The close binary Algol system contains a radio-bright KIV subgiant star in a very close (0.062 astronomical units) and rapid (2.86 day) orbit with a main sequence B8 star. Because the rotation periods of the two stars are tidally locked to the orbital period, the rapid rotation drives a magnetic dynamo. A large body of evidence points to the existence of an extended, complex coronal magnetosphere originating at the cooler K subgiant1,2,3,4. The detailed morphology of the subgiant's corona and its possible interaction with its companion are unknown, though theory predicts that the coronal plasma should be confined in a magnetic loop structure5, as seen on the Sun. Here we report multi-epoch radio imaging of the Algol system, in which we see a large, persistent coronal loop approximately one subgiant diameter in height, whose base is straddling the subgiant and whose apex is oriented towards the B8 star. This suggests that a persistent asymmetric magnetic field structure is aligned between the two stars. The loop is larger than anticipated theoretically6,7, but the size may be the result of a magnetic interaction between the two stars.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Chung, S. M., Drake, J. J., Kashyap, V. L., Lin, L. W. & Ratzlaff, P. W. Doppler shifts and broadening and the structure of the X-ray emission from Algol. Astrophys. J. 606, 1184–1195 (2004)
Mutel, R. L., Molnar, L. A., Waltman, E. B. & Ghigo, F. D. Radio emission from Algol. I. Coronal geometry and emission mechanisms determined from VLBA and Green Bank Interferometer observations. Astrophys. J. 507, 371–383 (1998)
Ness, J.-U., Güdel, M., Schmitt, J. H. M. M., Audard, M. & Telleschi, A. On the sizes of stellar X-ray coronae. Astron. Astrophys. 427, 667–683 (2004)
Retter, A., Richards, M. T. & Wu, K. Evidence for superhumps in the radio light curve of Algol and a new model for magnetic activity in Algol systems. Astrophys. J. 621, 417–424 (2005)
Aschwanden, M. J., Poland, A. I. & Rabin, D. M. The new solar corona. Annu. Rev. Astron. Astrophys. 39, 175–210 (2001)
Mullan, D. J., Mathioudakis, M., Bloomfield, D. S. & Christian, D. J. A comparative study of flaring loops in active stars. Astrophys. J. Suppl. Ser. 164, 173–201 (2006)
Rosner, R., Tucker, W. H. & Vaiana, G. S. Dynamics of the quiescent solar corona. Astrophys. J 220, 643–645 (1978)
Beasley, A. J. & Güdel, M. VLBA imaging of quiescent radio emission from UX Arietis. Astrophys. J. 529, 961–967 (2000)
Lestrade, J.-F., Mutel, R. L., Preston, R. A. & Phillips, R. B. Dual-frequency and dual-polarization VLBI observations of the stellar system Algol. Astrophys. J. 328, 232–242 (1988)
Massi, M., Franciosini, E., Paredes, J. M. & Estalella, R. Investigation of stellar loop structures using VLBI. N. Astron. Rev. 43, 539–543 (1999)
Mutel, R. L., Lestrade, J. F., Preston, R. A. & Phillips, R. B. Dual polarization VLBI observations of stellar binary systems at 5 GHz. Astrophys. J. 289, 262–268 (1985)
Ransom, R. R. et al. Possible corotation of the milliarcsecond radio structure of the close binary HR 1099. Astrophys. J. 572, 487–502 (2002)
Fey, A. L. et al. Merlin astrometry of 11 radio stars. Astron. J. 131, 1084–1089 (2006)
Lestrade, J.-F., Phillips, R. B., Hodges, M. W. & Preston, R. A. VLBI astrometric identification of the radio emitting region in Algol and determination of the orientation of the close binary. Astrophys. J. 410, 808–814 (1993)
Gatewood, G., de Jonge, J. K. & Heintz, W. D. Astrometric studies in the region of Algol. Astron. J. 109, 434–439 (1995)
Pan, X., Shao, M. & Colavita, M. M. High angular resolution measurements of Algol. Astrophys. J. 413, L129–L131 (1993)
Schmitt, J. H. M. M. & Favata, F. Continuous heating of a giant X-ray flare on Algol. Nature 401, 44–46 (1999)
Schmitt, J. H. M. M., Ness, J. U. & Franco, G. A spatially resolved limb flare on Algol B observed with XMM-Newton. Astron. Astrophys. 412, 849–855 (2003)
Boboltz, D. A. et al. Very Large Array plus Pie Town astrometry of 46 radio stars. Astron. J. 133, 906–916 (2007)
Warren, H. P., Winebarger, A. R. & Mariska, J. T. Evolving active region loops observed with the transition region and coronal explorer. II. Time-dependent hydrodynamic simulations. Astrophys. J. 593, 1174–1186 (2003)
Dulk, G. A. Radio emission from the sun and stars. Annu. Rev. Astron. Astrophys. 23, 169–224 (1985)
Petit, P. et al. Toroidal versus poloidal magnetic fields in sun-like stars: a rotation threshold. Mon. Not. R. Astron. Soc. 388, 80–88 (2008)
Morin, J. et al. Large-scale magnetic topologies of mid M dwarfs. Mon. Not. R. Astron. Soc. 390, 567–581 (2008)
Ottmann, R. Structure and stability of the X-ray corona of Algol. Astron. Astrophys. 286, L27–L30 (1994)
Albright, G. E. & Richards, M. T. Doppler tomography of accretion disks in Algol binaries. Astrophys. J. 459, L99–L102 (1996)
Richards, M. T., Waltman, E. B., Ghigo, F. D. & Richards, D. S. P. Statistical analysis of 5 year continuous radio flare data from β Persei, V711 Tauri, δ Librae, and UX Arietis. Astrophys. J. Suppl. Ser. 147, 337–361 (2003)
Franciosini, E., Massi, M., Paredes, J. M. & Estalella, R. Flaring loop structures at VLBI scale in UX Arietis. Astron. Astrophys. 341, 595–601 (1999)
Favata, F., Micela, G., Reale, F., Sciortino, S. & Schmitt, J. H. M. M. The structure of Algol's corona: a consistent scenario for the X-ray and radio emission. Astron. Astrophys. 362, 628–634 (2000)
Rogers, A. E. E. VLBI phase reference mapping techniques and the search for the third image of 0957+561. Lecture Notes Phys. 330, 77–81 (1989)
The NRAO is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. Support for this work was provided by the NSF through award GSSP08-0022 from the NRAO. R.L.M. is grateful to the Institute of Astronomy at ETH, Zurich, for logistic support during the preparation of this paper.
Author Contributions All authors contributed substantially to this work. R.L.M. and M.G. did the observation planning. W.M.P. and W.M.G. analysed the observations. R.L.M., M.G. and W.M.P. wrote and edited the manuscript.
The authors declare no competing financial interests.
About this article
Cite this article
Peterson, W., Mutel, R., Güdel, M. et al. A large coronal loop in the Algol system. Nature 463, 207–209 (2010). https://doi.org/10.1038/nature08643
Astronomy & Astrophysics (2020)
Proceedings of the International Astronomical Union (2019)
Astronomy & Astrophysics (2017)
Astrophysics and Space Science (2017)
Proceedings of the International Astronomical Union (2016)