Space-time profile variations of some spectral lines and their influence upon doppler velocity measurements

A technique for high-sensitivity measurements of spectral line profile fluctuations is suggested. Observations with spectral lines most commonly used to study the oscillations have been carried out. It is found that 5-min and 3-min fluctuations of Fei 5123, 5250, 5434 and NaDi 5896 line profiles are able to produce signals equivalent to line-of-sight velocities of 1–5 m s^–1 at a spatial resolution of 5 and 10–35 m s^–1 at 1.5 × 4 resolution. Such observations permit a better understanding of the particular physical factors responsible for the oscillations of line-of-sight velocity signals and the magnetic field which are the subject of study of helioseismology.     

THE EFFECT OF SEEING ON SOLAR MAGNETIC FLUX MEASUREMENTS

We investigate the influence of seeing upon measurement of magnetic flux of photospheric fields. For this purpose we quantify seeing variation in one day's observation at Big Bear Solar Observatory in terms of the Fried function, a Modulation Transfer Function for the atmospheric seeing. The temporal variation of seeing quality is compared with that of magnetic flux measured in a quiet region with size 5 \times 4 near the solar disk center. A good correlation is found between the seeing change and apparent evolution of magnetic flux values, implying, as a possibility, that magnetic flux measurement might have been modulated by seeing. Based on a simple model of ensembles of Gaussian magnetic elements we argue that even the net flux as well as the total flux can change due to seeing variation if the magnetograph has a finite detection threshold and if the intrinsic fluxes in one and the other polarities are unbalanced.     

Average photospheric poloidal and toroidal magnetic field components near solar minimum

Average (over longitude and time) photospheric magnetic field components are derived from 3 Stanford magnetograms made near the solar minimum of cycle 21. The average magnetograph signal is found to behave as the projection of a vector for measurements made across the disk. The poloidal field exhibits the familiar dipolar structure near the poles, with a measured signal in the line Fe i 5250 Å of 1 G. At low latitudes the poloidal field has the polarity of the poles, but is of reduced magnitude ( 0.1 G). A net photospheric toroidal field with a broad latitudinal extent is found. The polarity of the toroidal field is opposite in the nothern and southern hemispheres and has the same sense as subsurface flux tubes giving rise to active regions of solar cycle 21.These observations are used to discusse large-scale electric currents crossing the photosphere and angular momentum loss to the solar wind.Now at Kitt Peak National Observatory, Tucson, Ariz. 85726, U.S.A.     

The universal solution of Einstein's equations of general relativity

Einstein's equations of general relativity are solved in terms of gravitational potential derivatives, withT equal to mass and/or field energy such thatT 0 outside a body. The line element equation then describes the variance of test particle internal geometrical structure and time-rate due to work done in a field, not the space-time curvature. Specific properties of gravitational fields and bodies come from this new solution: (a) The gravitational field consists of electromagnetic spin 2 gravitons which produce the gravitational force through the magnetic vector. (b) The gravitational mass is the Newtonian mass, not the relativistic mass, of a moving body. (c) An action principle exists in gravitation theory. (d) Attractive gravity exists between matter and antimatter. (e) Unification with quantum physics appears possible.     

The spiral configuration of sunspot magnetic fields

Distributions of circularly and linearly polarized intensities are computed using an analytical magnetic field model for an isolated sunspot, and these intensity distributions are compared with observed intensities in all Stokes parameters in the 5250 line measured with the Marshall Space Flight Center's vector magnetograph. The qualitative agreement between measured and calculated linearly polarized intensity distributions is discussed with regard to implications as to the configuration of the transverse magnetic field of the isolated sunspot.     

Stray-Light Effect on Magnetograph Observations

To examine the stray-light effect in magnetograph observations, we have determined the point spread functions of the vector magnetograph mounted on the Japanese Solar Flare Telescope based on two indirect methods, one analyzing the solar limb intensity profile, and the other using the Fourier power spectra of photospheric intensity distributions. Point spread functions consist of two parts: a blurring part which describes seeing and small-spread-angle stray light, and a scattering part which describes large-spread-angle stray light. The FWHM spatial resolution is typically 3.0, and the amount of scattered light is about 15% on clear days. We find that the blurring part is well described by a Moffat function whose Fourier transform is given by an exponential function. Our results indicate that polarization measurements of low-intensity magnetic elements like sunspots may be significantly underestimated due to the large-spread-angle stray light, and polarization measurements of magnetic elements which are smaller than 5–7 appear to be disturbed by small-spread-angle stray light.     

Unsteady magnetohydrodynamic flows in a rotating elasto-viscous fluid

The unsteady flow of an incompressible electrically-conducting and elasto-viscous fluid (Walter's liquidB), filling the semi-infinite space, in contact with an infinite non-conducting plate, in a rotating medium and in the presence of a transverse magnetic field is investigated. An arbitrary time-dependent forcing effect on the motion of the plate is considered and the plate and fluid rotate uniformly as a rigid body. The solution of the problem is obtained with the help of the Laplace transform technique and the analytical expressions for the velocity field as well as for the skin-friction are given.     

