Pulsar radio emission

A new version of the theory of pulsar radio emission is developed for the case of a coaxial rotator. It is based on the electric field that we established [G. S. Sahakian, Astrofizika, 37, 97 (1994)] for the radiation channel (the channel of open magnetic field lines) and on convenient approximations for the electron energy obtained in [G. S. Sahakian and É. S. Chubarian, Astrofizika, 37, 255 (1994)]. It is shown that, owing to the emission of photons of curvature radiation by particles, e e+_c', and photon annihilation, _c e⁺e^– in the lower part of the radiation channel, a special region (the magnetic funnel) is formed in which vigorous cascade multiplication of particles occurs. The height of the magnetic funnel is h 6R^0.2, where R is the radius of the neutron star and is its angular rotation rate. As a result of supersaturation of the plasma density in the magnetic funnel, a discharge occurs after each time intervalt5·10^–7–0.8B ₁₂ ^–1.4 R ₆ ^–0.2 , i.e., the longitudinal electric field disappears (B is the magnetic induction in the star). During the active radiative processes in the magnetic funnel, two main fluxes of particles with high ultrarelativistic energies are formed: an upward flux of electrons and a positron flux falling onto the star's magnetic cap. These fluxes are accompanied by narrow strips of positron and electron fluxes, respectively, of considerably lower energy, which are fairly powerful, coherent radio sources. The pulsar's radio luminosity is calculated to be L7.4·10^223.8 ₃₀ ³ R ₆ ^–2 erg/sec, where =BR 3/2 is the star's magnetic moment. Comparing this result with observations, we conclude that the magnetic moment and hence the mass of the neutron star evidently must be considerably smaller, on the average, for fast pulsars than for slow ones. It is shown that the magnetic moment of the neutron star can be determined from the intervals between micropulses in the pulse profiles. The problem of the origin of the macrostructure of the radio pulse is discussed.Translated from Astrofizika, Vol. 38, No. 1, pp. 141–185, January – March, 1995.     

The flare star PP Ori

We give the results of photographic, photoelectric, and spectral observations of the flare star PP Ori. The 109 photographic observations used, which were obtained on the 40 Schmidt telescope of the Byurakan Observatory over a period of about 20 years, and four spectra obtained on the same telescope with a4° objective prism show no variation in brightness. Photoelectric observations in the UBVR bands using the 50cm and 60cm telescopes of the high-altitude Maidanak station of the Tashkent Astronomical Institute in 1987 and 1989 give grounds for suspecting a variation in brightness much larger than observational errors. Spectral observations of the star PP Ori made on the 2.6m telescope of the Byurakan Observatory show weak H emission. The results of all these observations show that PP Ori is an Orion variable of spectral class K7-M0 with absolute visual magnitude7 ^m 5–8 ^m 5.Translated fromAstrofizika, Vol. 38, No. 2, 1995.     

Axisymmetrical models for the origin and shaping of proto-planetary nebulae

Axisymmetrical models for protoplanetary nebulae are produced. We discuss the mechanism for mass loss from evolved cool stars and the characteristics of the gas outflow. By using two-dimensional magnetohydrodynamics, we find that the gas is preferentially ejected in a so-called equatorial plane. For a grid of models, the expansion velocities are found to be of the order ofv _escape/2 and the mass loss rates tilde 10^–5-10^–4 M /year which appear consistent with the available observational data. Magnetic fields intensities in the 10^–4 to 10^–3 gauss range are obtained in circumstellar envelopes, in good agreement with observations (Nedoluha and Bowers, 1992).     

Colliding winds model of X-ray radiation in SS 433: analysis of X-ray eclipses

Interpretation of X-ray eclipses in SS 433 binary system in the framework of wind-wind collision model yields high value of mass ratioq =m _x /m _v > 1 which implies high mass of relativistic objectm _x > 8M .     

Dark matter particles and the flat rotation curves of spiral galaxies

It is shown that a gas of massive bosonic particles (m 60 eV), e.g. Higgs particles, surrounding disk galaxies is able to generate the flat rotation curves of spiral galaxies without internal difficulties with physical principles. We have analyzed 36 galaxies and find good agreement with the empirical data.     

