This paper describes the numerical evolution of an N-body system with a slight
“temperature inversion”; i.e. the maximum velocity dispersion occurs not at the centre but
further out. Fluid models predict that the core of such a system expands on a time-scale
of thousands of central relaxation times, and here this behaviour is qualitatively confirmed
for an N-body system of over 3000 bodies

We report high-resolution spectroscopic observations for a sample of 38 T
Tauri stars (TTS), complemented by UBVRI photometry of 13 TTS, and CCD VRI
photometry for 2 visual binaries. Based on these observations and data taken from the
literature, we derive lithium abundances in 53 TTS, concentrating on weak-line TTS
(WTTS). The sample spans the range in spectral types from K0-M3, aproximately cor-
responding to masses between 1.2 and 0.2 M⊙.

We study the propagator of a non-relativistic, non-interacting particle in any
non-relativistic “time-machine” spacetime of the type shown in Fig. 1: an external,
flat spacetime in which two spatial regions

We present a number of new, exact scalar field cosmologies where the potential con-
sists of two or more exponential terms. Such potentials are motivated by supergravity
or superstring models formulated in higher dimensional spacetimes that have been
compactified to (3+1)-dimensions.

By a combination of analytical and numerical methods, the density prole of a
momentarily at rest spherical star is varied, and the corresponding response in the area
of the spherical shells is monitored. It is shown that the inner apparent horizon (if
it exists) must lie within or at most on the star's surface, while no such restriction is
found for the outer apparent horizon. However, an apparent horizon lying in the vacuum
region will always have non vanishing area, as long as the ADM mass of the system is
non zero. Furthermore for density proles not decreasing inwards, it appears that all
spherical trapped surfaces lie on a thick spherical shell. Finally for a uniform density
star a simple criterion is found, relating density and proper radius that guarantees the
presence or absence of trapped regions

The inflationary scenario is a favorable model to explain the homogeneity and isotropy of
the present universe. In this scenario, vacuum energy of the matter field plays a role of
the cosmological constant, and the universe enters the phase of deSitter expansion. Initial
inhomogeneity of the universe dumps due to the rapid cosmological expansion. To utilize
these aspects of inflation,

We update the analysis of the MSW and general astrophysical solutions to
the combined solar neutrino observations by including the GALLEX II result.
We also show that our parametrized flux uncertainties are equivalent to the
Monte-Carlo results of Bahcall and Ulrich.

The possible solution of dark matter problem with neutralinos of supersymmetric models
within the supergravity framework is reviewed. A novel correlation between the neutralino relic
abundance Ω
χ and the soft supersymmetry breaking patterns is demonstrated. It is explained
that, this generic result together with the proton-decay constraint could significantly reduce the
allowed parameter space of the minimal SU(5) supergravity model, and therefore makes this model
more easily testable. The prospect of obtaining further cosmological constraints from underground
experiments for the minimal SU(5) supergravity model is also briefly discussed.

Leading corrections to Planck’s formula and photon thermodynamics aris-
ing from the pair-mediated photon-photon interaction are calculated. This
interaction is attractive and causes an increase in occupation number for all
modes. Possible consequences, including the role of the cosmic photon gas in
structure formation, are considered.

Stars are gravitationally stabilized fusion reactors changing their chemical composition while trans-
forming light atomic nuclei into heavy ones. The atomic nuclei are supposed to be in thermal equilibrium
with the ambient plasma.

Strictly speaking, the process of 2 minimization is valid only if the errors of the correlation function at a xed separation
are Gaussian distributed and if the values at dierent separations are uncorrelated. The power law model is usually t to
the data for r <
20 h

Usually inflation ends either by a slow rolling of the inflaton field, which gradually
becomes faster and faster, or by a first-order phase transition. We describe a model
where inflation ends in a different way, due to a very rapid rolling (‘waterfall’) of a
scalar field
σ triggered by another scalar field
φ. This model looks as a hybrid of
chaotic inflation with
V
(
φ) =
m
2
φ
2
2
and the usual theory with spontaneous symmetry
breaking with
V
(
σ) =
14λ
(
M
2
− λσ
2
)
2
. The last stages of inflation in this model are
supported not by the inflaton potential
V
(
φ) but by the ‘non-inflationary’ potential
V
(
σ).

We present a simple, closed form expression for the potential of an axisymmetric
disk of stars interacting through gravitational potentials of the form
V
(
r) =
−β/r
+
γr/2, the potential associated with fundamental sources in the conformal invariant fourth
order theory of gravity which has recently been advanced by Mannheim and Kazanas as
a candidate alternative to the standard second order Einstein theory. Using the model
we obtain a reasonable fit to some representative galactic rotation curve data without the
need for any non-luminous or dark matter. Our study suggests that the observed flatness
of rotation curves might only be an intermediate phenomenon rather than an asymptotic
one.

In the first paper in this series we presented a typical set of galactic rotation curves
associated with the conformal invariant fourth order theory of gravity which has recently
been advanced by Mannheim and Kazanas as a candidate alternative to the standard
second order Einstein theory.

