Radiative hydrodynamics simulations of red supergiant stars

Chiavassa, A.; Haubois, X.; Young, John S.; Plez, B.; Josselin, E.; Perrin, G.; Freytag, B.

doi:10.1051/0004-6361/200913907

Cited by 124 publications

(146 citation statements)

References 31 publications

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“…Inhomogeneous distributed granulation cells, on the other hand, could produce low-contrast dark and bright spots and lanes. This was shown in box simulations of rotating magneto-convection by Ziegler (2002) as well as for pure hydrodynamical simulations of rotating stars with very large pressure scale heights, e.g., for the M supergiant Betelgeuse by Steffen & Freytag (2007) and Chiavassa et al (2010). Granulation on giant stars was simulated and discussed just recently by Tremblay et al (2013).…”

Section: Discussionmentioning

confidence: 80%

Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

Strassmeier

Carroll

Weber

et al. 2015

A&A

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Context. HD 233517 is among the most Li-rich stars in the sky. It is a rapidly rotating, single K giant thought to be on its first ascent on the red giant branch. The star has also the highest known infrared excess among any of the known first-ascent giants. Aims. We revisit the physical parameters of the system and aim to map its surface temperature distribution. Methods. New time-series photometry and high-resolution spectroscopy were obtained with our robotic facilities STELLA and Amadeus Automatic Photoelectric Telescope (APT) in 2007-2011. Inverse line-profile modelling is performed on a total of 167 échelle spectra and six Doppler images are presented.Results. Light and radial-velocity variations suggest a stellar rotation period of 47.6 ± 0.3 d. The atmospheric parameters agree with previous studies and verify a super-meteoritic log 7 Li abundance of 4.29 ± 0.10 with undetected 6 Li, while the metals are generally deficient by -0.4 dex with respect to the Sun. We determine a lower than normal isotopic carbon ratio of 12 C/ 13 C = 9 +4 −2 . Our Doppler images indicate warm and cool spots with an average temperature contrast of just ±65 K with respect to the effective temperature.Doppler maps from Li i 670.78 reveal practically identical surface morphology, with a higher average contrast of ±160 K and errors that are five times larger. Reconstructions with simultaneously 1617 and 3007 spectral lines showed both a signal degradation with respect to our 56-line final image. An error analysis indicates an average temperature error per surface pixel of just ±4 K. Conclusions. HD 233517 appears to be an old (≈10-Gyr) single 0.95-M giant currently undergoing mild mass loss in the form of a wind. The cool and warm photospheric features are interpreted to be merely locations of suppressed and enhanced convection, respectively, probably intermingled by a yet undetected weak magnetic field. The low carbon-isotope ratio is indicative of extra mixing rather than of an engulfing event. We tentatively conclude that HD 233517 operates an enhanced non-axisymmetric mixing process that leads to an inhomogeneous super-granulation pattern on the surface in form of large cool and warm features.

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Section: Discussionmentioning

confidence: 80%

Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

Strassmeier

Carroll

Weber

et al. 2015

A&A

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“…This is due to the small scale structure on the model stellar disk shown in Chiavassa et al (2010). This frequency range corresponds to surface structures of 2.27−2.94 R or 1500−2200 Mm, approximatively the size of one of the granules as shown in Fig.…”

Section: Visibility Curvesmentioning

confidence: 87%

“…Quirrenbach 2001, andChiavassa et al 2010 for an application to RHD simulations). In fact, the radius of Table 1 can be estimated using…”

Section: Visibility Curvesmentioning

confidence: 99%

Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for interpreting interferometric observations

