1995A&A...300..775M

This paper presents extreme ultraviolet (EUV) fluxes for 74 main-sequence stars observed with the Extreme Ultraviolet Explorer (EUVE). The sample of stars was chosen on the basis of rotational period and includes 23 new EUV detections. These detections are in addition to the ROSAT WFC and EUVE catalogs and have increased the number of main-sequence stars detected in the extreme ultraviolet by ∼12%. We present an activity-rotation relation in the EUV and show that in a sample of stars with different effective temperatures the Rossby number is a better parameter for describing the levels of EUV emission as compared to the rotational period. This is also known to be the case for the chromospheric emission. A comparison with the emission in the Mg II h and K lines shows that saturation in the EUV occurs in lower Rossby numbers than does chromospheric saturation, where saturation in X-rays occurs in the same Rossby numbers as in the EUV. The radiative losses in the EUV are comparable to the radiative losses in X-rays. The EUVE observations indicate that the low activity dM star Gl 685 has a cool corona with a characteristic temperature of <2.5x10⁶K. A large amount of the coronal radiative losses in low activity dwarfs is expected to emerge in EUV wavelengths.