scholarly journals Predicting the time variation of radio emission from MHD simulations of a flaring T-Tauri star

2020 ◽  
Vol 496 (3) ◽  
pp. 2715-2725
Author(s):  
C O G Waterfall ◽  
P K Browning ◽  
G A Fuller ◽  
M Gordovskyy ◽  
S Orlando ◽  
...  

ABSTRACT We model the time-dependent radio emission from a disc accretion event in a T-Tauri star using 3D, ideal magnetohydrodynamic simulations combined with a gyrosynchrotron emission and radiative transfer model. We predict for the first time, the multifrequency (1–1000 GHz) intensity and circular polarization from a flaring T-Tauri star. A flux tube, connecting the star with its circumstellar disc, is populated with a distribution of non-thermal electrons that is allowed to decay exponentially after a heating event in the disc and the system is allowed to evolve. The energy distribution of the electrons, as well as the non-thermal power-law index and loss rate, are varied to see their effect on the overall flux. Spectra are generated from different lines of sight, giving different views of the flux tube and disc. The peak flux typically occurs around 20–30 GHz and the radio luminosity is consistent with that observed from T-Tauri stars. For all simulations, the peak flux is found to decrease and move to lower frequencies with elapsing time. The frequency-dependent circular polarization can reach 10$-30{{\ \rm per\ cent}}$ but has a complex structure that evolves as the flare evolves. Our models show that observations of the evolution of the spectrum and its polarization can provide important constraints on physical properties of the flaring environment and associated accretion event.

2021 ◽  
Vol 502 (4) ◽  
pp. 5438-5454
Author(s):  
Joshua Pritchard ◽  
Tara Murphy ◽  
Andrew Zic ◽  
Christene Lynch ◽  
George Heald ◽  
...  

ABSTRACT We present results from a circular polarization survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of δ = +41○ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse include Stokes I and V polarization products to an RMS sensitivity of 250 μJy PSF−1. We searched RACS for sources with fractional circular polarization above 6 per cent, and after excluding imaging artefacts, polarization leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well-known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys.


2018 ◽  
Vol 859 (2) ◽  
pp. L28 ◽  
Author(s):  
Mihoko Konishi ◽  
Jun Hashimoto ◽  
Yasunori Hori
Keyword(s):  
T Tauri ◽  

2020 ◽  
Vol 500 (1) ◽  
pp. 1366-1379
Author(s):  
C Koen

ABSTRACT ‘Transiting Exoplanet Survey Satellite’ photometry of 10 young stars with very complex periodic light curves is considered. Previous findings that these cannot be due to dark surface spots are re-evaluated by allowing arbitrarily shaped areas on the stellar surface to have sub-photospheric fluxes. This is done by approximating flux integrals by sums over surface elements. The unknown ratios of spot to photospheric fluxes are determined by lasso or ridge regression procedures. It is found that almost all light curves can be modelled very accurately in this way. The usual, if rarely stated, caveat applies – star-spot models presented in the paper are not unique.


1986 ◽  
Vol 6 (3) ◽  
pp. 325-329 ◽  
Author(s):  
J . I. Harnet

AbstractThe five major members of the Sculptor Group of galaxies and NGC 45 have been observed with the Molonglo observatory synthesis telescope. NGC 247 and NGC 300 were not detected and upper limits to their 843 MHz flux densities are given. Radio emission from NGC 7793 is discussed with particular attention to its morphology, radial dependence compared with that of the blue light and possible coincidences between HII regions and 843 MHz peak flux densities.


2019 ◽  
Vol 19 (1) ◽  
pp. 007
Author(s):  
Jeewan Chandra Pandey ◽  
Subhajeet Karmakar ◽  
Arti Joshi ◽  
Saurabh Sharma ◽  
Shashi Bhushan Pandey ◽  
...  
Keyword(s):  

2018 ◽  
Vol 869 (2) ◽  
pp. L50 ◽  
Author(s):  
Laura M. Pérez ◽  
Myriam Benisty ◽  
Sean M. Andrews ◽  
Andrea Isella ◽  
Cornelis P. Dullemond ◽  
...  

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