2023A&A...677A..97F

Using observations with e-MERLIN and the Karl G. Jansky Very Large Array (VLA), together with archival data from the Atacama Large Millimeter/submillimeter Array (ALMA), we obtain high-resolution radio images of two binary YSOs: L1551 IRS 5 and L1551 NE, covering a wide range of frequencies from 5 to 336 GHz, and resolving emission from the radio jet on scales of only ∼15 au. By comparing these observations to those from a previous epoch, it is shown that there is a high degree of variability in the free-free emission from the jets of these sources. In particular, the northern component of L1551 IRS 5 shows a remarkable decline in flux density of a factor of ∼5, suggesting that the free-free emission of this source has almost disappeared. By fitting the spectra of the sources, the ionised mass-loss rates of the jets were derived and it was shown that there is significant variability of up to a factor of ∼6 on timescales of ∼20 years. Using radiative transfer modelling, we also obtained a model image for the jet of the southern component of L1551 IRS 5 to help study the inner region of the ionised high-density jet. The findings favour the X-wind model launched from a very small innermost region.