A Lithium Depletion Boundary Age Of 21 Myr For The Beta Pictoris Moving Group

Last year I submitted a paper that was accepted for publication in the Monthly Notices of the Royal Astronomical Society journal. If you search the article title in google you`ll find the paper there. Below is a slightly more `bite-size` overview of the paper.

My research mainly focuses on identifying and characterising young, nearby stars. Measuring the age of a young star is crucial if we want to test how stars evolve at young ages - hundreds of times younger than today`s Sun. Nearby, young stars give us great laboratories to test theories of star formation and also provide the ideal opportunity to obtain images of planetary systems outside the solar system - here`s a link to two of my favourite images in astronomy: Firstly the 4(!) planet system HR 8799 and secondly, Beta Pictoris b, 15 times the mass of Jupiter. A quick google search will show you some great images of these planets.

Both of these planets are members of what are known as `moving groups`. These are associations of several dozen young (less than 100 million years, or Myr for short), nearby (within 3 million, billion kilometres...which is nothing in astronomical terms...we astronomers prefer to use the parsec as our unit of length - see wikipedia and/or other sites for a descri ption of a parsec) stars that have the same age and are moving together in the same direction through the Galaxy.

The Beta Pictoris Moving Group, which was discovered around 1999 originally had it`s age measured at 12 Myr, and for 15 years this was the age used by most people. The work I did was to try and re-measure the age using a more precise technique called the `lithium depletion boundary` method. I won`t go into the details here, but the general idea is that lithium is one of the first elements to burn at about 3 million degrees as a star heats up as it gets older and in small stars all the lithium is burned up extremely quickly. But lithium is pretty much never created in a star...so the amount we observe is directly related to how old the star is! This works for a group of stars of different masses at the same age because there is a special boundary where a star has either a large amount of lithium, or hardly any lithium at all.

Well - I found this boundary and ran the test and found the age to come out at...21 Myr! Nearly twice as old. This changes a lot of things for our planet friend Beta Pic b, she`s now twice as old, thirty per cent heavier and twice as large (that`s no way to talk about a lady, sorry!).

This was what I`d call a `good day at the office` and I`m happy that this work paid off. It`s only 5 pages long but has over 50 other papers have referenced this age since it was published last year. It goes to show that sometimes the simplest ideas are the best ones!