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arXiv · 2507.17705

The Small Separation A-Star Companion Population: Tentative Signatures of Enhanced Multiplicity with Primary Mass

Matthew De Furio·Tyler Gardner·John D. Monnier·Michael R. Meyer·Kaitlin M. Kratter·Cyprien Lanthermann·Narsireddy Anugu·Stefan Kraus·Benjamin R. Setterholm
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Abstract

We present updated results from our near-infrared long-baseline interferometry (LBI) survey to constrain the multiplicity properties of intermediate-mass A-type stars within 80 pc. Previous adaptive optics surveys of A-type stars are incomplete at separations $<$ 20au. Therefore, a LBI survey allows us to explore separations previously unexplored. Our sample consists of 54 A-type primaries with estimated masses between 1.44-2.93 M$_{\odot}$ and ages 10-790 Myr, which we observed with the MIRC-X and MYSTIC instruments at the CHARA Array. We use the open source software CANDID to detect two new companions, seven in total, and we performed a Bayesian demographic analysis to characterize the companion population. We find the separation distribution consistent with being flat, and we estimate a power-law fit to the mass ratio distribution with index -0.13$^{+0.92}_{-0.95}$ and a companion frequency of 0.25$^{+0.17}_{-0.11}$ over mass ratios 0.1-1.0 and projected separations 0.01-27.54au. We find a posterior probability of 0.53 and 0.04 that our results are consistent with extrapolations based on previous models of the solar-type and B-type companion population, respectively. Our results suggest that the close companion population to A-type stars is comparable to that of solar-types and that close companions to B-type stars are potentially more frequent which may be indicative of increased disk fragmentation for stars $\gtrsim$ 3M$_{\odot}$.

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Matthew De Furio, Tyler Gardner, John D. Monnier, Michael R. Meyer, Kaitlin M. Kratter, Cyprien Lanthermann, Narsireddy Anugu, Stefan Kraus, Benjamin R. Setterholm. 2025-07-23. The Small Separation A-Star Companion Population: Tentative Signatures of Enhanced Multiplicity with Primary Mass. https://arxiv.org/abs/2507.17705

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