Oxygen Isotope Ratios in Hydrogen-Deficient Carbon Stars: A Correlation with Effective Temperature and Implications for White Dwarf Merger Outcomes
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| Format: | Preprint |
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2024
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| _version_ | 1866911004038791168 |
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| author | Mehla, Advait Kasliwal, Mansi M. Karambelkar, Viraj Tisserand, Patrick Crawford, Courtney Clayton, Geoffrey Soon, Jamie Bhalerao, Varun |
| author_facet | Mehla, Advait Kasliwal, Mansi M. Karambelkar, Viraj Tisserand, Patrick Crawford, Courtney Clayton, Geoffrey Soon, Jamie Bhalerao, Varun |
| contents | Hydrogen-deficient Carbon (HdC) stars are a class of supergiants with anomalous chemical compositions, suggesting that they are remnants of CO-He white dwarf (WD) mergers. This class comprises two spectroscopically similar subclasses - dusty R Coronae Borealis (RCB) and dustless Hydrogen-deficient Carbon (dLHdC) stars. Both subclasses have a stark overabundance of $^{18}\textrm{O}$ in their atmospheres, but spectroscopic differences between them remain poorly studied. We present high-resolution ($R \approx 75000$) K-band spectra of six RCB and six dLHdC stars, including four newly discovered dLHdC stars, making this the largest sample to date. We develop a semi-automated fitting routine to measure $^{16}\textrm{O}/^{18}\textrm{O}$ ratios for this sample, tripling the number of dLHdC stars with oxygen isotope ratios measured from high resolution spectra. All six dLHdC stars have $^{16}\textrm{O}/^{18}\textrm{O}<1$, while the RCB stars have $^{16}\textrm{O}/^{18}\textrm{O}>4$. Additionally, for the first time, we find a trend of decreasing $^{16}\textrm{O}/^{18}\textrm{O}$ ratios with increasing effective temperature for HdC stars, consistent with predictions of theoretical WD merger models. However, we note that current models overpredict the low $^{16}\textrm{O}/^{18}\textrm{O}$ ratios of dLHdC stars by two orders of magnitude. We also measure abundances of C, N, O, Fe, S, Si, Mg, Na, and Ca for these stars. We observe a correlation between the abundances of $^{14}\textrm{N}$ and $^{18}\textrm{O}$ in our sample, suggesting that a fixed fraction of the $^{14}\textrm{N}$ is converted to $^{18}\textrm{O}$ in these stars via $α$-capture. Our results affirm the emerging picture that the mass ratio/total mass of the WD binary determine whether an RCB or dLHdC is formed post-merger. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2412_03664 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Oxygen Isotope Ratios in Hydrogen-Deficient Carbon Stars: A Correlation with Effective Temperature and Implications for White Dwarf Merger Outcomes Mehla, Advait Kasliwal, Mansi M. Karambelkar, Viraj Tisserand, Patrick Crawford, Courtney Clayton, Geoffrey Soon, Jamie Bhalerao, Varun Solar and Stellar Astrophysics Astrophysics of Galaxies Hydrogen-deficient Carbon (HdC) stars are a class of supergiants with anomalous chemical compositions, suggesting that they are remnants of CO-He white dwarf (WD) mergers. This class comprises two spectroscopically similar subclasses - dusty R Coronae Borealis (RCB) and dustless Hydrogen-deficient Carbon (dLHdC) stars. Both subclasses have a stark overabundance of $^{18}\textrm{O}$ in their atmospheres, but spectroscopic differences between them remain poorly studied. We present high-resolution ($R \approx 75000$) K-band spectra of six RCB and six dLHdC stars, including four newly discovered dLHdC stars, making this the largest sample to date. We develop a semi-automated fitting routine to measure $^{16}\textrm{O}/^{18}\textrm{O}$ ratios for this sample, tripling the number of dLHdC stars with oxygen isotope ratios measured from high resolution spectra. All six dLHdC stars have $^{16}\textrm{O}/^{18}\textrm{O}<1$, while the RCB stars have $^{16}\textrm{O}/^{18}\textrm{O}>4$. Additionally, for the first time, we find a trend of decreasing $^{16}\textrm{O}/^{18}\textrm{O}$ ratios with increasing effective temperature for HdC stars, consistent with predictions of theoretical WD merger models. However, we note that current models overpredict the low $^{16}\textrm{O}/^{18}\textrm{O}$ ratios of dLHdC stars by two orders of magnitude. We also measure abundances of C, N, O, Fe, S, Si, Mg, Na, and Ca for these stars. We observe a correlation between the abundances of $^{14}\textrm{N}$ and $^{18}\textrm{O}$ in our sample, suggesting that a fixed fraction of the $^{14}\textrm{N}$ is converted to $^{18}\textrm{O}$ in these stars via $α$-capture. Our results affirm the emerging picture that the mass ratio/total mass of the WD binary determine whether an RCB or dLHdC is formed post-merger. |
| title | Oxygen Isotope Ratios in Hydrogen-Deficient Carbon Stars: A Correlation with Effective Temperature and Implications for White Dwarf Merger Outcomes |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2412.03664 |