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High resolution spectra from the Hinode EUV Imaging Spectrometer (EIS) haverevealed that coronal spectral line profiles are sometimes asymmetric, with afaint enhancement in the blue wing on the order of 100 km/s. These asymmetriescould be important since they may be subtle, yet diagnostically usefulsignatures of coronal heating or solar wind acceleration processes. It has alsobeen suggested that they are signatures of chromospheric jets supplying massand energy to the corona. Until now, however, there have been no studies of thephysical properties of the plasma producing the asymmetries. Here we identifyregions of asymmetric profiles in the outflows of AR 10978 using an asymmetricGaussian function and extract the intensities of the faint component usingmultiple Gaussian fits. We then derive the temperature structure and chemicalcomposition of the plasma producing the asymmetries. We find that theasymmetries are dependent on temperature, and are clearer and stronger incoronal lines. The temperature distribution peaks around 1.4-1.8 MK with anemission measure at least an order of magnitude larger than that at 0.6 MK. Thefirst ionization potential bias is found to be 3-5, implying that the highspeed component of the outflows may also contribute to the slow speed wind.Observations and models indicate that it takes time for plasma to evolve to acoronal composition, suggesting that the material is trapped on closed loopsbefore escaping, perhaps by interchange reconnection. The results, therefore,identify the plasma producing the asymmetries as having a coronal origin.

The coronal source of extreme-ultraviolet line profile asymmetries in solar active region outflows