May 19, 2010, 12:00 pm - 1:00 pm

May 19, 2010, 12:00 pm - 1:00 pm

The first measurement of the effective adiabatic index in the corona gives surprising results

Tom Van Doorsselaere (University of Warwick, UK)

We analyse an observation of a 5 minute quasi-periodic oscillation detected in multiple spectral lines with Hinode/EIS, near the foot-point of a coronal loop. There is strong evidence for the interpretation of the observed phenomenon in terms of a propagating slow magneto-acoustic MHD mode. For the first time, we use spectroscopy to detect oscillations in the electron density and temperature, using the CHIANTI atomic database. Comparing the density variations, the Doppler shifts and the electron temperature allows us to derive the line-of-sight component of the phase speed and the effective adiabatic index, using coronal seismology. This is the first measurement of the effective adiabatic index in the solar corona. Surprisingly, it is found to be strictly smaller than one. This shows that additional terms are important in the energy equation, and have a large contribution in the physics of these oscillations.