We present new ground-based data following up on the HST discovery of low-redshift
Lyman
α absorption in the sight-line to the quasar 3C273. Our goal is to investigate
the relationship between the low-column-density absorbers and higher column-density
objects such as galaxies or H II regions. Narrow-band filter observations with a corono-
graph show that there are no H II regions or other strong Hα line-emitting gas within a
12 kpc radius of the line-of-sight to the quasar, at the velocities of three of the absorbers.
Broad-band imaging in Gunn r shows that there are no dwarf galaxies at Virgo distances
with absolute magnitude above M
B
≈-13.5 and within a radius of 40 kpc from the line-
of-sight to the quasar

We have examined the effect of the environmental density on the arm classi-
fication of an extensive sample of spiral galaxies included in the Nearby Galaxy
Catalog (Tully, 1988a). We have also explored the dependence of the arm class
of a galaxy on other factors, such as its blue absolute magnitude and its disk-
to-total mass ratio, inferred in the literature either from the gradient of a good
galaxy rotation curve or from a photometric mass decomposition method.

CBS is a new program for binary system light curve analysis, it generates synthetic light curves
for a binary system, accounting for eclipses, tidal distortion, limb darkening, gravity darkening and
reflection; it is also possible to compute the light contribution and eclipses of an accretion disk. The
bolometric light curve is generated, as well as curves for the U,B,V,R,I colour bands. In the following
we give a brief description of the first version of the program and show some preliminary results.

We show how to use 21-cm emission and absorption studies to estimate the heat inputs
to the neutral gas in low pressure environments, such as in outer disks of spiral galaxies,
in galactic halos or in intergalactic space

Observations indicate that some extended outer disks have a sharp cut off in the surface
density of neutral hydrogen when this approaches the value of ∼ 2 × 1019 cm−2
. In this
paper we model these HI edges as places where the ratio of neutral to ionized hydrogen
drops rapidly due to ionizing radiation.

Extremely high velocity (EHV) wings, with full widths of 72 to 140 km s−1
, are seen on the
CO J = 3→2 lines toward W3 IRS 5, GL 490, NGC 2071, W28 A2 (G05.89–0.39), GL 2591,
S140, and Cepheus A. Observations of 12CO and 13CO J = 3→2 and J = 2→1 lines indicate
that optical depth generally decreases with increasing velocity separation from the ambient
cloud velocity. Maps of the extremely high velocity (|V −V0| >∼ 20 km s−1
) and the high-velocity
(5 <∼ |V − V0| <∼ 20 km s−1
) CO emission components show that the morphology of the two
components is similar in W3 IRS 5 and W28 A2 but may be different in GL 2591, S140, and
Cepheus A.

Physics beyond the simplest version of the standard electroweak model is re-
quired to reconcile the results of the chlorine and the Kamiokande solar neutrino
experiments.

A brief introduction to the gauge invariant classical and quantum theory of cosmological
perturbations is given. The formalism is applied to inflationary Universe models and yields a
consistent and unified description of the generation and evolution of fluctuations. A general
formula for the amplitude of cosmological perturbations in inflationary cosmology is derived.

Early photoionization of the intergalactic medium is discussed in
a nearly model-independent way, in order to investigate whether early
structures corresponding to rare Gaussian peaks in a CDM model can
photoionize the intergalactic medium sufficiently early to apprecia-
bly smooth out the microwave background fluctuations.

One still cannot conclusively assert that the universe underwent a
neutral phase, despite the new COBE FIRAS limit y < 2.5 × 10−5 on
Compton y-distortions of the cosmic microwave background. Although
scenarios where the very early (z ∼ 1000) ionization is thermal (caused
by IGM temperatures exceeding 104K) are clearly ruled out, there is
a significant loophole for cosmologies with typical CDM parameters
if the dominant ionization mechanism is photoionization. If the ion-
izing radiation has a typical quasar spectrum, then the y-constraint
implies roughly h
4/3ΩigmΩ
−0.28
0 < 0.06 for fully ionized models. This
means that BDM models with Ω0 ≈ 0.15 and reionization at z ≈ 1000
are strongly constrained even in this very conservative case, and can
survive the y test only if most of the baryons form BDM around the
reionization epoch.

This paper is in two unequal halves. After dealing with the
possibility of a genuine continuum background at
λ
>∼ 1 cm, and showing
that it is unlikely to arise in interesting circumstances, the remainder of
the discussion is devoted to discrete radio sources, and their consequences
for cosmology.

The energy scale of inflation is of much interest, as it suggests the scale of grand unified
physics and also governs whether cosmological events such as topological defect forma-
tion can occur after inflation. The COBE results are used to limit the energy scale of
inflation at around 60 e-foldings from the end of inflation. An exact dynamical treat-
ment based on the Hamilton-Jacobi equations is then used to translate this into limits
on the energy scale at the end of inflation. General constraints are given, and then
tighter constraints based on physically motivated assumptions regarding the allowed
forms of density perturbation and gravitational wave spectra. These are also compared
with the values of familiar models.

We present new magnitudes derived from 1.65 µm images for 23 galax-
ies in the Ursa Major cluster. Magnitudes now exist for all but one spiral
meeting our criteria for cluster membership and having H i velocity width
greater than 187 km s−1 and inclination greater than 45◦
.

We present results from a large area (552
′
) imaging
K-band survey of faint objects.
The survey is a high galactic latitude blank-field sample to a 5
σ limit of
K
≃ 17
.3.
The methods for constructing the infrared survey are described, including flatfielding,
astrometry, mosaicing and photometry