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Published February 2018 | Published + Submitted
Journal Article Open

Robo-AO Discovery and Basic Characterization of Wide Multiple Star Systems in the Pleiades, Praesepe, and NGC 2264 Clusters


We identify and roughly characterize 66 candidate binary star systems in the Pleiades, Praesepe, and NGC 2264 star clusters, based on robotic adaptive optics imaging data obtained using Robo-AO at the Palomar 60'' telescope. Only ~10% of our imaged pairs were previously known. We detect companions at red optical wavelengths, with physical separations ranging from a few tens to a few thousands of au. A three-sigma contrast curve generated for each final image provides upper limits to the brightness ratios for any undetected putative companions. The observations are sensitive to companions with a maximum contrast of ~6^m at larger separations. At smaller separations, the mean (best) raw contrast at 2'' is 3.^m8 (6^m), at 1'' is 3.^m0 (4.^m5), and at 0."5 is 1.^m9 (3^m). Point-spread function subtraction can recover nearly the full contrast in the closer separations. For detected candidate binary pairs, we report separations, position angles, and relative magnitudes. Theoretical isochrones appropriate to the Pleiades and Praesepe clusters are then used to determine the corresponding binary mass ratios, which range from 0.2 to 0.9 in q = m_2/m_1. For our sample of roughly solar-mass (FGK type) stars in NGC 2264 and sub-solar-mass (K and early M-type) primaries in the Pleiades and Praesepe, the overall binary frequency is measured at ~15.5% ± 2%. However, this value should be considered a lower limit to the true binary fraction within the specified separation and mass ratio ranges in these clusters, given that complex and uncertain corrections for sensitivity and completeness have not been applied.

Additional Information

© 2018 The American Astronomical Society. Received 2017 May 12; revised 2017 October 13; accepted 2017 December 4; published 2018 January 8. We acknowledge the Caltech SURF (Summer Undergraduate Research Fellowship) program for partially supporting the work of C. Zhang. Russ Laher provided appreciated guidance on use of the APT. Luisa Rebull provided the catalog photometry used in creating Figure 7. We thank Emma Hovanec for literature research on the targets of this study. The Robo-AO system at Palomar was supported by the collaborating partner institutions, the California Institute of Technology, the Inter-University Centre for Astronomy and Astrophysics, the National Science Foundation under grants AST-0906060 and AST-0960343, the Mount Cuba Astronomical Foundation, and by a gift from Samuel Oschin. C.B. acknowledges a Sloan Fellowship. We remain grateful to the Palomar Observatory staff for their efforts in support of astronomical research, and to the Palomar Observatory Director for the allocation of observing time to this project.

Attached Files

Published - Hillenbrand_2018_AJ_155_51.pdf

Submitted - 1712.01468.pdf


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August 19, 2023
October 18, 2023