Abstract. We present simultaneous ultraviolet and X-ray observations of the dMe-type flaring stars AT Mic, AU Mic, EV Lac, UV Cet and YZ CMi obtained with the XMM-Newton observatory. During 40 h of simultaneous observation we identify 13 flares which occurred in both wave bands. For the first time, a correlation between X-ray and ultraviolet flux for stellar flares has been observed. We find power-law relationships between these two wavelength bands for the flare luminosity increase, as well as for flare energies, with power-law exponents between 1 and 2. We also observe a correlation between the ultraviolet flare energy and the X-ray luminosity increase, which is in agreement with the Neupert effect and demonstrates that chromospheric evaporation is taking place.

The complex relationship between solar flares and coronal mass ejections is investigated using a comparison of flare parameters for a total of 69 ejective and non-ejective flares. In the case of solar flares which do not show mass ejection there seems to be a clear relationship between the peak intensity and duration, with higher intensity events being of longer duration. Systematic differences in the relationship between peak temperature and intensity for the two types of event are also evident, with flares associated with CMEs tending to have lower peak temperatures than non-ejective events of the same intensity. Whilst there appears to be a clear relationship between the length of rise and decay phase in a flare, there are no systematic differences in these parameters for ejective and non-ejective flares. A total of eleven "EIT waves" were found, all of which were associated with CMEs. There is no apparent correlation between the occurrence of an EIT wave and the peak temperature, intensity or rise time of the associated flare.

Using these parameters, a path length of ≈8000 km is derived. There is no evidence of opacity in the quiescent X-ray spectrum of the star.

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We present the results of a search for X-ray variability in the galactic open cluster NGC 2516. This cluster has been observed on 8 occasions using XMM-Newton making it an excellent target for such a study. We find 4 sources which show significant variability, implying the detection of one significantly variable source every 25ksec. All sources exhibit spectra which can be fitted using an absorbed one or two temperature thermal plasma model. The brightest of these flares also show a prominent Iron line near ~7.0keV. All 4 sources lie near the observed main sequence of NGC 2516 suggesting they are cluster members. We propose that at least 3 of the 4 objects are RS CVn systems. We compare the properties of the brightest flare with those of solar flares.Comment: Accepted for publication in MNRAS, 6 page