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- ID:
- ivo://CDS.VizieR/J/A+A/375/614
- Title:
- Astrolabe observations of the Sun in 1990-2000
- Short Name:
- J/A+A/375/614
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The two tables are an update of all observations (1990-2000) of the Sun performed at Santiago, Chile, with a modified Danjon astrolabe at 30{deg} and 60{deg} zenith distances.
- ID:
- ivo://CDS.VizieR/J/A+A/274/555
- Title:
- Asymmetry of FeI lines in solar spectrum
- Short Name:
- J/A+A/274/555
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 75 FeI lines were studied from wide slit FTS spectra obtained at Kitt Peak at the center of the disk, near the limb ({mu}=0.2)
- ID:
- ivo://CDS.VizieR/J/A+A/444/305
- Title:
- A-values + oscillator strength of Ca XIII
- Short Name:
- J/A+A/444/305
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ca XIII. The configurations used are 2s2.2p4, 2s.2p5, 2p6, 2s2.2p3.3s, 2s2.2p3.3p and 2s2.2p3.3d giving rise to 86 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies (40, 80, 120, 160 and 200Ry) in the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10^8-10^14cm^-3 at an electron temperature of logTe(K)=6.5, corresponding to maximum abundance of Ca XIII. Relative and absolute spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database.
- ID:
- ivo://CDS.VizieR/J/A+A/599/A131
- Title:
- Butterfly diagram wings
- Short Name:
- J/A+A/599/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The continuous spatio-temporal evolution (the so-called 'Maunder butterfly diagram') of sunspot activity was available since 1874 using data from the Royal Greenwich Observatory since 1875, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence continuously since 1826, using the recently digitized data from Schwabe (1826-1867) and Spoerer (1868-1874). The wings of the diagram are separated using a recently developed method based on long gaps in sunspot group occurrence in different latitude bands. Characteristic latitudes, corresponding to the start, end and the latitudinal span of the wings, F-, L- and H-latitudes, respectively, as well as times and asymmetries of the butterfly wings are analyzed. The F-latitude depict a weak tendency, especially in the S-hemisphere, to follow the wing strength (quantified in the total sum of monthly numbers of sunspot groups). The H-latitudes are highly significantly correlated with the strength of the wings during cycles 12-23. The L-latitudes show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have greater wing's span. A strong (5-6)-cycle periodic oscillation was found in many latitudinal parameters, such as dates of the start and end of the wings and, most pronounced, in the difference between the wing lengths in the two hemispheres. A barely significant oscillation of about 10 cycles period is found in the asymmetry of the L-latitudes. The new long database of butterfly wings and the results based on it provide new observational constraints to the spatio-temporal distribution of sunspot occurrence and their solar cycle related time-latitude evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/25
- Title:
- Calibrated solar S-index time series
- Short Name:
- J/ApJ/835/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most commonly used index of stellar magnetic activity is the instrumental flux scale of singly ionized calcium H & K line core emission, S, developed by the Mount Wilson Observatory (MWO) HK Project, or the derivative index R'_HK_. Accurately placing the Sun on the S scale is important for comparing solar activity to that of the Sun-like stars. We present previously unpublished measurements of the reflected sunlight from the Moon using the second-generation MWO HK photometer during solar cycle 23 and determine cycle minimum S_23,min_=0.1634+/-0.0008, amplitude {Delta}S_23_=0.0143+/-0.0012, and mean <S_23_>=0.1701+/-0.0005. By establishing a proxy relationship with the closely related National Solar Observatory Sacramento Peak calcium K emission index, itself well correlated with the Kodaikanal Observatory plage index, we extend the MWO S time series to cover cycles 15-24 and find on average <S_min_>=0.1621+/-0.0008, <{Delta}S_cyc_>=0.0145+/-0.0012, <S_cyc_>=0.1694+/-0.0005. Our measurements represent an improvement over previous estimates that relied on stellar measurements or solar proxies with non-overlapping time series. We find good agreement from these results with measurements by the Solar-Stellar Spectrograph at Lowell Observatory, an independently calibrated instrument, which gives us additional confidence that we have accurately placed the Sun on the S-index flux scale.
