J/A+A/615/A139 3D non-LTE Balmer line formation (Amarsi+, 2018)
Effective temperature determinations of late-type stars based on 3D non-LTE
Balmer line formation.
Amarsi A.M., Nordlander T., Barklem P.S., Asplund M., Collet R., Lind K.
<Astron. Astrophys. 615, A139 (2018)>
=2018A&A...615A.139A 2018A&A...615A.139A (SIMBAD/NED BibCode)
ADC_Keywords: Models, atmosphere ; Line Profiles ; Effective temperatures ;
Stars, late-type
Keywords: radiative transfer - line: formation - line: profiles -
stars: atmospheres - stars: late-type
Abstract:
Hydrogen Balmer lines are commonly used as spectroscopic effective
temperature diagnostics of late-type stars. However, reliable
inferences require accurate model spectra, and the absolute accuracy
of classical methods that are based on one-dimensional (1D)
hydrostatic model atmospheres and local thermodynamic equilibrium
(LTE) is still unclear. To investigate this, we carry out 3D non-LTE
calculations for the Balmer lines, performed, for the first time, over
an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For
Hα, Hβ, and Hγ we find significant 1D non-LTE versus
3D non-LTE differences (3D effects): the outer wings tend to be
stronger in 3D models, particularly for Hγ, while the inner
wings can be weaker in 3D models, particularly for Hα. For
Hα, we also find significant 3D LTE versus 3D non-LTE
differences (non-LTE effects): in warmer stars (Teff≈6500K) the
inner wings tend to be weaker in non-LTE models, while at lower
effective temperatures (Teff≈4500K) the inner wings can be
stronger in non-LTE models; the non-LTE effects are more severe at
lower metallicities. We test our 3D non-LTE models against
observations of well-studied benchmark stars. For the Sun, we infer
concordant effective temperatures from Hα, Hβ, and
Hγ; however the value is too low by around 50K which could
signal residual modelling shortcomings. For other benchmark stars, our
3D non-LTE models generally reproduce the effective temperatures to
within 1σ uncertainties. For Hα, the absolute 3D effects
and non-LTE effects can separately reach around 100K, in terms of
inferred effective temperatures. For metal-poor turn-off stars, 1D LTE
models of Hα can underestimate effective temperatures by around
150K. Our 3D non-LTE model spectra are publicly available, and can be
used for more reliable spectroscopic effective temperature
determinations.
Description:
File lineprof.txt: contains emergent total (I) and continuum (Ic)
intensities at specific wavelengths (wl, or wl_air) and viewing angles
(mu), the latter with weights (wmu), for the model atmospheres with
different effective temperatures (Teff), surface gravities (lgg), and
iron abundance ratios ([Fe/H]). If rotational broadening and
instrumental broadening are to be neglected, the normalised flux can
be obtained via Sum(I * mu * wmu) / Sum(Ic * mu * wmu), at a given
wavelength and for a given model atmosphere.
File flux_3d.fits: contains a regular grid of normalised fluxes
constructed by interpolation/extrapolation of the data in
lineprof.txt. The fluxes are given for different effective
temperatures (Teff), surface gravities (lgg), iron abundance ratios
([Fe/H]), projected rotational velocity (vsini), Gaussian instrumental
profile velocity widths (vbroad), vacuum wavelengths (wl), and lines.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
lineprof.dat 99 309270 Raw line profiles
flux_3d.fits 2880 666670 Regular grid of line profiles
--------------------------------------------------------------------------------
Byte-by-byte Description of file: lineprof.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 K Teff Effective temperature
7- 10 F4.2 [cm/s2] logg Base 10 logarithm of surface gravity
12- 16 F5.2 --- [Fe/H] Iron abundance
18- 31 E14.8 Hz nu Frequency
34- 42 F9.5 nm wl Vacuum wavelength
45- 53 F9.5 nm wlair Air wavelength
55- 61 F7.5 --- mu Viewing angle
63- 69 F7.5 --- wmu Viewing angle weight
71- 84 E14.8 W/m/Hz Ic Continuum intensity
86- 99 E14.8 W/m/Hz I Intensity
--------------------------------------------------------------------------------
Acknowledgements:
Anish Mayur Amarsi, amarsi(at)mpia.de
(End) Patricia Vannier [CDS] 14-Jun-2018