UV lines as a tracers for the XUV-fluxes of stars and the PLATOspec project

TL;DR

This paper discusses using UV spectral lines, particularly CaIIHK, as proxies for stellar XUV fluxes to study stellar activity and its effects on exoplanets, leveraging the new PLATOspec instrument for observations.

Contribution

It introduces the use of the PLATOspec spectrograph for observing CaIIHK lines to indirectly measure stellar XUV radiation, enabling large programs on a 1.5m telescope.

Findings

CaIIHK lines correlate with stellar XUV flux.

PLATOspec allows high-resolution UV observations on a smaller telescope.

Potential for studying stellar activity in large star samples.

Abstract

Observations in the UV-regime are very important for exoplanet research, because many diagnostically important lines for studying stellar activity are in this regime. Studying stellar activity is not only important because of its negative effects on the determination planetary parameters, but also because the XUV-radiation from the host stars affects the photochemistry and the erosion of planetary atmospheres . Unfortunately, the XUV-region is only accessible from space. However, since the XUV-radiation is correlated with the CaII,HK-lines, we can use these lines to study the XUV radiation indirectly. The CaIIHK lines for relatively bright stars can be observed with PLATOspec, a new high-resolution echelle spectrograph in development for the ESO 1.5m telescope at La Silla. One advantage compared to instruments on larger telescopes will be that large programs can be carried out. There will be two modes for obtaining precise RV-measurements. In the future, the CUBES instrument on the VLT will be able to study the same lines to probe the XUV-radiation in much fainter targets.