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arXiv · 2211.01465

The Small Separation A-Star Companion Population: First Results with CHARA/MIRC-X

Matthew De Furio·Tyler Gardner·John Monnier·Michael R. Meyer·Kaitlin Kratter·Gail Schaefer·Narsireddy Anugu·Claire L. Davies·Stefan Kraus·Cyprien Lanthermann·Jean-Baptiste Le Bouquin·Jacob Ennis
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Abstract

We present preliminary results from our long-baseline interferometry (LBI) survey to constrain the multiplicity properties of intermediate-mass A-type stars within 80pc. Previous multiplicity studies of nearby stars exhibit orbital separation distributions well-fitted with a log-normal with peaks > 15au, increasing with primary mass. The A-star multiplicity survey of De Rosa et al. (2014), sensitive beyond 30au but incomplete below 100 au, found a log-normal peak around 390au. Radial velocity surveys of slowly-rotating, chemically peculiar Am stars identified a significant number of very close companions with periods $\leq$ 5 days, ~ 0.1au, a result similar to surveys of O- and B-type primaries. With the improved performance of LBI techniques, we can probe these close separations for normal A-type stars where other surveys are incomplete. Our initial sample consists of 27 A-type primaries with estimated masses between 1.44-2.49M$_{\odot}$ and ages 10-790Myr, which we observed with the MIRC-X instrument at the CHARA Array. We use the open source software CANDID to detect five companions, three of which are new, and derive a companion frequency of 0.19$^{+0.11}_{-0.06}$ over mass ratios 0.25-1.0 and projected separations 0.288-5.481 au. We find a probability of 10$^{-6}$ that our results are consistent with extrapolations based on previous models of the A-star companion population, over mass ratios and separations sampled. Our results show the need to explore these very close separations to inform our understanding of stellar formation and evolution processes.

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Matthew De Furio, Tyler Gardner, John Monnier, Michael R. Meyer, Kaitlin Kratter, Gail Schaefer, Narsireddy Anugu, Claire L. Davies, Stefan Kraus, Cyprien Lanthermann, Jean-Baptiste Le Bouquin, Jacob Ennis. 2022-11-02. The Small Separation A-Star Companion Population: First Results with CHARA/MIRC-X. https://doi.org/10.3847/1538-4357/aca1ad

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