3,811 research outputs found
Exploiting ground-based optical sensing technologies for volcanic gas surveillance
Measurements of volcanic gas composition and flux are crucial to probing and understanding a range of magmatic,
hydrothermal and atmospheric interactions. The value of optical remote sensing methods has been recognised in this field for more than thirty years but several recent developments promise a new era of volcanic gas surveillance. This could see much higher time- and space-resolved data-sets, sustained at individual volcanoes
even during eruptive episodes. We provide here an overview of these optical methods and their application to ground-based volcano monitoring, covering passive and active measurements in the ultraviolet and infrared spectral regions. We hope thereby to promote the use of such devices, and to stimulate development of new optical
techniques for volcanological research and monitoring
Atmospheric, Evolutionary, and Spectral Models of the Brown Dwarf Gliese 229 B
Theoretical spectra and evolutionary models that span the giant planet--brown
dwarf continuum have been computed based on the recent discovery of the brown
dwarf, Gliese 229 B. A flux enhancement in the 4--5 micron window is a
universal feature from Jovian planets to brown dwarfs. We confirm the existence
of methane and water in Gl 229 B's spectrum and find its mass to be 30 to 55
Jovian masses. Although these calculations focus on Gliese 229 B, they are also
meant to guide future searches for extra-solar giant planets and brown dwarfs.Comment: 8 pages, plain TeX, plus four postscript figures, gzipped and
uuencoded, accepted for Scienc
Optimizing Private Land Conservation and Public Land Use Planning/Regulation
Report of the 2010 Berkley Workshop
Held at the Pocantico Conference Center of the Rockefeller Brothers Fund - July 201
A Budget and Accounting of Metals at z~0: Results from the COS-Halos Survey
We present a budget and accounting of metals in and around star-forming
galaxies at . We combine empirically derived star formation histories
with updated supernova and AGB yields and rates to estimate the total mass of
metals produced by galaxies with present-day stellar mass of
--. On the accounting side of the ledger, we
show that a surprisingly constant 20--25% mass fraction of produced metals
remain in galaxies' stars, interstellar gas and interstellar dust, with little
dependence of this fraction on the galaxy stellar mass (omitting those metals
immediately locked up in remnants). Thus, the bulk of metals are outside of
galaxies, produced in the progenitors of today's galaxies. The COS-Halos
survey is uniquely able to measure the mass of metals in the circumgalactic
medium (to impact parameters of kpc) of low-redshift
galaxies. Using these data, we map the distribution of CGM metals as traced by
both the highly ionized OVI ion and a suite of low-ionization species; combined
with constraints on circumgalactic dust and hotter X-ray emitting gas out to
similar impact parameters, we show that % of metals produced by
galaxies can be easily accounted for out to
150 kpc. With the current data, we cannot rule out a constant mass of metals
within this fixed physical radius. This census provides a crucial boundary
condition for the eventual fate of metals in galaxy evolution models.Comment: 19 pages, 12 figures, 2 tables. ApJ, in pres
Hubble Space Telescope Imaging of the Expanding Nebular Remnant of the Recurrent Nova RS Ophiuchi (2006)
We report Hubble Space Telescope imaging obtained 155 days after the 2006
outburst of RS Ophiuchi. We detect extended emission in both [O III] and [Ne V]
lines. In both lines, the remnant has a double ring structure. The E-W
orientation and total extent of these structures (580+-50 AU at d=1.6kpc) is
consistent with that expected due to expansion of emitting regions imaged
earlier in the outburst at radio wavelengths. Expansion at high velocity
appears to have been roughly constant in the E-W direction (v_{exp} = 3200+-300
km/s in the plane of the sky), with tentative evidence of deceleration N-S. We
present a bipolar model of the remnant whose inclination is consistent with
that of the central binary. The true expansion velocities of the polar
components are then v = 5600+-1100 km/s. We suggest that the bipolar morphology
of the remnant results from interaction of the outburst ejecta with a
circumstellar medium that is significantly denser in the equatorial regions of
the binary than at the poles. This is also consistent with observations of
shock evolution in the X-ray and the possible presence of dust in the infrared.