Weak-Field Magnetogram Calibration using Advanced Stokes Polarimeter Flux Density Maps – II. SOHO/MDI Full-Disk Mode Calibration

Cotemporal Nii 676.8 nm full-disk magnetograms from the Michelson Doppler Interferometer (MDI) instrument on SOHO and the Advanced Stokes Polarimeter (ASP) are quantitatively compared using observations of active region AR 8218, a large negative polarity sunspot group observed at S20 W22 on 13 May 1998. MDI produces flux density estimates based on a polarized line center-of-gravity algorithm using moderate spectral resolution filtergrams with approximately 4 arc sec angular resolution. The magnetograms are formed by an on-board image processor and sent to the ground where they are calibrated using an empirical model to produce flux density maps. The ASP uses high spectral resolution Stokes polarimetric observations to produce very high precision vector magnetic field maps at angular resolution values on the order of 1 arc sec in good seeing. We use ASP inversion results to create a reference ASP `longitudinal magnetic flux density map' with which to calibrate the MDI full-disk magnetograms. The magnetograms from each instrument are scaled to a common reference frame and co-aligned with an accuracy of about 1.6 arc sec. Regions of invalid data, poor field-of-view overlap, and sunspots are masked out in order to calibrate MDI predominately on the relatively vertical `weak-field' plage magnetic elements. Pixel-to-pixel statistical comparisons are used to determine an MDI magnetogram linear calibration relative to reference ASP flux density values. We find that the current Level-1.5 MDI full-disk calibration gives flux density values lower on average by a factor of 0.64±0.013 compared to the ASP reference in active region plage. In sunspot regions (penumbra and umbra) the factor is 0.69±0.007.     

High resolution polarimetry of the Sun at 3.7 and 11.1 cm wavelengths

Two methods of observing the neutral line of the large-scale photospheric magnetic field are compared: (1) neutral line positions inferred from H photographs (McIntosh, 1972a, 1975; McIntosh and Nolte, 1975) and (2) observations of the photospheric magnetic field made with low spatial resolution (3) and high sensitivity using the Stanford magnetograph. The comparison is found to be very favorable.     

Concerning five-minute variations of the global magnetic field of the Sun

For the purpose of identifying five-min oscillations we analyze long-term continuous observations of the solar magnetic field (with a duration from 3 to 11 hours) with 0.5 D spatial resolution obtained with the STOP telescope (Solar Telescope for Operative Predictions) at the Sayan observatory in 1987 and 1989. It is shown that global magnetic field fluctuations with such periods seem to be real, but the character of corresponding power spectra is strongly dependent on the mean field strength in the magnetograph aperture.     

Chaos and secondary resonances in the mimas–tethys system

We have investigated the role of the 200yr period discovered by Vienne and Duriez (1992) on the tidal evolution of the Mimas–Tethys system through the 2:4 ii present resonance. Three terms are found to generate this period. We present a perturbedpendulum model in which these terms bring about a perturbation to the ideal ii resonance pendulum, which is in a direct ratio to the eccentricity e of Tethys. Although e is now very small, it is shown that this quantity could have been much greater in the past. We also show, thanks to this model, that these terms may have brought about a stochastic layer of noticeable width at the time of capture in the ii resonance, with the consequence that the possible values of the inclination i of Mimas before capture range from 0.4° to 0.6° (these uncertainties arise from the present uncertainties on e). The role of each one of the three terms is examined in the appearance of chaos. A capture into the 1/1 secondary resonance (between the libration period of the primary ii resonance and the period of about 200yr) is found possible. It means that the system could have experienced several captures in the primary resonance, instead of a single one, and that i could have been, with this assumption, much lower than 0.4°. A probability of capture into this secondary resonance as a function of the eccentricity of Tethys on encounter is derived, using Malhotra's method (Malhotra, 1990). Allan's values of i = 0.42° and e 0 (Allan, 1969) are therefore called into question, and taking e 0 is shown to be absolutely necessary if we want to understand the phenomena at work in the Mimas–Tethys system.     

Simulations of cosmic-ray particle diffusion

The diffusion of charged particles in a stochastic magnetic field (strengthB) which is superimposed on a uniform magnetic fieldB ₀ k is studied. A slab model of the stochastic magnetic field is used. Many particles were released into different realizations of the magnetic field and their subsequent displacements z in the direction of the uniform magnetic field numerically computed. The particle trajectories were calculated over periods of many particle scattering times. The ensemble average was then used to find the parallel diffusion coefficient . The simulations were performed for several types of stochastic magnetic fields and for a wide range of particle gyro-radius and the parameterB/B ₀. The calculations have shown that the theory of charged particle diffusion is a good approximation even when the stochastic magnetic field is of the same strength as the uniform magnetic field.     

