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Solar total and spectral irradiance reconstruction over the last 9000 years
摘要： Context. Changes in solar irradiance and in its spectral distribution are among the main natural drivers of the climate on Earth. However, irradiance measurements are only available for less than four decades, while assessment of solar influence on Earth requires much longer records. Aims. The aim of this work is to provide the most up-to-date physics-based reconstruction of the solar total and spectral irradiance (TSI/SSI) over the last nine millennia. Methods. The concentrations of the cosmogenic isotopes 14C and 10Be in natural archives have been converted to decadally averaged sunspot numbers through a chain of physics-based models. TSI and SSI are reconstructed with an updated SATIRE model. Reconstructions are carried out for each isotope record separately, as well as for their composite. Results. We present the first ever SSI reconstruction over the last 9000 years from the individual 14C and 10Be records as well as from their newest composite. The reconstruction employs physics-based models to describe the involved processes at each step of the procedure. Conclusions. Irradiance reconstructions based on two different cosmogenic isotope records, those of 14C and 10Be, agree well with each other in their long-term trends despite their different geochemical paths in the atmosphere of Earth. Over the last 9000 years, the reconstructed secular variability in TSI is of the order of 0.11%, or 1.5 W m?2. After the Maunder minimum, the reconstruction from the cosmogenic isotopes is consistent with that from the direct sunspot number observation. Furthermore, over the nineteenth century, the agreement of irradiance reconstructions using isotope records with the reconstruction from the sunspot number by Chatzistergos et al. (2017, A&A, 602, A69) is better than that with the reconstruction from the WDC-SILSO series (Clette et al. 2014, Space Sci. Rev., 186, 35), with a lower χ2-value.
关键词： solar-terrestrial relations,Sun: faculae, plages,Sun: activity,Sun: magnetic fields
更新于2025-09-23 15:22:29
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Disentangling stellar activity from exoplanetary signals with interferometry
摘要： Stellar activity can express as many forms at stellar surfaces: dark spots, convective cells, bright plages. Particularly, dark spots and bright plages add noise on photometric data or radial velocity measurements used to detect exoplanets, and thus lead to false detection or disrupt their derived parameters. Since interferometry provides a very high angular resolution, it may constitute an interesting solution to distinguish the signal of a transiting exoplanet and that of stellar activity. It has also been shown that granulation adds bias in visibility and closure phase measurements, affecting in turn the derived stellar parameters. We analyze the noises generated by dark spots on interferometric observables and compare them to exoplanet signals. We investigate the current interferometric instruments able to measure and disentangle these signals, and show that there is a lack in spatial resolution. We thus give a prospective of the improvements to be brought on future interferometers, which would also significantly extend the number of available targets.
关键词： closure phase measurements,interferometry,bright plages,dark spots,granulation,exoplanetary signals,visibility,stellar activity
更新于2025-09-23 15:21:21
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Analysis of full disc Ca II K spectroheliograms
摘要： Context. Historical Ca II K spectroheliograms (SHG) are unique in representing long-term variations of the solar chromospheric magnetic field. They usually suffer from numerous problems and lack photometric calibration. Thus accurate processing of these data is required to get meaningful results from their analysis. Aims. In this paper we aim at developing an automatic processing and photometric calibration method that provides precise and consistent results when applied to historical SHG. Methods. The proposed method is based on the assumption that the centre-to-limb variation of the intensity in quiet Sun regions does not vary with time. We tested the accuracy of the proposed method on various sets of synthetic images that mimic problems encountered in historical observations. We also tested our approach on a large sample of images randomly extracted from seven different SHG archives. Results. The tests carried out on the synthetic data show that the maximum relative errors of the method are generally <6.5%, while the average error is <1%, even if rather poor quality observations are considered. In the absence of strong artefacts the method returns images that differ from the ideal ones by <2% in any pixel. The method gives consistent values for both plage and network areas. We also show that our method returns consistent results for images from different SHG archives. Conclusions. Our tests show that the proposed method is more accurate than other methods presented in the literature. Our method can also be applied to process images from photographic archives of solar observations at other wavelengths than Ca II K.
关键词： Sun: activity,Sun: chromosphere,Sun: faculae, plages,techniques: image processing
更新于2025-09-23 15:21:01
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Oscillations Accompanying a He?i 10830 ? Negative Flare in a Solar Facula
摘要： On 21 September 2012, we carried out spectral observations of a solar facula in the Si I 10827 ?, He I 10830 ?, and Hα spectral lines. Later, in the process of analyzing the data, we found a small-scale ?are in the middle of the time series. Based on the anomalous increase in the absorption of the He I 10830 ? line, we identi?ed this ?are as a negative ?are. The aim of this article is to study the in?uence of the negative ?are on the oscillation characteristics in the facular photosphere and chromosphere. We measured the line-of-sight (LOS) velocity and intensity of all the three lines as well as the half-width of the chromospheric lines. We also used the Helioseismic and Magnetic Imager (HMI) magnetic ?eld data. The ?are caused a modulation of all these parameters. In the location of the negative ?are, the amplitude of the oscillations increased four times on average. In the adjacent magnetic ?eld local maxima, the chromospheric LOS velocity oscillations appreciably decreased during the ?are. The facular region oscillated as a whole with a 5-minute period before the ?are, and this synchronicity was disrupted after the ?are. The ?are changed the spectral composition of the LOS magnetic ?eld oscillations, causing an increase in the low-frequency oscillation power.
关键词： Sun: faculae, plages,Sun: oscillations,Sun: ?ares
更新于2025-09-09 09:28:46