46 research outputs found
Photospheric constraints, current uncertainties in models of stellar atmospheres, and spectroscopic surveys
We summarize here the discussions around photospheric constraints, current
uncertainties in models of stellar atmospheres, and reports on ongoing
spectroscopic surveys. Rather than a panorama of the state of the art, we chose
to present a list of open questions that should be investigated in order to
improve future analyses.Comment: Proc. of the workshop "Asteroseismology of stellar populations in the
Milky Way" (Sesto, 22-26 July 2013), Astrophysics and Space Science
Proceedings, (eds. A. Miglio, L. Girardi, P. Eggenberger, J. Montalban
The elemental composition of the Sun II. The iron group elements Sc to Ni
We redetermine the abundances of all iron group nuclei in the Sun, based on
neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar
spectrum. We employ a realistic 3D hydrodynamic model solar atmosphere,
corrections for departures from local thermodynamic equilibrium (NLTE),
stringent line selection procedures and high quality observational data. We
have scoured the literature for the best quality oscillator strengths,
hyperfine constants and isotopic separations available for our chosen lines. We
find , , ,
, , ,
and . Our uncertainties factor in both statistical
and systematic errors (the latter estimated for possible errors in the model
atmospheres and NLTE line formation). The new abundances are generally in good
agreement with the CI meteoritic abundances but with some notable exceptions.
This analysis constitutes both a full exposition and a slight update of the
preliminary results we presented in Asplund, Grevesse, Sauval & Scott
(arXiv:0909.0948), including full line lists and details of all input data we
employed.Comment: 10 figures, 24 pages + 10 online-only pages of tables. v2. Matches
version accepted by A&
The elemental composition of the Sun III. The heavy elements Cu to Th
We re-evaluate the abundances of the elements in the Sun from copper ()
to thorium (). Our results are mostly based on neutral and singly-ionised
lines in the solar spectrum. We use the latest 3D hydrodynamic solar model
atmosphere, and in a few cases also correct for departures from local
thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in
1D. In order to minimise statistical and systematic uncertainties, we make
stringent line selections, employ the highest-quality observational data and
carefully assess oscillator strengths, hyperfine constants and isotopic
separations available in the literature, for every line included in our
analysis. Our results are typically in good agreement with the abundances in
the most pristine meteorites, but there are some interesting exceptions. This
analysis constitutes both a full exposition and a slight update of the relevant
parts of the preliminary results we presented in Asplund, Grevesse, Sauval &
Scott (arXiv:0909.0948), including full line lists and details of all input
data that we have employed.Comment: 5 figures, 18 pages + 6 online-only pages of tables. v2. Matches
version accepted by A&
The elemental composition of the Sun I. The intermediate mass elements Na to Ca
The composition of the Sun is an essential piece of reference data for
astronomy, cosmology, astroparticle, space and geo-physics. This article,
dealing with the intermediate-mass elements Na to Ca, is the first in a series
describing the comprehensive re-determination of the solar composition. In this
series we severely scrutinise all ingredients of the analysis across all
elements, to obtain the most accurate, homogeneous and reliable results
possible. We employ a highly realistic 3D hydrodynamic solar photospheric
model, which has successfully passed an arsenal of observational diagnostics.
To quantify systematic errors, we repeat the analysis with three 1D hydrostatic
model atmospheres (MARCS, MISS and Holweger & M\"{u}ller 1974) and a
horizontally and temporally-averaged version of the 3D model
(3D). We account for departures from LTE wherever possible.
We have scoured the literature for the best transition probabilities, partition
functions, hyperfine and other data, and stringently checked all observed
profiles for blends. Our final 3D+NLTE abundances are:
,
,
,
,
, , and
. The uncertainties include both
statistical and systematic errors. Our results are systematically smaller than
most previous ones with the 1D semi-empirical Holweger & M\"uller model. The
3D model returns abundances very similar to the full 3D
calculations. This analysis provides a complete description and a slight update
of the Na to Ca results presented in Asplund, Grevesse, Sauval & Scott
(arXiv:0909.0948), with full details of all lines and input data.Comment: 7 figures, 14 pages + 5 online-only pages of tables and an appendix.
