There are two principal problems in explaining, in terms of the emission from OB stars, the ionisation of gas which emits diffuse Hα in spiral galaxies. One is the long pathlength which the ionising photons need to traverse to reach their objectives, the other is whether sufficient photons can escape from within the H II regions which surround the hot stars. Here we treat the second point, assuming that the H II regions above a certain threshold luminosity are density bounded. We calculate the escaping Lyman continuum (Lyc) fluxes from the density bounded regions in four galaxies, and show that in each of them this is easily suffcient to produce the measured diffuse Hα emission.

We have used the TAURUS Fabry–Perot mapping spectrometer on the William Herschel telescope (WHT) to produce a complete kinematic map of the disk of M100 in Hα. Here we show how the internal velocity dispersion (σ) of the principal emission components of the brightest regions varies with their Hα luminosity. The plot shows ample scatter, but an upper envelope in σ is clearly linear (in the log–log plane) with a slope of 2·6, a result which agrees precisely with an earlier graph by Arsenault et al., who selected instead the regions of highest surface brightness. We show that this result, which differs from the conventional prediction from the virial theorem, is consistent with virialisation if the H II regions are density bounded, and thus offers evidence in support of the density bounding hypothesis for the most luminous regions in disk galaxies.

We have observed 12 interacting galaxies using the Fabry-Perot interferometer GHαFaS (Galaxy Hα Fabry-Perot system) on the 4.2m William Herschel Telescope (La Palma). We have extracted the physical properties (sizes, Hα luminosity and velocity dispersion) of 236 HII regions for the full sample of interacting galaxies. We have derived the physical properties of 664 HII regions for a sample of 28 isolated galaxies observed with the same instrument in order to compare both populations of HII regions, finding that there are brighter and denser star forming regions in the interacting galaxies compared with the isolated galaxies sample.

Three different types of evidence are presented in favour of the hypothesis that the HII regions in disk galaxies with Hα luminosities greater than a critical value of 1038·6 erg s−1 are density-bounded, and that the escaping Lyman continuum photons from these are the principal ionising agents for the diffuse ISM in disk galaxies. This has important implications for the ionisation of the intergalactic medium, and for computed star formation rates in spirals.

We measure the flux values in the 4 Spitzer-IRAC bands, of a sample of 78 isolated luminous HII regions in the grand design galaxy M100. We estimate the near-IR luminosities and compare them with the Hα-luminosities from the Knapen HII-region catalogue. We find a strong, and expected positive correlation between the total IR luminosity and the Hα luminosity, but no significant correlation between the luminosity and the IR temperature of the regions.

The structural and electronic properties of AlMgB14 are investigated using ab initio methods. The impact of vacancies and electron doping on the crystal’s atomic and electronic structure is investigated. It is found that removing metal atoms does not influence the density of states, except for changes to the Fermi energy. The density of states of the off-stoichiometric Al0.75Mg0.75B14 crystal and the AlMgB14 crystal with five electrons removed are nearly identical. The removal of six electrons results in an 11% contraction in the crystal’s volume. This is associate with the removal of electrons from the B atoms’ 2p-states.

We present a brief, comparative, study of the morphology of a sample of 9 late type, star forming, local galaxies, as seen in different bands. The objects are present in the “The Hα Galaxy Survey” by James et al., 2004 (J04 hereafter), in the Sloan Digital Sky Survey (“SDSSS”, York et al., 2000), and also in data from GALEX (Martin et al. 2005). We tested the pixel to pixel proportionality v. Hα of images in broad bands from FUV to NIR. We also analyzed the differences in the radial profiles of light in different bands. Finally, we also measured several parameters of the morphology of the distributions of light, as detected in bands of SDSS (u,g,r,i,z), GALEX (NUV, FUV) and in R and Hα from J04, aiming to test which bands better mimic the spatial distribution of the SF as traced by Hα. Our goal is to acquire as accurate a determination as possible of the spatial distribution of the massive star formation in local galaxies, to compare with the analogous distribution in galaxies at increasing redshift.

Giant HI shells, with diameters of hundreds of parsecs and expansion velocities of 10-20 s−1 are characteristic observed features of local gas rich galaxies. Although a predictable consequence of the impact of OB associations on the ISM doubts have been raised, as OB stars are not present in the centres of the majority of these shells. Here we combine our observations of expanding ionized shells in luminous H II regions with basic dynamical models to give support to the scenario in which OB associations do produce the HI shells.

Observations of interstellar Na I in the spectra of 93 stars within 315 pc from the Sun show that it lies in a tunnel of gas moving away from Scorpio-Centaurus and is surrounded by gas moving toward the Galactic center.

Gas approaches the Sun from Scorpio-Centaurus expanding from (r, l, b)=(160 pc, 313°7, +28°2) with LSR velocity 15.3 km s−1. The radius of this shell is 153 pc.

We identify these clouds:

D: velocity vector (υ d, l d, b d)=(+7.2 km s−1, 305°1, −13°5), above and below the Galactic plane (GP) in the range of Galactic longitudes 357°–55°.

C: velocity vector (υ c, l c, b c)=(+11.5 km s−1, 349°0, −35°2), above and below the GP in the range 30°≤l≤110°.

M: velocity vector (υ m, l m, b m)=(+21.9 km s−1, 34°2, +1°5), above and below the GP in the range 100°≤l≤130°.

P: velocity vector (υ p, l p, b p)=(+13.8 km s−1, 244°9, +5°4), above and below the GP from l~120° to the limit of our data at l~210°.

