Searching for X-Ray Luminous Starburst Galaxies

The existence or otherwise of X-ray luminous star-forming galaxies has been an open question since the era of the Einstein satellite. Various authors have claimed the discovery of X-ray luminous star-forming galaxies but in many cases more careful spectroscopic studies of these objects have shown that many of them are in fact obscured AGN. In order to investigate the possibility that such a class of galaxies do exist, we have carried out a cross-correlation between optical and IRAS samples of galaxies which are known to contain large numbers of star-forming galaxies and catalogues of sources detected in X-ray surveys. The selection criteria for the optical follow-up observations was based on their X-ray and infrared (IRAS) colours and their X-ray luminosities. We note that this sample is by no means complete or uniformly selected and hence cannot be used for statistical studies; nevertheless, confirmation of the existence of such a class of objects would be an important step and would require us to understand the physical process responsible for such powerful X-ray emission. We have initiated an optical spectroscopic survey in order to obtain accurate spectroscopic classifications for all the objects which are claimed to be starburst galaxies. Here we present preliminary results from this survey. We have discovered a number of starburst galaxies with X-ray luminosities above ～ 10⁴¹ erg s^-1 (for H ₀=50 km s^-1 Mpc^-1).We investigate possible origins for the X-ray emission in individual cases.     

Decision makers in migration--Papua New Guinea

The author critically examines the assumption that the decision to migrate is made by the individual. Data from surveys of individuals living in 16 towns and 50 rural villages are used to analyze patterns of population movement in Papua New Guinea in an attempt to determine the roles of institutions and of persons other than the migrant in decision-making.     

Star-forming regions in blue compact dwarf galaxies

We present near-infrared 2.1-μm continuum and Brγ and 1–0S(1) line images of three blue compact dwarf galaxies: II Zw 40, NGC 5253 and He 2-10. Comparison of the morphologies of the emission-line regions and continuum together with the line ratios shows that in these cases the starbursts are typified by strongly peaked Brγ and weak diffuse H₂ emission, indicating the presence of one or more compact nuclei, and also tidal tails. We consider the possible origins of the H₂ emission, and conclude that shock excitation in cloud collisions, and hence dynamical processes such as interactions or mergers, is important. By comparing models of the equivalent width of Brγ to other age constraints from the literature we show that the star formation must have occurred not only recently but in a short-duration burst. The current centres of star formation in all three galaxies are of a similar age but, whereas the hotspots in He 2-10 are coeval, we find phase differences between those in NGC 5253. We compare the masses and sizes of the star formation sites to those of present-day globular clusters.     

Far-infrared spectral observations of Venus,Mars, and Jupiter

Spectra of Venus, Mars, and Jupiter between 45 and 115 μm have been obtained at a resolving power of ～10, observing from the NASA Lear Jet at an altitude of 13.7 km. The results are calibrated with lunar observations, and show Mars and Venus to have relatively constant brightness temperatures over this wavelength region, with Venus appearing somewhat warmer at longer wavelengths. The brightness temperature of Jupiter decreases slightly toward longer wavelengths.     

Hydrochemical tracers in the middle Rio Grande Basin,USA: 2. Calibration of a groundwater-flow model

The calibration of a groundwater model with the aid of hydrochemical data has demonstrated that low recharge rates in the Middle Rio Grande Basin may be responsible for a groundwater trough in the center of the basin and for a substantial amount of Rio Grande water in the regional flow system. Earlier models of the basin had difficulty reproducing these features without any hydrochemical data to constrain the rates and distribution of recharge. The objective of this study was to use the large quantity of available hydrochemical data to help calibrate the model parameters, including the recharge rates. The model was constructed using the US Geological Surveys software MODFLOW, MODPATH, and UCODE, and calibrated using ¹⁴C activities and the positions of certain flow zones defined by the hydrochemical data. Parameter estimation was performed using a combination of nonlinear regression techniques and a manual search for the minimum difference between field and simulated observations. The calibrated recharge values were substantially smaller than those used in previous models. Results from a 30,000-year transient simulation suggest that recharge was at a maximum about 20,000 years ago and at a minimum about 10,000 years ago.

