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Natalie A Krivova - One of the best experts on this subject based on the ideXlab platform.
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Recovering the unsigned photospheric magnetic field from Ca II K observations
'EDP Sciences', 2019Co-Authors: Theodosios Chatzistergos, Natalie A Krivova, Ilaria Ermolli, Sami K. Solanki, Fabrizio Giorgi, Kok Leng YeoAbstract:Context. A number of studies have aimed at defining the exact form of the relation between magnetic field strength and Ca II H and K core brightness. All previous studies have however been restricted to isolated regions on the Solar Disc or to a limited set of observations. Aims. We reassess the relationship between the photospheric magnetic field strength and the Ca II K intensity for a variety of surface features as a function of the position on the Disc and the Solar activity level. This relationship can be used to recover the unsigned photospheric magnetic field from images recorded in the core of Ca II K line. Methods. We have analysed 131 pairs of high-quality, full-Disc, near-co-temporal observations from the Helioseismic and Magnetic Imager (SDO/HMI) and Precision Solar Photometric Telescope (Rome/PSPT) spanning half a Solar cycle. To analytically describe the observationally determined relation, we considered three different functions: a power law with an offset, a logarithmic function, and a power-law function of the logarithm of the magnetic flux density. We used the obtained relations to reconstruct maps of the line-of-sight component of the unsigned magnetic field (unsigned magnetograms) from Ca II K observations, which were then compared to the original magnetograms. Results. We find that both power-law functions represent the data well, while the logarithmic function is good only for quiet periods. We see no significant variation over the Solar cycle or over the Disc in the derived fit parameters, independently of the function used. We find that errors in the independent variable, which are usually not accounted for, introduce attenuation bias. To address this, we binned the data with respect to the magnetic field strength and Ca II K contrast separately and derived the relation for the bisector of the two binned curves. The reconstructed unsigned magnetograms show good agreement with the original ones. Root mean square differences are less than 90 G. The results were unaffected by the stray-light correction of the SDO/HMI and Rome/PSPT data. Conclusions. Our results imply that accurately processed and calibrated Ca II K observations can be used to reconstruct unsigned magnetograms by using the relations derived in our study
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are Solar brightness variations faculae or spot dominated
Astronomy and Astrophysics, 2016Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, W SchmutzAbstract:Context. Regular spaceborne measurements have revealed that Solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims. To understand whether the broader pattern of stellar variations is consistent with the Solar paradigm, we assess relative contributions of faculae and spots to Solar magnetically-driven brightness variability. We investigate how the Solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods. We performed calculations with the SATIRE model, which returns Solar brightness with daily cadence from Solar Disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-Disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results. Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Stromgren ( b + y )/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year Solar variability in the Stromgren ( b + y )/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions. The rotational Solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about i = 45°. Over the course of the 11-year activity cycle, the Solar brightness variability is faculae-dominated shortwards of 1.2 μ m independently of the inclination.
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are Solar brightness variations faculae or spot dominated
Astronomy and Astrophysics, 2016Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Wermer SchmutzAbstract:Context. Regular spaceborne measurements have revealed that Solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims. To understand whether the broader pattern of stellar variations is consistent with the Solar paradigm, we assess relative contributions of faculae and spots to Solar magnetically-driven brightness variability. We investigate how the Solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods. We performed calculations with the SATIRE model, which returns Solar brightness with daily cadence from Solar Disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-Disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results. Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Stromgren ( b + y )/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year Solar variability in the Stromgren ( b + y )/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions. The rotational Solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about i = 45°. Over the course of the 11-year activity cycle, the Solar brightness variability is faculae-dominated shortwards of 1.2 μ m independently of the inclination.
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the role of the fraunhofer lines in Solar brightness variability
Astronomy and Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:Context. The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. Aims. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Methods. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. Results. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.
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the role of the fraunhofer lines in Solar brightness variability
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.
S K Solanki - One of the best experts on this subject based on the ideXlab platform.
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are Solar brightness variations faculae or spot dominated
Astronomy and Astrophysics, 2016Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, W SchmutzAbstract:Context. Regular spaceborne measurements have revealed that Solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims. To understand whether the broader pattern of stellar variations is consistent with the Solar paradigm, we assess relative contributions of faculae and spots to Solar magnetically-driven brightness variability. We investigate how the Solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods. We performed calculations with the SATIRE model, which returns Solar brightness with daily cadence from Solar Disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-Disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results. Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Stromgren ( b + y )/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year Solar variability in the Stromgren ( b + y )/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions. The rotational Solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about i = 45°. Over the course of the 11-year activity cycle, the Solar brightness variability is faculae-dominated shortwards of 1.2 μ m independently of the inclination.
