Guildford Astronomical Society


The University Lecture theatres are CLOSED. This is an online Zoom meeting

May Meeting - Natalie Rees

Our next monthly meeting is on Thursday, 20th May 2021 at 7:30pm.

A Zoom Talk: AGB (Asymptotic giant branch) stars : thermal pulses, third dredge-up and binary interactions

The asymptotic giant branch (AGB) is a late stage in the evolution of intermediate mass stars. These stars are extremely luminous, with outer layers that are cool and expanded, causing them to be found in the upper right portion of the Hertzsprung-Russell diagram.
By this point in the star’s lifetime, helium has been exhausted in the core leading to a carbon and oxygen rich core surrounded by separate helium and hydrogen burning shells. The double shell burning results in dramatic thermal pulses when helium ignites under degenerate conditions in a thin shell.
The pulses give rise to the phenomena of third dredge-up where material from the core (primarily carbon) is mixed all the way up to the surface, where it can be detected by observers.
AGB stars are also thought to be the location of the slow-neutron capture process (s-process) which produces heavy elements such as barium and lead, making them important contributors to the galactic chemical evolution.
In addition, AGB stars are also likely to interact with a binary companion due to their large size and strong stellar winds, resulting in mass transfer and potentially even common envelope evolution.
This talk will investigate all of these processes and how they lead to a variety of different observed stars including carbon stars, nitrogen-rich stars, S stars, barium stars, cataclysmic variables and red stragglers.

Natalie Rees

For details of this seasons meetings go to the meetings page.


We support, along with the Federation of Astronomical Societies

the Dark Skies Matter initiative.

Dark Skies Matter seeks to reduce the prevalence and harmful effects of unnecessary, artificial light and to protect fragile oases of natural darkness wherever they are still to be found.
Light pollution is the soiling of the twilight and night-time environment by artificial light. The loss of natural night and the damage and waste caused by light pollution affect us all and should matter to everyone.

Dark Skies Matter

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In the light of the Coronavirus COVID-19 and the Government’s advice on social distancing we have suspended our monthly meetings.

For the 2020 – 2021 season We are starting Zoom talks initially for GAS members only. Details will be sent via email.

Please pop back to this page or our Facebook page (icon at top right of this web page) to check for updates.

During Lockdown we have a newsletter, GAS LIGHT, to help keep you entertained. You can find the current and previous issues at –
GAS Light.

If you’d like to contribute please contact the Editor & GAS President at –
The Editor

If you have questions about astronomy, choosing and using telescopes and other equipment, John Evans may be able to help here –

But before that !


John Axtell has a forty minute, once a month, programme on Brooklands Radio. Details of which and a  link to John’s podcast can be seen on our

News page.

Matt’s Books of the Month

(click the image)

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The Guildford Astronomical Society is a member of the Southern Area Group of Astronomical Societies (SAGAS)

The Guildford Astronomical Society is a member of both the
Southern Area Group of Astronomical Societies (SAGAS)
and the Federation of Astronomical Societies (FAS).

The Guildford Astronomical Society is a member of the Federation of Astronomical Societies (FAS)