New light on stellar abundance analyses: Departures from LTE and homogeneity.

By Martin Asplund. 2005

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View Paper: https://www.semanticscholar.org/paper/9e1914ca6d1b5d17bdcb87a85de507ad8061eb98

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In Astronomy and Astrophysics

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BPASS predictions for binary black hole mergers (2016, background): “…example, suggest the metal fraction in the Sun is rather higher than usually assumed, while some authors (Allende Prieto, Lambert, & Asplund 2002; Asplund 2005) suggest that Solar metal abundances should be revised downwards to closer to Z = 0.014 (also appropriate for massive stars within 500pc…”
An absolutely calibrated T eff scale from the infrared flux method. Dwarfs and subgiants (2010, background): “For H lines uncertainties related to observations and line broadening (Barklem et al. 2002), non-LTE (Barklem 2007) and granulation effects (Asplund 2005; Ludwig et al. 2009; Pereira et al. 2009) all influence the estimation of eff ctive temperatures.”
The GALAH+ survey: Third data release (2020, background): “…observed by HERMES per star with reliable line information for spectrum synthesis instead and include even more grids for an accurate computation of line strengths when the conditions depart from local thermodynamic equilibrium (LTE; e.g. Mihalas & Athay 1973; Asplund 2005; Amarsi et al. 2020).”
The s process: Nuclear physics, stellar models, and observations (2010, background): “…has made spectacular progress over the last decades by the deployment of new telescopes on the ground and in space and by the impressive increase in computing power, that led to enormous improvement in the modeling of stellar atmospheres and in synthetic spectrum calculations (Asplund, 2005).”
A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, methodology): “This non-LTE effect can lead to systematic underestimates of the Fe i number density when using the LTE approximation for the source function in metal-poor stars (e.g., Thévenin & Idiart 1999, Asplund 2005).”
Non-LTE line formation of Fe in late-type stars - II. 1D spectroscopic stellar parameters (2012, background): “The efficiency of excitation and ionisation (and charge exchange reactions) induced by collisions with neutral hydrogen is commonly the largest source of uncertainty in statistical equilibrium calculations for late-type stars (see discussion in e.g. Asplund 2005).”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, methodology): “These effects (differences in the slopes of linear fits to [X/Fe] vs. [Fe/H] between dwarfs and giants, differences in mean abundances between dwarfs and giants, and trends between [X/Fe] vs.Teff) likely signify the presence of non-LTE and/or 3D effects (Asplund 2005).”
The elemental composition of the Sun - I. The intermediate mass elements Na to Ca (2014, methodology): “…atmospheric modelling, detailed calculations of line formation including departures from local thermodynamic equilibrium (non-LTE or NLTE; see e.g. Asplund 2005), the most up-to-date atomic and molecular input data available, and an extremely stringent selection of photospheric absorption lines…”
GALACTIC CHEMICAL EVOLUTION AND SOLAR s-PROCESS ABUNDANCES: DEPENDENCE ON THE 13C-POCKET STRUCTURE (2014, background): “Since 1989, C, N, and O abundances have been steadily revised downward thanks to progress in atmospheric models (see, e.g., Asplund 2005), partially affecting the isotopic mass fraction of heavier isotopes.11 Moreover, the photospheric abundances observed today are different from those existing at…”
Improvements to stellar structure models, based on a grid of 3D convection simulations. II. Calibrating the mixing-length formulation (2014, background): “Instead it reflects the larger super-adiabatic gradient of the warm granules, which dominate the emergent spectrum, including the Balmer lines, due to their brightness (Asplund 2005; Trampedach 2010).”
The Solar Chemical Composition (2004, methodology): “These stellar abundances could be severely biased because of the use of theoretical 1D models instead of 3D models (Asplund 2005).”
A Spectroscopic Study of the Ancient Milky Way: F- and G-Type Stars in the Third Data Release of the Sloan Digital Sky Survey (2005, background): “Accurate analysis of relative chemical abundances is now routinely possible for F- and G-type stars within the framework of classical one-dimensional model atmospheres (but see, e.g., Asplund 2005 for caveats).”
The Hamburg/ESO R-process enhanced star survey (HERES) - III. HE 0338-3945 and the formation of the r + s stars (2006, background): “The abundance may be even higher, as∆NLTE is probably greater than+0.1 (Asplund 2005).”
Gaia FGK benchmark stars: Metallicity (2013, background): “NLTE effects can change significantly the metallicity of metal-poor stars (Thévenin & Idiart 1999; Asplund 2005).”
High-precision abundances of elements in solar twin stars - Trends with stellar age and elemental condensation temperature (2015, background): “This line is , however, sensitive to 3D hydrodynamical (granulation) effects on the temperature structure of the stellar atmosphere (Asplund 2005).”
The elemental composition of the Sun - III. The heavy elements Cu to Th (2014, background): “…elements however, perhaps the biggest reason for the dearth of NLTE analyses is a lack of necessary atomic data such as photo-ionisation cross-sections, transition probabilities and collisional rates for the many relevant atomic processes in what are often highly complicated atoms (Asplund 2005).”
Quantifying the uncertainties of chemical evolution studies II. Stellar yields (2010, background): “3, stars) should be given a lower weight, because unaccounted 3D effects likely affect the carbon molecular lines employed in the analysis (Asplund 2005).”
Accurate abundance patterns of solar twins and analogs - Does the anomalous solar chemical composition come from planet formation? (2009, background): “%) to the accuracy of abundance determinations (e.g., Asplund 2005).”
Precise radial velocities of giant stars. III. Spectroscopic stellar parameters (2007, background): “Finally, caution should be taken when comparing dwarfs with giants, since systematic errors are expected due to differences in their atmospheric structures and parameters (Asplund 2005).”