The stability of supermassive stars in the Parametrized Post-Newtonian framework

The binding energy and stability of supermassive stars (SMS's) is examined in the framework of the Parametrized Post-Newtonian (PPN) formalism of Will and Nordvedt. The PPN formalism encompasses the post-Newtonian limit of virtually every theory of gravity, differentiating between theories by means of nine PPN parameters. A general expression is derived for the energy integral in the PPN framework, and it is found that only in those theories in which the parameters ₁=₂=₃=₄=₃=0 will the energy be conserved. In all such theories, a SMS of radius less than a critical radius will be unstable against adiabatic radial perturbations. Present experimental limits on the PPN parameters and do not exclude the possibility of the existence of stable, non-rotating, hydrogen-burning SMS's of masses an order of magnitude larger than the upper limit for the mass of such stars predicted in general relativity.     

The Struggle to be Temperate: Climate and "Moral Masculinity" in Mid-Nineteenth Century Ceylon

This paper examines a particular type of imperial literature, the writing of the plantation in mid-nineteenth century Ceylon. These writings, by and for the male planting community, were written to recruit, instruct and entertain, and drew upon discourses of tropicality and moral masculinity. But discourses are constrained by the material conditions under which they are put into practice. Consequently, writings about a place such as highland Ceylon recognised the divergence of this place from the archetypal tropics. Accounts, nevertheless, remained within the conceptual grid that Livingstone (1991) has termed the "morality of climate." These texts were also pervaded by the discourse of moral masculinity. More particularly, the narrative structure of these writings was inflected by the masculinist adventure novel, which was cross-cut by concerns of race, class, religion and nationality. The tropical highlands were represented as an adversary that presented a moral test of the planters' manhood, race and class.     

Keck imaging of the globular cluster systems in the early-type galaxies NGC 1052 and 7332

The presence of two globular cluster subpopulations in early-type galaxies is now the norm rather than the exception. Here we present two more examples for which the host galaxy appears to have undergone a recent merger. Using multi-colour Keck imaging of NGC 1052 and 7332 we find evidence for a bimodal globular cluster colour distribution in both galaxies, with roughly equal numbers of blue and red globular clusters. The blue ones have similar colours to those in the Milky Way halo and are thus probably very old and metal-poor. If the red globular cluster subpopulations are at least of solar metallicity, then stellar population models indicate young ages. We discuss the origin of globular clusters within the framework of formation models. We conclude that recent merger events in these two galaxies have had little effect on their overall globular cluster systems. We also derive globular cluster density profiles, global specific frequencies and, in the case of NGC 1052, radial colour gradients and azimuthal distribution. In general these globular cluster properties are normal for early-type galaxies.     

Fitting strength criteria to intact rock

Summary Rock strength data covering the full range of possible stress conditions are presented for three rocks: a granite, a limestone and a salt rock. The Hoek and Brown square root parabola and the Johnston criteria are fitted to the strength data coming from around 500 laboratory tests. The fitting procedure is facilitated by a specially built PC code, ROCKER, which is available to anyone on request.The Hoek and Brown criterion is modified through the inclusion of a third parameter to account for the low tensile strength of the salt rock. A new criterion, the Rocker function is formulated to follow strength data closely in the tension-low confining pressure region.     

Migration of volcanism with time in the Marquesas Islands,French Polynesia

Samples from five islands of the Marquesas Island chain (southeast Pacific Ocean) have been dated by the K-Ar method and exhibit a northwest to southeast volcanic migration rate of 9.9 cm/yr. This movement is in the same direction but of intermediate magnitude to results from the Austral Island chain (lower rate) and the Hawaiian Island chain (considerably higher rate). The rate of migration of volcanism in the Marquesas Islands is consistent with the model of rigid Pacific plate movement over a fixed “hot spot” or mantle “plume” provided that the pole of rotation for the Pacific plate for the last 5 my is located near 55°S, 170°E.     

