Investigating mixing in massive hot giant stars

5 Sep

screen-shot-2016-10-15-at-2-22-17-pmTheory predicts that rotating massive stars “get stirred”, bringing elements from the deep center to the surface. Nathan Grin, former MSc student in Amsterdam, now PhD student in Bonn tried to test the model predictions.  He analyzed the spectra of more than 72 massive hot giant stars in the Tarantula nebula to determine their surface composition.  In particular he looked at the nitrogen abundance, which is known to be a good tracer of mixing processes.

Many of the slowly rotating stars in the sample show surprisingly high levels of nitrogen, much higher than the theory predict. This is worrying, since this group comprises about a third of the sample.  Nathan also tried to measure nitrogen for the rapidly rotating stars, but with the current data only upper limits could be determined.  Additional spectra will be needed for the full picture.

His paper “The VLT-FLAMES Tarantula Survey XXV. Surface nitrogen abundances of O-type giants and supergiants” has been accepted for publication in Astronomy & Astrophysics.  The team consists of N.J. Grin, O.H. Ramirez-Agudelo, A. de Koter, H. Sana, J. Puls, I. Brott, P.A. Crowther, P.L. Dufton, C.J. Evans, G. Graefener, A. Herrero, N. Langer, D.J. Lennon, J.Th. van Loon, N. Markova, S.E. de Mink, F. Najarro, F.R.N. Schneider, W.D. Taylor, F. Tramper, J.S. Vink, W.R. Walborn