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Published December 20, 2013 | Published + Submitted
Journal Article Open

The κ Andromedae System: New Constraints on the Companion Mass, System Age, and Further Multiplicity


κ Andromedae is a B9IVn star at 52 pc for which a faint substellar companion separated by 55 ± 2 AU was recently announced. In this work, we present the first spectrum of the companion, "κ And B," using the Project 1640 high-contrast imaging platform. Comparison of our low-resolution YJH-band spectra to empirical brown dwarf spectra suggests an early-L spectral type. Fitting synthetic spectra from PHOENIX model atmospheres to our observed spectrum allows us to constrain the effective temperature to ~2000 K as well as place constraints on the companion surface gravity. Further, we use previously reported log(g) and T_eff measurements of the host star to argue that the κ And system has an isochronal age of 220 ± 100 Myr, older than the 30 Myr age reported previously. This interpretation of an older age is corroborated by the photometric properties of κ And B, which appear to be marginally inconsistent with other 10–100 Myr low-gravity L-dwarfs for the spectral type range we derive. In addition, we use Keck aperture masking interferometry combined with published radial velocity measurements to rule out the existence of any tight stellar companions to κ And A that might be responsible for the system's overluminosity. Further, we show that luminosity enhancements due to a nearly "pole-on" viewing angle coupled with extremely rapid rotation is unlikely. κ And A is thus consistent with its slightly evolved luminosity class (IV), and we propose here that κ And, with a revised age of 220 ± 100 Myr, is an interloper to the 30 Myr Columba association with which it was previously associated. The photometric and spectroscopic evidence for κ And B combined with our reassessment of the system age implies a substellar companion mass of 50^(+16)_(-13) M_Jup, consistent with a brown dwarf rather than a planetary-mass companion.

Additional Information

© 2013 American Astronomical Society. Received 2013 May 10; accepted 2013 September 12; published 2013 December 3. We thank the anonymous referee for numerous helpful suggestions. S.H. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1203023. ALK was supported by a Clay Fellowship. E.E.M. is supported by NSF award AST-1008908 and the generous donations of Gabriela Mistral Pisco. G.V. is supported by a NASA OSS grant NMO7110830/102190. L.P. performed this work in part under contract with the California Institute of Technology funded by NASA through the Sagan Fellowship Program. R.N. performed this work with funding through a grant from Helge Axson Johnson's foundation. J.R.C. is supported by NASA Origins of Solar Systems Grant NNX13AB03G. A portion of this work is or was supported by the National Science Foundation under Grant Numbers AST-0215793, 0334916, 0520822, 0804417, and 1245018. A portion of the research in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA and was funded by internal Research and Technology Development funds. Our team is also grateful to the Plymouth Hill Foundation, an anonymous donor, and the efforts of Mike Werner, Paul Goldsmith and Jacob van Zyl. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Finally, the entire team expresses its sincere gratitude and appreciation for the hard work of the Palomar mountain crew, especially by Steve Kunsman, Mike Doyle, Greg van Idsinga, Bruce Baker, Jean Mueller, Kajsa Peffer, Kevin Rykowski, Carolyn Heffner, and Dan McKenna. This project would be impossible without the flexibility, responsiveness, and dedication of such an effective and motivated staff.

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Published - 0004-637X_779_2_153.pdf

Submitted - 1309.3372v1.pdf


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