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Confident Detection of Doubly-Ionized Thorium in the Extreme Ap Star CPD-62 2717
Solar and Stellar Astrophysics · Submitted 25 Apr 2023
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Here, we present convincing evidence not only for the first Th detection in a magnetic chemically peculiar Ap star but also for the first detection of Th III in a stellar spectrum.
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Despite the universe containing primordial thorium (Th) of sufficient abundance to appear in stellar spectra, detection of Th has to date been tentative and based on just a few weak and blended lines. Here, we present convincing evidence not only for the first Th detection in a magnetic chemically peculiar Ap star but also for the first detection of Th III in a stellar spectrum. CPD-62 2717 was initially recognized as a highly-magnetized Ap star thanks to resolved magnetically split lines captured in $H$-band spectra from the SDSS/APOGEE survey. The star was subsequently pinpointed as extraordinarily peculiar when careful inspection of the $H$-band line content revealed the presence of five lines of Th III, none of which are detected in the other $\sim1500$ APOGEE-observed Ap stars. Follow-up with the VLT+UVES confirmed a similarly peculiar optical spectrum featuring dozens of Th III lines, among other peculiarities. Unlike past claims of Th detection, and owing to high-resolution observations of the strong ($\sim$8$-$12$\,$kG) magnetic field of CPD-62 2717, the detection of Th III can in this case be supported by matches between the observed and theoretical magnetic splitting patterns. Comparison of CPD-62 2717 to stars for which Th overabundances have been previously reported (e.g., Przybylski's Star) indicate that only for CPD-62 2717 is the Th detection certain. Along with the focus on Th III, we use time series measurements of the magnetic field modulus to constrain the rotation period of CPD-62 2717 to $\sim$4.8 years, thus establishing it as a new example of a super-slowly-rotating Ap star.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Despite the universe containing primordial thorium (Th) of sufficient abundance to appear in stellar spectra, detection of Th has to date been tentative and based on just a few weak and blended lines. | background 0.58 | 0.04 | 0.03 | asserted 0.97 |
| s1 | Here, we present convincing evidence not only for the first Th detection in a magnetic chemically peculiar Ap star but also for the first detection of Th III in a stellar spectrum. | contribution 0.58 | 0.95 | 0.90 | asserted 1.00 |
| s2 | CPD-62 2717 was initially recognized as a highly-magnetized Ap star thanks to resolved magnetically split lines captured in $H$-band spectra from the SDSS/APOGEE survey. | background 0.55 | 0.27 | 0.04 | asserted 1.00 |
| s3 | The star was subsequently pinpointed as extraordinarily peculiar when careful inspection of the $H$-band line content revealed the presence of five lines of Th III, none of which are detected in the other $\sim1500$ APOGEE-observed Ap stars. | result 0.97 | 0.91 | 0.15 | asserted 1.00 |
| s4 | Follow-up with the VLT+UVES confirmed a similarly peculiar optical spectrum featuring dozens of Th III lines, among other peculiarities. | result 0.52 | 0.89 | 0.06 | asserted 1.00 |
| s5 | Unlike past claims of Th detection, and owing to high-resolution observations of the strong ($\sim$8$-$12$\,$kG) magnetic field of CPD-62 2717, the detection of Th III can in this case be supported by matches between the observed and theoretical magnetic splitting patterns. | interpretation 0.43 | 0.84 | 0.14 | asserted 0.80 |
| s6 | Comparison of CPD-62 2717 to stars for which Th overabundances have been previously reported (e.g., Przybylski's Star) indicate that only for CPD-62 2717 is the Th detection certain. | interpretation 0.55 | 0.69 | 0.26 | asserted 0.53 |
| s7 | Along with the focus on Th III, we use time series measurements of the magnetic field modulus to constrain the rotation period of CPD-62 2717 to $\sim$4.8 years, thus establishing it as a new example of a super-slowly-rotating Ap star. | result 0.92 | 0.96 | 0.08 | asserted 1.00 |
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Original abstract
Despite the universe containing primordial thorium (Th) of sufficient abundance to appear in stellar spectra, detection of Th has to date been tentative and based on just a few weak and blended lines. Here, we present convincing evidence not only for the first Th detection in a magnetic chemically peculiar Ap star but also for the first detection of Th III in a stellar spectrum. CPD-62 2717 was initially recognized as a highly-magnetized Ap star thanks to resolved magnetically split lines captured in $H$-band spectra from the SDSS/APOGEE survey. The star was subsequently pinpointed as extraordinarily peculiar when careful inspection of the $H$-band line content revealed the presence of five lines of Th III, none of which are detected in the other $\sim1500$ APOGEE-observed Ap stars. Follow-up with the VLT+UVES confirmed a similarly peculiar optical spectrum featuring dozens of Th III lines, among other peculiarities. Unlike past claims of Th detection, and owing to high-resolution observations of the strong ($\sim$8$-$12$\,$kG) magnetic field of CPD-62 2717, the detection of Th III can in this case be supported by matches between the observed and theoretical magnetic splitting patterns. Comparison of CPD-62 2717 to stars for which Th overabundances have been previously reported (e.g., Przybylski's Star) indicate that only for CPD-62 2717 is the Th detection certain. Along with the focus on Th III, we use time series measurements of the magnetic field modulus to constrain the rotation period of CPD-62 2717 to $\sim$4.8 years, thus establishing it as a new example of a super-slowly-rotating Ap star.
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The B8 temperature class reported by [ref] seems to be an error given that the 3rd data release of the Gaia mission [ref] indicates a far cooler $T_eff=6834$ K.
Gaia Data Release 3: Summary of the content and survey properties · Introduction · contest 0.80
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