227 research outputs found
Ethanol-water pulp enzymatic pretreatment: chemical and FTIR-PCA analyses
Pulps obtained from ethanol/water cooking of sugarcane bagasse were treated at different times
using xylanase enzyme obtained from Thermomyces lanuginosus IOC-4145 or commercially (Cartazyme
HS, Sandoz Products Ltd.). The enzyme dosage was 18 IU per g of dry pulp and the time
varied from 4 h to 12 h. When xylanase from T. lanuginosus was used, the kappa number and
viscosity improved independently of the processing time used (4 h, 8 h, and 12 h). After chemical
evaluation, the obtained pulps were classified using Fourier Transformed Infra-Red Spectroscopy
and Principal Component Analysis. The results showed that the first three principal components
explained more than 90 % of the total variance of the pulp spectra.FAPESP; CNPq
When Shape Matters: correcting the ICFs to derive the chemical abundances of bipolar and elliptical PNe
The extraction of chemical abundances of ionised nebulae from a limited
spectral range is usually hampered by the lack of emission lines corresponding
to certain ionic stages. So far, the missing emission lines have been accounted
for by the ionisation correction factors (ICFs), constructed under simplistic
assumptions like spherical geometry by using 1-D photoionisation modelling.
In this contribution we discuss the results (Goncalves et al. 2011, in prep.)
of our ongoing project to find a new set of ICFs to determine total abundances
of N, O, Ne, Ar, and S, with optical spectra, in the case of non-spherical PNe.
These results are based on a grid of 3-D photoionisation modelling of round,
elliptical and bipolar shaped PNe, spanning the typical PN luminosities,
effective temperatures and densities.
We show that the additional corrections --to the widely used Kingsburgh and
Barlow (1994) ICFs-- are always higher for bipolars than for ellipticals.
Moreover, these additional corrections are, for bipolars, up to: 17% for
oxygen, 33% for nitrogen, 40% for neon, 28% for argon and 50% for sulphur.
Finally, on top of the fact that corrections change greatly with shape, they
vary also greatly with the central star temperature, while the luminosity is a
less important parameter.Comment: Oral contribution (4 pages, 2 figures) to IAU Symposium 283:
"Planetary Nebulae: An Eye to the Future" held in Puerto de la Cruz,
Tenerife, Spain in July 25th-29th 201
Low-ionization structures in planetary nebulae -- II. Densities, temperatures, abundances and excitation of 6 PNe
Here we present the spatially resolved study of six Galactic planetary
nebulae (PNe), namely IC 4593, Hen 2-186, Hen 2-429, NGC 3918, NGC 6543 and NGC
6905, from intermediate-resolution spectra of the 2.5 m Isaac Newton Telescope
and the 1.54 m Danish telescope. The physical conditions (electron densities,
N, and temperatures, T), chemical compositions and dominant
excitation mechanisms for the different regions of these objects are derived,
in an attempt to go deeper on the knowledge of the low-ionization structures
(LISs) hosted by these PNe. We reinforce the previous conclusions that LISs are
characterized by lower (or at most equal) N than their associated rims
and shells. As for the T, we point out a \textit{possible} different
trend between the N and O diagnostics. T[NII] does not show significant
variations throughout the nebular components, whereas T[OIII] appears to be
slightly higher for LISs. The much larger uncertainties associated with the
T[OIII] of LISs do not allow robust conclusions. Moreover, the chemical
abundances show no variation from one to another PN components, not even
contrasting LISs with rims and shells, as also found in a number of other
works. By discussing the ionization photon flux due to shocks and stellar
radiation, we explore the possible mechanisms responsible for the excitation of
LISs. We argue that the presence of shocks in LISs is not negligible, although
there is a strong dependence on the orientation of the host PNe and LISs
Low-ionization structures in planetary nebulae - III: The statistical analysis of physico-chemical parameters and excitation mechanisms
Nearly 30 yr after the first detailed studies of low-ionization structures (LISs) in planetary nebulae (PNe), we perform a statistical analysis of their physical, chemical, and excitation properties, by collecting published data in the literature. The analysis was made through the contrast between LISs and high-ionization structures - rims or shells - for a large sample of PNe, in order to highlight significant differences between these structures. Our motivation was to find robust results based on the largest sample of LISs gathered so far. (i) Indeed, LISs have lower electron densities (Ne[S ii]) than the rims/shells. (ii) The nitrogen electron temperatures (Te[N ii]) are similar between the two groups, while a bimodal distribution is observed for the Te based on [O iii] of the rims/shells, although the high- and low-ionization structures have Te[O iii] of similar median values. (iii) No significant variations are observed in total abundances of He, N, O, Ne, Ar, Cl, and S between the two groups. (iv) Through the analysis of several diagnostic diagrams, LISs are separated from rims/shells in terms of excitation. From two large grids of photoionization and shock models, we show that there is an important overlap between both mechanisms, particularly when low-ionization line ratios are concerned. We found a good tracer of high-velocity shocks, as well as an indicator of high- and low-velocity shocks that depends on temperature-sensitive line ratios. In conclusion, both excitation mechanisms could be present; however, shocks cannot be the main source of excitation for most of the LISs of PNe.Fil: Mari, MarĂa BelĂ©n. Universidade Federal do Rio de Janeiro; Brasil. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba; ArgentinaFil: Akras, Stavros. National Observatory of Athens; GreciaFil: Gonçalves, Denise R.. Universidade Federal do Rio de Janeiro; Brasi
Extragalactic Planetary Nebulae: tracers of the chemical evolution of nearby galaxies
The study of the chemical composition of Planetary Nebulae in external
galaxies is of paramount importance in the fields of stellar evolution and of
the chemical enrichment history of galaxies. In the last years a number of
spectroscopic studies with 6-8m-class telescopes have been devoted to this
subject improving our knowledge of, among other, the time-evolution of the
radial metallicity gradient in disk galaxies, the chemical evolution of dwarf
galaxies, and the stellar evolution at low metallicity.Comment: 8 pages, 4 figures, Invited Review to IAU Symposium 283, "Planetary
Nebulae: an Eye to the Future", Tenerife, 25-29 July 201
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