ω Centauri’s red giants confirm stellar evolution models

A new study, led by Mariela Vieytes from the University of Buenos Aires, demonstrates one of the necessary conditions for predictions of stellar post-main sequence evolution.

Astronomers need to establish that stars undergo significant amounts of mass loss (~0.1-0.3 M_☉) during their red giant branch evolution. They expected to find confirmation of this by detecting gas congregating in the cores of globular clusters after being shed by stars evolving along the RGB. Yet searches for this gas came up mostly empty.

Eventually astronomers realized that gas would be stripped relatively quickly as globular clusters plunged through the galactic plane. But this left them with the need to confirm the prediction in some other manner.

One way to do this is to look at the stars themselves. If they show velocities in their photospheres greater than the escape velocity, they will lose mass. Just how much higher will determine the amount of mass lost.

By analyzing the Doppler shift of specific absorption lines of several stars in the cluster ω Centauri, the team was able to match the amount of mass being lost to predictions from evolutionary models. From this, the team concluded that their target stars were losing between the rates of mass loss are estimated as a few 10^-9 and 10^-10 M_☉ yr^-1. This is in general agreement with the predictions set forth by evolutionary models.

Image: As they get older, Sun-like stars become red giants and shed mass.

• Source: Universe Today • The paper is available at http://arxiv.org/1011.1260v1.pdf