Furthermore, it is in line with models of the shaping of planetary nebulae with
close binary central systems, and also with recent observations relating to the
progenitors of Type Ia supernovae, for which recurrent novae are a proposed
candidate. Our observations also reveal more extended structures to the S and E
of the remnant whose possible origin is briefly discussed.Comment: 13 pages, 2 figures, accepted for publication in ApJ
Rotating Neutron Stars in a Chiral SU(3) Model
We study the properties of rotating neutron stars within a generalized chiral
SU(3)-flavor model. The influence of the rotation on the inner structure and
the hyperon matter content of the star is discussed. We calculate the Kepler
frequency and moments of inertia of the neutron star sequences. An estimate for
the braking index of the associated pulsars is given.Comment: 14 pages, 9 figure
Black hole formation in perfect fluid collapse
We construct here a special class of perfect fluid collapse models which
generalizes the homogeneous dust collapse solution in order to include non-zero
pressures and inhomogeneities into evolution. It is shown that a black hole is
necessarily generated as end product of continued gravitational collapse,
rather than a naked singularity. We examine the nature of the central
singularity forming as a result of endless collapse and it is shown that no
non-spacelike trajectories can escape from the central singularity. Our results
provide some insights into how the dynamical collapse works, and into the
possible formulations of the cosmic censorship hypothesis, which is as yet a
major unsolved problem in black hole physics.Comment: Revtex4, To appear in Physical Review
Impossibility of Unlimited Gravitational Collapse
It is shown that the gravitational field, as a physical field developing in
the Minkowsky space, does not lead to unlimited gravitational collapse of
massive bodies and, hence, excludes a possibility of the formation of the
``black holes''.Comment: 6 page
Gravitational Collapse with a Cosmological Constant
We consider the effect of a positive cosmological constant on spherical
gravitational collapse to a black hole for a few simple, analytic cases. We
construct the complete Oppenheimer-Snyder-deSitter (OSdS) spacetime, the
generalization of the Oppenheimer-Snyder solution for collapse from rest of a
homogeneous dust ball in an exterior vacuum. In OSdS collapse, the cosmological
constant may affect the onset of collapse and decelerate the implosion
initially, but it plays a diminishing role as the collapse proceeds. We also
construct spacetimes in which a collapsing dust ball can bounce, or hover in
unstable equilibrium, due to the repulsive force of the cosmological constant.
We explore the causal structure of the different spacetimes and identify any
cosmological and black hole event horizons which may be present.Comment: 7 pages, 10 figures; To appear in Phys. Rev.
Time-Translation Invariance of Scattering Maps and Blue-Shift Instabilities on Kerr Black Hole Spacetimes
In this paper, we provide an elementary, unified treatment of two distinct
blue-shift instabilities for the scalar wave equation on a fixed Kerr black
hole background: the celebrated blue-shift at the Cauchy horizon (familiar from
the strong cosmic censorship conjecture) and the time-reversed red-shift at the
event horizon (relevant in classical scattering theory).
Our first theorem concerns the latter and constructs solutions to the wave
equation on Kerr spacetimes such that the radiation field along the future
event horizon vanishes and the radiation field along future null infinity
decays at an arbitrarily fast polynomial rate, yet, the local energy of the
solution is infinite near any point on the future event horizon. Our second
theorem constructs solutions to the wave equation on rotating Kerr spacetimes
such that the radiation field along the past event horizon (extended into the
black hole) vanishes and the radiation field along past null infinity decays at
an arbitrarily fast polynomial rate, yet, the local energy of the solution is
infinite near any point on the Cauchy horizon.
The results make essential use of the scattering theory developed in [M.
Dafermos, I. Rodnianski and Y. Shlapentokh-Rothman, A scattering theory for the
wave equation on Kerr black hole exteriors, preprint (2014) available at
\url{http://arxiv.org/abs/1412.8379}] and exploit directly the time-translation
invariance of the scattering map and the non-triviality of the transmission
map.Comment: 26 pages, 12 figure
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