Friday, June 3, 2016

Eating Planets Can Make Stars Appear Older Than They are

Effect of planet ingestion on low-mass stars evolution: the case of 2MASS J08095427–4721419 star in the Gamma Velorum cluster


Tognelli et al


We analysed the effects of planet ingestion on the characteristics of a pre-MS star similar to the Gamma Velorum cluster member 2MASS J08095427–4721419 (#52). We discussed the effects of changing the age t0 at which the accretion episode occurs, the mass of the ingested planet and its chemical composition. We showed that the mass of the ingested planet required to explain the current [Fe/H]#52 increases by decreasing the age t0 and/or by decreasing the Iron content of the accreted matter. We compared the predictions of a simplified accretion method – where only the variation of the surface chemical composition is considered – with that of a full accretion model that properly accounts for the modification of the stellar structure. We showed that the two approaches result in different convective envelope extension which can vary up to 10 percent. We discussed the impact of the planet ingestion on a stellar model in the colour-magnitude diagram, showing that a maximum shift of about 0.06 dex in the colour and 0.07 dex in magnitude are expected and that such variations persist even much later the accretion episode. We also analysed the systematic bias in the stellar mass and age inferred by using a grid of standard non accreting models to recover the characteristics of an accreting star. We found that standard non accreting models can safely be adopted for mass estimate, as the bias is \la6 percent, while much more caution should be used for age estimate where the differences can reach about 60 percent.

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