Are DY Persei Stars Cooler Cousins of R Coronae Borealis Stars?

In this paper we present, for the first time, the study of low resolution H- and K-band spectra of 7 DY Per type and suspect stars, as well as DY Persei itself. We also observed H- and K-band spectra of 3 R Coronae Borealis (RCB) stars, 1 hydrogen-deficient carbon (HdC) star, and 14 cool carbon stars, including normal giants as comparisons. High C-12/C-13 and low O-16/O-18 ratios are characteristic features of majority RCBs and HdCs. We have estimated O-16/O-18 ratios of the program stars from the relative strengths of the (CO)-C-12-O-16 and (CO)-C-12-O-18 molecular bands observed in K-band. Our preliminary analysis suggests that a quartet of the DY Per suspects, along with DY Persei itself, seem to show isotopic ratio strength consistent with that of RCB/HdC stars, whereas two of them do not show significant C-13 and O-18 in their atmospheres. Our analysis provides further indications that DY Per type stars could be related to the RCB/HdC class of stars.