K-band spectroscopy of pre-cataclysmic variables

TL;DR

This study uses K-band spectroscopy on 13 pre-cataclysmic variables to investigate chemical abundances, finding no evidence of CO anomalies seen in some cataclysmic variables, thus informing their evolutionary origins.

Contribution

It provides observational evidence that CO anomalies in CVs are not inherited from pre-CV phases, challenging previous assumptions about their origins.

Findings

Pre-CVs show normal CO abundances similar to single stars.

No evidence of enhanced 13CO in pre-CVs.

CO anomalies in CVs are likely due to processes after the pre-CV stage.

Abstract

We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to examine them for anomalous chemical abundances. In particular, we study the strength of the 12CO and 13CO absorption bands that have been found diminished and enhanced, respectively, in similar studies of CVs. All our systems show CO abundances that are within the range observed for single stars. The weakest 12CO bands with respect to the spectral type are found in the pre-CV BPM 71214, although on a much smaller scale than observed in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account that our sample is subject to the present observational bias that favours the discovery of young pre-CVs with secondary stars of late spectral types, we can conclude the following: 1) our study provides observational proof that the CO anomalies discovered in certain CVs are not due to any material acquired during the common envelope phase, and 2) if the CO anomalies in certain CVs are not due to accretion of processed material during nova outburst, then the progenitors of these CVs are of a significantly different type than the currently known sample of pre-CVs.