标题：An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres - I. Formation of the G-band in metal-poor dwarf stars
其他标题：I. Formation of the G-band in metal-poor dwarf
stars
摘要：Context. Recent developments in the three-dimensional (3D) spectral
synthesis code Linfor3D have meant that for the first time, large spectral wavelength
regions, such as molecular bands, can be synthesised with it in a short amount of time.
Aims. A detailed spectral analysis of the synthetic
G-band for several dwarf turn-off-type 3D atmospheres
(5850 ≲ Teff [ K
] ≲ 6550, 4.0 ≤
log g ≤ 4.5, − 3.0 ≤ [Fe/H] ≤−1.0) was conducted,
under the assumption of local thermodynamic equilibrium. We also examine carbon and oxygen
molecule formation at various metallicity regimes and discuss the impact it has on the
G-band.
Methods. Using a qualitative approach, we describe the different
behaviours between the 3D atmospheres and the traditional one-dimensional (1D) atmospheres
and how the different physics involved inevitably leads to abundance corrections, which
differ over varying metallicities. Spectra computed in 1D were fit to every 3D spectrum to
determine the 3D abundance correction.
Results. Early analysis revealed that the CH molecules that make up the
G-band
exhibited an oxygen abundance dependency; a higher oxygen abundance leads to weaker CH
features. Nitrogen abundances showed zero impact to CH formation. The 3D corrections are
also stronger at lower metallicity. Analysis of the 3D corrections to the G-band allows us to assign
estimations of the 3D abundance correction to most dwarf stars presented in the
literature.
Conclusions. The 3D corrections suggest that A(C) in carbon-enhanced
metal-poor (CEMP) stars with high A(C) would remain unchanged, but would decrease in
CEMP stars with lower A(C). It was found that the C/O ratio is an important
parameter to the G-band in 3D. Additional testing confirmed that the
C/O ratio is an equally important parameter for OH transitions under 3D. This presents a
clear interrelation between the carbon and oxygen abundances in 3D atmospheres through
their molecular species, which is not seen in 1D.