E: velocity vector (υ e, l e, b e)=(+16.8 km s−1, 208°4, +6°2) in the range 160°≤l≤185° and −10°≤b≤–35°.

A: velocity vector (υ a, l a, b a)=(+12.9 km s−1, 73°6, −5°6) towards the Galactic anti-center, below the GP.

I: velocity vector (υ i, l i, b i)=(+37.7 km s−1, 132°8, −64°3) towards the Galactic anti-center, above the GP.

We have developed a new stellar population synthesis model for calculating colours and absorption line indices in early type galaxies. This model can work either for single-age stellar populations or in an evolutionary scheme following the chemical evolution. The model is based on the isochrones of the Padova group and we have developed our own method of conversion to colours. Details can be found in Vazdekis A., Casuso E., Peletier R. & Beckman J. (submitted, 1995). To test the model we have obtained accurate observations in many colours and line indices of the three standard galaxies: NGC 3379, NGC 4472 and NGC 4594.

High-resolution optical and NIR observations are used to constrain a dynamical model of the circumnuclear star forming (SF) region in the barred galaxy M100 (NGC 4321). Small leading arms observed in our K-band image of the nuclear region have been reproduced in numerical modeling of M100, a galaxy with a double inner Lindblad resonance (ILR). We also present preliminary optical and NIR observations of NGC 6951: a barred galaxy with circumnuclear SF showing a distinctly different behavior to M100 at 2.2µm.

We have carried out optical and Far UV studies of the field around the EUV source EUVE J1027+323. We find two sources which contribute to this flux which are spatially unresolvable with EUVE. One is a non-cataloged QSO and one is a “hidden” hot white dwarf. Reasonable scenarios ascribe the majority of the flux to the white dwarf.

We present new high quality Ha continuum-subtracted images of the grand design galaxies NGC 157, NGC 3631, NGC 6764, and NGC 6951, two of them barred and two non-barred, and describe the statistical properties of the HII regions. We have determined the positions, angular sizes and fluxes of individual HII regions, and construct luminosity functions and diameter and density distributions. We find no significant differences between arm and interarm HII region properties, or between the barred and non-barred galaxies. This paper summarizes work described in more detail by Rozas et al. (1995a,b)

The Hα brightness distribution of a face-on galaxy is a classical representation of the massive star formation rate per unit surface area. Here, we present a test for the degree of symmetry in this distribution, aimed at deciding whether this parameter shows a significant difference between barred and non-barred galaxies. The test consists in deriving the cross-correlation function of the Hα brightness as a function of curvilinear distance along pairs of opposed arms. In order to use the test, we first apply a geometrical unfolding technique. Here we explain this technique, and present the initial results of applying the test to NGC 157 and NGC 6764.

Carbon dioxide is an attractive organic solvent in today's chemical process environment in that it is non-flammable, inexpensive, and exhibits low toxicity. Further, materials solubilized in carbon dioxide are easily and completely recovered/concentrated from solution via a simple pressure quench. Despite these favorable properties, CO2 is non-polar, and as such is a very poor solvent for materials such as conventional metal chelating agents, thus blocking application of carbon dioxide in metal extraction/recovery. Consequently, we are exploring the molecular design of materials which are highly CO2-philic, that is, they exhibit solubilities in carbon dioxide which are significantly greater than alkanes with the same number of main-chain atoms. By functionalizing chelating moieties with CO2-philic oligomers, we have generated materials which both effectively extract metals from solid matrices and which dissolve in carbon dioxide in significant quantities.

We have obtained the oxygen abundance in a sample of 44 F-type dwarfs in the Ursa Major group and the Hyades open cluster, using an NLTE analysis of the O I infrared triplet at λλ 7771-7775 Å. These clusters show the “lithium gap” in the F spectral range, and it has been suggested that if this phenomenon were due to microscopic diffusion, their Li-depleted stars could also show oxygen and/or nitrogen depletion. Our results here show a substantial measure of uniformity in the oxygen abundances. The data might indicate a very small dip (< 0.1 dex) in the O abundance for stars located in the Li gap. Microscopic diffusion seems to be the only known mechanism able to produce an oxygen dip. If this mechanism were responsible for the Li gap, it would have to account for a depletion of up to two orders of magnitude in Li and, at the same time, less than 0.1 dex in oxygen. We note that turbulent mixing could modify a microscopic diffusion pattern in order to yield the observed abundances of the two elements.

We present new beryllium abundances for three unevolved stars with [Fe/H] in the range −0.4 to −1.6. The Be II doublet is detected in the three stars. A spectral synthesis analysis has been conducted to derive the abundances. We briefly discuss their Be and Li abundances, together with a wide sample of stars from the literature, in the context of mixing processes below the convection zone.

Surveys of low-income women in Los Angeles County in 1985 and 1986 were used to examine the relative impact of child-bearing motivations versus life circumstances on the intention to have a(nother) child. Future child-bearing intentions are strongly related to current parity level regardless of marital status, race/ethnicity or economic status. Psychological motivating factors predict child-bearing intentions of nulliparous women, but not those of parous women. Multivariate analyses showed that motivation for parenthood and life circumstances combined predicted women's child-bearing intentions 88·6% of the time for nulliparous women, but 73·7% for parous women. These findings suggest that, in a low-income population, the onset of parenthood reduces the relationship between specific motivations for child-bearing and actual child-bearing intentions, and diminishes the ability to predict child-bearing intentions based on both attitudinal and social/structural factors.