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are Solar brightness variations faculae or spot dominated
Astronomy and Astrophysics, 2016Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Wermer SchmutzAbstract:Context. Regular spaceborne measurements have revealed that Solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims. To understand whether the broader pattern of stellar variations is consistent with the Solar paradigm, we assess relative contributions of faculae and spots to Solar magnetically-driven brightness variability. We investigate how the Solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods. We performed calculations with the SATIRE model, which returns Solar brightness with daily cadence from Solar Disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-Disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results. Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Stromgren ( b + y )/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year Solar variability in the Stromgren ( b + y )/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions. The rotational Solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about i = 45°. Over the course of the 11-year activity cycle, the Solar brightness variability is faculae-dominated shortwards of 1.2 μ m independently of the inclination.
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the role of the fraunhofer lines in Solar brightness variability
Astronomy and Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:Context. The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. Aims. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Methods. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. Results. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.
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the role of the fraunhofer lines in Solar brightness variability
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.
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point spread function of sdo hmi and the effects of stray light correction on the apparent properties of Solar surface phenomena
Astronomy and Astrophysics, 2014Co-Authors: K L Yeo, S K Solanki, A Feller, S Couvidat, S Danilovic, Natalie A KrivovaAbstract:Aims. We present a point spread function (PSF) for the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and Discuss the effects of its removal on the apparent properties of Solar surface phenomena in HMI data. Methods. The PSF was retrieved from observations of Venus in transit by matching it to the convolution of a model of the Venusian Disc and Solar background with a guess PSF. We described the PSF as the sum of five Gaussian functions, the amplitudes of which vary sinusoidally with azimuth. This relatively complex functional form was required by the data. Observations recorded near in time to the transit of Venus were corrected for instrumental scattered light by the deconvolution with the PSF. We also examined the variation in the shape of the Solar aureole in daily data, as an indication of PSF changes over time. Results. Granulation contrast in restored HMI data is greatly enhanced relative to the original data and exhibit reasonable agreement with numerical simulations. Image restoration enhanced the apparent intensity and pixel averaged magnetic field strength of photospheric magnetic features significantly. For small-scale magnetic features, restoration enhanced intensity contrast in the continuum and core of the Fe I 6173 A line by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For sunspots and pores, the enhancement varied strongly within and between features, being more acute for smaller features. Magnetic features are also rendered smaller, as signal smeared onto the surrounding quiet Sun is recovered. Image restoration increased the apparent amount of magnetic flux above the noise floor by a factor of about 1.2, most of the gain coming from the quiet Sun. Line-of-sight velocity due to granulation and supergranulation is enhanced by a factor of 1.4 to 2.1, depending on position on the Solar Disc. The shape of the Solar aureole varied, with time and between the two CCDs. There are also indications that the PSF varies across the FOV. However, all these variations were found to be relatively small, such that a single PSF can be applied to HMI data from both CCDs, over the period examined without introducing significant error. Conclusions. Restoring HMI observations with the PSF presented here returns a reasonable estimate of the stray light-free intensity contrast. Image restoration affects the measured radiant, magnetic and dynamic properties of Solar surface phenomena sufficiently to significantly impact interpretation.
Hanaoka Yoichiro - One of the best experts on this subject based on the ideXlab platform.
