Are DY\,Persei stars cooler cousins of R Coronae Borealis stars?

Abstract

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 suspects 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 ${}^{12}$C/${}^{13}$C and low ${}^{16}$O/${}^{18}$O ratios are characteristic features of majority RCBs and HdCs. We have estimated ${}^{16}$O/${}^{18}$O ratios of the programme stars from the relative strengths of the ${}^{12}$C${}^{16}$O and ${}^{12}$C${}^{18}$O molecular bands observed in $K$- band. Our preliminary analysis suggest that a quartet of the DY\,Per suspects along with DY\,Persei itself seems to show isotopic ratio strength consistent with the ones of RCB/HdC stars whereas two of them do not show significant ${}^{13}$C and ${}^{18}$O in their atmospheres. Our analysis provides further indications that DY\,Per type stars could be related to RCB/HdC class of stars.

16 pages including 4 tables and 4 figures, Accepted for publication in ApJ ,typos corrected