ~1.5 solar masses

An ages of ~1-2 Gyr

slide7

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 mag

Bolometric Mag. If cluster member –5.0 mag

slide8

Thus

~ 1.5 solar mass

~ 1.5 Gyr old

Mira variable

in a

~ 13 Gyr old globular cluster

slide9

Comparison with collisional and binary-evolution models.

FR Ferraro et al. Nature462, 1028-1031 (2009) doi:10.1038/nature08607

slide10

Which sequence is most likely

For the Lynga 7 Mira?

If matter transferred has changes composition

(H/He)

It will affect later evolution

Possibly direct collision most likely?

slide11

Are merged stars important in other contexts?

Does Galactic Bulge contain young

And intermediate age stars?

slide13

The two blue straggler sequences of M30.

FR Ferraro et al. Nature462, 1028-1031 (2009) doi:10.1038/nature08607