A Swift view of X-ray and UV radiation in the planet-forming T-Tauri system PDS 70

TL;DR

This study reports the first UV detection of the PDS 70 system, combined with X-ray observations, revealing that the star's high-energy emissions are likely coronal rather than accretion-driven, providing insights into its stellar activity.

Contribution

First UV detection of PDS 70 combined with X-ray data, indicating the star's UV emission is coronal, not accretion-related, and characterizing its high-energy radiation environment.

Findings

X-ray flux of 3.4×10^{-13} erg cm^{-2} s^{-1}

UV flux (U band) of 3.5×10^{-13} erg cm^{-2} s^{-1}

UV luminosity lower than expected from accretion processes

Abstract

PDS 70 is a $\sim$5 Myr old star with a gas and dust disc in which several proto-planets have been discovered. We present the first UV detection of the system along with X-ray observations taken with the \textit{Neil Gehrels Swift Observatory} satellite. PDS 70 has an X-ray flux of 3.4$\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the 0.3-10.0 keV range, and UV flux (U band) of 3.5$\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ . At the distance of 113.4 pc determined from Gaia DR2 this gives luminosities of 5.2$\times 10^{29}$ erg s$^{-1}$ and 5.4$\times 10^{29}$ erg s$^{-1}$ respectively. The X-ray luminosity is consistent with coronal emission from a rapidly rotating star close to the log $\frac{L_{\mathrm{X}}}{L_{\mathrm{bol}}} \sim -3$ saturation limit. We find the UV luminosity is much lower than would be expected if the star were still accreting disc material and suggest that the observed UV emission is coronal in origin.