103,893 research outputs found
The Intermediate Line Region and the Baldwin Effect
Statistical investigations of samples of quasars have established that
clusters of properties are correlated. The strongest trends among the
ultraviolet emission-line properties are characterized by the object-to-object
variation of emission from low-velocity gas, the so-called ``intermediate-line
region'' or ILR. The strongest trends among the optical emission-line
properties are characterized by the object-to-object variation of the line
intensity ratio of [O III] 5007 to optical Fe II. Additionally, the strength of
ILR emission correlates with [O III]/Fe II, as well as with radio and X-ray
properties. The fundamental physical parameter driving these related
correlations is not yet identified. Because the variation in the ILR dominates
the variation in the equivalent widths of lines showing the Baldwin effect, it
is important to understand whether the physical parameter underlying this
variation also drives the Baldwin effect or is a primary source of scatter in
the Baldwin effect.Comment: 11 pages, to appear in the proceedings of the meeting on "Quasars as
Standard Candles for Cosmology" held on May 18-22, 1998, at La Serena, Chile.
To be published by ASP, editor G. Ferlan
Estimates of global ocean cooling at the Last Glacial Maximum based on sea-surface temperature and oxygen-isotope reconstructions
Stability Issues for w < -1 Dark Energy
Precision cosmological data hint that a dark energy with equation of state and hence dubious stability is viable. Here we discuss for any
nucleation from to in a first-order phase
transition. The critical radius is argued to be at least of galactic size and
the corresponding nucleation rate is glacial, thus underwriting the dark
energy's stability and rendering remote any microscopic effect.Comment: 9 pages LaTeX. Significantly rewritten (including abstract
Scaling Relations for the Cosmological "Constant" in Five-Dimensional Relativity
When the cosmological "constant" is derived from modern five-dimensional
relativity, exact solutions imply that for small systems it scales in
proportion to the square of the mass. However, a duality transformation implies
that for large systems it scales as the inverse square of the mass
Heterotic String Corrections from the Dual Type II String
We introduce a method of using the a dual type IIA string to compute
alpha'-corrections to the moduli space of heterotic string compactifications.
In particular we study the hypermultiplet moduli space of a heterotic string on
a K3 surface. One application of this machinery shows that type IIB strings
compactified on a Calabi-Yau space suffer from worldsheet instantons, spacetime
instantons and, in addition, "mixed" instantons which in a sense are both
worldsheet and spacetime. As another application we look at the hyperkaehler
limit of the moduli space in which the K3 surface becomes an ALE space. This is
a variant of the "geometric engineering" method used for vector multiplet
moduli space and should be applicable to a wide range of examples. In
particular we reproduce Sen and Witten's result for the heterotic string on an
A1 singularity and a trivial bundle and generalize this to a collection of E8
point-like instantons on an ALE space.Comment: 21 pages, 5 figures, refs adde
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