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Analysis of full-Disc Ca II K spectroheliograms: III. Plage area composite series covering 1892-2019
'EDP Sciences', 2020Co-Authors: Chatzistergos Theodosios, Solanki, Sami K., Ermolli Ilaria, Krivova, Natalie A., Banerjee Dipankar, Barata Teresa, Belik Marcel, Gafeira Ricardo, Garcia Adriana, Hanaoka YoichiroAbstract:Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Context. Studies of long-term Solar activity and variability require knowledge of the past evolution of the Solar surface magnetism. The archives of full-Disc Ca II K observations that have been performed more or less regularly at various sites since 1892 can serve as an important source of such information. Aims. We derive the plage area evolution over the last 12 Solar cycles by employing data from all Ca II K archives that are publicly available in digital form, including several as-yet-unexplored Ca II K archives. Methods. We analysed more than 290 000 full-Disc Ca II K observations from 43 datasets spanning the period between 1892-2019. All images were consistently processed with an automatic procedure that performs the photometric calibration (if needed) and the limb-darkening compensation. The processing also accounts for artefacts affecting many of the images, including some very specific artefacts, such as bright arcs found in Kyoto and Yerkes data. Our employed methods have previously been tested and evaluated on synthetic data and found to be more accurate than other methods used in the literature to treat a subset of the data analysed here. Results. We produced a plage area time-series from each analysed dataset. We found that the differences between the plage areas derived from individual archives are mainly due to the differences in the central wavelength and the bandpass used to acquire the data at the various sites. We empirically cross-calibrated and combined the results obtained from each dataset to produce a composite series of plage areas. The 'backbone' approach was used to bridge the series together. We have also shown that the selection of the backbone series has little effect on the final composite of the plage area. We quantified the uncertainty of determining the plage areas with our processing due to shifts in the central wavelength and found it to be less than 0.01 in fraction of the Solar Disc for the average conditions found on historical data. We also found the variable seeing conditions during the observations to slightly increase the plage areas during the activity maxima. Conclusions. We provide the most complete so far time series of plage areas based on corrected and calibrated historical and modern Ca II K images. Consistent plage areas are now available on 88% of all days from 1892 onwards and on 98% from 1907 onwards. © T. Chatzistergos et al. 2020.The authors thank the observers at the Arcetri, Baikal, Big Bear, Brussels, Calern, Catania, Coimbra, Kanzelhohe, Kharkiv, Kenwood, Kislovodsk, Kodaikanal, Kyoto, Manila, Mauna Loa, McMathHulbert, Mees, Meudon, Mitaka, European Union's Horizon 2020 research and innovation program Mt Wilson, Pic du Midi, Rome, Sacramento Peak, San Fernando, Schauinsland, Teide, Upice, Valasske Mezi.ri.ci, Wendelstein, and Yerkes sites for all their work in carrying out the observing programs. We thank Isabelle Buale for all her e fforts to digitise the Meudon archive. We thank Je ff Kuhn and Cindy Maui for locating and sharing with us the Mees Ca II K data. We thank Satoru Ueno and Reizaburo Kitai for providing the Kyoto observations. We thank the anonymous referee for the constructive comments that improved this manuscript. We thank Ester Antonucci, Alexi Baker, Angie Cookson, Martina Exnerova, Bernhard Fleck, Detlef Groote, Laurent Koechlin, Libor Lenza, Mustapha Meftah, Werner Potzi, Roger Ulrich, John Varsik, and Hubertus Wohl for providing information about various Ca II K data. This work was supported by FP7 SOLID, and by the BK21 plus program through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. This research has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 824135 (SolarNET). The Coimbra researchers thank the project ReNATURE (CENTRO-01-0145-FEDER-000007-BPD16). We acknowledge the "Observateurs associes" for their commitment to image acquisition and processing; IRAP for the instrumental and database management; Universite de Toulouse, CNRS, and Fiducial for the funding. We acknowledge Paris Observatory for the use of spectroheliograms and the Royal Observatory of Belgium, Brussels for USET data. The Kanzelhohe Ca II K data were provided by the Kanzelhohe Observatory, University of Graz, Austria. ChroTel is operated by the Kiepenheuer-Institute for Solar Physics in Freiburg, Germany, at the Spanish Observatorio del Teide, Tenerife, Canary Islands. The ChroTel filtergraph has been developed by the Kiepenheuer-Institute in cooperation with the High Altitude Observatory in Boulder, CO, USA. We acknowledge www.observethesun.com and www.Solarstation.ru for storing the Kislovodsk data. This work used data provided by the MEDOC data and operations centre (CNES/CNRS/Univ. Paris-Sud). The Kenwood observations used here are from lantern slides in the Division of History of Science and Technology at Yale University's Peabody Museum of Natural History (objects YPM HST.340744, HST.340745, HST.340747, and HST.340752). The Yerkes observations are courtesy of the University of Chicago Photographic Archive, Special Collections Research Center, University of Chicago Library. This research has made use of NASA's Astrophysics Data System.Peer reviewe
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Analysis of full Disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019
