van Schaik, Michael (2019) λ Bootis stars: ISM gas accretion as an explanation for chemical peculiarity. Master's Thesis / Essay, Astronomy.
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Abstract
λ Bootis stars are a type of chemically peculiar star. Around 2% of A-type stars have a λ Bootis spectrum. There are many different theories about the origin of the peculiarity. Few studies have been made into quantifying the fraction of λ Bootis stars that can be explained with each method. Our aims are to investigate the validity of the ISM accretion theory and explore the effects of bow shocks. This is done by modelling the accretion onto the star with Bondi-Hoyle accretion. An ISM gas model is used to provide densities and velocities of the gas. To this model we have added molecular clouds. The effect of bow shocks are investigated through a scaling factor for the density and relative velocity. We find that bow shocks can increase the probability of finding a λ Bootis up to a factor10^3. The inclusion of molecular clouds had no significant effects on our conclusions. The ISM accretion theory matches the observed ratio of λ Bootis stars for an accretion threshold of 10^-11 Msol/yr when we include the effect of bow shocks.
| Item Type: | Thesis (Master's Thesis / Essay) |
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| Supervisor name: | Kamp, I.E.E. |
| Degree programme: | Astronomy |
| Thesis type: | Master's Thesis / Essay |
| Language: | English |
| Date Deposited: | 15 May 2019 |
| Last Modified: | 19 Jun 2019 08:44 |
| URI: | https://fse.studenttheses.ub.rug.nl/id/eprint/19475 |
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