v2. Matches version accepted by A&
The solar carbon, nitrogen, and oxygen abundances from a 3D LTE analysis of molecular lines
peer reviewedCarbon, nitrogen, and oxygen are the fourth, sixth, and third most abundant elements in the Sun. Their abundances remain hotly debated due to the so-called solar modelling problem that has persisted for almost 20 years. We revisit this issue by presenting a homogeneous analysis of 408 molecular lines across 12 diagnostic groups, observed in the solar intensity spectrum. Using a realistic 3D radiative-hydrodynamic model solar photosphere and local thermodynamic equilibrium (LTE) line formation, we find log ? C = 8.47 ± 0.02, log ? N = 7.89 ± 0.04, and log ? O = 8.70 ± 0.04. The stipulated uncertainties mainly reflect the sensitivity of the results to the model atmosphere; this sensitivity is correlated between the different diagnostic groups, which all agree with the mean result to within 0.03 dex. For carbon and oxygen, the molecular results are in excellent agreement with our 3D non-LTE analyses of atomic lines. For nitrogen, however, the molecular indicators give a 0.12 dex larger abundance than the atomic indicators, and our best estimate of the solar nitrogen abundance is given by the mean: 7.83 dex. The solar oxygen abundance advocated here is close to our earlier determination of 8.69 dex, and so the present results do not significantly alleviate the solar modelling problem. © ESO 2021
On the solar nickel and oxygen abundances
Determinations of the solar oxygen content relying on the neutral forbidden
transition at 630 nm depend upon the nickel abundance, due to a Ni I blend.
Here we rederive the solar nickel abundance, using the same ab initio 3D
hydrodynamic model of the solar photosphere employed in the recent revision of
the abundances of C, N, O and other elements. Using 17 weak, unblended lines of
Ni I together with the most accurate atomic and observational data available we
find log epsilon_Ni = 6.17 +/- 0.02 (statistical) +/- 0.05 (systematic), a
downwards shift of 0.06 to 0.08 dex relative to previous 1D-based abundances.
We investigate the implications of the new nickel abundance for studies of the
solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun.
Furthermore, we demonstrate that the oxygen abundance implied by the recent
sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be
revised downwards from log epsilon_O = 8.86 +/- 0.07 to 8.71 +/- 0.10. This
revision is based on the new nickel abundance, application of the best
available gf-value for the 630 nm forbidden oxygen line, and a more transparent
treatment of CO formation. Determinations of the solar oxygen content relying
on forbidden lines now appear to converge around log epsilon_O = 8.7.Comment: v2 matches published versio
The solar carbon, nitrogen, and oxygen abundances from a 3D LTE analysis of molecular lines
peer reviewedCarbon, nitrogen, and oxygen are the fourth, sixth, and third most abundant elements in the Sun. Their abundances remain hotly debated due to the so-called solar modelling problem that has persisted for almost 20 years. We revisit this issue by presenting a homogeneous analysis of 408 molecular lines across 12 diagnostic groups, observed in the solar intensity spectrum. Using a realistic 3D radiative-hydrodynamic model solar photosphere and local thermodynamic equilibrium (LTE) line formation, we find log ? C = 8.47 ± 0.02, log ? N = 7.89 ± 0.04, and log ? O = 8.70 ± 0.04. The stipulated uncertainties mainly reflect the sensitivity of the results to the model atmosphere; this sensitivity is correlated between the different diagnostic groups, which all agree with the mean result to within 0.03 dex. For carbon and oxygen, the molecular results are in excellent agreement with our 3D non-LTE analyses of atomic lines. For nitrogen, however, the molecular indicators give a 0.12 dex larger abundance than the atomic indicators, and our best estimate of the solar nitrogen abundance is given by the mean: 7.83 dex. The solar oxygen abundance advocated here is close to our earlier determination of 8.69 dex, and so the present results do not significantly alleviate the solar modelling problem. © ESO 2021
The solar chemical composition
We review our current knowledge of the solar chemical composition as
determined from photospheric absorption lines. In particular we describe the
recent significant revisions of the solar abundances as a result of the
application of a time-dependent, 3D hydrodynamical model of the solar
atmosphere instead of 1D hydrostatic models. This has decreased the metal
content in the solar convection zone by almost a factor of two compared with
the widely used compilation by Anders & Grevesse (1989). While resolving a
number of long-standings problems, the new 3D-based element abundances also
pose serious challenges, most notably for helioseismology.Comment: Invited review presented at "Cosmic abundances as records of stellar
evolution and nucleosynthesis", F.N. Bash & T.G Barnes(editors). ASP conf.
series, in press. The html-version of the talk is available at
http://www.mso.anu.edu.au/~martin/talks/Lambert0
The internal rotation of the Sun and its link to the solar Li and He surface abundances
peer reviewedThe Sun serves as a natural reference for the modelling of the various physical processes at work in stellar interiors. Helioseismology results, which inform us on the characterization of the interior of the Sun (such as, for example, the helium abundance in its envelope), are, however, at odds with heavy element abundances. Moreover, the solar internal rotation and surface abundance of lithium have always been challenging to explain. We present results of solar models that account for transport of angular momentum and chemicals by both hydrodynamic and magnetic instabilities. We show that these transport processes reconcile the internal rotation of the Sun, its surface lithium abundance, and the helioseismic determination of the envelope helium abundance. We also show that the efficiency of the transport of chemicals required to account for the solar surface lithium abundance also predicts the correct value of helium, independently from a specific transport process. © 2022, The Author(s), under exclusive licence to Springer Nature Limited