Temperatures of extreme-ultraviolet-emitting plasma structures observed by the Transition Region and Coronal Explorer

The Transition Region and Coronal Explorer has revealed, in unprecedented detail, various kinds of EUV-emitting plasma structures in the solar upper atmosphere. The filter ratio 195 Angstrom/171 Angstrom has been conventionally used to determine the plasma temperatures, but this method has a shortcoming in that it may not yield a unique temperature value for a given ratio. Therefore, we introduce a new method employing two filter ratios (195 Angstrom/171 Angstrom and 284 Angstrom/195 Angstrom). It is demonstrated that this color-color method is effective in determining a wide range of unambiguous plasma temperatures. We have obtained a temperature of 1x10(6) K for a loop that is bright in 171 Angstrom but hardly visible in 284 Angstrom, a higher temperature of 2x10(6) K for a loop that is clearly visible in 195 and 284 Angstrom but not in 171 Angstrom, and a transition-region temperature of 2.5x10(5) K for a low-lying loop that is clearly visible in all the EUV wavelengths. In addition, we have found that "moss" structures have temperatures of around 1x10(6) K and that EUV jets have temperatures of about 2.5x10(5) K.