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International audience; We explore the physics of Type Ia supernova (SN Ia) light curves and spectra using the 1D non-local thermodynamic equilibrium (non-LTE) time-dependent radiative-transfer code cmfgen. Rather than adjusting ejecta properties to match observations, we select as input one `standard' 1D Chandrasekhar-mass delayed-detonation hydrodynamical model, and then explore the sensitivity of radiation and gas properties of the ejecta on radiative-transfer modelling assumptions. The correct computation of SN Ia radiation is not exclusively a solution to an `opacity problem', characterized by the treatment of a large number of lines. We demonstrate that the key is to identify and treat important atomic processes consistently. This is not limited to treating line blanketing in non-LTE. We show that including forbidden-line transitions of metals, and in particular Co, is increasingly important for the temperature and ionization of the gas beyond maximum light. Non-thermal ionization and excitation are also critical since they affect the colour evolution and the Delta M-15 decline rate of our model. While impacting little the bolometric luminosity, a more complete treatment of decay routes leads to enhanced line blanketing, e.g. associated with Ti-48 in the U and B bands. Overall, we find that SN Ia radiation properties are influenced in a complicated way by the atomic data we employ, so that obtaining converged results is a real challenge. Nonetheless, with our fully fledged cmfgen model, we obtain good agreement with the golden standard Type Ia SN 2005cf in the optical and near-IR, from 5 to 60 d after explosion, suggesting that assuming spherical symmetry is not detrimental to SN Ia radiative-transfer modelling at these times. Multi-D effects no doubt matter, but they are perhaps less important than accurately treating the non-LTE processes that are crucial to obtain reliable temperature and ionization structures.

We are coming to that place in our journey where I am to share all I’ve come to know explicitly: my findings. Though I feel comfortable that these meanings are implicitly woven within the work, the potential usefulness of these findings to others may warrant a more overt, consolidated recapitulation.

As part of a multifaceted effort to exploit better the asteroseismological potential of the pulsating sdB star Feige 48, we present an improved spectroscopic analysis of that star based on new grids of NLTE, fully line-blanketed model atmospheres. To that end, we gathered four high S/N time-averaged optical spectra of varying spectral resolution from 1.0 \AA\ to 8.7 \AA, and we made use of the results of four independent studies to fix the abundances of the most important metals in the atmosphere of Feige 48. The mean atmospheric parameters we obtained from our four spectra of Feige 48 are : Teff= 29,850 $\pm$ 60 K, log $g$ = 5.46 $\pm$ 0.01, and log N(He)/N(H) = $-$2.88 $\pm$ 0.02. We also modeled for the first time the He II line at 1640 \AA\ from the STIS archive spectrum of the star and we found with this line an effective temperature and a surface gravity that match well the values obtained with the optical data. With some fine tuning of the abundances of the metals visible in the optical domain we were able to achieve a very good agreement between our best available spectrum and our best-fitting synthetic one. Our derived atmospheric parameters for Feige 48 are in rather good agreement with previous estimates based on less sophisticated models. This underlines the relatively small effects of the NLTE approach combined with line blanketing in the atmosphere of this particular star, implying that the current estimates of the atmospheric parameters of Feige 48 are reliable and secure., Comment: Accepted for publication in ApJ, April 2014

We carried out accurate (\(\sigma _{obs} \approx 0\mathop .\limits^m 003\)) W BV R photoelectric photometry of RR Lyn and obtained light curves of this eclipsing system. Our analysis of the light curves using an iterative differential-correction method yields a self-consistent system of geometrical and physical characteristics of the two components of the system and their evolutionary states. The system's age is estimated to be t=(1.08±0.15)×109 yr. Observations in all filters are fitted satisfactorily by the same geometry (r1,2, i, e, and ω). An analysisof blanketing effects in the W, B, V, and R bands indicates that the atmospheric chemical compositions of both components of the system are peculiar: the primary shows an excess ([Fe/H]I=0.31±0.08) and the secondary a deficit ([Fe/H]II=−0.24±0.06) of heavy elements. This is in qualitative and quantitative agreement with the results of an earlier spectroscopic study of RR Lyn by Lyubimkov and Rachkovskaya (1995). The derived physical characteristics of RR Lyn provide evidence that the metallicity effects are probably restricted to the stellar surface layers, while their interiors have normal chemical abundances.

