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

Stellar abundances and molecular hydrogen in high-redshift galaxies -the far-ultraviolet view

FUSE spectra of star-forming regions in nearby galaxies are compared to composite spectra of Lyman-break galaxies (LBGs), binned by strength of Lyman alpha emission and by mid-UV luminosity. Several far-UV spectral features, including lines dominated by stellar wind and by photospheric components, are very sensitive to stellar abundances. Their measurement in Lyman-break galaxies is compromised by the strong interstellar absorption features, allowing in some cases only upper limits. The derived C and N abundances in the LBGs are no higher than half solar (scaled to oxygen abundance for comparison with emission-line analyses), independent of the strength of Lyman alpha emission. P V absorption indicates abundances as low as 0.1 solar, with an upper limit near 0.4 solar in the reddest and weakest-emission galaxies. Unresolved interstellar absorption components would further lower the derived abundances. Trends of line strength, and derived abundances, are stronger with mid-UV luminosity than with Lyman-alpha strength. H2 absorption in the Lyman and Werner bands is very weak in the LBGs. Template H2 absorption spectra convolved to appropriate resolution show that strict upper limits N(H2)< 10^18 cm^-2 apply in all cases, with more stringent values appropriate for the stronger-emission composites and for mixes of H2 level populations like those on Milky Way sight lines. Since the UV-bright regions are likely to be widespread in these galaxies, these results rule out massive diffuse reservoirs of H2, and suggest that the dust/gas ratio is already fairly large at z~3.Comment: Astron J., in press (June 2006

Is There a Fundamental Line for Disk Galaxies?

We show that there are strong local correlations between metallicity, surface brightness, and dynamical mass-to-light ratio within M33, analogous to the fundamental line of dwarf galaxies identified by Prada & Burkert (2002). Using near-infrared imaging from 2MASS, the published rotation curve of M33, and literature measurements of the metallicities of HII regions and supergiant stars, we demonstrate that these correlations hold for points at radial distances between 140 pc and 6.2 kpc from the center of the galaxy. At a given metallicity or surface brightness, M33 has a mass-to-light ratio approximately four times as large as the Local Group dwarf galaxies; other than this constant offset, we see broad agreement between the M33 and dwarf galaxy data. We use analytical arguments to show that at least two of the three fundamental line correlations are basic properties of disk galaxies that can be derived from very general assumptions. We investigate the effect of supernova feedback on the fundamental line with numerical models and conclude that while feedback clearly controls the scatter in the fundamental line, it is not needed to create the fundamental line itself, in agreement with our analytical calculations. We also compare the M33 data with measurements of a simulated disk galaxy, finding that the simulation reproduces the trends in the data correctly and matches the fundamental line, although the metallicity of the simulated galaxy is too high, and the surface brightness is lower than that of M33.Comment: 14 pages, 14 figures (5 in color). Accepted for publication in Ap

Planning Complex Agro-Ecosystems: The Case of Analog Forestry

Traditional agroecosystems, aimed at maximizing the short term productivity, are characterized by oversimplification of ecological structure and dependence on the use of external inputs. Moreover, intensive agriculture is one of the main cause of deforestation. The main consequence of traditional agriculture is the loss of natural ecosystems and of their precious services. Analog forestry has emerged as a sustainable productive model able to be integrated in forest contexts, without degrading their ecological functions. The obtained agro-ecosystem is characterized by an ecological structure similar to the one of forest, and by the presence of several productive species in the same area. In this study we formalize a planning problem aimed at the optimized design of an analog forest on the medium term. In particular, besides the maximization of income, we considered both ecological (i.e., the presence of different vertical layers and several species) and socio-economic requirements (i.e., the smoothing of both inter- and intra-annual variability of income). We focus the analysis on the Peruvian Amazon, basing on a species database created by ArBio, a Peruvian association which promotes the analog forestry as tool for pursuing the conservation of forest ecosystem services. The obtained results show that the interannual income variability, characterizing an approach of short-term maximization, can be eliminated by adopting the gradual planting of individuals belonging to the same species. Secondly, we quantified the economic and ecological performance of the designed analog forest under different settings of the planning problem. The introduction of the defined ecological and socio-economic constraints affects the economic performance on the medium term, by reducing the annual economic income up to 80%

The He abundance in the metal-deficient blue compact dwarf galaxies Tol 1214-277 and Tol 65

We present high-quality Keck telescope spectroscopic observations of the two metal-deficient blue compact dwarf (BCD) galaxies Tol 1214-277 and Tol 65. These data are used to derive the heavy-element and helium abundances. We find that the oxygen abundances in Tol 1214-277 and Tol 65 are the same, 12+logO/H=7.54+/-0.01, or Zsun/24, despite the different ionization conditions in these galaxies. The nitrogen-to-oxygen abundance ratio in both galaxies is logN/O=-1.64+/-0.02 and lies in the narrow range found for the other most metal-deficient BCDs. We use the five strongest HeI emission lines 3889, 4471, 5876, 6678 and 7065, to correct self-consistently their intensities for collisional and fluorescent enhancement mechanisms and to derive the He abundance. Underlying stellar absorption is found to be important for the HeI 4471 emission line in both galaxies, being larger in Tol 65. The weighted He mass fractions in Tol 1214-277 and Tol 65 are respectively Y=0.2458+/-0.0039 and 0.2410+/-0.0050 when the three HeI emission lines, 4471, 5876 and 6678, are used, and are, respectively, 0.2466+/-0.0043 and 0.2463+/-0.0057 when the HeI 4471 emission line is excluded. These values are in very good agreement with recent measurements of the He mass fraction in others of the most metal-deficient BCDs by Izotov and coworkers. We find that the combined effect of the systematic uncertainties due to the underlying HeI stellar absorption lines, ionization and temperature structure of the HII region and collisional excitation of the hydrogen emission lines is likely small, not exceeding ~2% (the error is 2sigma). Our results support the validity of the standard big bang model of nucleosynthesis.Comment: 22 pages, 3 Postscript figures, accepted for publication in the Astrophysical Journa

Medical Image Segmentation to Estimate HER2 Gene Status in Breast Cancer

This work deals with the estimation of HER2 Gene status in breast tumour images treated with in situ hybridization techniques (ISH). We propose a simple algorithm to obtain the amplification factor of HER2 gene. The obtained results are very close to those obtained by specialists in a manual way. The developed algorithm is based on colour image segmentation and has been included in a software application tool for breast tumour analysis. The developed tool focus on the estimation of the seriousness of tumours, facilitating the work of pathologists and contributing to a better diagnosis

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