NGC 2419 does not challenge MOND, Part 2

I argue that, despite repeated claims of Ibata et al., the globular cluster NGC 2419 does not pose a problem for modified Newtonian dynamics (MOND). I present a new polytropic model with a running polytropic index. This model provides an improved representation of the radial distribution of surface brightness while maintaining a reasonable fit to the velocity dispersion profile. Although it may be argued that the differences with these observations remain large compared to the reported random errors, there are several undetectable systematic effects which render a formal likelihood analysis irrelevant. I comment generally upon these effects and upon the intrinsic limitations of pressure supported objects as tests of gravity.Comment: 3 page, 2 figure

A historical perspective on Modified Newtonian Dynamics

I review the history and development of Modified Newtonian Dynamics (MOND) beginning with the phenomenological basis as it existed in the early 1980s. I consider Milgrom's papers of 1983 introducing the idea and its consequences for galaxies and galaxy groups, as well as the initial reactions, both negative and positive. The early criticisms were primarily on matters of principle, such as the absence of conservation laws and perceived cosmological problems; an important step in addressing these issues was the development of the Lagrangian-based non-relativistic theory of Bekenstein and Milgrom. This theory led to the development of a tentative relativistic theory that formed the basis for later multi-field theories of gravity. On an empirical level the predictive success of the idea with respect to the phenomenology of galaxies presents considerable challenges for cold dark matter. For MOND the essential challenge remains the absence of a generally accepted theoretical underpinning of the idea and, thus, cosmological predictions. I briefly review recent progress in this direction. Finally I discuss the role and sociology of unconventional ideas in astronomy in the presence of a strongly entrenched standard paradigm.Comment: 25 pages, 9 figures, previous uploaded file was out of date, Canadian Journal of Physic

Hiding Lorentz Invariance Violation with MOND

Ho\v{r}ava gravity is a attempt to construct a renormalizable theory of gravity by breaking the Lorentz Invariance of the gravitational action at high energies. The underlying principle is that Lorentz Invariance is an approximate symmetry and its violation by gravitational phenomena is somehow hidden to present limits of observational precision. Here I point out that a simple modification of the low energy limit of Ho\v{r}ava gravity in its non-projectable form can effectively camouflage the presence of a preferred frame in regions where the Newtonian gravitational field gradient is higher than $cH_0$; this modification results in the phenomenology of MOND at lower accelerations.Comment: 5 pages, revised field equation, discussion added on potentials and dark energy, in press PR

The Circumnuclear Material in the Galactic Centre: A Clue to the Accretion Process

On the basis of ``sticky particle'' calculations, it is argued that the gas features observed within 10 pc of the Galactic Centre-- the circumnuclear disk (CND) and the ionized gas filaments-- as well as the newly formed stars in the inner one parsec can be understood in terms of tidal capture and disruption of gas clouds on low angular momentum orbits in a potential containing a point mass. The calculations demonstrate that a dissipative component forms a ``dispersion ring'', an asymmetric elliptical torus precessing counter to the direction of rotation, and that this shape can be maintained for many orbital periods. For a range of plausible initial conditions, such a sturcture can explain the morphology and kinematics of the CND and of the most conspicuous ionized filament. While forming the dispersion ring, a small cloud with low specific angular momentum is drawn into a long filament which repeatedly collides with itself at high velocity. The compression in strong shocks is likely to lead to star formation even in the near tidal field of the point mass. This process may have general relevance to accretion onto massive black holes in normal and active galactic nuclei.Comment: 10 pg text, 14 figures, LaTex, mn.sty, accepted MNRA

The ecology of the kākerōri (Rarotonga flycatcher) Pomarea dimidiata, with special reference to fledged young : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University

The Kakerori (Pomarea dimidiata) is a small flycatcher, endemic to Rarotonga in the Cook Islands. In August 1991 the total world population was estimated at 47 individuals, an increase of 14 birds from the previous year. Kakerori live in the forest canopy of small valleys in the steep, mountainous interior. This study concentrated on the ecology of young birds and factors affecting the breeding success (the number of fledged young produced) of pairs. Young birds remain in the parental territory for up to four months after fledging, where they are commonly found high in the leafy canopy (mean = 25.7m n=36). After parental care has ceased, young birds move to the high, exposed ridges up to 100m from their natal territories (mean = 87m n=14), and remain on average, 2.4m (n=14) from the ground. Successful Kakerori territories (those that have produced fledged young) have a relatively lowered canopy (10.3m) and few ferns (28.3%), with many juvenile trees (38.3%) and shrubs (33.4%) making up the shrub layer. These juvenile trees may ensure a continued closed canopy. Successful territories also have few, large trees (mean total basal area = 7.39m2) and a higher level of moss (16.5%) which may encourage larger populations of insects as well as providing possible nest sites for Kakerori. Unsuccessful territories (those that produced no fledged young) have many, immature trees (mean total basal area = 3.21 m2) and little moss (8.1%). In general, insect numbers varied little between successful and unsuccessful territories, however during February 1991 successful territories had a large percentage of flies (40.4% n=23) compared to unsuccessful (8.3% n=2). During February when adults are feeding newly fledged young, a greater availability of insects may positively affect breeding success. Poison baits for rats have been laid in the study area since 1988 and the number of fledged young found has increased from one in 1987/1988 to 14 in 1990/1991. The most effective method of conserving the Kakerori may be to continue indefinitely the rat-baiting campaign throughout the study area and neighbouring valleys. This would depend entirely on the availability of funds and committed personnel

Feed-through has polyterminal feature

Feed-through connector with individual solder pots in the polyterminal side provides good connections with small amounts of solder and permits visual inspection of bonds. Polyterminal also provides a friction mechanical bond to position conductors prior to soldering