Studies of non-adiabatic pulsations in the atmospheres of the roAp stars

Includes bibliographical references.The roAp stars are high overtone pulsators characterised by strong global magnetic fields with effective field strength of between a few hundred to a few thousand Gauss. They also show overabundances in rare-earths and iron peak element. Multi-colour photometry of roAp stars shows that their pulsation amplitudes decrease more rapidly with increasing wavelength compared to other classically pulsating stars (e.g. Medupe & Kurtz 1998). In addition, this thesis shows that the pulsation phase can vary by up to 80° from Johnson U to V filters. In an attempt to explain the amplitude vs wavelength Kurtz & Medupe (1996) derived an analytic formula that indicated that the steep variation of the temperature eigenfunction with depth in the roAp atmospheres is the possible reason the rapid decrease of amplitude with wavelength. Even though Medupe & Kurtz (1998) showed that the analytical formula they derived in 1996 was a special form of a more general formula presented in Watson (1988), they found limitations in both formulae (see also Medupe, Christensen-Dalsgaard & Kurtz 1998 and chapter 3 of this thesis). This motivated me to attempt a numerical solution of the pulsation equations with consistent treatment of radiative transfer to investigate the multi-colour photometric data. In this thesis, we report on the multi-colour pulsation amplitudes and phases for HD 128898, HD 101065, HD 134214 and HD 137949. We also report on the campaign undertaken in 1996 and 1998 to determine whether the HR 3831 amplitude and phase vs wavelength changes with rotation. No variations with rotation are found. We find that the pulsation phase varies by up to about 80° from Johnson U to V in HD 101065 and HR 3831

Atmospheric temperature structure in the RoAp stars

The rapidly oscillating Ap (roAp) stars are a sub-group of the chemically peculiar stars of class 2 (CP2), which are characterised by peculiar spectra and anomalously strong lines of Sr, Cr, Eu and other rare earth elements. They have strong global dipole magnetic fields with effective strengths of up to a few thousand gausses. Stars showing these phenomena cover the spectral range B8p to F0 V-IV. About 20 years ago rapid non-radial pulsations were discovered in the coolest members of the CP2 group, namely the roAp stars. These pulsations are due to high over-tone, low degree p modes with periods between 5.6 and 15 minutes. Since then, studies of these rapid oscillations have revealed a lot of information about these stars. The eigenfrequency spectra of roAp stars can potentially reveal information such as their rotation periods, rotational inclinations, magnetic geometries, internal magnetic field strengths, radii, masses, luminosities and ages. Matthews et al. (1990, 1996) suggested a technique to empirically determine the T(Ƭ) relation for roAp stars. This technique involves comparing the pulsation amplitudes obtained from multi-colour photometry to the ones calculated from black-body pulsator models (assuming dipole mode pulsations). This comparison yielded limb-darkening coefficients which were used to determine T(Ƭ) in a way similar to what was done for the sun. Matthews et al. based their idea on the observed fact that pulsation amplitudes of roAp stars drop sharply with increasing wavelength. They thus explained this sharp decline of amplitude with wavelength in terms of the strongly wavelength dependent limb-darkening. The initial aim of this thesis was to investigate the technique proposed by Matthews et al., and to apply it to a number of roAp stars. However, when a linearised expression for the variation of the pulsation amplitude with wavelength, limb-darkening, inclination of the pulsation axis α, and ΔT/T₀ (where ΔT is the polar pulsational temperature semi-amplitude and T₀ is the atmospheric temperature) was derived, it was discovered that limb-darkening is too small an effect to account for the observed amplitudes. The result is based on the Wien approximation and uses the Planck function to represent intensity. Therefore, limb-darkening cannot be measured from the amplitude vs wavelength data. This analysis and the results thereof are reported in this thesis. Numerical models based on realistic treatment of the intensity spectra (obtained from model atmospheres) are used to confirm and refine the analytical results. The linearised expression mentioned above suggests that an important factor that explains the sharp decline of amplitude with wavelength is the variation of the ratio ΔT/T₀ with wavelength. Therefore, if the T(Ƭ) structure of a star is known a priori (from model atmospheres), the variation of ΔT with wavelength can be determined. This new technique, together with the variation of opacity with wavelength in the atmospheres of roAp stars, is applied to HD 134214:, HD 137949, HD 128898, HD 101065 and HR 3831 to determine ΔT cos α as a function of atmospheric depth. HR 3831 was observed at various rotation phases to investigate the effect of rotation on the derived ΔT cos α vs atmospheric depth relation. Preliminary results on this are included in this thesis. Bibliography: pages 107-113

