Rotation and Granulation of the K2 Giant Α Ser

Gray, David F.

doi:10.3847/0004-637x/826/1/92

Cited by 10 publications

(2 citation statements)

References 46 publications

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“…Unlike late-type stars, where stellar rotation velocities are generally small (see, for example, Gray 2005Gray , 2016Gray , 2017, and references therein), rotation is an important phenomenon affecting both the observational and theoretical understanding of early-type stars. Important observational studies of early-type stellar rotation in our Galaxy include Slettebak (1949), Conti & Ebbets (1977), Penny (1996), Howarth et al (1997), Abt et al (2002), Huang et al (2010) and Simón-Díaz & Herrero (2014).…”

Section: Introductionmentioning

confidence: 99%

The VLT-FLAMES Tarantula Survey

Dufton

Thompson

Crowther

et al. 2018

A&A

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Previous analyses of the spectra of OB-type stars in the Magellanic Clouds have identified targets with low projected rotational velocities and relatively high nitrogen abundances; the evolutionary status of these objects remains unclear. The VLT-FLAMES Tarantula Survey obtained spectroscopy for over 800 early-type stars in 30 Doradus of which 434 stars were classified as B-type. We have estimated atmospheric parameters and nitrogen abundances using TLUSTY model atmospheres for 54 B-type targets that appear to be single, have projected rotational velocities, ve sin i ≤ 80 km s−1 and were not classified as supergiants. In addition, nitrogen abundances for 34 similar stars observed in a previous FLAMES survey of the Large Magellanic Cloud have been re-evaluated. For both samples, approximately 75–80% of the targets have nitrogen enhancements of less than 0.3 dex, consistent with them having experienced only small amounts of mixing. However, stars with low projected rotational velocities, ve sini ≤ 40 km s−1 and significant nitrogen enrichments are found in both our samples and simulations imply that these cannot all be rapidly rotating objects observed near pole-on. For example, adopting an enhancement threshold of 0.6 dex, we observed five and four stars in our VFTS and previous FLAMES survey samples, yet stellar evolution models with rotation predict only 1.25 ± 1.11 and 0.26 ± 0.51 based on our sample sizes and random stellar viewing inclinations. The excess of such objects is estimated to be 20–30% of all stars with current rotational velocities of less than 40 km s−1. This would correspond to ~2–4% of the total non-supergiant single B-type sample. Given the relatively large nitrogen enhancement adopted, these estimates constitute lower limits for stars that appear inconsistent with current grids of stellar evolutionary models. Including targets with smaller nitrogen enhancements of greater than 0.2 dex implies larger percentages of targets that are inconsistent with current evolutionary models, viz. ~70% of the stars with rotational velocities less than 40 km s−1 and ~6–8% of the total single stellar population. We consider possible explanations of which the most promising would appear to be breaking due to magnetic fields or stellar mergers with subsequent magnetic braking.

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Section: Introductionmentioning

confidence: 99%

The VLT-FLAMES Tarantula Survey

Dufton

Thompson

Crowther

et al. 2018

A&A

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“…Whereas the gravitational redshift can easily be computed from the mass and radius of a star, the convective blueshift is still poorly understood. Useful references concerning this phenomenon are the papers of Gray (2016), Meunier et al (2017a,b), and Dai et al (2019).…”

Section: Conclusion and Prospectsmentioning

confidence: 99%

Spectroscopic and seismic analysis of red giants in eclipsing binaries discovered by Kepler

Benbakoura,

Gaulme,

McKeever

et al. 2021

Preprint

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Eclipsing binaries (EBs) are unique targets for measuring accurate stellar properties and constraining stellar evolution models. In particular, it is possible to measure masses and radii at the few percent level for both components of a double-lined spectroscopic EB (SB2-EB). On the one hand, detached EBs hosting at least one star with detectable solar-like oscillations constitute ideal test objects to verify the ability of ensemble asteroseismology to derive stellar properties. On the other hand, the oscillations and surface activity of stars that belong to EBs offer unique information about the evolution of binary systems. This paper builds upon previous works dedicated to red giant stars (RG) in EBs; so far 20 known systems have been discovered by the NASA Kepler mission. We report the discovery of 16 RGs in EBs, which are also from the Kepler data, leading to a total of 36 confirmed RG stars in EBs from the original Kepler mission. This new sample includes three SB2-EBs with oscillations, resulting in a total of 14 known SB2-EBs with an oscillating RG component. This sample also includes six close systems in which the RG display a clear surface activity and complete oscillation suppression. Based on dedicated high-resolution spectroscopic observations (Apache Point Observatory, Observatoire de Haute Provence), we focus on three main aspects. Firstly, from the extended sample of 14 SB2-EBs, we confirm that the simple application of the asteroseismic scaling relations to RGs overestimates masses and radii of RGs by about 15 % and 5 %. This bias can be reduced by employing either new asteroseismic reference values for RGs or model-based corrections of the asteroseismic parameters. Secondly, we confirm that close binarity leads to a high level of photometric modulation (up to 10 %) and a suppression of solar-like oscillations. In particular, we show that it reduces the lifetime of radial modes by a factor of up to 10. Thirdly, we use our 16 new systems to complement previous observational studies that aimed to constrain tidal dissipation in interacting binaries. We confirm the important role of the equilibrium tide in binary evolution, but we also identify systems with circular orbits despite relatively young ages, which suggests the need to explore complementary tidal dissipation mechanisms in the future. Finally, as a by-product, we report the measurements of mass, radius, and age of three M-dwarf companion stars.

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Stellar Rotation

2021

The Observation and Analysis of Stellar Photospheres

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Rotation and Granulation of the K2 Giant Α Ser

Cited by 10 publications

References 46 publications

The VLT-FLAMES Tarantula Survey

The VLT-FLAMES Tarantula Survey

Spectroscopic and seismic analysis of red giants in eclipsing binaries discovered by Kepler

Stellar Rotation

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