Demographic transition in Sri Lanka: a spatial perspective

Demographic transition theory involves a lagging fertility transition induced by a leading mortality transition. This article focuses on the linkage between the mortality and fertility transitions in Sri Lanka; it discusses the measurement of areal fertility, demonstrates the use of a measure not commonly used in population geography, and shows areal association between past mortality and recent fertility. The Coale or Princeton fertility indices allow a reasonably good view of structural and behavioral aspects of fertility; the Coale indices examine the contribution of structure to total fertility and the contribution of marital fertility. Although recent fertility decline has been less rapid than the post-war mortality decline, Sri Lanka's crude birth rate in 1975 was the 5th lowest in Asia. Sri Lanka experienced very high crude death rates in 1930, and quite low rates in 1950 and in subsequent years. This demonstrates an association between historic mortality and recent fertility, and that association can be linked deductively to demographic transition theory. In 1930, malaria was endemic throughout the Dry Zone of Sri Lanka, and hyperendemic in several districts. The Spearman rank correlation coefficients reveal the strongest relationship between malaria and nuptiality; this lends evidence to the notion that structural influences on fertility--such as delayed marriage--are more important than influences on marital fertility--such as coital frequency. The evidence suggests that mortalily decline in Sri Lanka led to an increase in fertility in those areas where malaria had been concentrated. This suggests the possibility that measures constituting malaria control or eradication also stimulate increased fertility; therefore, anti-malarial programs must be integrated with family planning.     

Interpretation of3He abundance variations in the solar wind

The ion composition instrument (ICI) on ISEE-3 has observed the isotopes of helium of mass 3 and 4 in the solar wind almost continuously between August 1978 and July 1982. This period included the increase towards the maximum of solar activity cycle 21, the maximum period, and the beginning of the descent towards solar minimum. Observations were made when the solar wind speed was between 300 and 620 km s^–1. For part of the period evidence for regular interplanetary magnetic sector structure was clear and a number of³He flares occurred during this time.The long-term average⁴He⁺⁺/³He⁺⁺ flux ratio R, was 2050 ± 200, a agreement with a previously reported result obtained using part of this data set, and in very good agreement with the previous measurements made over much shorter periods of time with the foil technique. The R values for 6-month intervals show statistically significant differences. The highest of these values is 2300 and coincides with the solar maximum of cycle 21 indicating that at solar maximum there may be changes in the character and rate of occurrence of short-term variations in R. We also find that R drops under conditions of low proton flux in the solar wind, and that it is high when solar wind speeds are lowest.At solar wind speeds above 400 km s^–1 R is nearby constant at about 2000; at lower speeds it is larger and more variable, in agreement with the idea that the sources of high and low speed wind are different. At times of sector boundary current sheet crossings, identified with coronal streamers, there is a characteristic rise in the value of R indicating an encounter with a plasma with reduced³He⁺⁺ abundance. Autocorrelations have been computed for⁴He⁺⁺ and³He⁺⁺ and indicate correlation times of about 14 and 20 hr, respectively. Periods of duration of about one day whenR is less than 1000 tend to coincide with the observation of compound streams.The possibility of detectable increases in³He⁺⁺ flux in plasma which left the Sun at the time of³He flares has been investigated, but no significant increase was seen.     

A possible P-L relation for RR-Lyrae variables in globular clusters

A study of the mean photographic magnitudes of RR Lyrae variables in galactic globular clusters has shown that the luminosity of RR-ab variables decreases with period. It is found that RR-ab variables, in the cluster Centauri, whose distances are greater than 8 arc min from the centre of the cluster, are less luminous than such variables seen in the inner region. The possibility of two transition periods for RR-ab variables, one near 0 _. ^d 4 and the other near 0 _. ^d 9, is suggested to explain the sharp boundaries of the instability gap and of the periods of RR Lyrae variables. It is also shown that the inner RR Lyrae variables in Centauri are more massive than the outer ones.     

Observations of the Rosette Nebula using the Decameter Wave Radio Telescope at Gauribidanur

A map of Rosette Nebula in continuum absorption is made at 34.5 MHz using the Decameter Wave Radio Telescoe at Gauribidanur, India, with a resolution of 26×40, is presented. These observations are combined with the 2700 MHz measurements of Grahamet al. (1982) to derive the electron temperature distribution across the nebula. It is found that the temperatures in the southeastern parts of the nebula are around 5000 K and increase up to 8000 K towards the northwestern regions. It is suggested that the lower electron temperatures in the southeastern regions are due to the presence of more dust there compared to other regions in the nebula.     

Accretion spin-up of low-magnetic neutron stars

The present paper is concerned with the spin-up of low-magnetic neutron stars by the accretion of matter onto the star. Calculations have been made for the evolution of the rotation of a neutron star and applied to different stellar models. It is shown that the existence of a millisecond pulsar imposes no restriction on any of the equations of state considered. However, constraints would arise with the possible discovery of third-octave pulsars (with frequencies in excess of 1000 Hz). Predictions are made as to the distribution of bursters over the orbital periods of neutron stars (about half of these having similar orbital periods). It is demonstrated that in the case of continued accretion onto a star, after it has acquired the critical angular frequency allowing no diviation from axial symmetry, specific accretion disks can be formed with a smooth transition into a star. The specific angular momentum is computed for a neutron star for the instant of the attainment of the Oppenheimer-Volkoff limit.