The photospheric solar oxygen project

Caffau, E.; Ludwig, H.‐G.; Steffen, M.; Livingston, W.; Bonifacio, P.; Malherbe, J.-M.; Doerr, Hans-Peter; Schmidt, W.

doi:10.1051/0004-6361/201526331

Cited by 32 publications

(28 citation statements)

References 40 publications

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“…Green symbols show the predictions for N OVIII (square) and N OVII (star) of pSIS models at r 200 . Grey shading shows the range of Milky-Way N OVII observations compiled by Miller & Bregman (2013 (Caffau et al 2015) as a standard.…”

Section: Assumptions About Abundancesmentioning

confidence: 99%

Ambient Column Densities of Highly Ionized Oxygen in Precipitation-limited Circumgalactic Media

Voit

2019

ApJ

105

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Many of the baryons associated with a galaxy reside in its circumgalactic medium (CGM), in a diffuse volume-filling phase at roughly the virial temperature. Much of the oxygen produced over cosmic time by the galaxy's stars also ends up there. The resulting absorption lines in the spectra of UV and X-ray background sources are powerful diagnostics of the feedback processes that prevent more of those baryons from forming stars. This paper presents predictions for CGM absorption lines (O VI, O VII, O VIII, Ne VIII, N V) that are based on precipitation-regulated feedback models, which posit that the radiative cooling time of the ambient medium cannot drop much below 10 times the freefall time without triggering a strong feedback event. The resulting predictions align with many different observational constraints on the Milky Way's ambient CGM and explain why N OVI ≈ 10 14 cm −2 over large ranges in halo mass and projected radius. Within the precipitation framework, the strongest O VI absorption lines result from vertical mixing of the CGM that raises low-entropy ambient gas to greater altitudes, because adiabatic cooling of the uplifted gas then lowers its temperature and raises the fractional abundance of O 5+ . Condensation stimulated by uplift may also produce associated lowionization components. The observed velocity structure of the O VI absorption suggests that galactic outflows do not expel circumgalactic gas at the halo's escape velocity but rather drive circulation that dissipates much of the galaxy's supernova energy within the ambient medium, causing some of it to expand beyond the virial radius.

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Section: Assumptions About Abundancesmentioning

confidence: 99%

Ambient Column Densities of Highly Ionized Oxygen in Precipitation-limited Circumgalactic Media

Voit

2019

ApJ

105

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“…Since the impact of S H depends systematically on the depth of line formation and therefore on μ, the variation of the spectral lines with disk position adds another dimension to the analysis and helps to constrain the problem. Following a similar idea, Caffau et al (2015) utilized the center-to-limb variation of the oxygen and nickel blend at 630 nm to separate the contribution of the individual elements. We make use of the following three independent observational data sets:…”

Section: Observationsmentioning

confidence: 99%

The photospheric solar oxygen project

Steffen

Prakapavičius

Caffau

et al. 2015

A&A

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111

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Context. The solar photospheric oxygen abundance is still widely debated. Adopting the solar chemical composition based on the "low" oxygen abundance, as determined with the use of three-dimensional (3D) hydrodynamical model atmospheres, results in a well-known mismatch between theoretical solar models and helioseismic measurements that is so far unresolved. Aims. We carry out an independent redetermination of the solar oxygen abundance by investigating the center-to-limb variation of the O i IR triplet lines at 777 nm in different sets of spectra.Methods. The high-resolution and high signal-to-noise solar center-to-limb spectra are analyzed with the help of detailed synthetic line profiles based on 3D hydrodynamical CO5BOLD model atmospheres and 3D non-LTE line formation calculations with NLTE3D. The idea is to exploit the information contained in the observations at different limb angles to simultaneously derive the oxygen abundance, A(O), and the scaling factor S H that describes the cross-sections for inelastic collisions with neutral hydrogen relative to the classical Drawin formula. Using the same codes and methods, we compare our 3D results with those obtained from the semiempirical Holweger-Müller model atmosphere as well as from different one-dimensional (1D) reference models. Results. With the CO5BOLD 3D solar model, the best fit of the center-to-limb variation of the triplet lines is obtained when the collisions by neutral hydrogen atoms are assumed to be efficient, i.e., when the scaling factor S H is between 1.2 and 1.8, depending on the choice of the observed spectrum and the triplet component used in the analysis. The line profile fits achieved with standard 1D model atmospheres (with fixed microturbulence, independent of disk position μ) are clearly of inferior quality compared to the 3D case, and give the best match to the observations when ignoring collisions with neutral hydrogen (S H = 0). The results derived with the Holweger-Müller model are intermediate between 3D and standard 1D. Conclusions. The analysis of various observations of the triplet lines with different methods yields oxygen abundance values (on a logarithmic scale where A(H) = 12) that fall in the range 8.74 < A(O) < 8.78, and our best estimate of the 3D non-LTE solar oxygen abundance is A(O) = 8.76 ± 0.02. All 1D non-LTE models give much lower oxygen abundances, by up to −0.15 dex. This is mainly a consequence of the assumption of a μ-independent microturbulence. An independent determination of the relevant collisional cross-sections is essential to substantially improve the accuracy of the oxygen abundance derived from the O i IR triplet.

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“…These observations of narrow spectral ranges can be used to target specific spectral lines, for instance for chemical abundance analysis (e.g. Kiselman 1994;Pereira et al 2009;Caffau et al 2015), but many of the applications mentioned above rely instead on a broad-band highquality reference spectrum.…”

Section: Introductionmentioning

confidence: 99%

How different are the Liège and Hamburg atlases of the solar spectrum?

Doerr

Vitas

Fabbian

2016

A&A

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Context. The high-fidelity solar spectral atlas prepared by Delbouille et al. (Liège atlas, 1973) and the atlas by Neckel (Hamburg atlas, 1999, Sol. Phys., 184, 421) are widely recognised as the most important collection of reference spectra of the Sun at disc centre in the visible wavelength range. The two datasets serve as fundamental resources for many researchers, in particular for chemical abundance analyses. But despite their similar published specifications (spectral resolution and noise level), the shapes of the spectral lines in the two atlases differ significantly and systematically. Aims. Knowledge of any instrumental degradations is imperative to fully exploit the information content of spectroscopic data. We seek to investigate the magnitude of these differences and explain the possible sources. We provide the wavelength-dependent correction parameters that need to be taken into account when the spectra are to be compared with synthetic data, for instance. Methods. A parametrically degraded version of the Hamburg spectrum was fitted to the Liège spectrum. The parameters of the model (wavelength shift, broadening, intensity scaling, and intensity offset) represent the different characteristics of the respective instruments, observational strategies, and data processing. Results. The wavelength scales of the Liège and Hamburg atlases differ on average by 0.5 mÅ with a standard deviation of ±2 mÅ, except for a peculiar region around 5500 Å. The continuum levels are offset by up to 18% below 5000 Å, but remain stably at a 0.8% difference towards the red. We find no evidence for spectral stray light in the Liège spectrum. Its resolving power is almost independent of wavelength but limited to about 216 000, which is between two to six times lower than specified. When accounting for the degradations determined in this work, the spectra of the two atlases agree to within a few parts in 10 3 .

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The photospheric solar oxygen project

Cited by 32 publications

References 40 publications

Ambient Column Densities of Highly Ionized Oxygen in Precipitation-limited Circumgalactic Media

Ambient Column Densities of Highly Ionized Oxygen in Precipitation-limited Circumgalactic Media

The photospheric solar oxygen project

How different are the Liège and Hamburg atlases of the solar spectrum?

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