The genesis of refractory melts in the formation of oceanic crust

Refractory, primary liquids arising in various oceanic plate tectonic settings are characterized by high MgO, SiO₂, Ca/Na, low TiO₂ and generally low incompatible element abundances relative to primary liquids parental to MORB. We propose that the former melts segregate from upper mantle peridotite which has earlier been depleted by extraction of picritic melts which were parental to MORB. A compositional range in the second-stage melts is expected, depending on the extent of previous depletion of the peridotite, the temperature and pressure of melt segregation, and the possible influence of volatile phases (C-H-O) present during melting.An example of a second stage melt is of magnesian quartz tholeiite composition, identified from among the Upper Pillow Lavas, Troodos ophiolite, Cyprus. Experimental studies determine that this composition has appropriate liquidus phases to have segregated from depleted upper mantle peridotite at about 25 km, 1360° C leaving a harzburgite residue. The experimental studies are applied to interpretation of cooling histories and water contents of specific Upper Pillow Lavas. Magma batches are estimated to have contained 0.5–1.0% H₂O. Picritic lavas quenched from olivine +liquid at <5 kb. Magnesian, pyroxene-phyric lavas exhibit intratelluric crystallization at 5 kb, 1270° C (Mg₈₈ pigeonite and Mg₈₉ orthopyroxene).These and other second-stage melts will crystallize extremely refractory minerals identical to many found in cumulate sequences in ophiolites, in plutonic rocks dredged and drilled from ocean basins, and occurring as xenocrysts in ocean floor basalts. Multistage melting of upper mantle peridotite, with and without presence of water, reconciles some of the present difficulties in relating ophiolite and ocean floor basalt compositions, and is an important process in ocean crust formation in a variety of different oceanic settings (mid-ocean ridges, marginal basins, and island arcs).     

X-ray luminosities of galaxies in groups

We have derived the X-ray luminosities of a sample of galaxies in groups, making careful allowance for contaminating intragroup emission. The L _X: L _B and L _X: L _FIR relations of spiral galaxies in groups appear to be indistinguishable from those in other environments, however the elliptical galaxies fall into two distinct classes. The first class is central-dominant group galaxies, which are very X-ray luminous and may be the focus of group cooling flows. All other early-type galaxies in groups belong to the second class, which populates an almost constant band of L _X/ L _B over the range 9.8< log  L _B<11.3 . The X-ray emission from these galaxies can be explained by a superposition of discrete galactic X-ray sources together with a contribution from hot gas lost by stars, which varies a great deal from galaxy to galaxy. In the region where the optical luminosity of the non-central group galaxies overlaps with the dominant galaxies, the dominant galaxies are over an order of magnitude more luminous in X-rays.
We also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive L _X: L _B relations as a function of environment. The non-dominant group galaxies have mean L _X/ L _B ratios very similar to those of isolated galaxies, and we see no significant correlation between L _X/ L _B and environment. We suggest that previous findings of a steep L _X: L _B relation for early-type galaxies result largely from the inclusion of group-dominant galaxies in samples.     

HST imaging of the globular clusters in the Fornax cluster: NGC 1399 and NGC 1404

The Fornax cluster galaxies NGC 1399 and NGC 1404 are ideal for studying the effects of a cluster environment on globular cluster systems. Here we present new optical imaging of these two galaxies from both the Hubble Space Telescope 's Wide Field and Planetary Camera 2 and the Cerro Tololo Inter-American Observatory 1.5-m telescope. The combination of both data sets provides a unique insight on the spatial and colour distribution of globular clusters. From B − I colours, we find that both galaxies have a broad globular cluster metallicity distribution that is inconsistent with a single population. Two Gaussians provide a reasonable representation of the metallicity distribution in each galaxy. The metal-rich subpopulation is more centrally concentrated than the metal-poor one. We show that the radial metallicity gradient can be explained by the changing relative mix of the two globular cluster subpopulations. We derive globular cluster surface density profiles, and find that they are flatter (i.e., more extended) than the underlying starlight. The total number of globular clusters and specific frequency are calculated to be N =5700±500, S_N =11.5±1.0 for NGC 1399, and N =725±145, S_N =2.0±0.5 for NGC 1404. Our results are compared with the expectations of globular cluster formation scenarios.