Non-thermal radio continuum emission from young nearby stars

TL;DR

This study used the VLA to detect non-thermal radio emission from young nearby stars, revealing a decline in detection rate with age and spectral type, and identifying targets suitable for future VLBI astrometry.

Contribution

It provides the first systematic survey of radio emission in nearby young stars, establishing detection rates and identifying candidates for high-precision astrometric studies.

Findings

18% of surveyed stars emit detectable radio signals

Detection rate decreases with stellar age and temperature

Radio-bright stars are more likely to be in binary systems

Abstract

Young and magnetically active low-mass stars often exhibit non-thermal coronal radio emission due to the gyration of electrons in their magnetized chromospheres. This emission is easily detectable at centimeter wavelengths with the current sensitivity of large radio interferometers like the VLA. With the aim of identifying nearby stars adequate for future accurate radio astrometric monitoring using Very Long Baseline Interferometry (VLBI), we have used the VLA in its B\, configuration to search for radio emission at \mbox{$\nu \simeq 6$\,GHz} \mbox{($\lambda \simeq 5$\,cm)} toward a sample of 170 nearby ($<$130\,pc) mostly young (5\,--\,500\,Myr) stars of spectral types between F4 and M2. At our mean $3\sigma$ detection limit of $\simeq$\,50\,$\mu$Jy, we identify 31 young stars with coronal radio emission (an 18\% system detection rate) and more than 600 background (most likely extra-galactic) sources. Among the targeted stars, we find a significant decline of the detection rate with age from 56$\pm$20\% for stars with ages $\le10$\,Myr to 10$\pm$3\% for stars with ages 100\,--\,200\,Myr. No star older than 200\,Myr was detected. The detection rate also declines with $T_{\rm eff}$ from 36$\pm$10\% for stars with $T_{\rm eff}<4000$\,K to 13$\pm$3\% for earlier spectral types with $T_{\rm eff}>5000$\,K. The binarity fraction among the radio-bright stars is at least twice as high as among the radio-quiet stars. The radio-bright nearby young stars identified here provide an interesting sample for future astrometric studies using VLBI arrays aimed at searching for hitherto unknown tight binary components or even exoplanets.