A strategy for sustainable ICT development in deep rural environments

This study provides a strategy for sustainable Information and Communcation Technology (ICT) development in deep rural environments and describes a case study conducted within the community of the AmaJingqi traditional council. It investigates the sustainability of the ICT services within a rural environments, the income profile and affordability of different members of the community and the strategy formulation model. The study’s main focus is on creating a strategy to be used as a guideline for the successful development and implementation of sustainable ICT development in deep rural environments and on defining ICT Sustainability. Furthermore, the different ICT users are profiled based on affordability and access to services, and deep rural environments are also defined. Moreover, the study describes the complete composition of sustainable ICT. It discusses design science research methodology and the reasons why the method is used is motivated and advanced. The study also outlines various research paradigms and philosophies and a number of research strategies are also discussed. The literature review focuses on various policies and frameworks which have been formulated to advance the universal access of ICT services by rural communities. It also outlines some of the ICT initiatives which have failed and the reasons for the failures and what will be corrected for similar mistakes not to be repeated. The study discusses the concepts of a strategy framework that outlines the theoretical foundation of the strategy formulation model, strategy implementation and control. It also discusses the diagnostics and outlines the various strategy guiding polices. The strategy is validated, expert reviews are solicited and the strategy is revised and finalised

Asteroseismology of the Beta Cephei star Nu Eridani -- IV. The 2003-4 multisite photometric campaign and the combined 2002-4 data

The second multisite photometric campaign devoted to Nu Eri is reported. For Nu Eri, analysis of the new data adds four independent frequencies to the nine derived previously from the 2002-3 data, three in the range from 7.20 to 7.93 c/d, and a low one, equal to 0.614 c/d. Combining the new and the old data results in two further independent frequencies, equal to 6.7322 and 6.2236 c/d. Altogether, the oscillation spectrum is shown to consist of 12 high frequencies and two low ones. The latter have u amplitudes about twice as large as the v and y amplitudes, a signature of high radial-order g modes. Thus, the suggestion that Nu Eri is both a Beta Cephei and an SPB star, put forward on the basis of the first campaign's data, is confirmed. Nine of the 12 high frequencies form three triplets, of which two are new. The triplets represent rotationally split l=1 modes, although in case of the smallest-amplitude one this may be questioned. Mean separations and asymmetries of the triplets are derived with accuracy sufficient for meaningful comparison with models. The first comparison star, Mu Eri, is shown to be an SPB variable with an oscillation spectrum consisting of six frequencies, three of which are equidistant in period. The star is also found to be an eclipsing variable. The eclipse is a transit, probably total, the secondary is fainter than the primary by several magnitudes, and the system is widely detached. The second comparison star, Xi Eri, is confirmed to be a Delta Scuti variable. To the frequency of 10.8742 c/d seen already in the first campaign's data, another one, equal to 17.2524 c/d, is added.Comment: 13 pages, 8 figures, MNRAS, in pres

Improving dryland maize (Zea mays) productivity through crop rotation with cowpeas (Vigna unguiculata)

Maize is the most important cereal crop grown in areas of South Africa by both small-scale and commercial farmers. Maize monocropping without sufficient input and declining soil nitrogen content are some of the factors that limit yield. The objective of the study was to evaluate the effect of different cowpea cultivars and populations on growth, yield and yield components of succeeding maize. The effects of cropping systems on soil N content were also observed. Field experiments were conducted during the 2005/2006 and 2006/2007 growing seasons at Potchefstroom and Taung in North West province. The trial consisted of four cowpea cultivars: PAN 311 (short duration cowpea cultivar), CH 84, Bechuana white (medium duration cowpea cultivar) and TVU 1124 (long duration cowpea cultivar) and, four planting densities (10 000, 15 000, 20 000 and 40 000 plants ha-1). Maize was used as sequential test crop to determine the residual effect of previous cowpea treatments. Cowpea grain yield increased as planting density increased at both localities. TVU 1124 gave highest grain yield of all cowpea cultivars at both localities. Total dry matter yield also increased with increasing planting density. After cowpea soil NO3- and NH4+ content increased with increasing density. Similarly, soil NO3- content of maize following cowpea showed a considerable improvement, compared to maize monocropping. The highest soil NO3- and NH4+ content was observed when maize followed Bechuana White. Significant differences were also observed in soil microbial activities among the cultivars. Maize grain yields and plant height responded positively to the previous cowpea crop, compared with maize monocropping at both locations, but especially at Taung. Maize stover yield, cob length and KNC significantly responded to maize and cowpea rotation compared to maize monocropping at Taung. These results further confirm the potential of using cowpea to contribute soil N to subsequent maize crops in a rotational system. CopyrightDissertation (MScAgric)--University of Pretoria, 2010.Plant Production and Soil Scienceunrestricte