First experience in automatic spectral classification related to the MEGA program

The results of automatic quantitative spectral classification of stars in field No. 10 (₁₉₅₀ = 1^h18^m, ₁₉₅₀ = + 3°13)of the MEGA programme are presented. Some tentative stellar-statistical results are discussed.     

A comparison of vector magnetograms from the marshall space flight center and mees solar observatory

We compare completely independent vector magnetic field measurements from two very different polarimetric instruments. The Marshall Space Flight Center's imaging vector magnetograph is based on a birefringent filter, routinely measuring all four Stokes parameters integrated over the filter bandpass (1/8 Å) which is tunable across the Fei 5250 line in 10 mÅ steps. The Haleakala Stokes Polarimeter of the Mees Solar Observatory (MSO) is based on a spectrometer, routinely measuring all four Stokes parameters of the Fei 6302.5 line simultaneously and then spatially scanning to build up a vector magnetogram. We obtained active region magnetic field data with both the Marshall Space Flight Center (MSFC) and MSO systems on five days during June 1985. After interpolating the MSFC vector fields onto the more coarse spatial grid of MSO we make a point-by-point comparison of the two vector fields for data obtained on two of these days (June 8 and 9). From this comparison we conclude: (1) the spatially-averaged line-of-sight components agree quite well; (2) although the MSO spatial grid is coarser, the quality of the MSO image is better than that of the MSFC data because of better seeing conditions; (3) the agreement between the transverse magnitudes is affected by the poor image quality of the MSFC data; and (4) if the effects of Faraday rotation caused by including line-center linear polarization in the method of analysis are taken into account, the azimuths show good agreement within the scatter in the data caused by the averaging process.National Research Council Resident Research Associate.     

Free convection effects on the flow past a moving vertical infinite porous plate

An analysis of the effects of free convection currents on the flow field of an incompressible viscous fluid past an infinite porous plate, which is uniformly accelerated upwards in its own plane, is presented, when the fluid is subjected to a variable suction (or injection) velocity. It is assumed that this normal velocity at the porous plate varies att^–1/2, wheret denotes time. The equations governing the flow are solved numerically, using two-point boundary value shooting techniques.     

Ubiquitous chromospheric structures observed in the quiet Sun at millimeter and centimeter wavelengths

Unique long-term visibility variations are detected when the quiet Sun is observed with interferometers operating at 8 mm and 11 cm wavelength with angular resolutions of 0.5. Quasiperiodic fluctuations in fringe amplitude are observed with periods between 20 and 30 min, and with amplitude nulls which are correlated with 180° phase changes. These variations are interpreted in terms of a changing projected baseline while viewing a few sources with angular sizes of 0.5 which are distributed within the main interferometer beam with typical angular separations of 7. The observed variations cannot be due to expanding or contracting sources of the type envisaged by Bocchia and Poumeyrol (1976) when explaining similar variations observed at 8 mm wavelength. A comparison of the flux observed at 8 mm and 11 cm indicates that the individual sources are optically thick thermal radiators with a flux which decreases with increasing wavelength, but with a temperature which increases with increasing wavelength where higher, hotter levels of the chromosphere are observed. For a source whose angular size is 0.5, the observed flux values correspond to respective temperatures of 5000 K and 19 000 K at 8 mm and 11cm - suggesting that elements of the chromospheric network are being observed. A thermal origin for the individual sources is consistent with the lack of any detectable circular or linear polarization (< 10%) in the interferometer signal.     

Similarities between chromospheric and photospheric quiet-Sun magnetograms

Simultaneous observations of chromospheric (H) and photospheric (Fei 5324.19 Å) magnetograms in quiet solar regions enable us to study the spatial configuration of the magnetic field in the solar atmosphere. With the typical spatial resolution of the Huairou magnetograph, the photospheric and chromospheric magnetic structures of the quiet Sun maintain a very similar pattern. Moreover, the vertical magnetic flux is almost the same from the photosphere to the chromosphere. As an intermediate step, we analyze the formation of the working lines used by the Huairou video magnetograph of the Beijing Astronomical Observatory. The Stokes V contribution function of H and Fei 5324.19 Å are calculated. It is found that our H magnetograms provide the distribution of the chromospheric magnetic field at a height some 1000–1500 km above the photosphere.     

Structure and evolution of magnetic network features

Magnetogram series, obtained with the 512-diode-array magnetograph at KPNO, are used to investigate several properties of magnetic flux tubes in the solar atmosphere. Average size, lifetime and inclination of the flux elements are determined. Further we discuss the question, how magnetic flux appears and disappears on the solar surface. At last it is investigated, if our observational results are consistent with Piddington's flux-rope-fibre theory of solar magnetism.Visiting Astronomer at Kitt Peak National Observatory.     

