Nicolas Grevesse on the Solar Chemical Composition
Emerging Research Front Commentary, December 2010
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Article: The solar chemical composition
Authors: Grevesse, N;Asplund, M;Sauval,
AJ |
Nicolas Grevesse talks with ScienceWatch.com and answers a few questions about this month's Emerging Research Front paper in the field of Space Science.
Why do you think your paper(s) are highly
cited?
This paper, as well as several other more highly cited papers I have published over the years, is an invited review paper essentially containing new results. In these review papers we also give the main reasons why the new results are different from the previous ones as well as the main impacts of these new results in various fields of astrophysics. Details concerning these new results are published separately in more technical papers.
One of the main reasons for their success is also that the solar chemical composition is a real STANDARD for all fields of astrophysics. Changing the standard as we do thus has important impacts in many different fields. The success is shared by my highly qualified collaborators, Jacques Sauval, Arlette Noels-Grötsch, Martin Asplund, Pat Scott, and many others who contributed to the quality of the technical papers.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
"We expect progress in the accuracy of the solar results based on our progress in the modeling of the solar outer layers, but mostly of the physical processes of formation of the spectral lines present in the spectrum of the solar light."
The latest papers present new values, new methodologies, as well as synthesis of knowledge.
Would you summarize the significance of your
papers in laymen’s terms?
In astrophysics, we are forced to make models because we cannot travel to a star, visit the interstellar medium, etc. The first data we have to know to make a model of these objects is, of course, its chemical composition. That is what we provide to the astrophysicists with the solar chemical composition, since our Sun is, as we already mentioned above, the standard for the composition of most of the celestial bodies.
How did you become involved in this research, and
how would describe the particular challenges, setbacks, and successes
that you have encountered along the way?
I became involved in solar spectroscopy and the solar abundance business a long time ago. Actually I started my research activities in a group at the University of Liège (Belgium) that was involved in recording very high-quality solar spectra in the visible and infrared from the high elevation (3580m) International Scientific Station of the Jungfraujoch in the Swiss Alps near to Interlaken (Switzerland). These data are still considered as standard and among the best available nowadays. I was asked to interpret these high-quality spectra and this is how I started to be involved in the solar chemical composition and the associated model of the solar photosphere, the physical processes in these layers, and the required atomic and molecular data.
A spectral line profile is a real I.D. of the layers where it is formed. The challenge was—and still is—to extract, from the observed spectral line profiles, all the information printed in this profile (physical conditions, physical processes, composition, etc.). This business requires, among other data, the knowledge of a large number of very accurate atomic and molecular data.
This was for some time a frustrating setback. But I rapidly transformed it into a challenge: I started to spend much time convincing atomic and molecular spectroscopists to measure or compute the data we needed to interpret the solar spectrum. I did this thanks to talks I gave at atomic and molecular spectroscopy conferences. And these efforts have been very successful through a large number of friendly and fruitful collaborations I had with many atomic and molecular spectroscopists all over the world.
Please tell us about some of your other highly
cited papers and how they have influenced the field.
The journal Physica Scripta, published by the Royal Academy of Sciences of Sweden and by the Physics Societies of the Nordic Countries, recently celebrated its 40th birthday. The editors decided to reproduce the 25 most-cited papers and to produce a DVD containing these papers together with actual comments by their authors many years later.
One of my review papers, "Accurate Atomic Data and Solar Photospheric Spectroscopy" (T8, 49-58, 1984), ranks at number 9 among these most-cited papers (288 citations). This review paper was actually an invited review paper I gave at the Conference ASOS01 (Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas) held in Lund, Sweden, in August 1983. The 10th Conference of that series, ASOS10, took place last August in Berkeley, where I gave an invited talk, "The New Solar Chemical Composition."
In 1989, I published a review paper with Edward Anders (then at the University of Chicago, now retired) entitled, "Abundances of the Elements: Meteoritic and Solar" (Geochim. Cosmochim. Acta 53[1]: 197-214, 1989). This paper has been cited 5,844 times (and receives an average of 265 citations annually) in the Web of Science® as of November 13, 2010. Citations to this paper come from the fields of astrophysics, but also geophysics, geochemistry, mineralogy, and other fields. In astrophysics, this paper is among the 10 most-cited papers of all time.
