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The temperature scale of the late Main Sequence has not been well determined since its members are intrinsically faint, and broad molecular spectral features make their flux distributions uncertain. The result is that, to date, only very crude estimates of the effective temperatures for late K and early M dwarfs are available, and those estimates are based on an assumption of a black body flux distribution for the coolest stars. Since it is primarily in the photospheres of these very cool dwarfs where a multitude of molecular features dominate, they are among the the worst examples of a thermal flux distributions to be found in the heavens!
In our recent fine analysis of four late K dwarfs we determined that the available temperature scales were inadequate. We found, however, that the requirement of internal consistency throughout various phases of the chemical analysis of these stars sheds light on this problem. Through a painstaking iterative approach, we were able to find effective temperatures for each star which, when combined with the most recent model atmosphere grids, opacity data and spectrum synthesis techniques, provide reasonable abundance results and yield a consistent picture with regard to the temperature of these cool dwarfs.
We find that the temperature scale for the late Main Sequence must be shifted upward several hundred degrees.
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