Structure of Perseids from visual observations

A new method of processing of visual meteor data has been worked outand applied to Perseid meteor shower observations. Reduced meteor hourly rates with magnitudes brighter than +3 are proportional to meteor flux densities with a coefficient equals to the effective collecting area. Corrections due to moon light and for meteor path lenghts were applied. Our observations 1972–1979 and 1982–1990 gave similar hourly rate profiles with a maximum rate of 71 meteors at solar longitude L=140.36°. Perseids 1980 and 1981 were about 1.5 times more active. The maximum Perseid activity in 1991–1992 was 119 meteors at solar longitude 139.54° and narrow peaks are observed at the same longitude showing an enhanced activity up to 225 meteors.     

Perseid meteor stream as observed in 1993

Presented are results of Perseid 1993 meteor shower from radar observation at Ondejov observatory. Investigation of the shower activity profiles in four echo duration intervals proved the position of dominant peak at solar longitude L = 138.°8±0.°05 (epoch 1950.0) followed by series of secondary maxima positions of which depend on examined echo duration class. Extremely low value of the mass distribution indexs = 1.27 ± 0.01 near the maximum activity peak associated with high proportion of fragmenting particles leads to the suggestion that meteor particles concentrated in this filament are younger than those which form the other parts of the stream.     

Structure and evolution of solar radio bursts at 26.4 MHz

Two dimensional source brightness distributions at 26.4 MHz for solar bursts of spectral type II, III, IV, and V are derived from observations with a multiple-baseline, time-sharing interferometer system. It was designed explicitly to study the large angle (40 halo) component of low frequency solar bursts first reported by Weiss and Sheridan (1962). Thirty-two bursts occurring in the interval of June–August, 1975, were fit with a circular gaussian core and an elliptical gaussian halo component. Half-power halo diameters (E-W×N-S) averaged 30×28 for type III bursts and 42×27, 28×37, 30×25 for type V, II and IV bursts respectively. Typical core sizes fell in the range of 10±4 giving 31 halo to core size ratio. All burst types were found to have some large angle structure: the specific intensity was 10% compared to the core but the total power in each component was comparable. Two processes for producing the core-halo structure of type III bursts are compared: scattering and refraction of a point source and refraction from many sources over an extended region. It is concluded that the core can be explained by either model but the halo is more consistent with emission from an extended source region of 40° in longitude.     

Fine structure of the Solar Chromosphere: Arch-Shaped Mottles

We analyze a time series of high resolution observations near the solar limb, obtained in H and the Mg b1 line. We identified arch-shaped dark mottles, which are thin, faint H structures observable under very good seeing conditions, best seen in H +0.75 Å. Their mean length is about 15, their mean height about 6 and indicative lifetimes is of the order of 5 min. They show negative (away from the observer) line-of-sight velocities. A possible interpretation is that material flows from the apex towards the feet of the arches.     

Radiant ephemeris and radiant area of the Perseid meteoroid stream

More than 600 double-station photographic recordings of Perseid meteor trails have been obtained at various stations in the period 1937–1985. This large data sample has recently been used to determine the activity profile and mean orbit of the Perseid meteoroid stream (Lindblad and Poruban, 1994). In the present paper the radiant of the Perseid meteoroid stream is studied based on a sample of 592 double-station photographic recordings. The daily motion of the radiant and the change of the size of the radiant area with date is investigated. A daily motion of 1.40° in right ascension and 0.20° in declination is derived. These values are slightly larger than those previously found by other researchers. The contraction of the radiant area at shower maximum previously reported from visual observations is confirmed. In a further study radiant areas derived for the dates of the new and the old Perseid maxima are compared. It is found that the radiant area of the new maximum is smaller than that of the old maximum.     

Eclipse Observations of Compact Sources in the Outer Solar Corona

We report here on high angular resolution observations of solar noise storm sources at a frequency of 75 MHz. The data for the study were obtained at the Gauribidanur Radio Observatory (long.: 77°2612 E, lat.: 13°3612 N) about 100 km north of Bangalore, India, during the solar eclipse of 24 October 1995. Our main conclusion is that there are structures of angular size 2.5 arc min in the outer solar corona.     

