О природе квазаров и активных ядер галактик

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, 40 48 MAC (, 1976).     

Two Offner-based IR camera optical designs

Tracing results for two designs based on the Offner reimager are given: a practical 256×256 NICMOS-3 IR/CCD I-K camera designed for use on a f/13.5 1-m telescope yielding a 154×154 field, and a hypothetical 1024×1024 pixel nextgeneration IR camera for a f/7.5 2.5-m telescope yielding a 244×244 field. Both designs produce near-diffration limited results.     

On polarimetry in solar active regions

High resolved magnetograms ( 3) were obtained 3 hrs before and 1 hr after a 1b flare, respectively, the only bright flare reported for that active region. Careful comparison between both magnetograms shows that the line-of-sight component of the active region magnetic field remains constant. In particular there is no simplification of the rather complicated field structure in connection with the flare. Magnetic flux and field gradients also do not show any variation above the 3 scale. Essential changes, however, were observed after 19 hrs without flare activity. This indicates that evolutionary field changes predominate over flare related variations.     

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.     

B,V surface photometry of the UV continuum galaxy NGC 838

Surface photometry of the UV continuum galaxy NGC 838 has been carried out in theB, V system using photographic plates obtained with the 74 Kottamia telescope, Egypt. Isophotes, luminosity profiles, integrated photographic magnitudes, effective diameters and other photometric parameters are derived.The photoelectrically calibrated total apparent magnitudes areB _T =13.57 with maximum diameters 1.57×1.34 (at threshold _m =27.7 mag.//) andV _T =12.91 with maximum diameters 1.54×1.32 (at threshold _m =27.7 mag./). The integrated colour index(B–V) _T =0.66 and the effective surface brightness _e (B=19.0 mag./) and _e (V=19.7 mag./. The major axis is at position angle =85°±1°.The nucleus of NGC 838 is quite blue (integrated colour(B–V)=0.41 forr ^*<0.1) compared to normal galaxies while the colour becomes redder from the nucleus outwards. The UV excess, H emission and radio continuum emission previously observed from this galaxy by other investigators may be attributed to a recent burst of star formation in the nucleus of the galaxy of duration slightly greater than 2×10⁷ yr.     

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     

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.     

The dust grains in the coma of Comet West

The observed variation of reddening as function of the heliocentric distance and the spatial variation of reddening within the coma of Comet West in the visual wavelength range have been considered to infer the properties of the cometary dust grains. The relevant model incorporates the variation in the size distribution function as well as the composition of the spherical grains. The real part of the complex index of refraction (m = m – im) is chosen such thatm = 1.6. The imaginary part is required to vary from m = 0.2 to 0.05 over the wavelength range 0.4 to 0.7 m. This choice of refractive index corresponds to dirty silicate grains. As a by-product, the model also satisfies the observed polarization and albedo for the Comet West.     

YO molecule in the sun

Vibrational transition probabilities, namely Franck—Condon factors and -centroids have been evaluated by an approximate analytical method for the (A–X), (A–X), and (A–X) system of YO molecule. Morse potential energy curves forX ²⁺,A ²₂,A²₂, andA²₂, states of YO have been constructed using the latest spectroscopic data. The value of -centroids for the band have been found to decrease linearly with the corresponding wavelengths. We show results for two new transitions of (A–X) and (A–X) and five new bands of (A–X) of YO in the umbral spectrum of the Sun.     

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     

VLA and Trieste observations of type I storms,type IV and pulsations

A prime objective of this experiment was to determine whether type I or IV sources at 333 MHz contain features of small (arc sec) scale. With the VLA, our resolution was better than 4. However, we never observed any structure of size smaller than about 30, with the typical source sizes being between about 40 and 90.Many observations were simultaneous with the Trieste Astronomical Observatory records at 327 MHz. The observations were made on two days in November 1988. On 8 November the observations were of a type I storm about two hours after a major flare. On 14 November they were mostly of the main phase of a type IV event, including pulsations of a kind rarely seen, strongly circularly polarized, and having a well-defined period of about 12 s. The size of the pulsating source was about 40 by 60, and the brightness temperature was about 10⁹ K. We compare these pulsations with those observed earlier.     