Chiavassa¹,

Collet²,

Casagrande³

et al. 2010

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Context. Theoretical predictions from models of red giant branch stars are a valuable tool for various applications in astrophysics ranging from galactic chemical evolution to studies of exoplanetary systems. Aims. We use the radiative transfer code Optim3D and realistic 3D radiative-hydrodynamical (RHD) surface convection simulations of red giants to explore the impact of granulation on interferometric observables. We assess how 3D simulations of surface convection can be validated against observations. Methods. We computed intensity maps for the 3D simulation snapshots in two filters, the optical at 5000 ± 300 Å and the K band 2.14±0.26 μm FLUOR filter, corresponding to the wavelength-range of instruments mounted on the CHARA interferometer. From the intensity maps, we constructed images of the stellar disks and account for center-to-limb variations. We then derived interferometric visibility amplitudes and phases. We study their behavior with position angle and wavelength, and compare them with CHARA observations of the red giant star HD 214868. Results. We provide average limb darkening coefficients for different metallicities and wavelengths ranges. We explain prospects for detecting and characterizing granulation and center-to-limb variations of red giant stars with today's interferometers. Regarding interferometric observables, we find that the effect of convective-related surface structures depends on metallicity and surface gravity. We provide theoretical closure-phases that should be incorporated into the analysis of red giant planet companion closure phase signals. We estimate 3D−1D corrections to stellar radii determination: 3D models are ∼3.5% smaller to ∼1% larger in the optical than 1D, and roughly 0.5 to 1.5% smaller in the infrared. Even if these corrections are small, they are needed to properly set the zero point of effective temperature scale derived by interferometry and to strengthen the confidence of existing red giant catalogs of calibrating stars for interferometry. Finally, we show that our RHD simulations provide an excellent fit to the red giant HD 214868 even though more observations are needed at higher spatial frequencies and shorter wavelength.

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“…On the other hand, we also tried the higher resolution simulation (401 3 grid points) st36gm00n05 (also in Table 5). We considered several snapshots for each simulation and computed intensity maps in the wavelength range 1.90−2.60 μm with a constant Chiavassa et al (2009Chiavassa et al ( , 2010bChiavassa et al ( , 2011b. (b) Chiavassa et al (2011a).…”

Section: D Rhd Simulationsmentioning

confidence: 99%

What causes the large extensions of red supergiant atmospheres?

Arroyo-Torres

Wittkowski²,

Chiavassa

et al. 2015

A&A

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108

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Aims. This research has two main goals. First, we present the atmospheric structure and the fundamental parameters of three red supergiants (RSGs), increasing the sample of RSGs observed by near-infrared spectro-interferometry. Additionally, we test possible mechanisms that may explain the large observed atmospheric extensions of RSGs. Methods. We carried out spectro-interferometric observations of the RSGs V602 Car, HD 95687, and HD 183589 in the near-infrared K-band (1.92−2.47 μm) with the VLTI/AMBER instrument at medium spectral resolution (R ∼ 1500). To categorize and comprehend the extended atmospheres, we compared our observational results to predictions by available hydrostatic PHOENIX, available 3D convection, and new 1D self-excited pulsation models of RSGs. Results. Our near-infrared flux spectra of V602 Car, HD 95687, and HD 183589 are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models, allowing us to determine the angular diameter and the fundamental parameters of our sources. Nonetheless, in the case of V602 Car and HD 95686, the PHOENIX model visibilities do not predict the large observed extensions of molecular layers, most remarkably in the CO bands. Likewise, the 3D convection models and the 1D pulsation models with typical parameters of RSGs lead to compact atmospheric structures as well, which are similar to the structure of the hydrostatic PHOENIX models. They can also not explain the observed decreases in the visibilities and thus the large atmospheric molecular extensions. The full sample of our RSGs indicates increasing observed atmospheric extensions with increasing luminosity and decreasing surface gravity, and no correlation with effective temperature or variability amplitude. Conclusions. The location of our RSG sources in the Hertzsprung-Russell diagram is confirmed to be consistent with the red limits of recent evolutionary tracks. The observed extensions of the atmospheric layers of our sample of RSGs are comparable to those of Mira stars. This phenomenon is not predicted by any of the considered model atmospheres including available 3D convection and new 1D pulsation models of RSGs. This confirms that neither convection nor pulsation alone can levitate the molecular atmospheres of RSGs. Our observed correlation of atmospheric extension with luminosity supports a scenario of radiative acceleration on Doppler-shifted molecular lines.

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Radiative hydrodynamics simulations of red supergiant stars

Cited by 124 publications

References 31 publications

Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for interpreting interferometric observations

What causes the large extensions of red supergiant atmospheres?

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