614 research outputs found
Measuring Energy Poverty: Focusing on What Matters
The provision of modern energy services is recognised as a critical foundation for sustainable development, and is central to the everyday lives of people. Effective policies to dramatically expand modern energy access need to be grounded in a robust information-base. Metrics that can be used for comparative purposes and to track progress towards targets therefore represent an essential support tool. This paper reviews the relevant literature, and discusses the adequacy and applicability of existing instruments to measure energy poverty. Drawing on those insights, it proposes a new composite index to measure energy poverty. Both the associated methodology and initial results for several African countries are discussed. Whereas most existing indicators and composite indices focus on assessing the access to energy, or the degree of development related to energy, our new index – the Multidimensional Energy Poverty Index (MEPI) – focuses on the deprivation of access to modern energy services. It captures both the incidence and intensity of energy poverty, and provides a new tool to support policymaking.
Dielectronic recombination and stability of warm gas in AGN
Understanding the thermal equilibrium (stability) curve may offer insights
into the nature of the warm absorbers often found in active galactic nuclei.
Its shape is determined by factors like the spectrum of the ionizing continuum
and the chemical composition of the gas. We find that the stability curves
obtained under the same set of the above mentioned physical factors, but using
recently derived dielectronic recombination rates, give significantly different
results, especially in the regions corresponding to warm absorbers, leading to
different physical predictions. Using the current rates we find a larger
probability of having thermally stable warm absorber at 10^5 \kel than
previous predictions and also a greater possibility for its multiphase nature.
the results obtained with the current dielectronic recombination rate
coefficients are more reliable because the warm absorber models along the
stability curve have computed coefficient values, whereas previous calculations
relied on guessed averages for the same due to lack of available data.Comment: 5 pages, 3 figures, Accepted for publication in MNRAS Letters. The
definitive version is available at
http://www3.interscience.wiley.com/cgi-bin/hom
The Mid-infrared Fine-structure Lines of Neon as an Indicator of Star For mation Rate in Galaxies
The fine-structure lines of singly ([Ne II] 12.8 micron) and doubly ([Ne III]
15.6 micron) ionized neon are among the most prominent features in the
mid-infrared spectra of star-forming regions, and have the potential to be a
powerful new indicator of the star formation rate in galaxies. Using a sample
of star-forming galaxies with measurements of the fine-structure lines
available from the literature, we show that the sum of the [Ne II] and [Ne III]
luminosities obeys a tight, linear correlation with the total infrared
luminosity, over 5 orders of magnitude in luminosity. We discuss the formation
of the lines and their relation with the Lyman continuum luminosity. A simple
calibration between star formation rate and the [Ne II]+[Ne III] luminosity is
presented.Comment: To appear in ApJ. 8 page
Illumination in symbiotic binary stars: Non-LTE photoionization models. II. Wind case
We describe a non-LTE photoionization code to calculate the wind structure
and emergent spectrum of a red giant wind illuminated by the hot component of a
symbiotic binary system. We consider spherically symmetric winds with several
different velocity and temperature laws and derive predicted line fluxes as a
function of the red giant mass loss rate, \mdot. Our models generally match
observations of the symbiotic stars EG And and AG Peg for \mdot about 10^{-8}
\msunyr to 10^{-7} \msunyr. The optically thick cross- section of the red giant
wind as viewed from the hot component is a crucial parameter in these models.
Winds with cross-sections of 2--3 red giant radii reproduce the observed
fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models
favor winds with acceleration regions that either lie far from the red giant
photosphere or extend for 2--3 red giant radii.Comment: 51 pages, LaTeX including three tables, requires 15 Encapsulated
Postscript figures, to appear in Ap
Signature of Electron Capture in Iron-Rich Ejecta of SN 2003du
Late-time near-infrared and optical spectra are presented for the
normal-bright SN2003du. At about 300 days after the explosion, the emission
profiles of well isolated [FeII] lines (in particular that of the strong
1.644mu feature) trace out the global kinematic distribution of radioactive
material in the expanding. In SN2003du, the 1.644 mu [FeII] line shows a
flat-topped, profile, indicative of a thick but hollow-centered expanding
shell, rather than a strongly-peaked profile that would be expected from a
``center-filled'' distribution.Based on detailed models for exploding
Chandrasekhar mass white dwarfs, we show that the feature is consistent with
spherical explosion models.Our model predicts central region of non-radioactive
electron-capture elements up to 2500--3000km/s as a consequence of burning
under high density, and an extended region of 56Ni up to 9,000--10,000km/s.
