Is the solar spectrum latitude-dependent? An investigation with SST/TRIPPEL
2011 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 535, A14- p.Article in journal (Refereed) Published
Context. In studies of the solar spectrum compared to spectra of solar twin stars, it has been found that the chemical composition of the Sun seems to depart systematically from those of the twins. One possible explanation could be that the eﬀect is caused by the special aspect angle of the Sun when observed from Earth compared with the aspect angles of the twins. This means that a latitude dependence of the solar spectrum, even with the heliocentric angle constant, could lead to the observed eﬀects. Aims. We explore a possible variation in the strength of certain spectral lines that are used in the comparisons between the composition of the Sun and the twins at loci on the solar disk with diﬀerent latitudes but at constant heliocentric angle. Methods. We use the TRIPPEL spectrograph at the Swedish 1-m Solar Telescope on La Palma to record spectra in ﬁve spectral regions to compare diﬀerent locations on the solar disk at a heliocentric angle of 45◦ . Equivalent widths and other parameters are measured for ﬁfteen diﬀerent lines representing nine atomic species. Spectra acquired at diﬀerent times are used in averaging the line parameters for each line and observing position. Results. The relative variations in equivalent widths at the equator and at solar latitude ∼45◦ are found to be less than 1.5% for all spectral lines studied. Translated into elemental abundances as they would be measured from a terrestrial and a hypothetical pole-on observer, the diﬀerence is estimated to be within 0.005 dex in all cases. Conclusions. It is very unlikely that latitude eﬀects could cause the reported abundance diﬀerence between the Sun and the solar twins. The accuracy obtainable in measurements of small diﬀerences in spectral line strengths between diﬀerent solar disk positions is very high, and can be exploited in studies of, e.g. weak magnetic ﬁelds or eﬀects of solar activity on atmospheric structure.
Place, publisher, year, edition, pages
2011. Vol. 535, A14- p.
stars: abundances, instrumentation: spectrographs, line: formation, Sun: abundances
Astronomy, Astrophysics and Cosmology
Research subject Astronomy
IdentifiersURN: urn:nbn:se:su:diva-69402DOI: 10.1051/0004-6361/201117553ISI: 000297841200026OAI: oai:DiVA.org:su-69402DiVA: diva2:476588