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Resumen La calibración de un modelo de aguas subterráneas con el apoyo de datos hidroquímicos ha demostrado que la recarga relativamente baja en la cuenca media del Río Grande es probablemente responsable de una depresión de aguas subterráneas en el centro de la cuenca y de la presencia de una cantidad considerable de agua del Río Grande en el acuífero del Grupo Santa Fe. Los modelos propuestos con anterioridad para la cuenca tenían dificultades para reproducir estas características ya que no tenían datos hidroquímicos que permitieran delimitar los ritmos y distribución de recarga. El objetivo del presente estudio consistió en utilizar una gran cantidad de datos hidroquímicos disponibles para ayudar a calibrar los parámetros del modelo, incluyendo los ritmos de recarga. El modelo se construyó utilizando los modelos MODFLOW, MODPATH, y UCODE del USGS, mientras que la calibración se realizó en base a concentraciones de ¹⁴C y a la posición de ciertas zonas definidas con los datos hidroquímicos. La estimación de parámetros se realizó en base a una combinación de técnicas de regresiones no lineares y a una búsqueda a viva fuerza del error mínimo entre los datos observados y los simulados. Los valores de recarga calibrados fueron significativamente más bajos que los estimados en los modelos anteriores. Los resultados de una simulación transitoria de 30,000 años sugieren que la recarga durante la última glacial máxima (LGM) fue diez veces el ritmo moderno, pero que la recarga que ocurrió inmediatamente después de la LGM fue más baja que el ritmo moderno.

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Résumé Le calibrage dun modèle hydrogéologique avec laide de données hydrochimiques a démontré que la recharge relativement faible dans le Grand Bassin du Middle Rio est vraisemblablement responsable dune dépression des eaux souterraines dans le centre du bassin et de la présence dune quantité substantielle deau du Rio Grande dans laquifère du Groupe de Santa Fe. Les modèles antérieurs avaient des difficultés à reproduire ses conclusions sans laide de données hydrochimiques pour contraindre les taux et la distribution de la recharge. Lobjectif de cette étude était dutiliser une grande quantité de données hydrochimiques permettant de calibrer les paramètres du modèle, et notamment les taux de recharge. Le modèle a été construit avec les logiciels MODFLOW, MODPATH et UCODE, et calibré en utilisant les concentrations en ¹⁴C et la position de certaines zones définies par les données hydrochimiques. Lestimation de certains paramètres a été réalisée en utilisant une combinaison de techniques de régression non linéaire et une méthode de recherche exhaustive (Brute Force Search) de lerreur minimum entre les résultats des observations et les simulations. Les valeurs de la recharge calibrée sont substantiellement plus basses que celles estimées dans les modèles antérieurs. Les résultats dune simulation en régime transitoire sur 30.000 ans suggèrent que la recharge au maximum de la dernière glaciation (last glacial maximum, LGM) était 10 fois supérieure au taux actuel, mais que la recharge qui a suivit la LGM était plus bas que la recharge actuelle.

     

The effect of some systematic errors in the determination of the general circulation of the solar atmosphere

Summary A test was made of the effect of some measurement biases on the determination of the solar horizontal wind field. The effect of such biases is not detectable.     

The effects of oil exploration and production in the northern north sea: Part 1–The levels of hydrocarbons in water and sediments in selected areas, 1978–1981

In the light of increasing oil exploration and production in the northern North Sea, the Brent, Beryl and Forties oil fields, representing three different types of operation, and a number of stations between the Forties field and the Firth of Forth, were sampled to determine the levels of total (by fluorescence), alkane (by glass capillary gas chromatography) and aromatic (by gas chromatography-mass spectrometry) hydrocarbons in water and sediments. Close to the Beryl platform, where diesel-washed drill cuttings have been dumped, there was an accumulation of petrogenic hydrocarbons in the sediment, resulting in a build up of certain aryl hydrocarbons, notably the dibenzthiophenes and 3- and 4-ring aromatic compounds. In all the sediment samples analysed for aromatic hydrocarbons, relatively large amounts of 5- and 6-ring compounds were found in areas expected to be free of pollution, as well as from areas around oil platforms and from the Firth of Forth. Their source is likely to be windborne combustion products.