'EDP Sciences', 2020Co-Authors: Chatzistergos Theodosios, Solanki, Sami K., Ermolli Ilaria, Krivova, Natalie A., Banerjee Dipankar, Barata Teresa, Belik Marcel, Gafeira Ricardo, Garcia Adriana, Hanaoka YoichiroAbstract:We derive the plage area evolution over the last 12 Solar cycles employing data from all Ca II K archives available publicly in digital form known to us, including several as yet unexplored Ca II K archives. We analyse more than 290,000 full-Disc Ca II K observations from 43 datasets spanning the period 1892-2019. All images were consistently processed with an automatic procedure that performs the photometric calibration (if needed) and the limb-darkening compensation. The processing also accounts for artefacts plaguing many of the images, including some very specific artefacts such as bright arcs found in Kyoto and Yerkes data. We have produced a plage area time-series from each analysed dataset. We found that the differences between the plage areas derived from individual archives are mainly due to the differences in the central wavelength and the bandpass used to acquire the data at the various sites. We have empirically cross-calibrated and combined the results obtained from each dataset to produce a composite series of plage areas. "Backbone" series are used to bridge all the series together. We have also shown that the selection of the backbone series has little effect on the final plage area composite. We have quantified the uncertainty of determining the plage areas with our processing due to shifts in the central wavelength and found it to be less than 0.01 in fraction of the Solar Disc for the average conditions found on historical data. We also found the variable seeing conditions during the observations to slightly increase the plage areas during activity maxima. We provide the so far most complete time series of plage areas based on corrected and calibrated historical and modern Ca II K images. Consistent plage areas are now available on 88% of all days from 1892 onwards and on 98% from 1907 onwards.Comment: 23 pages, 19 figures, accepted for publication in A&
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Analysis of full-Disc Ca II K spectroheliograms
'EDP Sciences', 2020Co-Authors: Chatzistergos Theodosios, Ermolli Ilaria, Banerjee Dipankar, Barata Teresa, Belik Marcel, Gafeira Ricardo, Garcia Adriana, Krivova Natalie, Solanki Sami, Hanaoka YoichiroAbstract:International audienceContext. Studies of long-term Solar activity and variability require knowledge of the past evolution of the Solar surface magnetism. The archives of full-Disc Ca II K observations that have been performed more or less regularly at various sites since 1892 can serve as an important source of such information. Aims. We derive the plage area evolution over the last 12 Solar cycles by employing data from all Ca II K archives that are publicly available in digital form, including several as-yet-unexplored Ca II K archives. Methods. We analysed more than 290 000 full-Disc Ca II K observations from 43 datasets spanning the period between 1892–2019. All images were consistently processed with an automatic procedure that performs the photometric calibration (if needed) and the limb-darkening compensation. The processing also accounts for artefacts affecting many of the images, including some very specific artefacts, such as bright arcs found in Kyoto and Yerkes data. Our employed methods have previously been tested and evaluated on synthetic data and found to be more accurate than other methods used in the literature to treat a subset of the data analysed here. Results. We produced a plage area time-series from each analysed dataset. We found that the differences between the plage areas derived from individual archives are mainly due to the differences in the central wavelength and the bandpass used to acquire the data at the various sites. We empirically cross-calibrated and combined the results obtained from each dataset to produce a composite series of plage areas. The ’backbone’ approach was used to bridge the series together. We have also shown that the selection of the backbone series has little effect on the final composite of the plage area. We quantified the uncertainty of determining the plage areas with our processing due to shifts in the central wavelength and found it to be less than 0.01 in fraction of the Solar Disc for the average conditions found on historical data. We also found the variable seeing conditions during the observations to slightly increase the plage areas during the activity maxima. Conclusions. We provide the most complete so far time series of plage areas based on corrected and calibrated historical and modern Ca II K images. Consistent plage areas are now available on 88% of all days from 1892 onwards and on 98% from 1907 onwards
A I Shapiro - One of the best experts on this subject based on the ideXlab platform.
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are Solar brightness variations faculae or spot dominated
Astronomy and Astrophysics, 2016Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Wermer SchmutzAbstract:Context. Regular spaceborne measurements have revealed that Solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims. To understand whether the broader pattern of stellar variations is consistent with the Solar paradigm, we assess relative contributions of faculae and spots to Solar magnetically-driven brightness variability. We investigate how the Solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods. We performed calculations with the SATIRE model, which returns Solar brightness with daily cadence from Solar Disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-Disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results. Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Stromgren ( b + y )/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year Solar variability in the Stromgren ( b + y )/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions. The rotational Solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about i = 45°. Over the course of the 11-year activity cycle, the Solar brightness variability is faculae-dominated shortwards of 1.2 μ m independently of the inclination.
