The effects of sunspots on solar irradiance

Sunspots have an obvious direct effect upon the visible radiant energy falling upon the Earth. We show how to estimate this effect and compare it quantitatively with recent observations of the solar total irradiance (Willson et al., 1981). The sunspots explain about half of the total observed variance of one-day averages. Since the sunspot effect on irradiance produces an asymmetry of the solar radiation, rather than (necessarily) a variation of the total luminosity, we have also estimated the sunspot population on the invisible hemisphere. This extrapolation allows us to estimate the true luminosity deficit produced by sunspots, in a manner that tends toward the correct long-term average value. We find no evidence for instantaneous global re-emission to compensate for the sunspot flux deficit.     

The mystery of the cosmic boron abundance

The observed high abundance of boron in type I carbonaceous chondrites may be due to the presence in the primitive solar nebula of graphite grains which have been irradiated by high energy nucleons at some stage of their history. The boron atoms thus produced by spallation reactions are stably locked within interstellar graphite grains and could make a significant contribution to the boron abundance of C1 chondrites.     

The latitudinal motion of sunspots and solar meridional circulations

A fundamental distinction can be made between those theories of the solar general circulation which require a mean north-south circulation in the photosphere and those which do not. Regardless of the theoretical merits of either group, they must either explain the data, or a theoretical set of data which falls within the observed limits. A detailed analysis of the Greenwich sunspot data supports a mean meridional circulation in either direction with a velocity less than one meter per second. The sunspot data therefore cannot be used to establish the existence of a mean north-south circulation, but may be used as an argument against any theoretical requirement for such a circulation much in excess of 1 m s^–1.     

The rotation of sunspots in the solar active region NOAA 10930

The rotation of sunspots in the solar active region NOAA 10930 was investigated on the basis of the data on the longitudinal magnetic field and the Doppler velocities using magnetograms and dopplergrams taken with the Solar Optical Telescope installed aboard the HINODE mission. Under the assumption of axial symmetry, areally-mean vertical, radial, and azimuthal components of the magnetic field and velocity vectors were calculated in both sunspots. The plasma in the sunspots rotated in opposite directions: in the leading sunspot, clockwise, and in the following sunspot, counterclockwise. The magnetic flux tubes that formed sunspots of the active region on the solar surface were twisted in one direction, clockwise. Electric currents generated as a result of the rotation and twisting of magnetic flux tubes were also flowing in one direction. Azimuthal components of magnetic and velocity fields of both sunspot umbrae reached their maximum on December 11, 2006. By the start of the X3.4 flare (December 13, 2006), their values became practically equal to zero.     

The potassium abundance in the solar photosphere

High precision center-limb spectrograms of the K i resonance doublet line at λ 7699 Å were used to study the line formation and to determine the abundance of potassium in the solar atmosphere. The LTE assumption is not valid for these lines. Synthetic profiles computed in NLTE reproduce very well the observed center-limb line behaviour and yield log? _K = 5.14±0.10 for the solar abundance of potassium (on the scale of log? _H = 12 for Hydrogen).     

Measurement of the solar rotation, 1978, from recurrent and non-recurrent sunspots

Results are presented for the solar rotation, 1978, as derived from sunspots by two different methods. Using recurrent spots only, the latitude dependence of the sidereal rotation rate was calculated to be =(14.41±0.05)–(3.13±0.26) sin² . Using recognizable spots, both recurrent and non-recurrent, average rotation rates were obtained for 5-degree intervals of latitude. The results from these two approaches were found to be in agreement with observations made between 1878 and 1951, suggesting that the solar rotation has not changed in the past 100 years.Currently at Northwestern University, Evanston, Ill., U.S.A.     

The role of spiral sunspots in the solar activity of October 1972

From a collection of photographs of 192 knots relating to 68 flares of the activity region McMath 12094 of October 1972, and of spots and prominences, a correlation analysis was made which led to the following conclusions:

• 1.1. Flare activity began in the region above the leader spot A(N) which had the highest twisted magnetic energy of all the spots in the group. It rapidly developed to the region above the follower S-spots, and then to regions outside the spot area. This evolutionary process was in step with the morphological changes and the rotational movement of the spots in the group.
• 2.2. The flare activity around Spot A began in the interior of the twisted magnetic tube and was in step with the untwisting of magnetic features, and the flare knots spread from the vicinity of the umbra to the outside of the penumbra. When the knotted structure completely untwisted itself, the overall flare activity decreased in the region.
• 3.3. A spiral spot was found to be a strong centre of attraction below a giant coronal prominence. This shows that coronal prominences are formed through the contraction of strong electrical currents in the corona.

We also discussed the question whether the twisted magnetic structure of spot A could have provided most of the energy in the flare activity and lead to an instability.     

