Compton-thick X-ray absorption in the Seyfert galaxies Tololo 0109383 and ESO 138G1

We present analyses of the ASCA X-ray spectra of two Seyfert galaxies, Tololo 0109383 and ESO 138G1. In both cases, spectral fitting reveals two statistically acceptable continuum models: Compton reflection and partial covering. Both spectra have strong iron K lines, with equivalent widths greater than 1.5 keV. These large equivalent widths are suggestive of heavier obscuration than that directly indicated by the partial-covering models (  210²³ cm^-2),  with the actual column densities being 'Compton-thick' (i.e.   N _H1.510²⁴ cm^-2).  We use the hard X-ray/[O  iii ] flux correlation for Seyferts and data from the literature to provide additional support for this hypothesis. Since Tololo 0109383 is known to have optical type 1 characteristics such as broad Balmer line components and Fe  ii emission, this result marks it as a notable object.     

Large-scale variability in the profiles of Hα and Hβ in the spectrum of the Herbig B8e star MWC 419 and a model interpretation of it

Spectroscopic data taken with a moderate resolution spectrograph in the region of the Hα and Hβ lines are presented for the Herbig B8e star MWC 419. The spectroscopic observations were accompanied by broad band BVR photometric measurements. The observations reveal a variability in the line profiles that is typical of Herbig Ae/Be stars with signs of a strong stellar wind. The greatest changes are observed in the region of the absorption components of the line profiles, which convert the profile from a type P CygII to P CygIII, as well as in the intensities of the central emission components. A model technique is used for quantitative interpretation of this variability and it shows that the P Cyg profile conversion of the absorption component can be explained in terms of a stellar wind model in which its distribution over latitude varies on a time scale of a few days. __________ Translated from Astrofizika, Vol. 50, No. 2, pp. 259–280 (May 2007).     

A uvbyβ photometric analysis of the Monoceros star‐forming field

This investigation presents a new analysis of the spatial distribution of the bright early‐type stars in the field of Northern Monoceros. A database of all O–B9 stars with available uvbyβ photometry is collated and a homogeneous distance scale is established for the clusters and layers of field stars. We provide revised distances for NGC 2264 and NGC 2244 of 833±38 (s.e.) pc and 1585±60 (s.e.) pc, respectively. We present arguments that there might be substructures in the clusters projected along the line of sight. According to the present sample the classical Mon OB2 association at 1.6 kpc is represented by a relatively compact group at 1.26 kpc in the vicinity of NGC 2244 and a layer of massive stars located between 1.5 and 3 kpc (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Statistical properties of H II regions in the disc of M100

From a new mosaic image in the Hα line of the complete disc of the spiral galaxy M100, a catalogue is composed listing 1948 individual H II regions. I give details of the data collection and reduction procedure, and of the production of the H II region catalogue. For each H II region, the catalogue gives its position relative to the centre of the galaxy, its deprojected distance to the centre, its radius and its calibrated luminosity. An indication is included as to whether the H II region is located in the arms, between them, or in the circumnuclear star-forming region. I present the results of a statistical study of properties of the H II regions. The luminosity function of the complete ensemble of H II regions shows a characteristic shape well fitted by a power-law slope in the higher luminosity range, and complying with literature values for galaxies like M100. Luminosity function slopes for arm and interarm H II region populations separately are found to be equal within the errors of the fits, indicating that whereas the density wave accumulates material into the arm regions, and may trigger star formation there, it does not in fact change the mass distribution of the star-forming clouds, nor the statistical properties of the H II region population. Diameter distributions and the radial number density distribution are discussed. The latter indicates those areas where most star formation occurs: the circumnuclear region and the spiral arms. The huge number of H II regions allowed the construction of a number of independent luminosity functions at different distances to the nucleus. The slope of the luminosity function shows a marginal decrease with increasing distance from the centre, which could indicate a gradual change towards shallower IMF slopes with increasing galactocentric distance, or an evolutionary effect.     

Modelling the effects of temperature and food on individual growth and reproduction of Daphnia and their consequences on the population level

Individual based simulations of population dynamics require the availability of growth models with adequate complexity. For this purpose a simple-to-use model (non-linear multiple regression approach) is presented describing somatic growth and reproduction of Daphnia as a function of time, temperature and food quantity. The model showed a good agreement with published observations of somatic growth (r² = 0.954, n = 88) and egg production (r² = 0.898, n = 35). Temperature is the main determinant of initial somatic growth and food concentration is the main determinant of maximal body length and clutch size. An individual based simulation was used to demonstrate the simultaneous effects of food and temperature on the population level. Evidently, both temperature and food supply affected the population growth rate but at food concentrations above approximately 0.4 mg Cl⁻¹ Scenedesmus acutus temperature appeared as the main determinant of population growth.

Four simulation examples are given to show the wide applicability of the model: (1) analysis of the correlation between population birth rate and somatic growth rate, (2) contribution of egg development time and delayed somatic growth to temperature-effects on population growth, (3) comparison of population birth rate in simulations with constant vs. decreasing size at maturity with declining food concentrations and (4) costs of diel vertical migration. Due to its plausible behaviour over a broad range of temperature (2–20 °C) and food conditions (0.1–4 mg Cl⁻¹) the model can be used as a module for more detailed simulations of Daphnia population dynamics under realistic environmental conditions.     

Light curves of SN 1998A and comparison with similar unusual SNe

Following the proposal by Damineli that the central object of Eta Carinae may be an early-type binary, we perform numerical simulations of the X-ray emission from colliding stellar winds. A synthetic light curve has been generated which qualitatively agrees with the recent X-ray variability, and provides further support for the binary model. In particular, the model predicts a rise in the observed X-ray emission towards periastron, followed by a sharp drop and subsequent recovery. This is indeed what is seen in the RXTE light curve, although some problems concerning the X-ray spectrum at periastron still need to be explained. The simulations suggest that the width of the periastron dip will provide strong constraints on the binary and stellar wind properties of the components of Eta Car.