Spectrophotometry of Stars near the Cool end of the White Dwarf Sequence

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Abstract
The spectra of five stars near the cool end of the white dwarf sequence are described. Two of these, GH7-21 and W489, have CH bands and relatively weak C2, metal hydride, and metal line features in their spectra and thus appear hydrogen rich and metal deficient. It is suggested that they are examples of cooled down DA stars. The stars GH7-22 and L97-12 seem to have nearly continuous spectra with weak lines of Ca I and Ca II, but other weak molecular features appear present as well. This would be consistent with them being both metal and hydrogen deficient. The spectrum of LFT 526 shows strong molecular bands, notably of MgH, and metal lines, the most important being due to Ca I, Ca II and Na I. From the reduced proper motion, this star is probably intermediate between the Main Sequence and classical white dwarfs. It could therefore be either a low mass degenerate or a sdM star. From the spectra of the five stars, a few hypotheses are made regarding the appearances of the spectra of cool white dwarfs and their evolution.

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