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are Solar brightness variations faculae or spot dominated
Astronomy and Astrophysics, 2016Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, W SchmutzAbstract:Context. Regular spaceborne measurements have revealed that Solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims. To understand whether the broader pattern of stellar variations is consistent with the Solar paradigm, we assess relative contributions of faculae and spots to Solar magnetically-driven brightness variability. We investigate how the Solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods. We performed calculations with the SATIRE model, which returns Solar brightness with daily cadence from Solar Disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-Disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results. Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Stromgren ( b + y )/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year Solar variability in the Stromgren ( b + y )/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions. The rotational Solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about i = 45°. Over the course of the 11-year activity cycle, the Solar brightness variability is faculae-dominated shortwards of 1.2 μ m independently of the inclination.
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the role of the fraunhofer lines in Solar brightness variability
Astronomy and Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:Context. The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. Aims. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Methods. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. Results. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.
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the role of the fraunhofer lines in Solar brightness variability
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.
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are Solar brightness variations faculae or spot dominated
Astronomy and Astrophysics, 2016Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, W SchmutzAbstract:Context. Regular spaceborne measurements have revealed that Solar brightness varies on multiple timescales, variations on timescales greater than a day being attributed to a surface magnetic field. Independently, ground-based and spaceborne measurements suggest that Sun-like stars show a similar, but significantly broader pattern of photometric variability. Aims. To understand whether the broader pattern of stellar variations is consistent with the Solar paradigm, we assess relative contributions of faculae and spots to Solar magnetically-driven brightness variability. We investigate how the Solar brightness variability and its facular and spot contributions depend on the wavelength, timescale of variability, and position of the observer relative to the ecliptic plane. Methods. We performed calculations with the SATIRE model, which returns Solar brightness with daily cadence from Solar Disc area coverages of various magnetic features. We took coverages as seen by an Earth-based observer from full-Disc SoHO/MDI and SDO/HMI data and projected them to mimic out-of-ecliptic viewing by an appropriate transformation. Results. Moving the observer away from the ecliptic plane increases the amplitude of 11-year variability as it would be seen in Stromgren ( b + y )/2 photometry, but decreases the amplitude of the rotational brightness variations as it would appear in Kepler and CoRoT passbands. The spot and facular contributions to the 11-year Solar variability in the Stromgren ( b + y )/2 photometry almost fully compensate each other so that the Sun appears anomalously quiet with respect to its stellar cohort. Such a compensation does not occur on the rotational timescale. Conclusions. The rotational Solar brightness variability as it would appear in the Kepler and CoRoT passbands from the ecliptic plane is spot-dominated, but the relative contribution of faculae increases for out-of-ecliptic viewing so that the apparent brightness variations are faculae-dominated for inclinations less than about i = 45°. Over the course of the 11-year activity cycle, the Solar brightness variability is faculae-dominated shortwards of 1.2 μ m independently of the inclination.
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the role of the fraunhofer lines in Solar brightness variability
Astronomy and Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:Context. The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. Aims. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Methods. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. Results. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.
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the role of the fraunhofer lines in Solar brightness variability
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: A I Shapiro, Natalie A Krivova, S K Solanki, Rinat Tagirov, W SchmutzAbstract:The Solar brightness varies on timescales from minutes to decades. A clear identification of the physical processes behind such variations is needed for developing and improving physics-based models of Solar brightness variability and reconstructing Solar brightness in the past. This is, in turn, important for better understanding the Solar-terrestrial and Solar-stellar connections. We estimate the relative contributions of the continuum, molecular, and atomic lines to the Solar brightness variations on different timescales. Our approach is based on the assumption that variability of the Solar brightness on timescales greater than a day is driven by the evolution of the Solar surface magnetic field. We calculated the Solar brightness variations employing the Solar Disc area coverage of magnetic features deduced from the MDI/SOHO observations. The brightness contrasts of magnetic features relative to the quiet Sun were calculated with a non-LTE radiative transfer code as functions of Disc position and wavelength. By consecutive elimination of molecular and atomic lines from the radiative transfer calculations, we assessed the role of these lines in producing Solar brightness variability. We show that the variations in Fraunhofer lines define the amplitude of the Solar brightness variability on timescales greater than a day and even the phase of the total Solar irradiance variability over the 11-year cycle. We also demonstrate that molecular lines make substantial contribution to Solar brightness variability on the 11-year activity cycle and centennial timescales. In particular, our model indicates that roughly a quarter of the total Solar irradiance variability over the 11-year cycle originates in molecular lines. The maximum of the absolute spectral brightness variability on timescales greater than a day is associated with the CN violet system between 380 and 390 nm.