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

Abstract

ABSTRACT PDS 70 is a ∼5-Myr-old star with a gas and dust disc in which several protoplanets have been discovered. We present the first ultraviolet (UV) detection of the system along with X-ray observations taken with the Neil Gehrels Swift Observatory satellite. PDS 70 has an X-ray flux of 3.4 × 10−13 erg cm−2 s−1 in the 0.3–10.0 keV range, and UV flux (U band) of 3.5 × 10−13 erg cm−2 s−1 . At the distance of 113.4 pc determined from Gaia Data Release 2, this gives luminosities of 5.2 × 1029 and 5.4 × 1029 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.