http://arxiv.org/abs/2210.11440
We have searched for thermal gyro-synchrotron radio emission from a sample of five radio-loud stars whose X-ray coronae contain a hot ($T>10^7$ K) thermal component. We used the JVLA to measure Stokes I and V/I spectral energy distributions (SEDs) over the frequency range 15–45 GHz, determining the best-fitting model parameters using power-law and thermal gyro-synchrotron emission models. The SEDs of the three chromospherically active binaries (Algol, UX Arietis, HR 1099) were well-fit by a power-law gyro-synchrotron model, with no evidence for a thermal component. However, the SEDs of the two pre-main-sequence (PMS) stars (V410 Tau, HD 283572) had a circularly polarized enhancement above 30 GHz that was inconsistent with a pure power-law distribution. These spectra were well-fit by summing the emission from an extended coronal volume of power-law gyro-synchrotron emission and a smaller region with thermal plasma and a much stronger magnetic field emitting thermal gyro-synchrotron radiation. We used Bayesian inference to estimate the physical plasma parameters of the emission regions (characteristic size, electron density, temperature, power-law index, and magnetic field strength and direction) using the independently VLBI-measured radio sizes, X-ray luminosity, and magnetic field strength as priors, where available. The derived parameters were well-constrained but highly degenerate. The best-fitting temperatures for both PMS stars were $\sim0.5$ dex higher than the X-ray-derived temperatures. We argue that the power-law and thermal volumes in the PMS stars are probably not co-spatial and speculate that they may arise from two distinct regions, the stellar corona and the inner edge of their accretion disc, respectively.
W. Golay, R. Mutel, D. Lipman, et. al.
Fri, 21 Oct 22
33/76
Comments: 17 pages, 10 figures