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تسجيل مستخدم جديدOn the mechanism of polarised metrewave stellar emission
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H. K. Vedantham
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Two coherent radio emission mechanisms operate in stellar coronae: plasma emission and cyclotron emission. They directly probe the electron density and magnetic field strength respectively. Most stellar radio detections have been made at cm-wavelengths where it is often not possible to uniquely identify the emission mechanism, hindering the utility of radio observations in probing coronal conditions. In anticipation of stellar observations from a suite of sensitive low-frequency ($ usim 10^2,{rm MHz}$) radio telescopes, here I apply the general theory of coherent emission in non-relativistic plasma to the low-frequency case. I consider the recently reported low-frequency emission from dMe flare stars AD Leo and UV Ceti and the quiescent star GJ 1151 as test cases. My main conclusion is that unlike the cm-wave regime, for reasonable turbulence saturation regimes, the emission mechanism in metre-wave observations ($ usim 10^2,{rm MHz}$) can often be identified based on the observed brightness temperature, emission duration and polarisation fraction. I arrive at the following heuristic: M-dwarf emission that is $gtrsim ,$hour-long with $gtrsim 50%$ circular polarised fraction at brightness temperatures of $gtrsim 10^{12},$K at $sim 100,{rm MHz}$ in canonical M-dwarfs strongly favours a cyclotron maser interpretation.
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