The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode

We undertook a time-series photometric multi-site campaign for the rapidly oscillating Ap star HD 99563 and also acquired mean light observations over two seasons. The pulsations of the star, that show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 microHertz and some first harmonics of these. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 +/- 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break the distorted oscillation mode up into its pure spherical harmonic components and find it is dominated by the l=1 pulsation, and also has a notable l=3 contribution, with weak l=0 and 2 components. The geometrical configuration of the star allows one to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes was modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the Delta Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03 solar mass object, seen at a rotational inclination of 44 degrees, which then predicts a magnetic obliquity of 86.4 degrees.Comment: 10 pages, 6 figures, accepted for publication by MNRA

Why did foraging, horticulture and pastoralism persist after the Neolithic transition? The oasis theory of agricultural intensification

Despite the global spread of intensive agriculture, many populations retained foraging or mixed subsistence strategies until well into the twentieth century. Understanding why has been a longstanding puzzle. One explanation, called the marginal habitat hypothesis, is that foraging persisted because foragers tended to live in marginal habitats generally not suited to agriculture. However, recent empirical studies have not supported this view. The alternative but untested oasis hypothesis of agricultural intensification claims that intensive agriculture developed in areas with low biodiversity and a reliable water source not reliant on local rainfall. We test both the marginal habitat and oasis hypotheses using a cross-cultural sample drawn from the 'Ethnographic atlas' (Murdock 1967 Ethnology 6, 109–236). Our analyses provide support for both hypotheses. We found that intensive agriculture was unlikely in areas with high rainfall. Further, high biodiversity, including pathogens associated with high rainfall, appears to have limited the development of intensive agriculture. Our analyses of African societies show that tsetse flies, elephants and malaria are negatively associated with intensive agriculture, but only the effect of tsetse flies reached significance. Our results suggest that in certain ecologies intensive agriculture may be difficult or impossible to develop but that generally lower rainfall and biodiversity is favourable for its emergence

A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry

Observations of Epsilon UMa obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed. This is one of the most precise photometry of an Ap star. The amplitude spectrum is used to set an upper limit of 75 parts per million for the amplitude of stellar pulsations in this star unless it accidentally oscillates with a single mode at the satellite orbit, its harmonics or their one day aliases. This is the tightest limit put on the amplitude of oscillations in an Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it cannot be argued that the observations were made at a wrong rotational phase. Our results thus support the idea that some Ap stars do not pulsate at all.Comment: 4 pages, 4 figures, 2 style files, accepted for publication in ApJ

The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode

We undertook a time-series photometric multisite campaign for the rapidly oscillating Ap (roAp) star HD 99563 and also acquired mean light observations over four seasons. The pulsations of the star, which show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 μHz and some first harmonics of it. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 ± 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break up the distorted oscillation mode into its pure spherical harmonic components and find it is dominated by the ℓ= 1 pulsation, and also has a notable ℓ= 3 contribution, with weak ℓ= 0 and 2 components. The geometrical configuration of the star allows us to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes has been modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the δ Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03-M⊙, object, seen at a rotational inclination of 44°, which then predicts a magnetic obliquit

Norm violations and punishments across human societies

Punishments for norm violations are hypothesized to be a crucial component of the maintenance of cooperation in humans but are rarely studied from a comparative perspective. We investigated the degree to which punishment systems were correlated with socioecology and cultural history. We took data from the Standard Cross-Cultural Sample database and coded ethnographic documents from a sample of 131 largely nonindustrial societies. We recorded whether punishment for norm violations concerned adultery, religion, food, rape, or war cowardice and whether sanctions were reputational, physical, material, or execution. We used Bayesian phylogenetic regression modeling to test for culture-level covariation. We found little evidence of phylogenetic signals in evidence for punishment types, suggesting punishment systems change relatively quickly over cultural evolutionary history. We found evidence that reputational punishment was associated with egalitarianism and the absence of food storage; material punishment was associated with the presence of food storage; physical punishment was moderately associated with greater dependence on hunting; and execution punishment was moderately associated with social stratification. Taken together, our results suggest that the role and kind of punishment vary both by the severity of the norm violation, but also by the specific socio-economic system of the society