Solutions to the dispersion relation (32) for the values in Table 1 as a function of temperature. The imaginary component of the wave frequency (the growth rate) is shown. Green, red and blue denote the thermal, slow and fast mode growth rates, respectively. The thermal, slow and fast growth rates were multiplied by a factor 10, 100 and 1000, respectively. Inset: a zoom-in near 2 million Kelvin, where the fast and slow wave modes become overstable for our adopted parameters.