DO R CORONAE BOREALIS STARS FORM FROM DOUBLE WHITE DWARF MERGERS?
- Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Tower Drive, Baton Rouge, LA 70803-4001 (United States)
- Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada)
- Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
- Department of Science, Mathematics and Informatics, Indiana University Kokomo, Kokomo, IN 46904-9003 (United States)
- Gemini Observatory, 670 North A'ohoku Place, Hilo, HI 96720 (United States)
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland)
A leading formation scenario for R Coronae Borealis (RCB) stars invokes the merger of degenerate He and CO white dwarfs (WDs) in a binary. The observed ratio of {sup 16}O/{sup 18}O for RCB stars is in the range of 0.3-20 much smaller than the solar value of {approx}500. In this paper, we investigate whether such a low ratio can be obtained in simulations of the merger of a CO and a He WD. We present the results of five three-dimensional hydrodynamic simulations of the merger of a double WD system where the total mass is 0.9 M{sub Sun} and the initial mass ratio (q) varies between 0.5 and 0.99. We identify in simulations with q {approx}< 0.7 a feature around the merged stars where the temperatures and densities are suitable for forming {sup 18}O. However, more {sup 16}O is being dredged up from the C- and O-rich accretor during the merger than the amount of {sup 18}O that is produced. Therefore, on the dynamical timescale over which our hydrodynamics simulation runs, an {sup 16}O/{sup 18}O ratio of {approx}2000 in the 'best' case is found. If the conditions found in the hydrodynamic simulations persist for 10{sup 6} s the oxygen ratio drops to 16 in one case studied, while in a hundred years it drops to {approx}4 in another case studied, consistent with the observed values in RCB stars. Therefore, the merger of two WDs remains a strong candidate for the formation of these enigmatic stars.
- OSTI ID:
- 22092270
- Journal Information:
- Astrophysical Journal, Vol. 757, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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