1,737 research outputs found
Prospects for the Search for a Doubly-Charged Higgs in the Left-Right Symmetric Model with ATLAS
We estimate the potential for observation at the LHC of a doubly charged
Higgs boson, as predicted in Left-Right symmetric models. Single production by
vector boson fusion, and pair production by the
Drell-Yan process are
considered. Various decay channels are investigated: dileptons, including pairs
of 's, as well as $WW
Revisiting He-like X-ray Emission Line Plasma Diagnostics
A complete model of helium-like line and continuum emission has been
incorporated into the plasma simulation code Cloudy. All elements between He
and Zn are treated, any number of levels can be considered, and radiative and
collisional processes are included. This includes photoionization from all
levels, line transfer including continuum pumping and destruction by background
opacities, scattering, and collisional processes. The model is calculated
self-consistently along with the ionization and thermal structure of the
surrounding nebula. The result is a complete line and continuum spectrum of the
plasma. Here we focus on the ions of the He I sequence and reconsider the
standard helium-like X-ray diagnostics. We first consider semi-analytical
predictions and compare these with previous work in the low-density,
optically-thin limit. We then perform numerical calculations of helium-like
X-ray emission (such as is observed in some regions of Seyferts) and predict
line ratios as a function of ionizing flux, hydrogen density, and column
density. In particular, we demonstrate that, in photoionized plasmas, the
-ratio, a density indicator in a collisional plasma, depends on the
ionization fraction and is strongly affected by optical depth for large column
densities. We also introduce the notion that the -ratio is a measure of the
incident continuum at UV wavelengths. The -ratio, which is
temperature-sensitive in a collisional plasma, is also discussed, and shown to
be strongly affected by continuum pumping and optical depth as well. These
distinguish a photoionized plasma from the more commonly studied collisional
case.Comment: 28 pages, 7 figures, accepted to Ap
Cosmic rays and the emission line regions of active galactic nuclei
The effects that the synchrotron emitting relativistic electrons could have on the emission line regions which characterize active nuclei are discussed. Detailed models of both the inner, dense, broad line region and the outer, lower density, narrow line region are presented, together with the first models of the optically emitting gas often found within extended radio lobes. If the relativistic gas which produces the synchrotron radio emission is mixed with the emission line region gas then significant changes in the emission line spectrum will result. The effects of the synchrotron emitting electrons on filaments in the Crab Nebula are discussed in an appendix, along with a comparison between the experimental calculations, which employ the mean escape probability formalism, and recent Hubbard and Puetter models
Which Stars are Ionizing the Orion Nebula ?
The common assumption that Theta-1-Ori C is the dominant ionizing source for
the Orion Nebula is critically examined. This assumption underlies much of the
existing analysis of the nebula. In this paper we establish through comparison
of the relative strengths of emission lines with expectations from Cloudy
models and through the direction of the bright edges of proplyds that
Theta-2-Ori-A, which lies beyond the Bright Bar, also plays an important role.
Theta-1-Ori-C does dominate ionization in the inner part of the Orion Nebula,
but outside of the Bright Bar as far as the southeast boundary of the Extended
Orion Nebula, Theta-2-Ori-A is the dominant source. In addition to identifying
the ionizing star in sample regions, we were able to locate those portions of
the nebula in 3-D. This analysis illustrates the power of MUSE spectral imaging
observations in identifying sources of ionization in extended regions.Comment: 7 pages with 5 figure
Atomic Data for Permitted Resonance Lines of Atoms and Ions from H to Si, and S, Ar, Ca and Fe
We list vacuum wavelengths, energy levels, statistical weights, transition
probabilities and oscillator strengths for permitted resonance spectral lines
of all ions of 18 astrophysically important elements (H through Si, S, Ar, Ca,
Fe). Using a compilation of experimental energy levels, we derived accurate
wavelengths for 5599 lines of 1828 ground-term multiplets which have gf-values
calculated in the Opacity Project. We recalculated the Opacity Project
multiplet gf-values to oscillator strengths and transition probabilities of
individual lines. For completeness, we added 372 resonance lines of NeI, ArI,
FeI and FeII ions which are not covered by the Opacity Project.