Lyrids 1994 observed by a forward scatter system

Radio observations of the Lyrid meteor shower obtained by a forward scatter radio system (Bologna-Lecce) in 1994 are analysed and discussed. The shower maximum appeared at solar longitude 31.0°(1950.0) and a distinct displacement between the maxima of the short-duration (< 1s) and long-duration ( 1s) echoes is observed. The shower has displayed a high activity, but no exceptional burst similar to that one observed in 1982, was recorded. It has been shown that the shower activity continues down to the smallest particle size of which existence in a meteoroid stream means their recent origin.     

Effects of mass transfer on the unsteady free convection flow past an accelerated vertical porous plate with variable suction

An exact analysis of the effects of mass transfer on the flow of a viscous incompressible fluid past an uniformly accelerated vertical porous and non-porous plate has been presented on taking into account the free convection currents. The results are discussed with the effects of the Grashof number Gr, the modified Grashof number Sc, the Schmidt number Sc, and the suction parametera for Pr (the Prandtl number)=0.71 representating air at 20°C.Nomenclature a suction parameter - C species concentration - C species concentration at the free stream - g acceleration due gravity - Gc modified Grashof number (vg^*(C –C )/U ₀ ³ ) - Pr Prandtl number (C _p/K) - T temperature of the fluid near the plate - T dimensionless temperature near the plate ((T-T )/(T -T )) - U(t) dimensionless velocity of the plate (U/U ₀) - v normal velocity component - v ₀ suction/injection velocity - x, y coordinate along and normal to the plate - v kinematic viscosity (/gr) - C _p specific heat at constant pressure - C _w species concentration at the plate - C non-dimensional species concentration ((C-C )/(C _w -C )) - Gr Grashof number (g(T _w -T )/U ₀ ³ ) - D chemical molecular diffusivity - K thermal conductivity - Sc Schmidt number (/D) - T _w temperature of the plate - T free stream temperature - t time variable - t dimensionless time (tU ₀ ² /) - U ₀ reference velocity - u velocity of the fluid near the plate - u non-dimensional velocity (u/U ₀) - v dimensionless velocity (v/U ₀) - v ₀ non-dimensionalv ₀ (v ₀ /U₀)=–at^–1/2 - y dimensionless ordinate (yU ₀/) - density of the fluid - coefficient of viscosity     

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.     

Almost stable regions for an area-preserving mapping

The area preserving mapping x = x + a(y – y ³), y = y – a(x – x³), for 0.3 a 2.0 has been studied to locate approximately the x-axis points bounding almost stable regions. For each value of a, these are fixed points with variational trace just greater than 2.0. Transition to chaos can occur rapidly as a increases (with n/k fixed).     

Observations of discrete emissions at the low latitude ground station Gulmarg

This paper presents discrete chorus type emissions observed in January/July, 1970 during the routine recording of whistlers and VLF emissions at our low latitude ground station Gulmarg (geomag. lat., 24°26N; geomag. long., 147°09 E). The chorus type emissions are comprised of discrete, sometimes overlapping, tones of one or more spectral shapes (risers, falling tones, hooks, etc.). It is shown that these emissions are generated in the equatorial plane (L1.2) by cyclotron resonance between the propagating wave and gyrating electrons.     

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.     

Contour Observations of the Leonid Shower in 1999

Contour visual observations of the Leonid meteor shower were made on December 18, 1999 by the method in which different groups of observers counted meteors in zenith, near the horizon, and observed through binoculars to study the luminosity function and the space density of the swarm. The luminosity function was obtained in the range of magnitudes from –8 ^m to +9 ^m . Over a wide range of magnitudes, the luminosity function is found to be nonlinear and is adequately approximated with a second-order curve. The logarithm of the meteor space density (m) reaches saturation at about 10 ^m , indicating that particles that give rise to meteors fainter than 10 ^m are absent in the swarm. The meteor stream reached its activity peak at a solar longitude of 235°, 287 (2 ^h 05 ^m UT). The peak visual zenithal hourly rate was about 7000 per one observer over an averaging interval of 1 min. The swarm space density increased by a factor of 6 within 0.5 hours and exceeded 600 particles per 10⁹ km³ for meteors brighter than +4 ^m . In the peak night, the luminosity-function exponent demonstrates no regular trend and reflects the intercepting of certain swarm clouds by the Earth.     

The Gauribidanur Radioheliograph

A new radio heliograph for obtaining two-dimensional images of the solar corona sequentially at many frequencies in the range 40–150 MHz has been built by the Indian Institute of Astrophysics at the Gauribidanur Radio Observatory (lat. 13°3612 N and long. 77°2707 E) about 100 km north of Bangalore, India. This paper describes various aspects of the antenna system, receiver front end, digital hardware, the data acquisition and the calibration procedure. The performance of the instrument is illustrated with maps of the continuum emission from the undisturbed corona at different frequencies.     

