Vibration rotation bands of SiO in sunspots

The equivalent widths of P(51) and R(43) lines of the 1-0 and P(45) and R(56) lines of the 2-1 vibration rotation bands of SiO near 8 m region, have been computed for Zwaan's (1974) sunspot model at the centre of the disc. The predicted equivalent widths suggest a possible presence of these SiO bands in the sunspot spectrum.     

The Faraday rotation of sunspots

In this paper the numerical solutions of the Unno-Beckers's equations for the magneto-sensitive line Fei 5250.216 are used to demonstrate the importance and role of Faraday rotation in sunspot magnetic fields and to study the influence of this effect on the measurements of the azimuth of the transverse field. We propose a method to determine the intrinsic direction of the transverse field with the observed azimuthal angle of the plane of linear polarization.     

High abnormal rotation rates of sunspots and flare productivity

Solar activity, such as flares and CMEs, affect the interplanetary medium, and Earth’s atmosphere. Therefore, to understand the Space Weather, we need to understand the mechanisms of solar activity. Towards this end, we use 1135 events of solar H_α flares and the positional data of sunspots from the archive of Solar Geophysical Data (SGD) for the period January–April, 2000 and compute the abnormal rotation rates that lead to high flare productivity. We report that the occurrence of 5 or more flares in a day in association with a given sunspot group can be defined as high flare productivity and the sunspots that have an abnormal rotation rates of ～4–10 deg day^?1 trigger high flare productivity. Further, in order to compare the flare productivity expressed as the strength of the flux emitted, especially the soft X-ray (SXR) flares in the frequency range of 1–8 Å, we compute the flare index of SXR flares and find that 8 out of 28 active regions used in this study satisfy the requirement for being flare productive. This enables us to conclude that the high rotation rates of sunspots are an important mechanism to understand the flare productivity, especially numerical flare productivity that includes flares of all class.     

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.     

On the determination of heliographic positions and rotation velocities of sunspots

The north-south asymmetry in the intensity of the 530.3 nm emission coronal line is examined in the time period 1958 to 1980 using data at all latitudes. The results show that overall the northern hemisphere of the Sun is more active in this line. The general pattern has changed after the beginning of the 21st cycle with the southern polar region being more active after the last solar minimum (1975). These anisotropies may be related to phase differences between the activity of northern and southern hemispheres. North-south asymmetries may have implications in the structure and evolution of the heliosphere, its current sheet and even in the cosmic ray propagation.     

On the determination of heliographic positions and rotation velocities of sunspots

Heliographic coordinates of several small but stable sunspots, which were determined at five different observatories in 1979, are compared. Some systematic differences within these results are found, which suggest a more detailed analysis of the data accumulation procedures and the physical interpretation. The same holds for the rotation velocities derived from the position data.     

On the determination of heliographic positions and rotation velocities of sunspots

In an earlier paper of this series it was shown how the Wilson depression influences the determination of sunspot rotation velocities. Using this finding and the fact that stable recurrent sunspots show a very constant rotation velocity it is possible to determine the effect of wrong solar image radii on the determination of sunspot rotation velocities and correct them.Mitteilungen aus dem Kiepenheuer-Institut Nr. 238.     

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.     

Differential rotation of the sun determined tracing sunspots and oscillations of sunspot tilt angle

The time and spatial characteristics of 324 large sunspots (S50 millionths of the solar hemisphere) selected from the Abastumani Astrophysical Observatory photoheliogram collection (1950–1990) have been studied. The variations of sunspot angular rotation velocity residuals and oscillations of sunspot tilt angle were analyzed. It has been shown that the differential rotation rate of selected sunspots correlates on average with the solar cycle. The deceleration of differential rotation of large sunspots begins on the ascending arm of the activity curve and ends on the descending arm reaching minimum near the epochs of solar activity maxima. This behavior disappears during the 21st cycle. The amplitudes and periods of sunspot tilt-angle oscillations correlate well with the solar activity cycle. Near the epochs of activity maximum there appear sunspots with large amplitudes and periods showing a significant scatter while the scatter near the minimum is rather low. We also found evidence of phase difference between the sunspot angular rotation velocity and the amplitudes and periods of tilt-angle oscillations.     

