The Infrared-X-ray continuum correlation in Active Galactic Nuclei

The correlation between the soft X-ray and near infrared emission from AGN is analysed using composite models by the code SUMA. We find new evidences for differences in ranges of parameters which characterize the NLR of Seyfert galaxies and LINERs. Results obtained by modelling the Einstein and the ROSAT samples of galaxies are in full agreement. In order to fit the infrared and X-ray continua, an eta factor is defined, which accounts for the emitting area of the cloud. If the infrared emission is due to bremsstrahlung and comes from the same cloud producing the soft X-rays, the eta values obtained from both emissions must be the same. Therefore, if eta_IR < eta_soft-X there must be a strong contribution of soft X-rays from the active centre. From the eta values we expect to identify the objects that could present strong variability. \Comment: 11 pages,13 figures, in press in MNRAS. in press in MNRA

Temperature Fluctuations and Abundances in HII Galaxies

There is evidence for temperature fluctuations in Planetary Nebulae and in Galactic HII regions. If such fluctuations occur in the low-metallicity, extragalactic HII regions used to probe the primordial helium abundance, the derived 4He mass fraction, Y_P, could be systematically different from the true primordial value. For cooler, mainly high-metallicity HII regions the derived helium abundance may be nearly unchanged but the oxygen abundance could have been seriously underestimated. For hotter, mainly low-metallicity HII regions the oxygen abundance is likely accurate but the helium abundance could be underestimated. The net effect is to tilt the Y vs. Z relation, making it flatter and resulting in a higher inferred Y_P. Although this effect could be large, there are no data which allow us to estimate the size of the temperature fluctuations for the extragalactic HII regions. Therefore, we have explored this effect via Monte Carlos in which the abundances derived from a fiducial data set are modified by \Delta-T chosen from a distribution with 0 < \Delta-T < \Delta-T_max where \Delta-T_max is varied from 500K to 4000K. It is interesting that although this effect shifts the locations of the HII regions in Y vs. O/H plane, it does not introduce any significant additional dispersion.Comment: 11 pages, 9 postscript figures; submitted to the Ap

Avaliação agrotécnica dos seringais Marathon, São Francisco e Santana, situados no município de São Francisco do Pará.

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Efeito da adubação mineral na produção de matéria seca de pimenta longa (Piper hispidinervium).

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Doses de N, P e K na nutrição e no crescimento de mudas de dendezeiro.

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Sintomas de desordens nutricionais em plantas de ipeca (Cephaelis ipecacuanha B. Richard).

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Comportamento de clones amazônicos de seringueira nas condições ecológicas de Belém, PA.

Foi estudado o desempenho de quatorze clones amazonicos de seringueira (Hevea sp.): IAN 8000, IAN 500, IAN 710, IAN, IAN 713, IAN 717, IAN 833, IAN 873, IAN 936, Fx 1042, Fx 2261, Fx 3810, Fx 3925, Fx 4098 e Fx 25, nas condicoes ecologicas de Belem, PA. Onze anos apos a instalacao do experimento, os clones Fx 25, IAN 717, Fx 3925, Fx 4098, Fx3810 e Fx2261, apresentaram as maiores producoes de borracha seca/corte, respectivamente, de 36,6; 33,2; 29,8; 22,9; 19,5; 19,2. Destes, os mais resistentes ao mal-das-folhas foram os clones IAN 717, Fx 3810, Fx 3925 e Fx4098

The Evolution of Helium and Hydrogen Ionization Corrections as HII Regions Age

Helium and hydrogen recombination lines observed in low-metallicity, extragalactic, HII regions provide the data used to infer the primordial helium mass fraction, Y_P. In deriving abundances from observations, the correction for unseen neutral helium or hydrogen is usually assumed to be absent; i.e., the ionization correction factor is taken to be unity (icf = 1). In a previous paper (VGS), we revisited the question of the icf, confirming a "reverse" ionization correction: icf < 1. In VGS the icf was calculated using more nearly realistic models of inhomogeneous HII regions, suggesting that the published values of Y_P needed to be reduced by an amount of order 0.003. As star clusters age, their stellar spectra evolve and so, too, will their icfs. Here the evolution of the icf is studied, along with that of two, alternate, measures of the "hardness" of the radiation spectrum. The differences between the icf for radiation-bounded and matter-bounded models are also explored, along with the effect on the icf of the He/H ratio (since He and H compete for some of the same ionizing photons). Particular attention is paid to the amount of doubly-ionized helium predicted, leading us to suggest that observations of, or bounds to, He++ may help to discriminate among models of HII regions ionized by starbursts of different ages and spectra. We apply our analysis to the Izotov & Thuan (IT) data set utilizing the radiation softness parameter, the [OIII]/[OI] ratio, and the presence or absence of He++ to find 0.95 < icf < 0.99. This suggests that the IT estimate of the primordial helium abundance should be reduced by Delta-Y = 0.006 +- 0.002, from 0.244 +- 0.002 to 0.238 +- 0.003.Comment: 27 double-spaced pages, 11 figures, 5 equations; revised to match the version accepted for publication in the Ap

Ionization Corrections For Low-Metallicity H II Regions and the Primordial Helium Abundance

Helium and hydrogen recombination lines observed in low-metallicity, extragalactic H II regions provide the data used to infer the primordial helium mass fraction, Y_P. The ionization corrections for unseen neutral helium (or hydrogen) are usually assumed to be absent; i.e., the ionization correction factor is taken to be unity (icf = 1). In this paper we revisit the question of the icf for H II regions ionized by clusters of young, hot, metal-poor stars. Our key result is that for the H II regions used in the determination of Y_P, there is a ``reverse'' ionization correction: icf < 1. We explore the effect on the icf of more realistic inhomogeneous H II region models and find that for those regions ionized by young stars, with ``hard'' radiation spectra, the icf is reduced further below unity. In Monte Carlos using H II region data from the literature (Izotov and Thuan 1998) we estimate a reduction in the published value of Y_P of order 0.003, which is roughly twice as large as the quoted statistical error in the Y_P determination.Comment: 23 pages, 2 postscript figures; ApJ accepted; minor change