A dual-band centimetre continuum monitoring survey of young stellar objects in the Coronet Cluster

ABSTRACT We present sensitive ($\sim 9\ \mu$Jy), sub-arcsecond resolution radio continuum observations at 9.0 GHz (3.3 cm) and 14.0 GHz (2.1 cm) obtained with the Karl G. Jansky Very Large Array (VLA) towards the nearby Coronet Cluster in Corona Australis ($d \approx 150$ pc). We monitored the region from March 2012 to February 2015 using all available VLA configurations, allowing us to construct deep X- and Ku-band maps at multiple angular resolutions. We detected 20 radio sources, including 14 previously known young stellar objects (YSOs), five sources possibly associated with shock emission, and one background galaxy. We resolved IRS 5, previously known to be a binary system, and identified IRS 7A and IRS 7B as multiple systems at centimetre wavelengths. The younger Class 0 and I YSOs exhibit spectral indices $\alpha _{\mathrm{pk}}$ ranging from $-0.4$ to 1.7, while the more evolved Class II YSOs show flatter values between 0 and 0.8, consistent with free–free emission, with minor contributions from non-thermal emission. The Class III source is only constrained by an upper limit. Radio variability, measured as a fraction of the mean intensity peak, is found to be ubiquitous and independent of evolutionary stage. Variability structure functions computed for nine sources indicate no preferred time-scales for most of them. We also investigate spectral index variability for six sources and find significant variations in only one object. Finally, we analyse the extended radio emission towards IRS 7B, where some subcomponents exhibit negative spectral indices suggestive of non-thermal processes.