Sodium enhancement in evolved cataclysmic variables

• DOI: 10.48550/arxiv.2304.13750
• Publication Date: 2023-01-01
• Authors: Natsuko Yamaguchi; Kareem El-Badry; Antonio C. Rodriguez; Maude Gull; Benjamin R. Roulston; Zachary P. Vander...
• Keywords: Sequence (biology); Low Mass

We present follow-up spectroscopy of 21 cataclysmic variables (CVs) with evolved secondaries and ongoing or recently-terminated mass transfer. Evolutionary models predict that the should have anomalous surface abundances owing to nuclear burning in their cores during main-sequence evolution subsequent envelope stripping by companion white dwarfs. To test these models, we measure sodium (Na) donors from Fraunhofer "D" doublet. Accounting for interstellar absorption, find {\it all} objects our sample enhanced Na abundances. 0.3 $\lesssim$ [Na/H] 1.5 dex across sample, a median = 0.956 dex, i.e., about an order magnitude enhancement over solar values. interpret values, run MESA binary CVs which transfer begins just as donor leaves main sequence. These generically initial masses $\gtrsim 1\,M_{\odot}$, consistent observations. In enrichment occurs donors' via NeNa cycle near end evolution. Na-enhanced material is exposed when binaries reach orbital periods few hours. Donors higher are predicted at fixed period core temperatures The observed values on average $\approx$0.3 than models. Surface CV provide unique opportunity study products intermediate-mass stars.