The solar abundance of silver

Low noise, high resolution spectral scans have been obtained for the resonance lines of silver 3280.7 and 3382.9, observed at the centre of the solar disk. A double pass-monochromator is used in conjunction with the Snow telescope at Mount Wilson; the transparency of the sky is monitored during the observations in order to achieve required accuracy. The data are analyzed by the method of spectral synthesis wherein we employ a model atmosphere resembling Elste's (1968) model and checked by limb-darkening observations. The present kinematical model adopts a macroturbulent velocity of 2.2 km s^–1 and no microturbulence. With this model line profiles can be reproduced without invoking implausibly large collisional damping constants.The silver abundance turns out to be {Ag}=log[N(Ag)/N(H)]+12;=0.85, a factor of four under the value found from the Type I carbonaceous chondrites.     

The solar abundance of titanium

A solar titanium abundance has been derived from measurements of eight selected very weak lines.     

The solar abundance of thulium

The solar spectrum contains one relatively unblended line λ 3131.258 Tm ii which yields a thulium abundance of log N(Tm)/N(H) + 12 = {Tm} = 0.80 ± 0.10, with the Corliss and Bozman f-value. A recent beam-foil experiment suggests that the thulium abundance may be reduced to {Tm} = 0.30.     

The solar abundance of gold

From 13 scans obtained with a double-band pass spectrograph at the Snow telescope at Mount Wilson, interpreted by the method of spectral synthesis, the abundance of gold turns out to be log [N(Au)/N(H)] + 12 = 0.70, assuming loggf = – 0.57.     

The solar abundance of germanium

The solar abundance of germanium, deduced from two relatively unblended Ge i lines, λ3039.06 and λ3269.50 is found to be log N(Ge) = 3.50 ± 0.05 on the scale log N(H) = 12.00 in good agreement with Cameron's recent solar system abundance logN(Ge) = 3.56 (on assumption log N(Si) = 7.50).     

The solar abundance of tungsten

Recent measurements of Wi oscillator strengths (Obbarius and Kock, 1982) lead to a solar photospheric abundance of tungsten, log _W = 1.06 ± 0.15 on the scale log _H = 12. The solar W/Si abundance ratio, 0.32 W atoms/10⁶ Si, coincides with that found in carbonaceous chrondrites. Implications for solar-system r-processes abundances are pointed out.     

The abundance of cadmium in the solar atmosphere

The solar spectrum at 3261 Å has been studied using the spectrograph at the Oslo Solar Observatory. From analysis of this wavelength region and recent results at 5085 Å, a solar cadmium abundance log N _Cd = 1.86 ± 0.15 is obtained.     

Determination of lithium abundance in sunspots: Observations in 1973

Spectra of sunspots in the region of the lithium 6708 ? line, as well as certain CaI, AlI, FeI, YI, ScI, VI lines, were studied. The observations were performed on July 8, 1973 using a BST-2 telescope at the Crimean Astrophysical Observatory. A sunspot model was developed based on the observed profiles of CaI, AlI, FeI, YI, ScI, and VI lines. Using the developed model and observed profile of the Li 6708 ? line, the abundance of lithium was determined. The obtained result is log(N_Li) = 0.95.     

The solar abundance of thorium and lead

Two new Th ii lines have been identified in the spectrum of the solar photosphere. The abundance derived from these lines together with the previously known Th ii line at 4019 Å, is log _Th = 0.85 ± 0.20 in the log _H = 12.00 scale. Analysis of three Pb i lines in the photospheric spectrum resulted in an abundance of log _pb = 1.90 ± 0.10. The solar Th/Pb ratio is: _Th/ _Pb = 0.09 _-0.005 ^0.09 .     

The solar photospheric abundance of iron

A new value of the solar photospheric abundance of iron, independent of line-shape parameters, is derived. Our analysis is based on a study of 40 weak infrared lines (0.85<λ<2.5 μ) for which theoretical oscillator strengths (calculated with configuration interactions taken into account) have recently been computed by Kurucz (1974). The abundance obtained, A _Fe = 7.57±0.11 (in the usual scale where log N _H = 12.00) is in agreement with the ‘high’ solar values recently reported in the literature and with the meteoritic abundance.     

The solar photospheric abundance of zirconium

Zirconium (Zr), together with strontium and yttrium, is an important element in the understanding of the Galactic nucleosynthesis. In fact, the triad Sr‐Y‐Zr constitutes the first peak of s‐process elements. Despite its general relevance not many studies of the solar abundance of Zr were conducted. We derive the zirconium abundance in the solar photosphere with the same CO⁵BOLD hydrodynamical model of the solar atmosphere that we previously used to investigate the abundances of C‐N‐O. We review the zirconium lines available in the observed solar spectra and select a sample of lines to determine the zirconium abundance, considering lines of neutral and singly ionised zirconium. We apply different line profile fitting strategies for a reliable analysis of Zr lines that are blended by lines of other elements. The abundance obtained from lines of neutral zirconium is very uncertain because these lines are commonly blended and weak in the solar spectrum. However, we believe that some lines of ionised zirconium are reliable abundance indicators. Restricting the set to Zr II lines, from the CO⁵BOLD 3D model atmosphere we derive A (Zr) = 2.62 ± 0.06, where the quoted error is the RMS line‐to‐line scatter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)