A high-resolution radio study of the L1551 IRS 5 and L1551 NE jets^⋆

¹ Dublin Institute for Advanced Studies, Astronomy & Astrophysics Section, 31 Fitzwilliam Place, Dublin D02 XF86, Ireland
e-mail: antonfj@astron.s.u-tokyo.ac.jp
² National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
³ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield, Cheshire SK11 9FT, UK
⁴ Instituto de Radioastronomía y Astrofísica (IRyA-UNAM), Morelia, Mexico
⁵ Instituto de Astronomía Teórica y Experimental (IATE, CONICET-UNC), Laprida 854, X5000BGR Córdoba, Argentina
⁶ Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba, Laprida 854, X5000BGR Córdoba, Argentina
⁷ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
⁸ Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong
⁹ Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan
¹⁰ East Asian Observatory, 660 N. A’ohōkū Place, Hilo, HI 96720, USA
¹¹ School of Physics and Astronomy, University of Leeds, Leeds, UK

Received: 25 April 2023
Accepted: 19 July 2023

Abstract

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.