Free convection and mass transfer effects on the hydro-magnetic oscillatory flow past an infinite vertical porous plate

Two-dimensional unsteady free convection and mass transfer, flow of an incompressible viscous dissipative and electrically conducting fluid, past an infinite, vertical porous plate, is considered, when the flow, is subjected in the action of uniform transverse magnetic field. The magnetic Reynolds number is taken to be small enough so that the induced magnetic field is negligible. The solution of the problem is obtained in the form of power series of Eckert numberE, which is very small for incompressible fluids. Analytical expressions for the velocity field and temperature field are given, as well as for the skin friction and the rate of heat transfer for the case of the mean steady flow and for the unsteady one. The influence of the magnetic parameter,M, modified Grashof numberG _c , Schmidt numberS _c and frequency , on the flow field, is discussed with the help of graphs, when the plate is being cooled, by the free convection currents (G _r ,E>0), or heated (G _r ,E<0). A comparative study with hydrodynamic case (M=0) and the hydromagnetic one (M0) is also made whenever necessary.List of symbols B₀ applied magnetic field - |B| amplitude of the skin friction - C concentration inside the boundary layer - C concentration in the free stream - C _w concentration at the porous plate - C _p specific heat at constant pressure - D diffusion coefficient - E Eckert number - g _x acceleration due to gravity - G _c modified Grashof number - G _r Grashof number - M magnetic parameter - N _u Nusselt number - P Prandtl number - |Q| amplitude of the rate of heat transfer - S _c Schmidt number - T temperature of the fluid - T _w temperature of the plate - T temperature of the fluid in the free stream - T _r ,T _i fluctuating parts of the temperature profile - u, v velocity components in thex, y directions - u dimensionless velocity in thex direction - u ₀ mean steady velocity - u ₁ unsteady part of the velocity - u _r ,u _i fluctuating parts of the velocity profile - U dimensionless free stream volocity - U ₀ mean free stream velocity - v ₀ suction velocity - x, y co-rodinate system Greek Symbols phase angle of the skin-friction - coefficient of volume expansion - _* coefficient of expansion with concentration - phase angle of the rate of heat transfer - dimensionless co-ordinate normal to the plate - dimensionless temperature - ₀ mean steady temperature - ₁ unsteady part of temperature - k thermal conductivity - v kinematic viscocity - density of fluid in the boundary layer - density of fluid in the free stream - electrical conductivity of the fluid - skin friction - ₀ mean skin friction - frequency - dimensionless frequency     

Weak-Field Magnetogram Calibration using Advanced Stokes Polarimeter Flux-Density Maps – I. Solar Optical Universal Polarimeter Calibration

Cotemporal Fei 630.2 nm magnetograms from the Solar Optical Universal Polarimeter (SOUP) filter and the Advanced Stokes Polarimeter (ASP) are quantitatively compared using observations of active region AR 8218, a large negative polarity sunspot group observed at S20 W22 on 13 May 1998. The SOUP instrument produces Stokes V/I `filter magnetograms' with wide field of view and spatial resolution below 0.5 arc sec in good seeing, but low spectral resolution. In contrast, the ASP uses high spectral resolution to produce very high-precision vector magnetic field maps at spatial resolution values on the order of 1 arc sec in good seeing. We use ASP inversion results to create an ASP `longitudinal magnetic flux-density map' with which to calibrate the less precise SOUP magnetograms. The magnetograms from each instrument are co-aligned with an accuracy of about 1 arc sec. Regions of invalid data, poor field-of-view overlap, and sunspots are masked out in order to calibrate SOUP predominately on the relatively vertical `weak-field' plage magnetic elements. Pixel-to-pixel statistical comparisons are used to determine the SOUP magnetogram linear calibration constant relative to ASP flux-density values. We compare three distinct methods of scaling the ASP and SOUP data to a common reference frame in order to explore filling factor effects. The recommended SOUP calibration constant is 17000 ± 550 Mx cm^–2 per polarization percent in plage regions. We find a distinct polarity asymmetry in SOUP response relative to the ASP, apparently due to a spatial resolution effect in the ASP data: the smaller, less numerous, minority polarity structures in the plage region are preferentially blended with the majority polarity structures. The blending occurs to a lesser degree in the high-resolution SOUP magnetogram thus leading to an apparent increase in SOUP sensitivity to the minority polarity structures relative to the ASP. One implication of this effect is that in mixed polarity regions on the Sun, lower spatial resolution magnetograms may significantly underestimate minority polarity flux levels, thus leading to apparent flux imbalances in the data. ^*Visiting Astronomer, National Solar Observatory, operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation. The National Center for Atmospheric Research is sponsored by the National Science Foundation.