Lambda Bootis star

A lambda bootis star is a special type of pecular star (“ peculiar ” - English for special, peculiar in connection with the chemical composition) with a low proportion of “ iron-peak ” elements (a measure of the low proportion the particularly stable elements in the vicinity of iron ) in its surface layers. In this star class with the spectral classes late B to early F, the elements of the iron group are less abundant by a factor of 100 , while the lighter elements such as C , N , O and S have a solar abundance. Less than 2% of all main sequence stars in these spectral classes belong to the Lambda Bootis stars.

The possible explanations for the different chemical composition of the photosphere of these stars are:

• atmospheric diffusion
• Accretion from interstellar matter using an accretion disk

Since the abundances in the photosphere of the Lambda Bootis star are similar to that of interstellar matter, accretion is likely to play the dominant role. The depletion of the elements of the iron group in interstellar matter is a consequence of the dust formation in the last phase of life of stars with medium mass, the AGB stars . The duration of the underfrequency of the iron-peak elements in lambda bootis stars should only be a few million years, since the rotation of the stars leads to a slow mixing of the layers of the atmosphere after the star has left a cloud with interstellar matter.

Examples

• Lambda Bootis , Wega , HR 8799

See also

• Pecular star
• At the star
• Ap star
• Mercury Manganese Star

Individual evidence

• Gray, RO and Corbally, CJ: A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters . In: Astronomical Journal . 124, No. 2, 2002, pp. 989-1000. bibcode : 2002AJ .... 124..989G . doi : 10.1086 / 341609 .
• E. Paunzen, U. Heiter, L. Fraga, O. Pintado: HD 210111: a new lambda Bootis type SB system . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1201.0098v1 .