The methods and techniques for the slitless spectroscopy software aXe, which was designed to reduce data from the various slitless spectroscopy modes of Hubble Space Telescope instruments, are described. aXe can treat slitless spectra from different instruments such as ACS, NICMOS and WFC3 through the use of a configuration file which contains all the instrument dependent parameters. The basis of the spectral extraction within aXe are the position, morphology and photometry of the objects on a companion direct image. Several aspects of slitless spectroscopy, such as the overlap of spectra, an extraction dependent on object shape and the provision of flat-field cubes, motivate a dedicated software package, and the solutions offered within aXe are discussed in detail. The effect of the mutual contamination of spectra can be quantitatively assessed in aXe, using spectral and morphological information from the companion direct image(s). A new method named 'aXedrizzle' for 2D rebinning and co-adding spectral data, taken with small shifts or dithers, is described. The extraction of slitless spectra with optimal weighting is outlined and the correction of spectra for detector fringing for the ACS CCD's is presented. Auxiliary software for simulating slitless data and for visualizing the results of an aXe extraction is outlined.Comment: 18 pages, 10 figures, accepted for publication in PASP. A high resolution version is available at http://www.stecf.org/software/slitless_software/axe/axe_PASP.pd

Context. Starbursts are one of the main contributors to the chemical enrichment of the interstellar medium. However, mechanisms governing the interaction between the recent star formation and the surrounding gas are not fully understood. Because of their a priori simplicity, the subgroup of galaxies constitute an ideal sample to study these mechanisms.Aims. A detailed 2D study of the central region of NGC 5253 has been performed to characterize the stellar and ionized gas structure as well as the extinction distribution, physical properties and kinematics of the ionized gas in the central ~210 pc × 130 pc.Methods. We utilized optical integral field spectroscopy (IFS) data obtained with FLAMES.Results. A detailed extinction map for the ionized gas in NGC 5253 shows that the largest extinction is associated with the prominent Giant region. There is an offset of ~05 between the peak of the optical continuum and the extinction peak in agreement with findings in the infrared. We found that stars suffer less extinction than gas by a factor of ~0.33. The [S ii]λ6717/[S ii]λ6731 map shows an electron density (N e) gradient declining from the peak of emission in Hα (790 cm-3) outwards, while the argon line ratio traces areas with N e ~ 4200–6200 cm-3. The area polluted with extra nitrogen, as deduced from the excess [N ii]λ6584/Hα, extends up to distances of 33 (~60 pc) from the maximum pollution, which is offset by ~15 from the peak of continuum emission. Wolf-Rayet features are distributed in an irregular pattern over a larger area (~100 pc × 100 pc) and associated with young stellar clusters. We measured He+ abundances over most of the field of view and values of He++/H+ 0.0005 in localized areas which do not coincide, in general, with the areas presenting W-R emission or extra nitrogen. The line profiles are complex. Up to three emission components were needed to reproduce them. One of them, associated with the giant region, presents supersonic widths and [N ii]λ6584 and [S ii]6717,6731 emission lines shifted up to 40 km s-1 with respect to Hα. Similarly, one of the narrow components presents offsets in the [N ii]λ6584 line of 20 km s-1. This is the first time that maps with such velocity offsets for a starburst galaxy have been presented. The observables in the giant region fit with a scenario where the two super stellar clusters (SSCs) produce an outflow that encounters the previously quiescent gas. The south-west part of the FLAMES IFU field is consistent with a more evolved stage where the star clusters have already cleared out their local environment.

The kinematic structure of a sample of planetary nebulae, consisting of 23 [WR] central stars, 21 weak emission line stars (wels), and 57 non-emission line central stars, is studied. The [WR] stars are shown to be surrounded by turbulent nebulae, a characteristic shared by some wels but almost completely absent from the non-emission line stars. The fraction of objects showing turbulence for non-emission-line stars, wels, and [WR] stars is 7%, 24%, and 91%, respectively. The [WR] stars show a distinct IRAS 12-micron excess, indicative of small dust grains, which is not found for wels. The [WR]-star nebulae are on average more centrally condensed than those of other stars. On the age-temperature diagram, the wels are located on tracks of both high and low stellar mass, while [WR] stars trace a narrow range of intermediate masses. Emission-line stars are not found on the cooling track. One group of wels may form a sequence wels–[WO] stars with increasing temperature. For the other groups, both the wels and the [WR] stars appear to represent several, independent evolutionary tracks. We find a discontinuity in the [WR] stellar temperature distribution and suggest different evolutionary sequences above and below the temperature gap. One group of cool [WR] stars has no counterpart among any other group of PNe and may represent binary evolution. A prime factor distinguishing wels and [WR] stars appears to be stellar luminosity. We find no evidence for an increase in the nebular expansion velocity with time.

We present values for angular diameter, flux and extinction for 70 Galactic planetary nebulae observed using narrow-band filters. Angular diameters are derived using constant emissivity shell and photoionization line emission models. The mean of the results from these two models are presented as our best estimate. Contour plots of 36 fully resolved objects are included and the low-intensity contours often reveal an elliptical structure that is not always apparent from full width at half maximum measurements. Flux densities are determined, and for both Hα and [O _iii] there is little evidence of any systematic differences between observed and catalogued values. Observed Hα extinction values are determined using observed Hα and catalogued radio fluxes. Hα extinction values are also derived from catalogued Hα and Hβ flux values by means of an R_V dependent extinction law. R_V is then calculated in terms of observed extinction values and catalogued Hα and Hβ flux values. Comparing observed and catalogue extinction values for a subset of bulge objects, observed values tend to be lower than catalogue values calculated with R_V= 3.1. For the same subset we calculate 〈R_V〉= 2.0, confirming that toward the bulge interstellar extinction is steeper than R_V= 3.1. For the inner Galaxy, a relation with the higher supernova rate is suggested, and that the low-density warm ionized medium is the site of the anomalous extinction. Low values of extinction are also derived using dust models with a turnover radius of 0.08 μm.