Stellar spectral classification, and especially the Yerkes system, has been
highly useful in the study of stars. While there is a currently accepted
classification system for carbon stars, the subset of Hydrogen-deficient Carbon
(HdC) stars has not been well described by such a system, due in part to their
rarity and their variability. Here we present a new system for the
classification of HdCs based on their spectra, which is made wholly on their
observable appearance. We use a combination of dimensionality reduction and
clustering algorithms with human classification to create such a system. We
classify over half of the known sample of HdC stars using this, and roughly
calibrate the temperatures of each class using their colors. Additionally, we
express trends in the occurrence of certain spectral peculiarities such as the
presence of Hydrogen and Lithium lines. We also present three previously
unpublished spectra, and report the discovery of three new Galactic dustless
HdC (dLHdC) stars and additionally discuss one especially unique star that
appears to border between the hottest HdCs and the coolest Extreme Helium (EHe)
stars.Comment: 30 pages, 18 figures, submitted to MNRA