Department of Theoretical Physics and Astrophysics
Faculty of Science
Masaryk University

Scientists are puzzling out the secrets of the rare stars

Brno, 24 August 2015

Astrophysicists from the Masaryk University in Brno investigated more than 170 000 photometric measurements of the fifteen peculiar stars to figure out why these stars show strong underabundance of iron and similar metals. The scientists have confirmed that it can be caused by metal-poor circumstellar medium that gradually falls down upon the star's surface. This process causes, that the star appears to have lack of heavy elements.

Austrian team led by astrophysicist Ernst Paunzen, working since 2012 at the Faculty of Science, Masaryk University, conducted a detailed analysis of fifteen stars of Lambda Bootis type. These stars belong to the group of very rare stars that show an enormous shortage of iron and nearby elements in their spectra. The fundamental question is whether these stars deplete metals only on their surfaces (in the photosphere) or whether this decreasement extends into the stars interior. Scientists, who have found among the sample also eight pulsating stars, could also do (astero)seismological data analysis. They found that the inner parts of stars are not depleted from iron and therefore their lack applies only to the surface of the stars.

Thus, the result corresponds to the hypothesis from 1990 pronounced by scientists Venn and Lambert. It says that Lambda Bootis stars are surrounded by interstellar gas depleted in metals like iron. The gas from this disk gradually falls on the star's surface and causes decrease of metal directly on the surface of the star. It is therefore a very rare phenomenon occurring only in a percentage of stars. A research of these unusual objects provide important information to scientists, for example, a knowledge about diffusion of elements in stars or their internal structure.

Chemicaly peculiar stars, together with the research of stellar winds and variable stars, is the main domein of researchers working at the Department of Theoretical Physics and Astrophysics at the Faculty of Science at Masaryk University.

The original paper (more publications of the Department of Theoretical Physics and Astrophysics can be found here).

Mgr. Lenka Zychová,

Asteroseismology is a scientific field studying internal stellar structure based of the pulsating stars based on the way how these stars are pulsating.

Chemically Peculiar Stars (CP Stars) are stars showing unusual chemical composition of the surface layers. It can be caused for instance by slow rotation of the star of by strong magnetic field. An example of the chemically peculiar stars are λ Bootis stars.

Illustration of the λ Bootis star. Collage: Lenka Zychová