A polarimetric investigation of the eclipsing binary XY ursae majoris

On three nights in February 1976 we carried out polarimetric measurements, in V, of the short periodic eclipsing binary XY UMa, covering a complete cycle. The results are as follows:

1. Within all phase intervals the linear polarization does not exceed 0.1%.
2. In the phase range 0 ^p .95–1 ^p .35 the scatter of the Stokes parametersQ andU is about twice that within the phase interval 0 ^p .35–0 ^p .95.
3. A periodogram analysis of these data revealed a period of 21000 s, which is equal to half the orbital periodP _o=0^d.47899 within 1.5%.

From these we derive the conclusions that no circumstellar envelope can be made responsible for the observed long-term changes of the light curve and system brightness, supporting the earlier spectroscopic finding. The different scatter of the Stokes parameters at different phase intervals and theP _o/2 periodicity are in favor of the star spot model for XY UMa proposed by one of the authors (E. G.).     

Optimal curve fitting procedures applied to the light curves of classical cepheids

Optimal curve fitting procedures based on the well known Baade/Wesselink methodology have been applied to Stebbinset al.'s 6-colour photometry of the classical cepheids Cep and Aql. Radial velocity data have been represented by a Fourier series, while the brightness temperature at the effective wavelength of observation forms a convenient temperature variable in the fitting function. This fitting function requires the specification of six parameters which thus play the role of unknowns in the optimization problem, though, in fact, all six parameters cannot be independently determined.The formulation involves a simple connection between colours and brightness temperatures, and model stellar atmosphere calculations can provide such a connection. The model stellar atmosphere data of Carbon and Gingerich (1969), which take careful account of line blanketing effects are, to some extent, supported by the results for Aql, though the position is less certain in the case of Cep. On the basis of the Carbon and Gingerich data, and if we take into account various estimates of the interstellar reddening, the absolute magnitudes of Cep and Aql areM _v=–3.57 andM _v=–3.79, respectively; but optimal curve fits would decrease both these values by about 0^m.09.     

Some comments on the Oort cloud

The arguments used by Lyttleton to prove the nonexistence of the Oort cloud are reviewed, and it is shown that Oort's hypothesis remains consistent with observation. The 1950 model of the cloud cannot be correct and, by use of the results from a number of more recent papers, an improved model is described and compared with observations. It is emphasized that comparison of the predictions of theory with observations should concentrate on thea-distribution, as the 1/a-distribution masks much of the detailed structure of the theory. An order of magnitude argument is given which shows that 20% of so-called new comets have passed through the planetary system before, and the implications of this to the statistics of near-parabolic comet orbits are briefly investigated.     

A model for a structure in the galactic nebula S206

The galactic nebula S206 contains a half shell of high excitation nebulosity which is centred on the associated exciting star. The suggestion has been made that this structure is caused by the interaction of stellar mass loss from the star with nebular gas. A steady state model of such an interaction is investigated quantitatively. The required mass loss rate from the star is about 10^–7 M yr^–1 which is compatible with the observationally derived mass-loss rates from early-type stars.     

Density wave-star interaction in the theory of spiral galaxies

The dispersion relation has been derived for density waves propagating at an arbitrary angle. The analysis has shown the existence of a resonance which for a two-arm galaxy can be stable, neutral or unstable as }2$$ " align="middle" border="0"> , respectively.     

Outward transport of angular momentum by gas convection and the equatorial acceleration of the Sun

A new mechanism for sustaining enhanced rotational velocity of the outer layers of the solar convective envelope is considered.The gas density inside turbulent eddies decreases because of centrifugal scattering of matter. The decrease of density in eddies rotating in the same sense as the Sun on the whole is larger than that in eddies rotating in the opposite sense. As a result, the former ascend while the latter sink down, thus producing a continuous outward flux of angular momentum.A distribution of angular velocity in the radius of the solar convective envelope in the equatorial plane was obtained in the approximation of the mixing length theory of thermal convection. The results agree rather well with observations.     

Energetic properties of interplanetary plasma at the earth's orbit following the August 4, 1972 flare

Solar wind and interplanetary magnetic field data were obtained by the PROGNOZ 1 and PROGNOZ 2 satellites during the period following the August 4, 1972 (0621 UT) solar flare. A thermalized plasma was recorded one hour after the shock followed two hours later by the plasma piston with a bulk velocity higher than 1700 km s^-1. The comparison between the PROGNOZ and PIONEER 9 solar wind data shows an attenuation of the plasma properties with the deflection from the flare's meridian.     

