Improving 1D stellar atmosphere models with insights from multi-dimensional simulations I. 1D vs 2D stratifications and spectral comparison for O stars

Abstract

We compare current 1D and multi-dimensional atmosphere modelling approaches for massive stars to understand their strengths and shortcomings. We calculate averaged stratifications from selected 2D calculations for O stars -- corresponding to the spectral types O8, O4, and O2 -- to approximate them with 1D stellar atmosphere models using the PoWR model atmosphere code and assuming a fixed $\beta -$law for the wind regime. We then study the effects of our approximations and assumptions on current spectral diagnostics. In particular, we focus on the impact of an additional turbulent pressure in the subsonic layers of the 1D models. To match the 2D averages, the 1D stellar atmosphere models need to account for turbulent pressure in the hydrostatic equation. Moreover, an adjustment of the connection point between the (quasi-)hydrostatic regime and the wind regime is required. The improvement between the density stratification of 1D model and 2D average can be further increased if the mass-loss rate of the 1D model is not identical to those of the 2D simulation, but typically $\sim 0.2$dex higher. Especially for the early type star, this implies a significantly more extended envelope with a lower effective temperature. Already the inclusion of a constant turbulence term in the solution of the hydrostatic equation sufficiently reproduces the 2D-averaged model density stratifications. The addition of a significant turbulent motion also smoothens the slope of the radiative acceleration term in the (quasi-)hydrostatic domain, with several potential implications on the total mass-loss rate inferred from 1D modelling. Concerning the spectral synthesis, the addition of a turbulence term in the hydrostatic equation mimics the effect of a lower surface gravity, potentially presenting a solution to the ``mass discrepancy problem'' between the evolutionary and spectroscopy mass determinations.

Accepted for publication in A&A

References in corpus (42)

• The chemical composition of the Sun
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones
• Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. II. Line-Blanketed Models
• Quantitative Spectroscopy of O Stars at Low Metallicity. O Dwarfs in NGC 346
• Sub-surface convection zones in hot massive stars and their observable consequences
• A coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, $\delta$ Orionis Aa: IV. A multiwavelength, non-LTE spectroscopic analysis
• MPI-AMRVAC 2.0 for Solar and Astrophysical Applications
• Properties of Galactic early-type O-supergiants: A combined FUV-UV and optical analysis
• On the nature of massive helium star winds and Wolf-Rayet-type mass loss
• Local Radiation Hydrodynamic Simulations of Massive Star Envelopes at the Iron Opacity Peak
• On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
• The IACOB project: III. New observational clues to understand macroturbulent broadening in massive O- and B-type stars
• L-band spectroscopy of Galactic OB-stars
• Mass loss from inhomogeneous hot star winds I. Resonance line formation in 2D models
• Analysis of Galactic late-type O dwarfs: more constraints on the weak wind problem
• Coupling hydrodynamics with comoving frame radiative transfer: I. A unified approach for OB and WR stars
• 2D wind clumping in hot, massive stars from hydrodynamical line-driven instability simulations using a pseudo-planar approach
• The VLT-FLAMES Tarantula Survey XXIV. Stellar properties of the O-type giants and supergiants in 30 Doradus
• Spectroscopic and physical parameters of Galactic O-type stars. III. Mass discrepancy and rotational mixing
• 2D Simulations of the Line-Driven Instability in Hot-Star Winds: II. Approximations for the 2D Radiation Force
• PoWR grids of non-LTE model atmospheres for OB-type stars of various metallicities
• 3-D radiative transfer in clumped hot star winds I. Influence of clumping on the resonance line formation
• New predictions for radiation-driven, steady-state mass-loss and wind-momentum from hot, massive stars. I. Method and first results
• X-Shooting ULLYSES: massive stars at low metallicity. I. Project Description
• First 3D Radiation-Hydrodynamic Simulations of Wolf-Rayet Winds
• Empirical mass-loss rates and clumping properties of Galactic early-type O supergiants
• The temperature dependency of Wolf-Rayet-type mass loss: An exploratory study for winds launched by the hot iron bump
• Very Massive Stars and Pair-Instability Supernovae: Mass-loss Framework for low Metallicity
• Stochastic Low Frequency Variability in 3-Dimensional Radiation Hydrodynamical Models of Massive Star Envelopes
• The stellar and wind parameters of six prototypical HMXBs and their evolutionary status
• Global hot-star wind models for stars from Magellanic Clouds
• Radiation-Hydrodynamics with MPI-AMRVAC: Flux-Limited Diffusion
• Stellar population of the superbubble N206 in the LMC I. Analysis of the Of-type stars
• Quantitative spectroscopy of B-type supergiants
• Quantitative spectroscopy of late O-type main-sequence stars with a hybrid non-LTE method
• X-Shooting ULLYSES: Massive Stars at low metallicity IX: Empirical constraints on mass-loss rates and clumping parameters for OB supergiants in the Large Magellanic Cloud
• 3D radiative transfer: Continuum and line scattering in non-spherical winds from OB stars
• X-Shooting ULLYSES: Massive stars at low metallicity. IV. Spectral analysis methods and exemplary results for O stars
• Method and new tabulations for flux-weighted line-opacity and radiation line-force in supersonic media
• Exploring the influence of different velocity fields on Wolf-Rayet star spectra
• To clump or not to clump The impact of wind inhomogeneities on the optical and NIR spectroscopic analysis of massive OB stars

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