Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published June 2013 | Submitted + Published
Journal Article Open

Spin-orbit alignment in the very low mass binary regime: The L dwarf tight binary 2MASSW J0746425+200032AB


Studies of solar-type binaries have found coplanarity between the equatorial and orbital planes of systems with <40 AU separation. By comparison, the alignment of the equatorial and orbital axes in the substellar regime, and the associated implications for formation theory, are relatively poorly constrained. Here we present the discovery of the rotation period of 3.32 ±  0.15 h from 2MASS J0746+20A – the primary component of a tight (2.7 AU) ultracool dwarf binary system (L0+L1.5). The newly discovered period, together with the established period via radio observations of the other component, and the well constrained orbital parameters and rotational velocity measurements, allow us to infer alignment of the equatorial planes of both components with the orbital plane of the system to within 10 degrees. This result suggests that solar-type binary formation mechanisms may extend down into the brown dwarf mass range, and we consider a number of formation theories that may be applicable in this case. This is the first such observational result in the very low mass binary regime. In addition, the detected period of 3.32 ± 0.15 h implies that the reported radio period of 2.07 ± 0.002 h is associated with the secondary star, not the primary, as was previously claimed. This in turn refutes the claimed radius of 0.78 ± 0.1 R_J for 2MASS J0746+20A, which we demonstrate to be 0.99 ± 0.03 R_J.

Additional Information

© 2013 ESO. Article published by EDP Sciences. Received 7 December 2012; Accepted 17 April 2013. Published online 13 June 2013. This work was largely carried out under the National University of Ireland Traveling Studentship in the Sciences (Physics). L.K.H. gratefully acknowledges the support of the Science Foundation Ireland (Grant Number 07/RFP/PHYF553) as well as Dr. Mark Lang of NUI Galway. We thank the VATT team for their help and guidance. Finally, we would like to thank the referee for their careful reading of our work, and for their valuable input and suggestions on how to improve this manuscript.

Attached Files

Published - aa20865-12.pdf

Submitted - 1304.5290v1.pdf


Files (2.7 MB)
Name Size Download all
1.3 MB Preview Download
1.5 MB Preview Download

Additional details

August 19, 2023
October 24, 2023