The Relationship between Accretion and Ionised Ejection among Young Stellar Objects in the Coronet Cluster

TL;DR

The study demonstrates a sublinear coupling between mass accretion and ionised jet mass loss across Class I–II YSOs in the Coronet cluster, using Br$\gamma$ as an accretion tracer and 3.3 cm free–free emission as a jet indicator from quasi-simultaneous KMOS and VLA data. By converting Br$\gamma$ fluxes to $\dot{M}_{\mathrm{acc}}$ and radio fluxes to $\dot{M}_{\mathrm{ion}}$, the authors find $\log(\dot{M}_{\mathrm{ion}}) = (-7.1\pm0.8) + (0.26\pm0.13)\log(\dot{M}_{\mathrm{acc}})$ on time-averaged scales, and they observe an anti-correlation between the ionised-to-accreted mass-loss ratio and $\dot{M}_{\mathrm{acc}}$, implying evolving jet-launching efficiency or ionisation fraction. The short-term variability shows no consistent temporal correlation between accretion and ionised ejection within months, highlighting the complexity of magnetohydrodynamic coupling in jets. Overall, the results support a linked, but evolving, accretion–ejection connection over the YSO lifetime, while also underlining the importance of multi-epoch, multiwavelength studies to capture their intricate, time-dependent interplay.

Abstract

We present results from a coordinated, multi-epoch near-infrared and centimeter radio survey of young stellar objects (YSOs) in the Coronet, aimed at probing the connection between mass accretion and ionised mass loss. Using VLT-KMOS, we detect Br$γ$ emission in 5 of the 26 targets, which also exhibit 3.3-cm continuum emission in VLA images, consistent with partially ionised jets. For seven additional sources, stringent flux upper limits were obtained. The derived accretion and ionised mass-loss rates for class I and class II YSOs follow a sublinear correlation $\dot{M}_{\mathrm{ion}} \propto \dot{M}_{\mathrm{acc}}^{0.3}$, consistent with previous results for class II YSOs but extended here to earlier stages. Multi-epoch observations reveal modest variability in both tracers but no clear temporal correlation between accretion and ejection within timescales of a few months. The ratio $\dot{M}_{\mathrm{ion}}/\dot{M}_{\mathrm{acc}}$ shows an anti-correlation with $\dot{M}_{\mathrm{acc}}$, increasing with time from class I YSOs to class II YSOs, suggesting an increase in jet-launching efficiency or ionisation fraction with evolution. These findings support a direct connection between accretion and outflow across the $\sim$ Myr timescale of YSO evolution, while highlighting the complexity of their short-term interplay.

Figures (6)

• Figure 1: Relationship between the Br$\gamma$ and the 3.3 cm radio continuum fluxes for the class I and II sources. Detected sources are denoted by black symbols and upper limits by red symbols. Grey curves illustrate posterior regression lines consistent with the $68\%$ credible interval of the slope; the median relation is shown in red.
• Figure 2: Temporal evolution of individual measurements of $\dot{M}_{\mathrm{acc}}$ and $\dot{M}_\mathrm{ion}$ for the two class I (IRS1, IRS2, top and middle panels) and one class II YSO (TCrA, bottom) with Br$\gamma$ in emission and VLA detection in individual epochs. CrA43 was excluded due to its unphysically large ejection rate compared to its accretion rate (see Section \ref{['outlier']}). The blue and green points refer to values around the individual epochs marked in the plot legends, whereas the red star is the mean value.
• Figure 3: Correlation between the logarithm of the mass accretion rate and the logarithm of the ionised mass-loss rate, including the data from IRS1, IRS2, CrA16, TCrA, Peterson 1, Peterson 6, and CrA 26, but excluding CrA43 (inset) from the fit. We present two fitting scenarios: in the left panel the fit is obtained utilizing the averaged Br$\gamma$ spectra and epoch-concatenated VLA image; in the right panel the fit is obtained from averaging the near-simultaneous measurements shown in Fig. \ref{['fig:fig2']} for the detections, and upper limits as described in the text. The light grey lines show regression relations drawn from posterior samples restricted to the central $68\%$ credible interval of the slope; the red line indicates the posterior median. The overplotted gray squares, marked with the suffix "-old", show previous measurements obtained from 2014ApJ...780..155L and 2005AA...429..543N.
• Figure 4: Logarithm of the ratio of the ionised mass-loss rate to the mass-accretion rate, as a function of the latter. The horizontal lines mark efficiency factors $\xi_\mathrm{ion} =$ 0.001, 0.01, 0.1, and 1. The red and grey lines are defined as in Fig. \ref{['fig:fig2']}.
• Figure 5: Br$\gamma$ line profiles of the seven YSOs with a detection listed in Table \ref{['tab:source_data']}. The broken grey lines show the spectra in individual epochs, whereas the step plot in black shows their average. The red line represents the Gaussian fit to the mean spectrum.