Total Solar Irradiance and the Fe XIV Corona

Analyzing daily values of the total solar irradiance (TSI), the coronal index of solar activity (CI), and the Mg II 280-nm core-to-wing ratio (Mg II index), we have found that the temporal variations of these indices are very similar to each other during the period from 1978 to 2005. The correlation between CI and TSI, with the PSI correction lying within the interval under study, has been found to be 0.699, which is very close to the value of 0.703 of the correlation between Mg II and TSI for 27-day averages (the CI – Mg correlation is 0.824). The regression equation between CI and TSI is almost linear, except for TSI depletions when a large number of sunspots are present on the visible disk. By employing CI, an extrapolation of TSI back to 1947 is presented.     

Proposed Mg V,Fe XIV and forbidden Fe XVII line identifications in the EUV solar spectrum

Some line identifications in solar disk and limb spectra are proposed on the basis of recent laboratory and theoretical results reported in the literature, including allowed lines of Mgi and Fexiv in the EUV spectrum and an expected forbidden line of Fexvii near 1190 Å.     

Fine structure in solar microwave bursts

We have designed and constructed a new multi-channel radio spectrograph for the study of short-lived structures in solar microwave bursts. It measured the integrated flux over the whole solar disc in two circular polarizations at 36 frequencies between 4 and 8 GHz, with a time constant of 0.5 ms. We have analyzed all 119 recorded bursts observed in 1981 and 1983. We focused our attention on events with a lifetime of less than 1 s. Fine structure occurs in about 30% of the observed bursts, and can be as rich in detail as in bursts observed at lower frequencies. We found at least four different classes of events. In one event neither bandwidth nor time resolution of the receiver appear to be sufficient to resolve the fine structure. The bulk of the drifts is found to be towards higher frequencies. Periodic flux variations were found in two cases.     

Fine structure of solar magnetic fields

The deduction of magnetic fields from chromospheric structure is extended to active regions and transverse fields. Fields independently predicted by these rules from a high resolution H filtergram are compared with a high resolution magnetogram. The H method has the advantage over conventional magnetograms that it shows transverse fields and relates the fields to the real Sun. It has the disadvantage that higher spatial resolution is required and that it is difficult and time consuming in very complicated regions.The response of the chromosphere to magnetic fields is most consistent. Vertical field is invariably marked by bright plage, with brightness roughly proportional to the field strength (except for sunspots). All dark fibrils mark transverse fields and are parallel to field lines. All polarity changes are marked by dark fibrils, which may be transverse fibrils perpendicular to the field boundary, or filaments (prominences) which connect more distant points, and in which the field lines run nearly parallel to the boundary. The asymmetry between preceding and following polarity found by Veeder and Zirin (1970) does not exist; it was due to the low resolution of the Mount Wilson magnetograms.The complexity of active region field structure depends on the history of the region; all flux erupts in simple bipolar form, and lines of force remain connected to sibling spots until reconnection takes place. Thus the complex structure only occurs after eruption of several dipoles which reconnect. The phenomenon of inverted polarity turns out to be due to the emergence of satellite bipolar fields, where the p spot merges with the rest of the p field and the f spot appears as an included f field. Flares usually occur when the field lines from f spot reconnect from its sibling to the main spot.     

Fine structure of solar magnetic fields

The problem of inequality of results of longitudinal magnetic fields measured in the magnotosensetive lines FeI 5250 and FeI 5247 is investigated. The observed ratio of longitudinal components of magnetic field H ₁₁(5250)/H ₁₁(5247) is compared to the calculated for different combinations of magnetic field elements. The calculations have been made with standard model photosphere for quiet regions. It was concluded that the underestimated value of magnetic field obtained with the FeI 5250 line is explained by the presence of unresolved elements with kilogauss magnetic fields.     

