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Published March 20, 2010 | Published
Journal Article Open

Discovery and characterization of a faint stellar companion to the A3V star ζ Virginis


Through the combination of high-order adaptive optics and coronagraphy, we report the discovery of a faint stellar companion to the A3V star ζ Virginis. This companion is ~7 mag fainter than its host star in the H band, and infrared imaging spanning 4.75 years over five epochs indicates this companion has common proper motion with its host star. Using evolutionary models, we estimate its mass to be 0.168^(+0.012) _(–0.016) M_☉, giving a mass ratio for this system q = 0.082^(+0.007)_(–0.008). Assuming the two objects are coeval, this mass suggests an M4V-M7V spectral type for the companion, which is confirmed through integral field spectroscopic measurements. We see clear evidence for orbital motion from this companion and are able to constrain the semimajor axis to be ≳24.9 AU, the period ≳124 yr, and eccentricity ≳0.16. Multiplicity studies of higher mass stars are relatively rare, and binary companions such as this one at the extreme low end of the mass ratio distribution are useful additions to surveys incomplete at such a low mass ratio. Moreover, the frequency of binary companions can help to discriminate between binary formation scenarios that predict an abundance of low-mass companions forming from the early fragmentation of a massive circumstellar disk. A system such as this may provide insight into the anomalous X-ray emission from A stars, hypothesized to be from unseen late-type stellar companions. Indeed, we calculate that the presence of this M-dwarf companion easily accounts for the X-ray emission from this star detected by ROSAT.

Additional Information

© 2010 The American Astronomical Society. Issue 1 (2010 March 20). Received 2009 November 2, accepted for publication 2010 February 5. Published 2010 March 2. We thank the anonymous referee for his or her comments. This work was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. The Lyot Project is based upon work supported by the National Science Foundation under grants AST-0804417, 0334916, 0215793, and 0520822, as well as grant NNG05GJ86G from the National Aeronautics and Space Administration under the Terrestrial Planet Finder Foundation Science Program. A portion of the research in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration and was funded by internal Research and Technology Development funds. The Lyot Project gratefully acknowledges the support of the US Air Force and NSF in creating the special Advanced Technologies and Instrumentation opportunity that provides access to the AEOS telescope. Eighty percent of the funds for that program are provided by the US Air Force. This work is based on observations made at the Maui Space Surveillance System, operated by Detachment 15 of the U.S. Air Force Research Laboratory Directed Energy Directorate. This work has been partially supported by the NSF Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement AST 98-76783. The Lyot Project is also grateful to the Cordelia Corporation, Hilary and Ethel Lipsitz, the Vincent Astor Fund, Judy Vale, and an anonymous donor, who initiated the project.

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