Automatic guiding of the primary image of solar Gregory telescopes

The primary image reflected from the field stop of solar Gregory telescopes is used for automatic guiding. This new system avoids temporal varying influences from the bending of the telescope tube by the main mirror's gravity and from offsets between the telescope and a separate guiding refractor. The required stiffness of the guider mechanics and the small areas of the sensors demand small f numbers for the guider optics, which cause problems with the image quality and with heat. Problems also arise from the pinhole in the telescope's field stop which is imaged as a dark dot on the sensor. Pointing errors introduced by the telescope affect shifts of the solar image on the sensor. These are numerically determined by Fourier methods which are found to be less sensitive to noise than profile centering methods. Several types of guiders are tested, the final equipment, now installed at the Gregory telescopes at Tenerife and at Locarno, is described.     

Large-scale motion of solar filaments

Precise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.     

Rotating motion in solar surges

The line-of-sight velocity field of the solar limb surge of 1980 Oct 11, observed at Yunnan Observatory, showed a rotating motion. The velocity of rotation and the true ascending speed of the surge were determined from H observations. We also found an accompanying expansion at several tens of km/s and the presence of a pulsed phenomenon with a period of a few minutes at the root of the surge. We point out that the steep density gradient between the surge plasma and its surrounding atmosphere causes double-pole diffusion, and the electric field generated by the double-pole diffusion causes electric drift of the surge plasma, hence the rotation.     

Mass motion in the solar chromosphere

A high resolution profile of the solar Oi 1304.9 Å line has been measured from rocket spectrograms. The profile is nearly flat-topped, showing only a slight solar reversal after instrument effects and absorption due to atomic oxygen in the earth's atmosphere have been allowed for. A theoretical analysis of this line, under the assumption of non-LTE conditions and a homogeneous, spherically symmetric chromosphere, predicts a rather deep solar reversal. The theoretical profile may be made consistent with the observed profile if mass motion is present in the chromospheric region where the line is formed. A Gaussian distribution of up and down velocities with a root mean square velocity of about 7 km/sec gives best agreement between the predicted and observed profile. This result is consistent with the conclusion made from a study of high resolution profiles of solar lines in the visible spectrum that mass vertical velocities increase with height above the photosphere.     

D-region measurements during a solar eclipse

Observations of positive ion density in the _D-region during the solar eclipse of 1966 May 20, were made by means of a cylindrical Langmuir probe carried on a small rocket. the launch site was near Karystos in Greece. The ion density between 70 and 80 km was found to vary rapidly during the eclipse and the main ionising source at the time is considered to have been an X-ray emitting region on the Sun (McMath 8302). From the X-ray intensity of the Sun on this day, the maximum NO concentration at 80 km is found to be 1·8 × 10⁶cm⁻³. this is consistent with other D-region and some laboratory observations, but not with airglow measurements. Some evidence was also found for day-to-day variations in D-region density not associated with variations either in solar X-rays or in atmospheric density. These are presumed to be due to variations in the concentration of a minor atmospheric constituent such as NO, perhaps with atmospheric temperature.     

Enigmas in measurements of solar magnetic field

The mean magnetic field (MMF) of the photosphere of the Sun as a star was measured in 2001?C2010 at the Crimean Astrophysical Observatory using two Fe I absorption lines with ?? = 524.7 nm and ?? = 525.0 nm. The regression coefficient b for 1054 pairs of daily values measured simultaneously on both lines equals 0.82 (a correlation coefficient is 0.94; magnetic field strengths determined by the line with ?? = 525.0 nm are lower than those for the line with ?? = 524.7 nm). However, the b value varied significantly along with phases of the 11-year cycle from 0.88 in 2003 to 0.49 in 2009. It is difficult to ascribe these variations to purely instrumental or solar causes. Moreover, the semiannual value of b decreased with the decrease in the absolute strength of the MMF, which contradicts the model of thin magnetic flux ropes of the photosphere. Similar behavior of b was also observed in the comparison of MMF measured at the Crimean Astrophysical Observatory and Stanford by the line with ?? = 525.0 nm. The inconsistency of the results obtained by these two iron lines on different instruments has been noted. It has been concluded that the variance in and odd behavior of b are predetermined not only by the instrument and the Sun (by the so-called fine structure of the photosphere field), but also by the act of measuring. When recording solar (and stellar) magnetic fields and modeling atmospheric processes, quantum effects have to be taken into account, such as nonlocality, indistinguishability, and the entanglement of photons, as well as that a photon only acquires its properties at the exact moment of its detection. The best approximation to reality can be achieved by averaging the MMF measurements carried out with different magnetographs and in different spectral lines.     

Stratospheric ozone measurements by solar ultraviolet absorption

Vertical distributions of ozone in the stratosphere have been determined by means of u.v. differential absorption technique, using the Sun as a source. The filter radiometer and the data processing are described. Results obtained between altitudes of 22 and 32 km during the Intercomparison Ozone Campaign held in France in June 1981 are presented and discussed.     