Fine structure of large flare radioemission

Several recent phenomena with zebra patterns (ZPs) and fiber bursts on the dynamic spectra of solar type IV radio bursts have been complexly analyzed using all available ground-based and satellite data (SOHO, TRACE, RHESSI). ZPs and fiber bursts were observed at frequencies of 50–3800 MHz. The main relative spectral parameters and the degree of circular polarization of ZPs and fiber bursts are almost identical. The fine structure was observed in powerful and weak phenomena (and was more impressive in weak phenomena) during impulsive and decline phases at instants of recurring continuum bursts. The shape of the fine structure depends on that of the magnetic loops in a radio source, the type of fast particle acceleration (impulsive or prolonged), and the presence of shock waves and coronal mass ejections. Several new effects of the interaction between zebra stripes and fiber bursts have been detected. Specifically, up to 40 fiber bursts with different frequency ranges were simultaneously observed in the frequency range 1–2 GHz against a background of sudden absorptions. It has been indicated that different effects in the ZP stripe behavior can be explained within the scope of the model with whistlers, if the quasi-linear diffusion of fast particles on whistlers (which deforms the particle velocity distribution function) is taken into account.     

Fine structure of motions in a quiescent prominence

The Ca⁺ K line of the quiescent prominence of 15 October 1969 observed at the Abastumani Astrophysical Observatory of the Academy of Sciences of Georgia, U.S.S.R. is studied in detail. The behaviour of various fragments of the prominence with the line-of-sight Doppler velocities is investigated for different places of the prominence along the spectrum height. Due to superposition of the fragments and the radial velocities a complex non-gaussian profile of the spectral line is formed. Decomposition of the non-gaussian profile into suitable gaussian ones is made with a computer yielding objectivity and high accuracy. The rms error for the intensities in the decomposition is about 5%.It is found that the components into which the Ca⁺ K line decomposes at each level, are traced while proceeding from one photometric section to another throughout the spectral height.A hypothesis on the preferably filamentary structure of the prominence is put forward.     

Fine structure in Ca ii on the solar disc

High-dispersion spectra of the core of the K line of Ca ii as seen at the center of the solar disc have been reduced. Resolution on the spectra approach 1 arc sec. Line profiles of individual elements are very asymmetric and often are peaked on only one side of the line center. Variations of the line profiles and the emission peaks are discussed. The doubly reversed mean profile of the K line is explained as a spatial average of individual profiles, and it is suggested that single peaks may be caused by Doppler-shifted discrete elements in the chromosphere.Donald H. Menzel Research Fellow in Astronomy.     

Fine structure and evershed motions in the sunspot penumbra

The observed inhomogeneity of the intensity and Evershed motions means any model of the penumbra must be essentially inhomogeneous. A simple model is put forward in which the interaction of convection rolls with an initially homogeneous magnetohydrostatic sunspot field causes a concentration of flux in the dark filaments. This process drives Evershed motions outwards in these regions; the motions are superficial and shear the lines of force, so that the field appears stronger and more horizontal in the dark filaments. This situation must be time-dependent to avoid rapid destruc tion of the whole spot.     

The excitation mechanism of [Fe XIV] 5303 å line in the inner regions of solar corona

The line intensity of the green coronal line and the continuum intensity are derived from the filter and white light photographs of the solar corona obtained during the 1980 total solar eclipse. Ratio of the line to continuum intensity is plotted against the radial distancer(=R/R₀,R ₀ is the solar radius), in various position angles. A simple model assuming an electron density dependence of the line and continuum intensities suggests a dominant collisional mechanism for the excitation of the line in the innermost regions (～ 1.4R ₀). The measured line to continuum ratio tends to a constant value at different radial distances in different position angles. The constancy of the measured line to continuum ratio indicates significant radiative excitation beyond 1.4 R₀, in some of the position angles.     

Fine structure in the sunspot spectrum-2 to 70 years

Application of a new data adaptive approach to power spectrum estimation has yielded evidence for a double solar cycle line in the Zurich sunspot time history. There is significant power from 8 to 15 yr in the spectrum with the primary line at 11.1 yr and three attendant multiplets that may be significant. The first four harmonics of the solar cycle are detected too. Quite marginal evidence for a peak at 65 yr in the spectrum is presented. These results closely correspond to those recently found in the geomagnetic spectrum.     