Furthermore our analysis indicates that the 1.644mu [FeII] profile is not
consistent with strong mixing between the regions of electron- capture isotopes
and the 56Ni layers as is predicted by detailed 3D models for nuclear
deflagration fronts. We discuss the possibility that the flat-topped profile
could be produced as a result of an infrared catastrophe and conclude that such
an explanation is unlikely. We put our results in context to other SNeIa and
briefly discuss the implications of our result for the use of SNe Ia as
cosmological standard candles.Comment: 12 pages + 8 figures, ApJ (in press, Dec. 20, 2004) For high
resolution figures send E-mail to [email protected]
UV and X-ray Spectral Lines of FeXXIII Ion for Plasma Diagnostics
We have calculated X-ray and UV spectra of Be-like Fe (FeXXIII) ion in
collisional-radiative model including all fine-structure transitions among the
2s^2, 2s2p, 2p^2, 2snl, and 2pnl levels where n=3 and 4, adopting data for the
collision strengths by Zhang & Sampson (1992) and by Sampson, Goett, & Clark
(1984). Some line intensity ratios can be used for the temperature diagnostics.
We show 5 ratios in UV region and 9 ratios in X-ray region as a function of
electron temperature and density at 0.3keV < T_e < 10keV and . The effect of cascade in these line ratios and in the level
population densities are discussed.Comment: LaTeX, 18 pages, 10 Postscript figures. To appear in Physica Script
Fe VII lines in the spectrum of RR Telescopii
Thirteen transitions within the ground 3d^2 configuration of Fe VII are
identified in ultraviolet and optical spectra of the symbiotic star RR
Telescopii obtained with the STIS instrument of the Hubble Space Telescope. The
line fluxes are compared with theoretical data computed with the recent atomic
data of K.A. Berrington et al., and high resolution optical spectra from
VLT/UVES are used to identify blends. Seven branching ratios are measured, with
three in good agreement with theory and one affected by blending. The
lambda5277/lambda4943 branching ratio is discrepant by > 3 sigma, indicating
errors in the atomic data for the lambda5277 line. A least-squares minimization
scheme is used to simultaneously derive the temperature, T, and density, N_e,
of the RR Tel nebula, and the interstellar extinction, E(B-V), towards RR Tel
from the complete set of emission lines. The derived values are: log T/K = 4.50
+/- 0.23, log N_e/cm^-3=7.25 +/- 0.05, and E(B-V)<0.27. The extinction is not
well-constrained by the Fe VII lines, but is consistent with the more accurate
value E(B-V)=0.109^{+0.052}_{-0.059} derived here from the Ne V
lambda2974/lambda1574 ratio in the STIS spectrum. Large differences between the
K.A. Berrington et al. electron excitation data and the earlier F.P. Keenan &
P.H. Norrington data-set are demonstrated, and the latter is shown to give
worse agreement with observations.Comment: To be published in Astronomy & Astrophysics; 7 pages, 4 figure
Far-UV Spectroscopic Analyses of Four Central Stars of Planetary Nebulae
We analyze the Far-UV/UV spectra of four central stars of planetary nebulae
with strong wind features -- NGC 2371, Abell 78, IC 4776 and NGC 1535, and
derive their photospheric and wind parameters by modeling high-resolution FUSE
(Far-Ultraviolet Spectroscopic Explorer) data in the Far-UV and HST-STIS and
IUE data in the UV with spherical non-LTE line-blanketed model atmospheres.