Rapid sunspot motion during a major solar flare

A major solar flare on 15 November, 1991 produced a striking perturbation in the position and shape of the sunspot related most closely to the flare. We have studied these perturbations by use of the aspect-sensor images from the Soft X-ray Telescope on board YOHKOH, and with ground-based data from the Mees Solar Observatory. The perturbation occurred during the impulsive phase of the flare, with a total displacement on the order of 1 arc sec. The apparent velocity of approximately 2 km s^–1 exceeds that typically reported for sunspot proper motions even in flare events. We estimate that the magnetic energy involved in displacing the sunspot amounted to less than 4 × 10³⁰ ergs, comparable to the radiant energy from the perturbed region. Examination of the Mees Observatory data shows that the spot continued moving at lower speed for a half-hour after the impulsive phase. The spot perturbation appears to have been a result of the coronal restructuring and flare energy release, rather than its cause.     

The correlation between the Calern solar diameter measurements and the solar irradiance

The objective of this paper is to present some results deduced from the analysis of (space-based) solar irradiance observations used jointly with (ground-based) solar diameter variations. The idea which is explored consists in searching a possible influence of the variability of the Sun's whole shape on the luminosity. It is shown that such an effect, albeit small, may occur. Thus, the global geometry of the Sun – which is not a perfect static ellipsoid – would have to be taken into account when attempting to model the irradiance. Our very preliminary results may help to construct empirical models that can be used, in turn to force any model of the thermal structure of the ocean and atmosphere to deduce climate variations, if any.     

Proper motion measurements of umbral and penumbral structure

Horizontal proper motions of penumbral structure and umbral dots have been measured from a 17-min-long time series of sunspot images by numerical techniques. In the penumbra, inflows are seen to occur predominantly in the inner region, with an average velocity of 290 m s^–1. Penumbral outflows take place mostly in the outer part, where they reach velocities as high as 1.5 km s^–1, with an average velocity of 500 m s^–1. In the umbra, proper motions of 28 bright dots have been measured with an accuracy better than 50 m s^–1. The mean velocity of the umbral dots is 210 m s^–1. Most of the umbral dots display the well-known inward motion away from the peripheral umbra.     

A non imaging approach to solar oblateness measurements

A design is presented for an instrument to measure solar oblateness without forming a solar image and having two identical prisms as the only optical elements. Feasibility calculations indicate that this might be sensitive and quite free from instrumental induced errors.     

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.     

Numerical image processing applied to the solar corona

Numerical data processing is applied to the high-resolution images-of the solar corona obtained with the 20 cm coronagraph of the Pic du Midi observatory. Two complementary methods are proposed to solve some classical difficulties usually met in the morphological analysis of the solar corona, namely the brightness gradient in the inner and medium corona, the low contrast of numerous emissive regions and the superimposition along the line of sight of different structures. The methods which are described in this paper may help to resolve the complex coronal active regions into fine structures which is now necessary to interpret all observed corona data.     

Limits on radiative decays of solar neutrinos from measurements during a total solar eclipse

During the 1999 total solar eclipse we intended to search for photons emitted by a possible radiative decay of the heavier component of solar neutrinos, using two telescopes: an airborne one, and another at mountain altitude, in Romania(the NOTTE experiment). The weather conditions did not allow us to perform the measurements. Alternatively, we analyzed a video tape of the eclipse offered to us by a local television, obtaining some qualitative estimations on the neutrino lifetimes. We present also a first report on the observations made 21 June 2001, from Zambia. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photometric intensity and polarization measurements of the solar corona

During the 7 March, 1970, total eclipse of the Sun, the NASA Langley Research Center's Satellite Photometric Observatory (SPO) was used to measure the solar corona from Miahuatlan, Mexico. The SPO is equipped with a 24-inch Cassegrainian telescope, a four-channel photoelectric photometer, a Wollaston prism, and a rotating half-wave plate. Simultaneous measurements were made of the two orthogonal components of coronal light in the B and R bands of the UBVRI system. A 1-minute arc aperture was scanned from the lunar disk center out to five solar radii in a series of spirals of gradually increasing radius. For the first time, simultaneous multicolor intensity, degree, and angle of polarization profiles are computed from photoelectric measurements. Comparison of the variations of the measurements for each spiral scan yield a detailed picture of the intensity and polarization features in the K corona.     

Structure in the solar corona from radio scintillation measurements

Since the 1950s, a wide variety of radio observations based on scattering by electron density fluctuations in the solar wind has provided much of our information on density fluctuations and solar wind speed near the source region of the solar wind. This paper reviews recent progress in the understanding of the nature of these density fluctuations and their relationship to features on the Sun. The results include the first measurements of fine-scale structure within coronal streamers and evidence for structure in solar wind speed in the inner corona.     

The effect of spatial smearing on solar Doppler measurements

A general mathematical formulation of the effect of spatial smearing on solar velocity measurements is presented. The variations of the straylight induced error with wavelength and line parameters are discussed. The spatial and time dependence of the error will influence the measurement of solar limb effect and may introduce fictitious large scale velocity fields with amplitudes of the order of a few m/s.Present address: Space Science Department of ESA, ESTEC, Noordwijk, The Netherlands.