Donald Lynden-Bell

Spectroscopy and photometry of elliptical galaxies. I: a new distance estimator

On presente des donnees cinematiques et photometriques concernant 97 galaxies elliptiques, membres de six amas riches

An orphan in the "field of streams"

We use Sloan Digital Sky Survey Data Release 5 photometry and spectroscopy to study a tidal stream that extends over ~50° in the north Galactic cap. From the analysis of the path of the stream and the colors and magnitudes of its stars, the stream is ~20 kpc away at its nearest detection (the celestial equator). We detect a distance gradient: the stream is farther away from us at higher declination. The contents of the stream are made up from a predominantly old and metal-poor population that is similar to the globular clusters M13 and M92. The integrated absolute magnitude of the stream stars is estimated to be Mr ~ -7.5. There is tentative evidence for a velocity signature, with the stream moving at ~-40 km s-1 at low declinations and ~+100 km s-1 at high declinations. The stream lies on the same great circle as Complex A, a roughly linear association of H I high-velocity clouds stretching over ~30° on the sky, and as Ursa Major II, a recently discovered dwarf spheroidal galaxy. Lying close to the same great circle are a number of anomalous, young, and metal-poor globular clusters, including Palomar 1 and Ruprecht 106.

Negative specific heat in astronomy, physics and chemistry

Starting from Antonovs discovery that there is no maximum to the entropy of a gravitating system of point particles at fixed energy in a spherical box if the density contrast between centre and edge exceeds 709, we review progress in the understanding of gravitational thermodynamics.

Global Scaling Relations for Elliptical Galaxies and Implications for Formation

Two recent surveys of elliptical galaxy structural properties are described. E galaxies are seen to populate a planar distribution in the global logarithmic parameter space (R e , σ e , I e ). Two-dimensionality implies that the virial theorem is the only tight constraint on E structure. There is an additional, weaker constraint on radius versus mass that was presumably imposed at formation. The best-fitting plane in logarithmic coordinates has the equation R e ~ σ1.35±0.07 I e-0.84±0.03, implies (M/L) e ~L 0.24±0.04 I e 0.00±0.06. The planar relation can be used to determine distances to E galaxies to an accuracy of ±23%. M/Ls agree well, implying that ellipticals are mainly baryon dominated within R e and that M/Ls are stellar. The effects of other variables such as ellipticity, aspect angle, and rotation on the basic planar relation seem to be small.

Wiener reconstruction of density, velocity, and potential fields from all sky galaxy redshift surveys

We present a new method for recovering the cosmological density, velocity, and potential fields from all-sky redshift catalogues. The method is based on an expansion of the fields in orthogonal radial (Bessel) and angular (spherical harmonic) functions. In this coordinate system, peculiar velocities introduce a coupling of the radial harmonics describing the density field in redshift space but leave the angular modes unaffected. In the harmonic transform space, this radial coupling is described by a distortion matrix which can be computed analytically within the context of linear theory; the redshift space harmonics can then be converted to their real space values by inversion of this matrix. Statistical noise is mitigated by regularizing the matrix inversion with a Wiener filter. The method yields a minimum variance estimate of the density field in real space. In this coordinate system, the minimum variance harmonics of the peculiar velocity and potential fields are related to those of the density field by simple linear transformations. Tests of the method with simulations of a CDM universe and comparison with previously proposed methods demonstrate it to be a very promising new reconstruction method for the local density and velocity field. A first application to the 1.2 Jy IRAS redshift survey is presented.

The chemical evolution of galaxies

Abstract Emphasis is placed on the simplest models of the chemical evolution of galaxies, and the role played by the concentration of the interstellar gas to gravitational stable regions is taken into account. Although Schmidts simple model is improved when concentration is allowed for, it still predicts too wide a spread of metal abundances for agreement with the observations. An exactly solvable accretion model in which the gas mass rises to a maximum and then declines gives the smaller spread observed. This model gives a rather prompt initial enrichment automatically. Finally the models with a linear relationship between star formation rate and gas mass are used to demonstrate effects occurring when the cooking times of elements are taken into account.

Classical monopoles: Newton, NUT space, gravimagnetic lensing and atomic spectra

This article reviews the dynamics and observational signatures of particles interacting with monopoles, beginning with a scholium in NewtonsPrincipia. The orbits of particles in the field of a gravomagnetic monopole, the gravitational analog of a magnetic monopole, lie on cones; when the cones are slit open and flattened, the orbits are the ellipses and hyperbolas that one would have obtained without the gravomagnetic monopole. The more complex problem of a charged, spinning sphere in the field of a magnetic monopole is then discussed. The quantum-mechanical generalization of this latter problem is that of monopolar hydrogen. Previous work on monopolar hydrogen is reviewed and details of the predicted spectrum are given. Protons around uncharged monopoles have a bound continuum. Around charged ones, electrons have levels and decaying resonances, so magnetic monopoles can grow in mass by swallowing both electrons and protons. In general relativity, the spacetime produced by a gravomagnetic monopole is NUT space, named for Newman, Tamborino, and Unti (1963). This space has a nonspherical metric, even though a mass with a gravomagnetic monopole is spherically symmetric. All geodesics in NUT space lie on cones, and this result is used to discuss the gravitational lensing by bodies with gravomagnetic monopoles.

Exact optics: a unification of optical telescope design

A perfect-focus telescope is one in which all rays parallel to the axis meet at a point and give equal magnification there. It is shown that these two conditions define the shapes of both primary and secondary mirrors. Apart from scale, the solution depends upon two parameters: s, which gives the mirror separation in terms of the effective focal length, and K, which gives the relative position of the final focus in that unit. The two conditions ensure that the optical systems have neither spherical aberration nor coma, no matter how fast the F ratio. All known coma-free systems emerge as approximate special cases. In his classical paper, K. Schwarzschild studied all two-mirror systems for which the profiles were conic sections. We make no such a priori shape conditions but demand a perfect focus and solve for the shapes of the mirrors.

Inconsistency in theories of violent relaxation

We examine an inconsistency in theories of violent relaxation by Lynden-Bell and Nakamura. The inconsistency arises from the non-transitive nature of these theories: a system that undergoes a violent relaxation, relaxes and then, upon an addition of energy, undergoes violent relaxation once again would settle in an equilibrium state that is different from the one that is predicted had the system gone directly from the initial to the final state. We conclude that a proper description of the violent relaxation process cannot be achieved by an equilibrium statistical mechanics approach, but instead a dynamical theory for the coarse-grained phase-space density is needed.

Disc sources for conformastationary metrics

Conformastationary metrics - those of the form have been derived by Perjes and by Israel and Wilson as source-free solutions of the Einstein-Maxwell equations. By analogy with the conformastatic metrics which have charged dust sources it was assumed that conformastationary metrics would be the external metrics of charged dust in steady motion. However, for axially symmetric conformastationary metrics we show that, as well as moving dust, hoop tensions are always necessary to balance the centrifugal forces induced by the motion. Exact examples of conformastationary metrics with disc sources are worked out in full. Generalizations to non-axially symmetric conformastationary metrics are indicated.