http://arxiv.org/abs/2108.10296
Numerous protoplanetary discs show distinct spiral arms features. While possibly caused by a range of processes, detailed pattern analysis points at close stellar flybys as cause for some of them. Surprisingly, these discs reside in young low-mass clusters, where close stellar flybys are expected to be rare. This fact motivated us to take a fresh look at the frequency of close flybys in low-mass clusters. In the solar neighbourhood, low-mass clusters have smaller half-mass radii than their more massive counterparts. We show that this observational fact results in the mean and central stellar density of low-mass clusters being approximately the same as in high-mass clusters, which is rarely reflected in theoretical studies. We perform N-body simulations of the stellar dynamics in young clusters obeying the observed mass-radius relation. Taking the mean disc truncation radius as a proxy for the degree of influence of the environment, we find that the influence of the environment on discs is more or less the same in low- and high-mass clusters. Even the fraction of small discs($<$ 10 au) is nearly identical. Our main conclusion is that the frequency of close flybys seems to have been severely underestimated for low-mass clusters. A testable prediction of this hypothesis is that low-mass clusters should contain 10%-15% of discs smaller than 30 au truncated by flybys. These truncated discs should be distinguishable from primordially small discs by their steep outer edge.
S. Pfalzner and A. Govind
Tue, 24 Aug 21
60/76
Comments: 18 pages, 9 figures, accepted for ApJ
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