4 April 2019 – Next Club Meeting
An Astronomy Guest Speaker Series Event – a collaboration of the Astronomy Club of Asheville and UNC Asheville
Thursday night, 7:00 – 9:00 p.m. – In the Reuter Center‘s Manheimer Room, located on the UNC Asheville campus. The meeting is free and open to the general public.
“The Lambda Bootis Star System: A 75-Year-Old Mystery” – presented by Richard Gray, Appalachian State University
The Lambda Boötis stars (Lambda Boo for short) were discovered 75 years ago by one of the founders of the MK Spectral classification system (the system that astronomers use for classifying stars by their spectra), W.W. Morgan. What was special about these stars was that nothing other than strong spectral lines of hydrogen appeared in their spectra. Compared with other stars of the same temperature and age, the Lambda Boötis stars, at least in Morgan’s photographic record, showed no signs of metals or any other element other than hydrogen.
Modern digital spectra show that metals and other elements are present in the spectra of Lambda Boötis stars, but at very low levels. The most extreme Lambda Boo stars show metal abundances down by a factor of 100 or more from the Sun. And this is very curious, because for all other stars, metal abundance is correlated with age – old stars have low abundances of metals, whereas young stars have high abundances. So, that must mean Lambda Boo stars are really old? No! Interestingly, all known Lambda Boo stars are much younger than our Sun, and a few have “just” started fusing hydrogen in their cores.
So this is a 75 year-old mystery. Scientists think they know why the Lambda Boo stars are metal poor. That low metal abundance, it is believed from many lines of evidence, is simply a skin disease. Underneath the surface layers, metal abundances are normal. But there is one niggling piece of evidence from a new field of astronomy that contradicts that.
Lambda Boo stars may be interesting for other reasons. It is thought that the stars are in the process of planet formation, which may be related to the metal deficiencies. This means that studying Lambda Boo stars may give us insights into planet formation! So, this 75-year mystery and our dogged pursuit of it is still yielding dividends.