Differential rotation on both components of the pre-main-sequence binary system HD 155555

Dunstone, N. J. and Hussain, G. A. J. and Collier Cameron, A. and Marsden, S. C. and Jardine, M. and Barnes, J. R. and Ramirez Velez, J. C. and Donati, J. -F. (2008) Differential rotation on both components of the pre-main-sequence binary system HD 155555. Monthly Notices of the Royal Astronomical Society, 387 (4). pp. 1525-1536. ISSN 0035-8711

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Abstract

We present the first measurements of surface differential rotation on a pre-main-sequence binary system. Using intensity (Stokes I) and circularly polarized (Stokes V) time-series spectra, taken over 11 nights at the Anglo-Australian Telescope (AAT), we incorporate a solarlike differential rotation law into the surface imaging process. We find that both components of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) binary system show significant differential rotation. The equator-pole lap times as determined from the intensity spectra are 80 d for the primary star and 163 d for the secondary. Similarly, for the magnetic spectra we obtain equator-pole lap times of 44 and 71 d, respectively, showing that the shearing timescale ofmagnetic regions is approximately half of that found for stellar spots. Both components are therefore found to have rates of differential rotation similar to those of the same spectraltype main-sequence single stars. The results for HD 155555 are therefore in contrast to those found in other, more evolved, binary systems where negligible or weak differential rotation has been discovered. We discuss two possible explanations for this: first that at the age of HD 155555 binary tidal forces have not yet had time to suppress differential rotation and secondly that the weak differential rotation previously observed on evolved binaries is a consequence of their large convection zone depths. We suggest that the latter is the more likely solution and show that both temperature and convection zone depth (from evolutionary models) are good predictors of differential rotation strength. Finally, we also examine the possible consequences of the measured differential rotation on the interaction of binary star coronae.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: © 2008 The Authors. This publication is copyright. It may be reproduced in whole or in part for the purposes of study, research, or review, but is subject to the inclusion of an acknowledgment of the source.
Faculty / Department / School: Historic - Faculty of Sciences - Department of Biological and Physical Sciences
Date Deposited: 16 Oct 2014 02:20
Last Modified: 16 Oct 2014 06:14
Uncontrolled Keywords: binaries; spectroscopic; pre-main-sequence; stars; coronae; imaging; magnetic fields; rotation
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020102 Astronomical and Space Instrumentation
01 Mathematical Sciences > 0101 Pure Mathematics > 010102 Algebraic and Differential Geometry
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1111/j.1365-2966.2008.13338.x
URI: http://eprints.usq.edu.au/id/eprint/26207

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