Dynamical evolution of comets and the problem of cometary fading

Possibilities to explain the observed 1/a-distribution are discussed in the light of improved understanding of the dynamical evolution of long-period comets. It appears that the fading problem applies both to single-injection and continuous-injection models. Although uncertainties due to nongravitational effects do not allow detailed results to be drawn from the observed 1/a-distribution at small perihelion distance q, that for q 1.5 AU shows that a constant fading probability cannot explain all the features of the observed distribution. Assuming that comets can reappear following a period of fading, values for the assumed constant fading and renewal probabilities, and the total cometary flux have been estimated for q > 1.5 AU.     

Temporal evolution of the chromospheric electron density in the flare of January 5, 1992

The analysis of the dynamic evolution of the chromospheric electron density during solar flares is fundamental for the testing of solar flare models. For this purpose we developed a digital imaging spectrograph for the observation of higher Balmer lines below 400 nm with a time resolution of 1 s and an algorithm for the determination of the electron density from the observed line profiles. On January 5, 1992 a M1/1N flare was observed in H, H and Caii H and the temporal evolution of the electron density was determined. The chromospheric electron density rises several times from less than 3 × 10¹⁹ to 1 × 10²⁰ m^–3 during the hard X-ray peaks.     

Spectrophotometry of a Galaxy with UV-excess

We present the results of a spectral study of Galaxy No. 47 of the list [1]. We determine the equivalent widths of the lines for the compact part of the galaxy and the relative intensities for both the compact part and the halo. We estimate the mass of the galaxy from the inclination of the H line. We obtain the electron density and the mass of the gas component of the compact part of the galaxy.Translated fromAstrofizika, Vol. 38, No. 2, 1995.     

TVZHR profile for the 1991 Perseid shower

Image intensified video detection systems were used to observe the 1991 Perseid meteor shower from two locations in eastern Canada. In 29.6 hours of total observing time a total of 668 meteors were detected, of which 403 were Perseids. We derived a profile of TVZHR (television zenithal hourly rate) values for the 1991 Perseid shower over the solar longitude (epoch 2000) interval 138°51 to 141°01. The apparent limiting stellar magnitudes of the observing systems were +9.4 and +8.8 (corresponding to limiting meteor magnitudes for our geometry ranging from +8.7 to +7.0). Within the observing period, the maximum TVZHR rate was approximately 1600, and occurred at solar longitude 139.9°. This is in good agreement with the second peak observed by visual observers. The data suggest that TVZHR values should be divided by a factor of approximately 5 to compare TVZHR and ZHR values.     

The geography of dual career households: a research agenda and selected evidence from secondary data sources for Britain

"Amongst the key dimensions of population and labour market change in most parts of western Europe and other similar economies in the 1990s are low fertility rates, rising numbers of smaller households, increasing female participation rates, growth in higher level non-manual occupations and the spread of flexible employment patterns. This paper explores how these trends have led to an increase in the number and significance of one particular subgroup: dual career households. An overview from available secondary sources of the geography and socio-economic characteristics of such households in Britain is presented, and directions for possible future research on dual career households are outlined."     

Thinking of England and taking care: family building strategies and infant mortality in England and Wales, 1891-1911

"Debates concerning the origins and development of the late nineteenth- to early twentieth-century declines in marital fertility and infant mortality in England and Wales have been centred largely on the material provided by answers to the ?special' questions in the 1911 census. In their published form these figures have restricted researchers to an examination of large scale geographic and social class differences in the levels and rates of decline of the two phenomena. This paper outlines research conducted on a sample of individual census returns from the 1911 census. From this data it becomes clear that for Victorian and Edwardian England ?where one lived' was rather more important than ?who one was' in determining both family building strategies and the survival of those children born."     

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 .     

The densest prestellar condensations: H2CO Studies ofρ Oph B1

We present new images of the well-known molecular outflow and Herbig-Haro complex L 1551-IRS 5. Deep, high-resolution images of the central region of the flow in [SII] 6716,6731 and H (6565 Å) are complemented by a mosaic of much of the CO outflow in H₂ v=1-0 S(1). While the optical data trace the intermediate-to-high excitation shocks in the flow (v _shock > 30 – 50 km s^–1), the near-IR data reveal the lower-excitation, molecular shocks (v _shock 10–50 km s^–1). In particular, the H₂ data highlight the regions where the flow impacts and shocks ambient molecular gas.     

Fitting matrix-valued variogram models by simultaneous diagonalization (Part I: Theory)

Suppose that ¯(x₁),...,¯Z(x_n). are observations of vector-valued random function ¯(x). In the isotropic situation, the sample variogram γ^*(h) for a given lag h is $$\bar \gamma ^ * (h) = \frac{1}{{2N(h)}}\mathop \sum \limits_{s(h)} (\overline Z (x_1 ) - \overline Z (x_1 )) \overline {(Z} (x_1 ) - \overline Z (x_1 ))^T $$ where s(h) is a set of paired points with distance h and N(h) is the number of pairs in s(h).. For a selection of lags h₁, h₂, .... h_k such that N (h₁) > O. we obtain a ktuple of (semi) positive definite matrices $\bar \gamma ^ * (h_{ 1} ),. . . ., \bar \gamma ^ * (h_{ k} )$ . We want to determine an orthonormal matrix B which simultaneously diagonalizes the $\bar \gamma ^ * (h_{ 1} ),. . . ., \bar \gamma ^ * (h_{ k} )$ or nearly diagonalizes them in the sense that the sum of squares of offdiagonal elements is small compared to the sum of squares of diagonal elements. If such a B exists, we linearly transform $\overline Z (x)$ by $\overline Y (x) = B\overline Z (x)$ . Then, the resulting vector function $\overline Y (x)$ has less spatial correlation among its components than $\overline Z (x)$ does. The components of $\overline Y (x)$ with little contribution to the variogram structure may be dropped, and small crossvariograms fitted by straightlines. Variogram models obtained by this scheme preserve the negative definiteness property of variograms (in the matrix-valued function sense). A simplified analysis and computation in cokriging can be carried out. The principles of this scheme arc presented in this paper.     

Ejection from pulsars in binary systems

Interaction of an ejecting pulsar in a binary with a matter surrounding it is considered. Around the pulsar a cavern is formed, and its shape calculated. Non-stationary regime of floating caverns filled with binary radioemission is discussed. This regime can lead to a special radio-burster. It is noticed that in binaries with rather large separation between components a pulsed radioemission from a pulsar can be observable. In this case, the pulsar will be a fine probe for exploration of physical characteristics of a stellar wind from a normal expansion.