GMRT detections of low-mass young stars at 323 and 608 MHz

Abstract

We present the results of a pathfinder project conducted with the Giant Metrewave Radio Telescope (GMRT) to investigate protostellar systems at low radio frequencies. The goal of these investigations is to locate the break in the free-free spectrum where the optical depth equals unity in order to constrain physical parameters of these systems, such as the mass of the ionised gas surrounding these young stars. We detect all three target sources, L1551 IRS 5 (Class I), T Tau and DG Tau (Class II), at frequencies 323 and 608 MHz (wavelengths 90 and 50 cm, respectively). These are the first detections of low mass young stellar objects (YSOs) at such low frequencies. We combine these new GMRT data with archival information to construct the spectral energy distributions for each system and find a continuation of the optically thin free-free spectra extrapolated from higher radio frequencies to 323 MHz for each target. We use these results to place limits on the masses of the ionised gas and average electron densities associated with these young systems on scales of ~1000 au. Future observations with higher angular resolution at lower frequencies are required to constrain these physical parameters further.