Fine structure of decametric type II radio bursts

We have performed a comparative analysis of the fine structure of two decametric type II bursts observed on July 17 and August 16, 2002, with the 1024-channel spectrograph of the UTR-2 radio telescope in the frequency range 18.5–29.5 MHz and with the IZMIRAN spectrograph in the frequency range 25–270 MHz. The August 16 burst was weak, ～2–5 s.f.u., but exhibited an unusual fine structure in the form of broadband fibers (Δf _e > 250–500 kHz) that drifted at a rate characteristic of type II bursts and consisted of regular narrow-band fibers (Δf _e > 50–90 kHz at 24 MHz) resembling a rope of fibers. The July 17 burst was three orders of magnitude more intense (up to 4500 s.f.u. at 20 MHz) and included a similar fiber structure. The narrow fibers were irregular and shorter in duration. They differed from an ordinary rope of fibers by the absence of absorption from the low-frequency edge and by slow frequency drift (slower than that of a type II burst). Both type II bursts were also observed in interplanetary space in the WIND/WAVES RAD2 spectra, but without any direct continuation. Analysis of the corresponding coronal mass ejections (CMEs) based on SOHO/LASCO C2 data has shown that the radio source of the type II burst detected on August 16 with UTR-2 was located between the narrow CME and the shock front trailing behind that was catching up with the CME. The July 17 type II fiber burst also occurred at the time when the shock front was catching up with the CME. Under such conditions, it would be natural to assume that the emission from large fibers is related to the passage of the shock front through narrow inhomogeneities in the CME tail. Resonant transition radiation may be the main radio emission mechanism. Both events are characterized by the possible generation of whistlers between the leading CME edge and the shock front. The whistlers excited at shock fronts manifest themselves only against the background of enhanced emission from large fibers (similar to the continuum modulation in type IV bursts). The reduction in whistler group velocity inside inhomogeneities to 760 km s^?1 may be responsible for the unusually low drift rate of the narrow fibers. The magnetic field inside inhomogeneities determined from fiber parameters at 24 MHz is ～0.9 G, while the density should be increased by at least a factor of 2.     

Fine core-jet structure of the galaxy M87

The fine core-jet structure of the radio galaxy M87 has been investigated in the millimeter-decimeter wave band. A counterjet whose extent is ρ(λ) ≈ 0.036λ pc, where the wavelength λ is expressed in centimeters, has been identified. At a wavelength of 2 cm, the brightness of the jet and counterjet decreases exponentially to the minimally detectable level. However, the decline for the jet slows down from a level of several percent of the peak value. The bipolar jet consists of a highly collimated relativistic plasma flow surrounded by a nonrelativistic low-velocity component. The low-velocity jet flow includes a helical component observable up to a distance of 20 mas or 1.6 pc. The reaction of the flow produces a multimode precession responsible for the helical shape of the relativistic jet with a variable pitch and a curved axis. The helical structures of the jet and counterjet are mirror reflections of each other relative to the ejector. The apparent size of the accretion disk seen edge-on reaches 1.5 mas or 0.12 pc.     

Fine structure in the inner corona observed at the 1970 eclipse

On the slit spectrogram obtained at the 1970 eclipse in Mexico, the intensities of four coronal lines (Nixiii 5116, Fexiv 5303, Fex 6374, and Nixv 6702) and the continuum were measured as a function of distance along the slit. It is found that there exist a lot of fine fluctuations both in the lines and in the continuum intensities superposed on a large scale formation. The correspondence of such fluctuations between the continuum and the lines is good, with the exception of the line 6374 which shows a peculiar fluctuation. It is shown that the intensities of the three lines 5116, 5303, and 6702 seem to be proportional to the square of the continuum intensity while the 6374 line intensity may be proportional to the fourth power or more.     

Fine structure of the Sun at 1.3 cm wavelength

The two-element interferometer at Hat Creek Observatory was used at 1.3 cm wavelength to study the fine structure of the radio emissive regions on the Sun. Observations of the quiet Sun at 1.3 cm show sudden changes in the fringe amplitude and phase, lasting for typically about 5–8 min. Assuming that these events are identical in nature, a plot of peak amplitude vs the projected baseline at the time of the event suggests emission from a region of angular size of about 10″. The corresponding brightness temperature is 50000 K. It is possible that these events may be related to the appearance and disappearance of groups of spicules or mottles.     

Fine structure on the surface of bare strange stars

The surface fine structure of bare strange stars is determined. The distribution of electrons and quarks in the surface layer is determined using a phenomenological Thomas-Fermi model. For the MIT bag model, the quark density at the free surface is found to fall off continuously to zero in a layer of finite thickness. Unlike the results of other authors, here the electric field in the transition layer changes direction. The coefficient of surface tension of the quark matter is determined in terms of this model. Depending on the model parameters, it is 60–150 MeV/Fm².Translated from Astrofizika, Vol. 48, No. 1, pp. 139–150 (February 2005).