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Capella (alpha Aurigae) revisited: New binary orbit, physical properties, and evolutionary state
Solar and Stellar Astrophysics · Submitted 27 May 2015
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Three different sets of models place the primary star firmly at the end of the core helium-burning phase (clump), while the secondary is known to be evolving rapidly across the Hertzprung gap.
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The abstract, sentence by sentence
Knowledge of the chemical composition and absolute masses of Capella are key to understanding the evolutionary state of this benchmark binary system comprising two giant stars. Previous efforts, including our own 2009 study, have largely failed to reach an acceptable agreement between the observations and current stellar evolution models, preventing us from assessing the status of the primary. Here we report a revision of the physical properties of the components incorporating recently published high-precision radial velocity measurements, and a new detailed chemical analysis providing abundances for more than 20 elements in both stars. We obtain highly precise (to about 0.3%) masses of 2.5687 +/- 0.0074 and 2.4828 +/- 0.0067 solar masses, radii of 11.98 +/- 0.57 and 8.83 +/- 0.33 solar radii, effective temperatures of 4970 +/- 50 K and 5730 +/- 60 K, and independently measured luminosities based on the orbital parallax (78.7 +/- 4.2 and 72.7 +/- 3.6 solar luminosities). We find an excellent match to stellar evolution models at the measured composition of [Fe/H] = -0.04 +/- 0.06. Three different sets of models place the primary star firmly at the end of the core helium-burning phase (clump), while the secondary is known to be evolving rapidly across the Hertzprung gap. The measured lithium abundance, the C/N ratio, and the 12C/13C isotopic carbon abundance ratio, which change rapidly in the giant phase, are broadly in agreement with expectations from models. Predictions from tidal theory for the spin rates, spin-orbit alignment, and other properties do not fare as well, requiring a 40-fold increase in the efficiency of the dissipation mechanisms in order to match the observations.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Knowledge of the chemical composition and absolute masses of Capella are key to understanding the evolutionary state of this benchmark binary system comprising two giant stars. | background 1.00 | 0.05 | 0.04 | asserted 1.00 |
| s1 | Previous efforts, including our own 2009 study, have largely failed to reach an acceptable agreement between the observations and current stellar evolution models, preventing us from assessing the status of the primary. | gap 0.72 | 0.44 | 0.02 | asserted 0.99 |
| s2 | Here we report a revision of the physical properties of the components incorporating recently published high-precision radial velocity measurements, and a new detailed chemical analysis providing abundances for more than 20 elements in both stars. | contribution 0.99 | 0.95 | 0.07 | asserted 0.99 |
| s3 | We obtain highly precise (to about 0.3%) masses of 2.5687 +/- 0.0074 and 2.4828 +/- 0.0067 solar masses, radii of 11.98 +/- 0.57 and 8.83 +/- 0.33 solar radii, effective temperatures of 4970 +/- 50 K and 5730 +/- 60 K, and independently measured luminosities based on the orbital parallax (78.7 +/- 4.2 and 72.7 +/- 3.6 solar luminosities). | result 1.00 | 0.97 | 0.13 | asserted 1.00 |
| s4 | We find an excellent match to stellar evolution models at the measured composition of [Fe/H] = -0.04 +/- 0.06. | result 0.85 | 0.96 | 0.25 | asserted 1.00 |
| s5 | Three different sets of models place the primary star firmly at the end of the core helium-burning phase (clump), while the secondary is known to be evolving rapidly across the Hertzprung gap. | interpretation 0.53 | 0.72 | 0.50 | asserted 1.00 |
| s6 | The measured lithium abundance, the C/N ratio, and the 12C/13C isotopic carbon abundance ratio, which change rapidly in the giant phase, are broadly in agreement with expectations from models. | result 0.64 | 0.85 | 0.06 | hedged possibility 0.58 |
| s7 | Predictions from tidal theory for the spin rates, spin-orbit alignment, and other properties do not fare as well, requiring a 40-fold increase in the efficiency of the dissipation mechanisms in order to match the observations. | result 0.76 | 0.62 | 0.07 | asserted 0.99 |
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The paper
Original abstract
Knowledge of the chemical composition and absolute masses of Capella are key to understanding the evolutionary state of this benchmark binary system comprising two giant stars. Previous efforts, including our own 2009 study, have largely failed to reach an acceptable agreement between the observations and current stellar evolution models, preventing us from assessing the status of the primary. Here we report a revision of the physical properties of the components incorporating recently published high-precision radial velocity measurements, and a new detailed chemical analysis providing abundances for more than 20 elements in both stars. We obtain highly precise (to about 0.3%) masses of 2.5687 +/- 0.0074 and 2.4828 +/- 0.0067 solar masses, radii of 11.98 +/- 0.57 and 8.83 +/- 0.33 solar radii, effective temperatures of 4970 +/- 50 K and 5730 +/- 60 K, and independently measured luminosities based on the orbital parallax (78.7 +/- 4.2 and 72.7 +/- 3.6 solar luminosities). We find an excellent match to stellar evolution models at the measured composition of [Fe/H] = -0.04 +/- 0.06. Three different sets of models place the primary star firmly at the end of the core helium-burning phase (clump), while the secondary is known to be evolving rapidly across the Hertzprung gap. The measured lithium abundance, the C/N ratio, and the 12C/13C isotopic carbon abundance ratio, which change rapidly in the giant phase, are broadly in agreement with expectations from models. Predictions from tidal theory for the spin rates, spin-orbit alignment, and other properties do not fare as well, requiring a 40-fold increase in the efficiency of the dissipation mechanisms in order to match the observations.
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References
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Uses the method or tool of 1 paper
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The uclsyn code [ref] was used to synthesize spectra, based on initial temperatures and surface gravities from T09 and a built-in grid of LTE model atmospheres by [ref] with a scaled-solar mixture.
New Grids of ATLAS9 Model Atmospheres · Atmospheric parameters and abundance analysis · 0.99
Compares with 1 paper
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A recent study by [ref] of the coronae of stars with super-solar photospheric abundances found the same effect shown by Capella in $α$ Cen A and B, which have somewhat similar temperatures, although these are dwarfs so it is unclear how significant this may be.
Coronae of Stars with Super Solar Elemental Abundances · Discussion and concluding remarks · 0.87
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