The lithium abundances of the Capella giants

Pilachowski, Catherine A.; Sowell, James R.

doi:10.1086/116183

Cited by 16 publications

(17 citation statements)

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“…McWilliam (1990) envelope-expanding phase. These evolutionary phases agree with previous works (Pilachowski & Sowell 1992 ;Barlow, Fekel, & Scarfe 1993 ;Hummel et al 1994 ;SPE97).…”

Section: A Aursupporting

confidence: 93%

A Comparison of Stellar Evolution with Binary Systems

Iwamoto

Saio

1999

ApJ

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We have compared stellar evolution models with the three intermediate-mass binary systems V2291 Oph, a Aur, and g And, whose masses are determined accurately within 7%. These systems were recently regarded by and coworkers as systems that favor evolution with moderate overshoot mixing Schro der from the convective cores. While they assumed a standard Population I metallicity for these binaries, we have taken into account the available heavy-element abundance data in the literature. We have taken two approaches for each system. First, assuming no core overshooting, we have adjusted helium abundance for each binary to obtain the best Ðt. Second, adopting a helium abundance from a standard metallicity-helium relation, we have estimated a required extent of core overshooting Our results l ov . indicate that the required extent of core overshooting is less than which is smaller than the D0.15H p , extent estimated by and his collaborators. The main reason for the di †erence is attributed to Schro der the fact that we have taken into account published estimates of metallicity for each system. We have found that to obtain a good Ðt with red components we have to modify the ratio of mixing length to pressure scale height for each system. The required ratio is found to be smaller for a metal-poor system and vice versa.

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“…McWilliam (1990) envelope-expanding phase. These evolutionary phases agree with previous works (Pilachowski & Sowell 1992 ;Barlow, Fekel, & Scarfe 1993 ;Hummel et al 1994 ;SPE97).…”

Section: A Aursupporting

confidence: 93%

A Comparison of Stellar Evolution with Binary Systems

Iwamoto

Saio

1999

ApJ

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“…Regarding Li, we obtained A p ≃ 1.0 (primary) and A s ≃ 3.2 (secondary), which are almost consistent with the previous studies (see, e.g., Pilachowski &Sowell 1992 or Torres et al 2015, andthe references therein). This means that the former is within the expected range shown by normal giants while the latter is the typical abundance of Li-rich giants (cf.…”

Section: Behaviors Of Light Elementssupporting

confidence: 92%

Spectroscopic Determination of Capella’s Photospheric Abundances: Possible Influence of Stellar Activity

Takeda

Hashimoto

Honda

2018

ApJ

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Capella is a spectroscopic binary consisting of two G-type giants, where the primary (G8 iii) is a normal red-clump giant while the secondary (G0 iii) is a chromospherically-active fast rotator showing considerable overabundance of Li as Li-enhanced giants. Recently, Takeda & Tajitsu (2017) reported that abundance ratios of specific light elements (e.g., [C/Fe] or [O/Fe]) in Li-rich giants of high activity tend to be anomalously high, which they suspected to be nothing but superficial caused by unusual atmospheric structure due to high activity. Towards verifying this hypothesis, we determined the elemental abundances of the primary and the secondary of Capella based on the disentangled spectrum of each component, in order to see whether any apparent disagreement exists between the two, which should have been formed with the same chemical composition. We found that the primary is slightly supersolar (by ∼ +0.1 dex) while the secondary is subsolar (by several tenths dex) for heavier elements such as Fe, resulting in a marked discrepancy between the primary and secondary, though such a trend is not seen for light elements (e.g., C or O). These observational facts suggest that anomalously large [X/Fe] ratios found in Li-rich giants were mainly due to an apparent decrease of Fe abundance, which we speculate is caused by the overionization effect due to chromospheric UV radiation. We thus conclude that conventional model atmosphere analysis would fail to correctly determine the abundances of fast-rotating giants of high activity, for which proper treatment of chromospheric effect is required for deriving true photospheric abundances.

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“…Few details of this determination were given, aside from the fact that the equivalent widths of the iron lines for each component were corrected for the light contribution from the other star using the light ratio of Wright (1954), which we now know to be reversed (see § 5). In their lithium study of Capella Pilachowski & Sowell (1992) did not report an iron abundance, but pointed out that the calcium abundance is essentially solar for both components. Randich et al (1994) reported [Fe/H] = −0.4 for the primary of Capella, and solar metallicity for the secondary.…”

Section: Chemical Compositionmentioning

confidence: 99%

Binary Orbit, Physical Properties, and Evolutionary State of Capella (Α Aurigae)

Torres

Claret

Young

2009

ApJ

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We report extensive radial-velocity measurements of the two giant components of the detached, 104day period binary system of Capella. Our highly accurate three-dimensional orbital solution based on all existing spectroscopic and astrometric observations including our own yields much improved masses for the primary and secondary of 2.466 ± 0.018 M ⊙ and 2.443 ± 0.013 M ⊙ , with relative errors of only 0.7% and 0.5%, respectively. The mass ratio is considerably closer to unity than previously believed, which has an impact on assessing the evolutionary state of the system. Improved values are presented also for the radii (11.87 ± 0.56 R ⊙ and 8.75 ± 0.32 R ⊙ ), effective temperatures (4920 ± 70 K and 5680 ± 70 K), and luminosities (79.5 ± 4.8 L ⊙ and 72.1 ± 3.6 L ⊙ ). The distance is determined to be 13.042 ± 0.028 pc, based on the accurate orbital parallax. The projected rotational velocities and individual rotation periods are also known. Capella is unique among evolved stars in that, in addition to all of the above, the chemical composition is known as well. This includes the overall metallicity [m/H], the carbon isotope ratio 12 C/ 13 C for the primary, and the lithium abundance and C/N ratios for both components. We present new or revised values for some of these. The latter three quantities are sensitive diagnostics of evolution, and change drastically for giants as a result of the deepening of the convective envelope during the first dredge-up. The secondary is crossing the Hertzprung gap, while the primary is believed to be in the longer-lived core-helium burning phase. Previous studies using only the masses, temperatures, and luminosities have found good agreement with stellar evolution models placing the primary in the clump. Here we compare all of the constraints simultaneously against three sets of current models. We find that they are unable to match all of the observations for both components at the same time, and at a single age, for any evolutionary state of the primary. This shows the great importance of chemical information for assessing the evolutionary state of giant stars. A comparison with models of tidal evolution yields similarly disappointing results, when tested against the fact that the orbit is circular, the primary is rotating synchronously, the secondary ∼12 times faster than synchronous, and the spin axes are apparently aligned with the axis of the orbit. When confronted in detail, our understanding of the advanced stages of stellar evolution is thus still very incomplete.

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The lithium abundances of the Capella giants

Cited by 16 publications

References 0 publications

A Comparison of Stellar Evolution with Binary Systems

A Comparison of Stellar Evolution with Binary Systems

Spectroscopic Determination of Capella’s Photospheric Abundances: Possible Influence of Stellar Activity

Binary Orbit, Physical Properties, and Evolutionary State of Capella (Α Aurigae)

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