- ID:
- ivo://CDS.VizieR/J/A+A/384/650
- Title:
- CCD solar diameter measurements in 1999-2000
- Short Name:
- J/A+A/384/650
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Solar diameter observations are presented covering a period close to the maximum of the solar activity cycle 23, from July 1999 to December 2000, at the Observatorio Nacional, Rio de Janeiro. The observations were made at {lambda}=5635{AA}, with a CCD Solar Astrolabe, thus timing the limb crossing through a fixed zenith distance. The formal precision of a single measurement is typically 0.18". The results represent daily means from 4625 independent measurements. The series obtained has 225 homogeneously distributed points with a mean precision of 0.12". The average value obtained for the solar semi-diameter within the analyzed period is 959.01"+/-0.02". The average of the observations, made under a wide range of different geometric, instrumental and environmental conditions, aims to provide results representing global variations of the solar radius. From this data, variations with amplitude equal to or larger than 0.02" can be investigated. No statistically significant linear trend is obtained for the examined series. There is, however, some indication of an increasing trend for 1999 followed by a stabilization during 2000. Periodic variations are obtained with amplitudes between 0.02" and 0.07". Periods related to the solar rotation and the sunspot characteristic lifetime can be recognized.
- ID:
- ivo://CDS.VizieR/J/A+A/423/1109
- Title:
- Center-to-limb variation of quiet Sun
- Short Name:
- J/A+A/423/1109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new observations of the center-to-limb variation of spectral lines in the quiet Sun. Our long-slit spectra are corrected for scattered light, which amounts to 4-8% of the continuum intensity, by comparison with a Fourier transform spectrum of the disk center. Different spectral lines exhibit different behaviors, depending on their sensitivity to the physical conditions in the photosphere and the range of depths they probe as a function of the observing angle, providing a rich database to test models of the solar photosphere and line formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/845/36
- Title:
- Complex network for solar active regions
- Short Name:
- J/ApJ/845/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we developed a complex network of solar active regions (ARs) to study various local and global properties of the network. The values of the Hurst exponent (0.8-0.9) were evaluated by both the detrended fluctuation analysis and the rescaled range analysis applied on the time series of the AR numbers. The findings suggest that ARs can be considered as a system of self-organized criticality (SOC). We constructed a growing network based on locations, occurrence times, and the lifetimes of 4227 ARs recorded from 1999 January 1 to 2017 April 14. The behavior of the clustering coefficient shows that the AR network is not a random network. The logarithmic behavior of the length scale has the characteristics of a so-called small-world network. It is found that the probability distribution of the node degrees for undirected networks follows the power law with exponents of about 3.7-4.2. This indicates the scale-free nature of the AR network. The scale-free and small-world properties of the AR network confirm that the system of ARs forms a system of SOC. Our results show that the occurrence probability of flares (classified by GOES class C>5, M, and X flares) in the position of the AR network hubs takes values greater than that obtained for other nodes.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A57
- Title:
- Convective blueshifts in solar atmos.
- Short Name:
- J/A+A/624/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Convective motions in the solar atmosphere cause spectral lines to become asymmetric and shifted in wavelength. For photospheric lines, this differential Doppler shift varies from the solar disk center to the limb. Precise and comprehensive observations of the convective blueshift and its center-to-limb variation improve our understanding of the atmospheric hydrodynamics and ensuing line formation, and provide the basis to refine 3D models of the solar atmosphere. We performed systematical spectroscopic measurements of the convective blueshift of the quiet Sun with the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum Tower Telescope. The spatial scanning of the solar disk covered 11 heliocentric positions each along four radial (meridional and equatorial) axes. The high-resolution spectra of 26 photospheric to chromospheric lines in the visible range were calibrated with a laser frequency comb to absolute wavelengths at the 1m/s accuracy. Applying ephemeris and reference corrections, the bisector analysis provided line asymmetries and Doppler shifts with an uncertainty of only few m/s. To allow for a comparison with other observations, we convolved the results to lower spectral resolutions.