О лагранжевых и зйлеровых решеиях обощенной задачи трех тел

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This paper is a continuation and a generalization of one published earlier (Duboshin, 1969): it discusses the problem whether there exist the Lagrangian and the Eulerian solutions of the generalized three-body (material points) problem. Every point in this generalized problem acts on another, one with a force (attractive or repulsive) directed along the straight line passing through these points, and in an arbitrary manner depending on time, mutual distance and its derivatives, the first and the second. Here, generally speaking, the third axiom of dynamics (law of action and reaction) is not presupposed as fulfilled, that is, it is supposed that every two material points interact in a different way.This most general assumption being made, we establish the conditions which must dictate the laws of the interactions, so that the three points can always remain at the apexes of the equilateral triangle (Langrangian solution), or remain always on a straight line (Eulerian solution).The author believes that such general treatment of the three-body problem can be useful for theoretical studies in celestial mechanics and also for practical applications in the study of isolated stellar systems.

     

Systematic reductions of 19th century planetary observations

Systematic reductions of nineteenth century observations to the system of the FK4 are discussed. Reductions made on a nightly basis are described and compared with the results obtained through the use of conventional tables. The series of observations made at the Paris Observatory from 1837 to 1881 was used to compare the two methods, and a combined system of 24 000 FK4, FK4 Sup and AGK 3R positions and proper motions provided the reference stars. The results show that for Uranus the mean error of a single observation in right ascension is ±1..33 when tables are used for the reductions, and ±1.12 when nightly reductions are made, while in declination the corresponding mean errors are ±0.88 and ±0.80. The observations of Neptune show an even greater difference between the two methods; the mean errors for the tabular and nightly reductions are ±1.57 and ±1.09 in right ascension and ±0.88 and ±0.75 in declination. Secular rates in the (0–C)'s of Uranus of –0.029/year in right ascension and ±0.030/year in declination are present when the observations are reduced with tables. These rates are reduced to –0.007/year and +0.015/year, respectively, when nightly reductions are made.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978.     

Morphological properties and origin of the photospheric facular granules

From time series of high resolution photographs, morphological properties of the photospheric facular granules were derived. The facular granules are cells of the common granular pattern, brighter than the normal granules when seen between cos = 0.6 and the limb. Their apparent diameter, which decreases towards the limb, is smaller than that of the normal granules: 0.65 and 1.25 respectively at cos = 0.55; their lifetime is 25 min but their bright stage lifetime is only 15 min; they are visible closer to the limb than the normal granules: 1.2 compared to 2–5; the brightening of the facular granules occurs at a faster rate than their fading. From the great similitude of both morphological properties and temperature models of facular and normal granules, it appears possible that the photospheric facular granules are convective cells modified by the presence of a magnetic field of some hundreds Gauss.     

Effects of viscous dissipation and free convection currents on the flow of an electrically conducting fluid past an accelerated vertical porous plate

In the present paper, the effects of free convection currents and the viscous dissipation on the unsteady flow of an electrically conducting and viscous incompressible fluid around an uniformly accelerated vertical porous plate subjected to a suction or injection velocity inversely proportional to the square root of time, in presence of a transverse magnetic field, have been investigated. Analytical solutions for the velocity and the temperature distributions, the skin-friction and the rate of heat transfer are obtained for small magnetic parameterM. During the course of discussion the effects of the Grashof number Gr, the Eckert number Ec, the suction/injection parametera have been considered for unit value of the Prandtl number Pr.Nomenclature a suction/injection parameter - C _p specific heat at constant pressure - B ₀ magnetic induction - g acceleration due to gravity - Gr Grashof number (g(T _w –T )/U ₀ ³ ) - K thermal conductivity - M magnetic field parameter (B ₀ ² /U ₀ ² ) - Pr Prandtl number (C _p/K) - T temperature of the fluid near the plate - T _w temperature of the plate - T temperature of the fluid at infinity - t time - t dimensionless time (tU ₀ ² /) - u velocity of the fluid - u non-dimensional velocity (u/U ₀) - U velocity of the plate - U dimensionless velocity of the plate (U/U ₀) - U ₀ reference velocity - v ₀ suction velocity - v ₀ non-dimensional suction velocity (v ₀/U ₀)=at ^–1/2 - Ec Eckert number ((U ₀)^2/3/C _p(T _w –T )) - T dimensionless temperature of the fluid near the plate ((T–T )/(T _w ^–T )) - x, y coordinates along and normal to the plate - x, y dimensionless coordinates (y=yU ₀/) - kinematic viscosity - coefficient of volume expansion - electric conductivity of the fluid - y/2t ^1/2 - density of the fluid - skin-friction - dimensionless skin-friction - q rate of heat transfer - q non-dimensional rate of heat transfer - coefficient of viscosity - _e magnetic permeability On leave of absence from Department of Mathematics, University of Dhaka, Bangladesh     