Intercombination and forbidden lines are not included in the present
compilation.Comment: 6 pages of text, latex, 1 figure, 4 tables; tables in ASCII format
available at ftp://asta.pa.uky.edu/dima/lines/ or at
http://www.pa.uky.edu/~verner/atom.html Accepted by Atomic Data Nucl. Data
Table
Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
We present a complete set of analytic fits to the non-relativistic
photoionization cross sections for the ground states of atoms and ions of
elements from H through Si, and S, Ar, Ca, and Fe. Near the ionization
thresholds, the fits are based on the Opacity Project theoretical cross
sections interpolated and smoothed over resonances. At higher energies, the
fits reproduce calculated Hartree-Dirac-Slater photoionization cross sections.Comment: 24 pages including Postscript figures and tables, uses aaspp4.sty,
accepted for publication in Astrophysical Journal. Misprint in Eq.(1) is
correcte
The Impact of Public Policy on Portland\u27s Waterfront
In May, 1987, Portland voters approved by a 2-to-1 margin a referendum preventing non-marine development along its waterfront for at least five years. It has become clear that the vote was not just a Portland waterfront issue. To many, the vote was a statement of no confidence in growth regulations and unhappiness with the pace of development throughout the Greater Portland region. The vote illustrated that there is no consensus on Greater Portland\u27s future. For Portland\u27s waterfront, a lack of consensus is nothing new. Portland has debated waterfront policy in fits and starts for most of the 20th century. As will be explained, this is no local phenomenon. But what is clear is that Portland in the 198-s continues to suffer from inconsistent public policies, political infighting and unawareness by the general public of how the Harbor operates. The intent of this paper is to record the impact of public policy on Portland\u27s waterfront and suggest methods for improving local waterfront planning. The methodology used for this book included the review, analysis and evaluation of public records, planning documents, published guidebooks, academic reports and media coverage; interviews; and the documentation of the experiences of other ports
The H II Region/PDR Connection: Self-Consistent Calculations of Physical Conditions in Star-Forming Regions
We have performed a series of calculations designed to reproduce infrared
diagnostics used to determine physical conditions in star forming regions. We
self-consistently calculate the thermal and chemical structure of an H II
region and photodissociation region (PDR) that are in pressure equilibrium.
This differs from previous work, which used separate calculations for each gas
phase. Our calculations span a wide range of stellar temperatures, gas
densities, and ionization parameters. We describe improvements made to the
spectral synthesis code Cloudy that made these calculations possible. These
include the addition of a molecular network with ~1000 reactions involving 68
molecular species and improved treatment of the grain physics. Data from the
Spitzer First Look Survey, along with other archives, are used to derive
important physical characteristics of the H II region and PDR. These include
stellar temperatures, electron densities, ionization parameters, UV radiation
flux, and PDR density. Finally, we calculate the contribution of the H II
region to PDR emission line diagnostics, which allows for a more accurate
determination of physical conditions in the PDR.Comment: 60 pages, 35 figures, to be published in the Astrophysical Journal.
Version with full resolution is available at
http://www.pa.uky.edu/~nicholas/hii_pdr_high_res.pd
Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--II:Physical Conditions
We have performed a detailed analysis of the electron temperature and density
in the the Ring Nebula using the calibrated HST WFC3 images described in the
preceding paper. The electron temperature (Te) determined from [N II] and [O
III] rises slightly and monotonically towards the central star. The observed
equivalent width (EW) in the central region indicates that Te rises as high as
13000 K. In contrast, the low EW's in the outer regions are largely due to
scattered diffuse Galactic radiation by dust. The images allowed determination
of unprecedented small scale variations in Te. These variations indicate that
the mean square area temperature fluctuations are significantly higher than
expected from simple photoionization. The power producing these fluctuations
occurs at scales of less than 3.5E15 cm. This scale length provides a strong
restriction on the mechanism causing the large t^2 values observed.Comment: Accepted for publication in the Astronomical Journa
- …