Thanks to progress being made in the determination of solar chemical composition, particularly by our group, we have been invited to present new reviews on the topic over the years. In 1993, at a colloquium organized in Paris to celebrate the 60th birthday of Hubert Reeves, we gave the much-cited review, "Cosmic Abundances of the Elements" (Grevesse N and Noels A, Origin and Evolution of the Elements, 15-25, 1993, Cambridge University Press, 428 cites), with Arlette Noels, also at the University of Liège.
"...I started to spend much time convincing atomic and molecular spectroscopists to measure or compute the data we needed to interpret the solar spectrum."
In 1998, new data were presented at the colloquium, "Solar Composition and its Evolution—from Core to Corona," organized by the International Space Science Institute (ISSI) of Bern, Switzerland. Our review paper, with A.J. Sauval of the Observatoire Royal de Belgique in Brussels, "Standard Solar Composition" (Grevesse N and Sauval AJ, Space Sci. Rev. 85[1-2]: 161-74, 1998), has been and is still very well cited, with 1,444 cites.
A few years ago, A.J. Sauval and I started a very fruitful collaboration with Martin Asplund, now at the Max Planck Institut für Astrophysik in Garching, Germany. A first review of our initial results, which are rather different than the older ones, was presented by invitation at a conference in Austin, Texas, and has been cited 908 times in the five years since its publication (Asplund M, Grevesse N, Sauval AJ, "The Solar Chemical Composition," Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis 336: 25-38, 2005).
When new results became available, we presented an update of the solar chemical composition at a conference in honor of the 80th birthday of Johannes Geiss (the pioneer in the measurements of the solar wind, who had an aluminum foil detector installed on the moon by Neil Armstrong in July 1969). This paper, "The solar chemical composition," (Grevesse N, Asplund M, Sauval AJ, Space Sci. Rev. 130[1-4]: 105-14, 2007), has 147 citations.
In June 2006, I received an invitation from the prestigious American review journal, the Annual Review of Astronomy and Astrophysics, to compile a new synthesis of our present knowledge concerning the chemical composition of our Sun. With my friends Martin Asplund, Jacques Sauval, and Pat Scott (who had recently received his Ph.D. from the University of Stockholm in Sweden and is now a postdoc at McGill University in Canada), we, of course, accepted this offer.
We decided to do more that a literature review and actually to redo everything from A to Z, i.e. to re-determine the abundances of all the chemical elements present in the Sun with new, very demanding techniques concerning the physical conditions, the physical processes, and the choice of the spectral lines to be used. It took us three years of intense labor to go through this giant work; it was published in 2009, "The Chemical Composition of the Sun," (Asplund M, Grevesse N, Sauval AJ, Scott P, Annual Review Astronomy Astrophysics 47: 481-522, 2009).
This very recent paper is also largely cited (191 cites) and used in many fields of astrophysics as a standard. The end result of this work is a comprehensive and homogeneous compilation of the solar elemental abundances. We find significantly lower abundances of important abundant elements like Carbon, Nitrogen, Oxygen, and Neon compared to the widely used values of a decade or so ago. These new values have important impacts not only in solar physics but actually in many different fields of astrophysics and elsewhere.
Finally, very recently, the American science magazine ScienceNews gave a comprehensive report of the problems with the solar chemical composition, "Solar secrets revealed—exposing the Sun's true makeup" (178[3]: 18-21, 31 July 2010), which extensively quotes our work.
Where do you see your research leading in the
future?
We expect progress in the accuracy of the solar results based on our progress in the modeling of the solar outer layers, but mostly of the physical processes of formation of the spectral lines present in the spectrum of the solar light. Such progress will only be made if we have more and more accurate atomic and molecular data we urgently need.
Do you foresee any social or political
implications for your research?
No. I only see scientific implications in many different fields as
explained above. But who knows!
Dr. Nicolas Grevesse
Centre Spatial de Liège
and
Institut d'Astrophysique et de Géophysique
University of Liège
Liège, Belgium
KEYWORDS: SUN : ABUNDANCES, PHOTOSPHERE, CORONA, LABORATORY TRANSITION-PROBABILITIES; METAL-POOR STARS; R-PROCESS-RICH; LINE FORMATION; NE/O ABUNDANCE; OSCILLATOR-STRENGTHS; ISOTOPIC ABUNDANCES; MODEL PROBLEM; QUIET SUN; GRANULATION.