From radio to X-ray: The quiescent atmosphere of the dMe flare star EV Lacertae

We report on multiwavelength observations spanning radio to X-ray wavelengths of the M dwarf flare star EV Lacertae and probing the characteristics of the outer atmospheric plasma from the upper chromosphere to the corona. We detect the star at a wavelength of 2 cm ( 15 GHz) for the first time. UV and FUV line profiles show evidence of nonthermal broadening, and the velocity width appears to peak at lower temperatures than in the Sun; this trend is confirmed in another active M dwarf flare star. Electron density measurements indicate nearly constant electron pressures between log T = 5.2 and 6.4. At higher coronal temperatures, there is a sharp increase of 2 orders of magnitude in density (n(e) similar to 10(13) cm(-3) at log T = 6: 9). X-ray, EUV, FUV, and NUV spectra constrain the differential emission measure (DEM) from the upper chromosphere through the corona. The coronal pressures are inconsistent with the assumption of hydrostatic equilibrium, either through emission measure ( EM) modeling or application of scaling laws, and imply large conductive loss rates and a large energy input at the highest temperatures. The time-scales for radiative and conductive losses in EV Lac's upper atmosphere imply that significant continued heating must occur for the corona to maintain its quiescent properties. The high-frequency radio detection requires the high-temperature X-ray-emitting coronal plasma to be spatially distinct from the radio emission source. Length scales in the low-temperature corona are markedly larger than those in the high-temperature corona, further suggestions of an inhomogeneous mixture of thermal and nonthermal coronal plasma.