Abell 78 is a hydrogen-deficient transitional [WR]-PG 1159 object, and we find
NGC 2371 to be in the same stage, both migrating from the constant-luminosity
phase to the white dwarf cooling sequence with Teff ~= 120 kK, Mdot ~= 5x10^-8
Msun/yr. NGC 1535 is a ``hydrogen-rich'' O(H) CSPN, and the exact nature of IC
4776 is ambiguous, although it appears to be helium burning. Both objects lie
on the constant-luminosity branch of post-AGB evolution and have Teff ~= 65 kK,
Mdot ~= 1x10^-8 Msun/yr. Thus, both the H-rich and H-deficient channels of PN
evolution are represented in our sample. We also investigate the effects of
including higher ionization stages of iron (up to FeX) in the model atmosphere
calculations of these hot objects (usually neglected in previous analyses), and
find iron to be a useful diagnostic of the stellar parameters in some cases.
The Far-UV spectra of all four objects show evidence of hot (T ~ 300 K)
molecular hydrogen in their circumstellar environments.Comment: 38 pages, 8 figures (6 color). Accepted for publication in Ap
Central Stars of Planetary Nebulae in the Large Magellanic Cloud: A Far-UV Spectroscopic Analysis
We observed seven central stars of planetary nebulae (CSPN) in the Large
Magellanic Cloud (LMC) with the Far Ultraviolet Spectroscopic Explorer (FUSE),
and performed a model-based analysis of these spectra in conjunction with
Hubble Space Telescope (HST) spectra in the UV and optical range to determine
the stellar and nebular parameters. Most of the objects show wind features, and
they have effective temperatures ranging from 38 to 60 kK with mass-loss rates
of ~= 5x10^-8 Msun/yr. Five of the objects have typical LMC abundances. One
object (SMP LMC 61) is a [WC4] star, and we fit its spectra with He/C/O-rich
abundances typical of the [WC] class, and find its atmosphere to be
iron-deficient. Most objects have very hot (T ~> 2000 K) molecular hydrogen in
their nebulae, which may indicate a shocked environment. One of these (SMP LMC
62) also displays OVI 1032-38 nebular emission lines, rarely observed in PN.Comment: 53 pages, 15 figures (11 color). Accepted for publication in Ap
The evolution of ultraviolet emission lines from the circumstellar material surrounding SN 1987A
The presence of narrow high-temperature emission lines from nitrogen-rich gas
close to SN 1987A has been the principal observational constraint on the evolu-
tionary status of the supernova's progenitor. A new analysis of the complete
five-year set of low and high resolution IUE ultraviolet spectra of SN 1987A
(1987.2--1992.3) provide fluxes for the N V 1240, N IV] 1486, He II 1640, OIII]
1665, NIII] 1751, and CIII] 1908 lines with significantly reduced random and
systematic errors and reveals significant short-term fluctuations in the light
curves. The N V, N IV] and N III] lines turn on sequentially over 15 to 20 days
and show a progression from high to low ionization potential, implying an ioni-
zation gradient in the emitting region. The line emission turns on suddenly at
83+/-4 days after the explosion, as defined by N IV]. The N III] line reaches
peak luminosity at 399+/-15 days. A ring radius of (6.24+/-0.20)E{17} cm and
inclination of 41.0+/-3.9 is derived from these times, assuming a circular
ring. The probable role of resonant scattering in the N V light curve
introduces systematic errors that leads us to exclude this line from the timing
analysis. A new nebular analysis yields improved CNO abundance ratios
N/C=6.1+/-1.1 and N/O=1.7+/-0.5, confirming the nitrogen enrichment found in
our previous paper. From the late-time behavior of the light curves we find
that the emission origi- nates from progressively lower density gas. We
estimate the emitting mass near maximum (roughly 400 days) to be roughly
4.7E{-2} solar masses, assuming a filling factor of unity and an electron
density of 2.6E4 cm^{-3}. These results are discussed in the context of current
models for the emission and hydrodynamics of the ring.Comment: 38 pages, AASTeX v.4.0, 13 Postscript figures; ApJ, in pres
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