Water vapour in sunspots

The line intensities are calculated at temperatures of 263 K and 3500 K for the H₂O band 201 at 0.94 m. The possibility of detecting these lines in sunspots is discussed. The amount of H₂O is estimated to be 4.2 × 10²⁰ molecules or 0.013 g cm^–2 above optical depth equal to unity. However, other bands at longer wavelengths are more favourable for detection of H₂O.     

Material flow in sunspots

Observations nowadays reveal more and more details about the small‐scale structure of the penumbra and umbra. Recent measurements of the motions in the penumbra indicate that (i) the Evershed flow is confined to a thin photospheric layer and (ii) the material rises from and sinks to subphotospheric layers within the penumbra. This flow pattern solves the question of the mass budget of the Evershed flow in a natural way. The nature of umbral dots and their role for the spot's energy budget remains unclear, since they are obviously unresolved even in the best existing measurements.     

On molecules in sunspots

Spectra of umbrae of several sunspots in the wavelength region 4000–8000 Å scanned photoelectrically at the Göttingen Locarno Observatory were used in order to search for absorption lines of molecules. Several thousands of lines of known molecules were reidentifled (see Table II and Table III). Newly identified molecules are CoH, NiH and H₂O (see Table IV and Wöhl (1969a)). The Zeemann effect on molecular lines (of MgH and CaH; see Table V and Wöhl (1969b)) in spectra of umbrae was detected.     

Lithium abundance in sunspots

The observations of lithium were carried out with the TST-2 telescope at CrAO on August 15–20, 2006. A sunspot model was calculated for the dates of observations. The lithium abundance in a sunspot and in the undisturbed photosphere was determined. It is log(N _Li) = 1.35 for the sunspot and log (N _Li) = 1.05 for the undisturbed photosphere.     

Structure of sunspots

The sunspot models published so far do not reproduce the observed run of the umbral continuum intensities over the entire spectral range 0.5 < < 4 m. Moreover, in several previous models is the temperature gradient smaller than both the adiabatic and the radiative equilibrium gradient.Agreement between intensities computed from acceptable models and measured intensities can be obtained by introducing an additional opacity for 0.8 m, which is probably caused by the crowding of atomic and molecular lines. We present a new umbral model atmosphere with a wavelength dependent opacity enhancement factor which explains the continuum intensities and also reproduces plausible center-to-limb variations and line profiles. This model is in radiative equilibrium down to _0.5 = 1.5, with an effective temperature of 4000 ± 100K. For the deeper superadiabatic layers a small but probably significant departure from radiative equilibrium is indicated by the intensities in the range 1.5 < < 2.4 m.The uncertainties in the present model and the effect of the additional opacity on line profiles are briefly discussed.     

Oscillatory motions in sunspots

We observe vertical velocity oscillations in some sunspot umbrae with periods of about 180 s and peak to peak amplitudes up to 1 km s^–1. These oscillations are not visible in either the line depth, line width or the continuum intensity. No correlation seems to exist between the occurence of these oscillations and the presence of the chromospheric umbral flashes (Solar Phys. 7, 351, 1069). In the spot penumbra there is an indication of a long period oscillation, the period increasing from about 300 s in the inner penumbra to nearly 1000 s at the penumbra-photosphere boundary. An attempt has been made to interpret these oscillations in terms of gravity or acoustic waves, travelling along the magnetic field lines, taking into account the variation of scale height and magnetic field direction across the sunspot.     

The filamentary structure in sunspots

I use the method given in Ref. [l] to solve the nonaxisymmetric magnetostatic equation, to explain the filamentary structure in sunpots. I shall show that the dark filaments in the penumbral region of sunspots are associated with stronger magnetic fields.     

Vector magnetic fields in sunspots

Observations of a round, unipolar sunspot in the Zeeman triplet Fe i 6302.5 with the High Altitude Observatory Stokes Polarimeter are used to derive the vector magnetic field in the spot. The behavior of the magnitude, inclination, and azimuth of the field vector B across the spot is discussed. A linear relation is found between the continuum intensity I _c and the field magnitude B. Time series obtained in the umbra show significant power in the magnitude of the field at a period of t 180 s but the other components of the field vector do not display this behavior.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

On AlF lines in sunspots

Intensity factors for bands of the C-A transition of the AlF molecule are calculated. A reinvestigation for the lines of (0, 0) band of the C-A system in sunspot spectra is suggested, so as to resolve the questionable existence of AlF absorption lines in sunspots.