  High resolution spectra from the Hinode EUV Imaging Spectrometer (EIS) have
revealed that coronal spectral line profiles are sometimes asymmetric, with a
faint enhancement in the blue wing on the order of 100 km/s. These asymmetries
could be important since they may be subtle, yet diagnostically useful
signatures of coronal heating or solar wind acceleration processes. It has also
been suggested that they are signatures of chromospheric jets supplying mass
and energy to the corona. Until now, however, there have been no studies of the
physical properties of the plasma producing the asymmetries. Here we identify
regions of asymmetric profiles in the outflows of AR 10978 using an asymmetric
Gaussian function and extract the intensities of the faint component using
multiple Gaussian fits. We then derive the temperature structure and chemical
composition of the plasma producing the asymmetries. We find that the
asymmetries are dependent on temperature, and are clearer and stronger in
coronal lines. The temperature distribution peaks around 1.4-1.8 MK with an
emission measure at least an order of magnitude larger than that at 0.6 MK. The
first ionization potential bias is found to be 3-5, implying that the high
speed 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 a
coronal composition, suggesting that the material is trapped on closed loops
before escaping, perhaps by interchange reconnection. The results, therefore,
identify the plasma producing the asymmetries as having a coronal origin.
