A Lambda Boötis star is a type of chemically peculiar star which has an unusually low abundance of iron peak elements in its surface layers. One possible explanation for this is that it is the result of accretion of metal-poor gas from a circumstellar disc, and a second possibility is the accretion of material from a hot Jupiter suffering from mass loss. The prototype is Lambda Boötis.
References
Further reading Paunzen, Ernst (2004). "The λ Bootis stars". In Zverko, J.; Ziznovsky, J.; Adelman, S.J.; Weiss, W.W. (eds.). The A-Star Puzzle. IAU Symposium, No. 224. Proceedings of the International Astronomical Union. Vol. 2004. pp. 443–450. arXiv:astro-ph/9805051. Bibcode:2004IAUS..224..443P. doi:10.1017/S1743921304004867. ISBN 0521850185. Gray, R.O.; Corbally, C.J. (2002). "A Spectroscopic Search for λ Bootis and Other Peculiar A-Type Stars in Intermediate-Age Open Clusters". The Astronomical Journal. 124 (2): 989–1000. Bibcode:2002AJ....124..989G. doi:10.1086/341609.