The Solar Wind in Time II: 3D stellar wind structure and radio emission

• Published in: Monthly notices of the Royal Astronomical Society Vol. 483; pp. 873 - 886
• Main Authors: Ó Fionnagáin, D., Vidotto, A.A., Petit, P., Folsom, C.P., Jeffers, S.V., Marsden, S.C., Morin, J., Do Nascimento, J.-D.
• Format: Journal Article
• Language: English
• Published: Oxford University Press (OUP): Policy P - Oxford Open Option A 01-08-2019
• Subjects: Astrophysics; Sciences of the Universe; Solar and Stellar Astrophysics
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stz1308

In this work, we simulate the evolution of the solar wind along its main-sequence lifetime andcompute its thermal radio emission. To study the evolution of the solar wind, we use a sample ofsolar mass stars at different ages. All these stars have observationally reconstructed magneticmaps, which are incorporated in our 3D magnetohydrodynamic simulations of their winds.We show that angular-momentum loss and mass-loss rates decrease steadily on evolutionarytime-scales, although they can vary in a magnetic cycle time-scale. Stellar winds are knownto emit radiation in the form of thermal bremsstrahlung in the radio spectrum. To calculate theexpected radio fluxes from these winds, we solve the radiative transfer equation numericallyfrom first principles. We compute continuum spectra across the frequency range 100 MHz to100 GHz and find maximum radio flux densities ranging from 0.05 to 2.2μJy. At a frequencyof 1 GHz and a normalized distance ofd=10 pc, the radio flux density follows 0.24 (/)0.9(d/[10pc])-2μJy, whereis the rotation rate. This means that the best candidates for stellarwind observations in the radio regime are faster rotators within distances of 10 pc, such asκ1Ceti (0.73μJy) andχ1Ori (2.2μJy). These flux predictions provide a guide to observingsolar-type stars across the frequency range 0.1–100 GHz in the future using the next generationof radio telescopes, such as ngVLA and Square Kilometre Array.