1,297 research outputs found
O stars effective temperature and HII regions ionization parameter gradients in the Galaxy
Extensive photoionization model grids are computed for single star HII
regions using stellar atmosphere models from the WM-basic code. Mid-IR emission
line intensities are predicted and diagnostic diagrams of [NeIII]/[NeII] and
[SIV]/[SIII] excitation ratio are build, taking into account the metallicities
of both the star and the HII region. The diagrams are used in conjunction with
galactic HII region observations obtained with the ISO Observatory to determine
the effective temperature Teff of the exciting O stars and the mean ionization
parameter U. Teff and U are found to increase and decrease, respectively, with
the metallicity of the HII region represented by the [Ne/Ne_sol] ratio. No
evidence is found for gradients of Teff or U with galactocentric distance Rgal.
The observed excitation sequence with Rgal is mainly due to the effect of the
metallicity gradient on the spectral ionizing shape, upon which the effect of
an increase in Teff with Z is superimposed. We show that not taking properly
into account the effect of metallicity on the ionizing shape of the stellar
atmosphere would lead to an apparent decrease of Teff with Z and an increase of
Teff with Rgal.Comment: Accepted in Ap
HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects
ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst
galaxies. We present for the first time in a starburst galaxy a 2D study of the
spatial behavior of collisional and radiative transfer effects in He^+. The HeI
lines are analysed based on data obtained with FLAMES and GMOS. Collisional
effects are negligible for transitions in the singlet cascade while relatively
important for those in the triplet cascade. In particular, they can contribute
up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are
important over an extended and circular area of 30pc in diameter centered at
the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction
corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the
stellar absorption equivalent width as well as the most recent emissivities. We
found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the
excitation and the total helium abundance, y_tot, is consistent with no
abundance gradient. Uncertainties in the derivation of He abundances are
dominated by the adopted assumptions. We illustrated the difficulty of
detecting a putative He enrichment due to the presence of Wolf-Rayet stars in
the main GHIIR. Data are marginally consistent with an excess in the N/He ratio
in the N enriched area of the order of both, the atmospheric N/He ratios in WR
stars and the uncertainties estimated for the N/He ratios.Comment: Accepted in Astronomy and Astrophysics; the emissivities presented in
the Corrigendum, Porter et al. 2013, arXiv:1303.5115, have been include
Detection of [OI] 6300 and Other Diagnostic Emission Lines in the Diffuse Ionized Gas of M33 with Gemini-North
We present spectroscopic observations of diffuse ionized gas (DIG) in M33
near the HII region NGC 604. We present the first detection of [OI] 6300 in the
DIG of M33, one of the critical lines for distinguishing photo- from shock
ionization models. We measure [OI]/Ha in the range of 0.04 to 0.10 and an
increase in this ratio with decreasing emission measure. Our measurements of
[SII]/Ha and [NII]/Ha also rise with decreasing emission measure, while our
[OIII]/Hb measurements remain fairly constant. We have one tentative detection
of He I in the region of brightest emission measure, with a ratio of He I/Ha =
0.033 +- 0.019, indicating that the helium is at least partially ionized. We
compare our observed emission line ratios to photoionization models and find
that field star ionization models do not fit our data well. Leaky HII region
models are consistent with our data, without the need to invoke additional
ionization mechanisms to fit our [OI] or [OIII] measurements. The closest large
HII region is NGC 604 and is therefore a likely candidate for the source of the
ionizing photons for the gas in this region.Comment: 12 pages, 4 figures, accepted by ApJ
The Impact of Electric Cars on Oil Demand and Greenhouse Gas Emissions in Key Markets
This book explores the extent to which electric cars might reduce oil demand and greenhouse gas emissions in key markets: China, France, Germany, India, Japan and the United States. The developed model consists of an econometric sub-model, soft-linked with a system dynamics sub-model. The model captures feedback loops that may stimulate the market development of electric cars. The six countries are interlinked to simulate technological progress concerning the electric vehicle battery
The Impact of Electric Cars on Oil Demand and Greenhouse Gas Emissions in Key Markets
This thesis explores the extent to which electric cars might reduce oil demand and greenhouse gas emissions in key markets: China, France, Germany, India, Japan and the United States. To meet this objective, a dynamic model capable of simulating the market evolution of nine powertrain technologies between 2000 and 2030 is developed.
The model consists of an econometric sub-model, soft-linked with a system dynamics sub-model. The purpose of the time-series econometric sub-model is to project country-specific total car stock. To this end, six single-equation regressions based on autoregressive integrated moving average or autoregressive distributed-lag techniques are estimated. The purpose of the system dynamics sub-model is to represent feedback processes and facilitate policy analysis. The effects of six policy measures are examined: emission standards, energy taxation, electric car purchase subsidies, investment in recharging stations, investment in hydrogen refuelling infrastructure and desired car occupancy. The dynamic hypothesis of the model captures feedback loops that may stimulate the market development of electric cars. The six countries are interlinked to simulate technological progress concerning the electric vehicle battery. In particular, its cost, price and capacity, together with the resulting electric range of the car, are investigated. Two scenarios are constructed: under the Alternative Scenario, the market uptake of electric cars is faster due to a favourable policy package. This leads to a decline in oil demand and direct greenhouse gas emissions as well as to an increase in electricity demand from cars compared to the Reference Scenario.
The methodological linkage of econometrics and system dynamics, together with the endogenisation of the electric vehicle battery price evolution by explicitly modelling six major car markets, is the main contribution of this study. Its major limitations prompt further research on the representation of supply-side aspects (i.e. battery and vehicle manufacturers) using alternative methods such as agent-based modelling
Tramp Novae Between Galaxies in the Fornax Cluster: Tracers of Intracluster Light
We report the results of a survey for novae in and between the galaxies of
the Fornax cluster. Our survey provides strong evidence that intracluster novae
exist and that they provide a useful, independent measure of the intracluster
light in Fornax. We discovered six strong nova candidates in six distinct
epochs spanning eleven years from 1993 to 2004. The data were taken with the 4m
and the 1.5m telescopes at CTIO. The spatial distribution of the nova
candidates is consistent with 16-41% of the total light in the cluster
being in the intracluster light, based on the ratio of the number of novae we
discovered in intracluster space over the total number of novae discovered plus
a simple completeness correction factor. This estimate is consistent with
independent measures of intracluster light in Fornax and Virgo using
intracluster planetary nebulae. The accuracy of the intracluster light
measurement improves with each survey epoch as more novae are discovered.Comment: 30 pages, 10 figures, accepted for publication in the Astrophysical
Journal (Sep 9, 2004). Version 2: Added references. Full resolution versions
of figures 1-7 and 10 can be found at
http://astrowww.phys.uvic.ca/~neill/fnx
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