An Investigation of the Fine Spatial Structure of Meteor Streams Using the Relational Database “Meteor”

We have restored and ordered the archive of meteor observations carried out with a meteor radar complex KGU-M5 since 1986. A relational database has been formed under the control of the Database Management System (DBMS) Oracle 8. We also improved and tested a statistical method for studying the fine spatial structure of meteor streams with allowance for the specific features of application of the DBMS. Statistical analysis of the results of observations made it possible to obtain information about the substance distribution in the Quadrantid, Geminid, and Perseid meteor streams.     

Observations and interpretation of the slowly varying component of solar radio emission at decameter wavelengths

We have observed the slowly varying component of solar radio emission at a frequency of 34.5 MHz with half power beam widths of 26/40 in the east-west and north-south directions, respectively. It is found that the observed brightness temperatures vary within the limits of 0.3×10⁶K to 1.5×10⁶K, and the average half power widths of the brightness distribution on the Sun is about 3R . Thermal emission from coronal regions of various electron densities and temperatures with and without the magnetic field has been computed and compared with the observed results.     

Free-convection flow of water at 4°C past an infinite vertical porous plate with constant heat flux

An analysis of the two-dimensional flow of water at 4°C past an infinite porous plate is presented, when the plate is subjected to a normal suction velocity and the heat flux at the plate is constant. Approximate solutions are derived for the velocity and temperature fields and the skin-friction. The effects ofG (Grashof number) andE (Eckert number) on the velocity and temperature fields are discussed.Nomenclature u, v velocity components of the fluid inx, y direction - g acceleration due to gravity - coefficient of thermal expansion of water at 4°C - v kinematic viscosity - density - T temperature inside thermal boundary layer - T free-stream temperature - k thermal conductivity - C _p specific heat at constant pressure     

Research on sunspot Oscillations – I. The Pulkovo CCD Spectroheliograph-Magnetograph

The CCD spectroheliograph-magnetograph is a focal-plane ancillary instrument for the Pulkovo horizontal solar telescope ACU-5. The instrument is placed at an exit port of an isothermal high-resolution diffraction-grating spectrograph. A modified Leighton optical scheme for registration of sunspot magnetic fields is used. The instrument provides FITS-format digital video maps of radial velocities, magnetic fields, and spectroheliograms in any line of the spectral region 3900–11000 Å. The time to obtain one video map of size 91×154 is equal to 10.24 s. The angular resolution of the instrument is 0.8; spectral resolution is 0.01–0.03 Å. Since 1996 the Pulkovo CCD spectroheliograph-magnetograph has been used to obtain high spatial and temporal resolution observations of oscillations of radial velocities and magnetic fields in the photospheric layers of sunspots.     

Intensity variation of Oi λ5577 Å line of atomic oxygen at allahabad during morning and evening twilight

Intensity variation of Oi green line observed at Allahabad (25°32 N, 81°53 E) by a laboratorymade photometer has been reported here for the period January 1988 to December 1988. During the summer period of observation, slight enhancement in the intensity of evening and morning twilight emission is observed for a short duration of 4 min. However, winter observations show less pronounced enhancement in the intensity of evening twilight, while it does not occur during morning twilight. These observations are closely in agreement with those of Schaffer (1975).     

A CCD imaging spectrograph in the improved solar tower of Nanjing University

Since 1992 the solar tower telescope of Nanjing University (118°51 E, 32°03 N) as well as its multichannel solar spectrograph, originally established in 1982, have been reconstructed and a two-channel imaging spectrograph has been operated successfully. The apertures of the coelostat and the secondary mirror are both 60 cm. The spherical objective mirror, having an aperture of 43 cm and a focal length of 2170 cm, produces a solar image of 20 cm diameter. Two auxiliary telescopes using a small fraction of the coelostat's aperture were set up for guiding and H monochromatic monitoring. A multichannel spectrograph can be operated in six wavebands simultaneously. A CCD imaging spectrograph can be used for data acquisition at H and Caii K line wavebands automatically and simultaneously. The instrument consists of two CCD cameras, an image processor (SR-151), a personal computer, and a mechanical scanning device. The principal characteristics of the instruments are described. Some observational results are presented as examples.