Plasmasphere response to the onset of quiet magnetic conditions: Plasma convection patterns

A whistler study has been made of plasma convection within the plasmasphere during a transition from steady moderate geomagnetic activity to quiet conditions. Continuous whistler data recorded at Sanae, Antarctica (L= 3.98) for the period 0400 UT, 10 July to 0400 UT, 11 July 1973 have been analyzed in 15 min intervals.This study has revealed two distinct bulges in the plasmasphere centred on 1700 and 0100 UT. The bulges appear to result from the outward flow of plasma rather than the addition of new plasma. We tentatively interpret the late bulge at 0100 UT as being the duskside bulge of earlier studies rotated into the midnight region. In this bulge, plasma above L = 3.8 appears to convect outwards to form the bulge whereas plasma at lower L-values is relatively undisturbed. For the early bulge (1700 UT) the plasma convection pattern is similar over all observable L-values and closely reflects the shape of the estimated plasmapause in that region. Comparison of the bulges, with those obtained by Carpenter (1966) suggests that the onset of quiet conditions results in a general displacement of the bulges in an eastward direction by about 3 hr.     

The equations of motion of an artificial satellite in nonsingular variables

The equations of motion of an artificial satellite are given in nonsingular variables. Any term in the geopotential is considered as well as luni-solar perturbations up to an arbitrary power ofr/r, r being the geocentric distance of the disturbing body. Resonances with tesseral harmonics and with the Moon or Sun are also considered. By neglecting the shadow effect, the disturbing function for solar radiation is also developed in nonsingular variables for the long periodic perturbations. Formulas are developed for implementation of the theory in actual computations.     

Basaltic magmatism and the bulk composition of the moon

The lunar interior is comprised of two major petrological provinces: (1) an outer zone several hundred km thick which experienced partial melting and crystallization differentiation 4.4–4.6 b.y. ago to form the lunar crust together with an underlying complementary zone of ultramafic cumulates and residua, and (2) the primordial deep interior which was the source region for mare basalts (3.2–3.8 b.y.) and had previously been contaminated to varying degrees with highly fractionated material derived from the 4.4–4.6 b.y. differentiation event. In both major petrologic provinces, basaltic magmas have been produced by partial melting. The chemical characteristics and high-pressure phase relationships of these magmas can be used to constrain the bulk compositions of their respective source regions.Primitive low-Ti mare basalts (e.g., 12009, 12002, 15555 and Green Glass) possessing high normative olivine and high Mg and Cr contents, provide the most direct evidence upon the composition of the primordial deep lunar interior. This composition, as estimated on the basis of high pressure equilibria displayed by the above basalts, combined with other geochemical criteria, is found to consist of orthopyroxene + clinopyroxene + olivine with total pyroxenes > olivine, 100 MgO/(MgO + FeO) = 75–80, about 4% of CaO and Al₂O₃ and 2× chondritic abundances of REE, U and Th. This composition is similar to that of the earth's mantle except for a higher pyroxene/olivine ratio and lower 100 MgO/(MgO + FeO).The lunar crust is believed to have formed by plagioclase elutriation within a vast ocean of parental basaltic magma. The composition of the latter is found experimentally by removing liquidus plagioclase from the observed mean upper crust (gabbroic anorthosite) composition, until the resulting composition becomes multiply saturated with plagioclase and a ferromagnesian phase (olivine). This parental basaltic composition is almost identical with terrestrial oceanic tholeiites, except for partial depletion in the two most volatile components, Na₂ and SiO₂. Similarity between these two most abundant classes of lunar and terrestrial basaltic magmas strongly implies corresponding similarities between their source regions. The bulk composition of the outer 400 km of the Moon as constrained by the 4.6-4.4 b.y. parental basaltic magma is found to be peridotitic, with olivine > pyroxene, 100 MgO/ (MgO + FeO) 86, and about 2× chondritic abundances of Ca, Al and REE. The Moon thus appears to have a zoned structure, with the deep interior (below 400 km) possessing somewhat higher contents of FeO and SiO₂ than the outer 400 km. This zoned model, derived exclusively on petrological grounds, provides a quantitative explanation of the Moon's mean density, moment of inertia and seismic velocity profile.The bulk composition of the entire Moon, thus obtained, is very similar to the pyrolite model composition for the Earth's mantle, except that the Moon is depleted in Na (and other volatile elements) and somewhat enriched in iron. The similarity in major element composition extends also to the abundances of REE, U and Th. These compositional similarities, combined with the identity in oxygen isotope ratios between the Moon and the Earth's mantle, are strongly suggestive of a common genetic relationship.