Effects of metal abundances on the evolutionary period changes of classical Cepheids

Some peculiarities in the behaviour of a model self-gravitating system described by hydrodynamical equations and isothermal equation of state connected with the presence of thermodynamical fluctuations in real systems were investigated in numerical experiment. The values of density and velocity , , respectively, were computed by numerical code perturbed on each time-step and in each computational cell by random values , for modeling such fluctuations. Perturbed values _i = _i + _i ,v _i = _i + v _i were used to initiate the next step of computations. This procedure is equivalent to an introduction into original hydrodynamical equations of Langevin sources which are random functions. It is shown that these small fluctuations (= v =0,² =v ² = 10^–8) grow many times in marginally-stable state.     

CASPIR: A cryogenic array spectrometer imager for the MSSSO 2.3 m telescope

CASPIR is a near-infrared spectrometer/imager being built for the Mount Stromlo and Siding Spring Observatories' 2.3 m telescope. The instrument is based on a SBRC 256×256 InSb detector array and uses AR-coated Sapphire, MgO, CaF₂, and BaF₂ optics to produce two imaging focal plane scales with 0.5/pixel and 0.25/pixel. Spectral resolving powers of 500 will be achieved through a 1×128 slit with three grisms designed for the J, H, and K bands. IJ, JH, and HK cross-dispersed échelle grisms will achieve resolving powers of 1100 through a 1×15 slit. Coronograph and imaging polarimetry modes will also be available. The various observing configurations are selected via five remotely controlled wheels. The instrument design and system architecture are discussed, and preliminary detector performance figures reported.     

Hubble expansion in a euclidean framework

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CH3CN J = 8 − 7 and CS J = 3 − 2 emission in orion KL

The data of the line series CH₃CN 8(K) – 7(K) K = 0 – 7 and line CS J = 3 – 2 were taken simultaneously. At beam size of 16 the emissions of CH₃CN and CS have a common center position located near IRc2 with deviations -8 and 5. The observed data show that in Orion KL core the integrated intensities of the two species have double peaks separated by a space of 14. The 2-dimension Gaussian fitting plots (FWHM) are ellipses ofD _maj = 26 andD _min = 22 for CH₃CN 8(K) – 7(K) K = 3 – 6 andD_maj = 39 D_min = 31 for CS J = 3 – 2 at a distance about 450 pc. Towards the multiple line emission region of CH₃CN 8(K) – 7(K) K = 3 – 6, using a simplified very large velocity gradient model to solve the statistical equilibrium and radiative transfer equations, we find to fit the observed results, the optimum physical parameters and kinetic temperatureT _k 120 K, densityn(H _a) 1.2 × 10⁵ cm^–3, velocity gradientV _gr 92 km s^–1 pc^–1 and the local abundance of CH₃CNF _ab 3 × 10^–8. However towards the region of single line emission of CS J = 3 – 2 we have to use LTE and the optical thin approximation on the assumption ofT _k= 120 K to obtain the lower limits of column density and then, an averaged abundance of CS of 6 × 10^–8.     

Несколько замечаний о гамма-излучении и химическом составе квазаров

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