One of the surprises of the NEAR-Shoemaker mission was that Eros's surface exhibits a wide variety of landforms, which are indicative of a global covering of loose fragmental debris1. At one extreme in roughness is the Shoemaker Regio area, which is characterized by a high density of boulders up to 100 m across, slumps, slides, and finer blanketing material. At the other extreme are distinctive, flat deposits that appear smooth down to a resolution of 1.2 cm per pixel. Here we report the results of global mapping and colour analysis of these smooth deposits. They have formed most efficiently in restricted areas, and appear to be the result of deposition of finer material sorted from the upper portion of the asteroid's regolith. The smooth deposits constitute a family of features with a range of morphologies, but all appear to be the result of sedimentation. The geography of the deposits is consistent with some predicted aspects of photoelectric sorting, but these exotic transport and depositional mechanisms are not well understood. Deposits with the properties seen on Eros have no obvious analogues in previous lunar or asteroid data.

We have modeled a large sample of infrared starburst galaxies using both the PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution of the young star clusters. PEGASE utilizes the Padova group tracks while STARBURST99 uses the Geneva group tracks, allowing comparison between the two. We used our MAPPINGS III code to compute photoionization models which include a self-consistent treatment of dust physics and chemical depletion. We use the standard optical diagnostic diagrams as indicators of the hardness of the EUV radiation field in these galaxies. These diagnostic diagrams are most sensitive to the spectral index of the ionizing radiation field in the 1-4 Rydberg region. We find that warm infrared starburst galaxies contain a relatively hard EUV field in this region. The PEGASE ionizing stellar continuum is harder in the 1-4 Rydberg range than that of STARBURST99. As the spectrum in this regime is dominated by emission from Wolf-Rayet (W-R) stars, this difference is most likely due to the differences in stellar atmosphere models used for the W-R stars. We believe that the stellar atmospheres in STARBURST99 are more applicable to the starburst galaxies in our sample, however they do not produce the hard EUV field in the 1-4 Rydberg region required by our observations. The inclusion of continuum metal blanketing in the models may be one solution. Supernova remnant (SNR) shock modeling shows that the contribution by mechanical energy from SNRs to the photoionization models is << 20%. The models presented here are used to derive a new theoretical classification scheme for starbursts and AGN galaxies based on the optical diagnostic diagrams., 36 pages, 16 figures, to be published in ApJ, July 20, 2001

We present a method to estimate the contribution of line opacity to the total opacity as a function of wavelength. The estimated line-opacity function can then be used to simulate line-blanketing in NLTE radiative transfer calculations. Given a reference flux distribution (either observed or theoretical), our method allows to ob- tain a good estimate of the spectrum without the need for considering in detail all the millions of lines contributing to line blanketing. We applied the method to the spectra computed from a sample of photospheric models with eective temperatures Te = 4200, 5200 and 6200 K, logg =4 :0, 4.5, 5.0 and (A/H) = 0:0, 1:0, 2:0, taken from the NextGen database (Allard & Hauschildt 1995). The computed flux distributions agree quite well with the corresponding LTE line-blanketed NextGen fluxes when we introduce the estimated line-opacity contribution as a multiplicative factor of the continuum opacity in the radiative transfer calculations. In particular we discuss the importance of a correct estimate of the continuum flux, mainly in the UV, in the NLTE formation of the Ca ii H & K, the Ca ii InfraRed Triplet (IRT: = 8498, 8542, 8662), Na i D, Li i and K i resonance lines.

New opacity distribution functions (ODF) have been computed for use with the ATLAS9 model atmosphere code of Kurucz. One of the improvements upon the Kurucz (1990) ODFs is the addition to the line blanketing of the Lyman- H{H and H{H + quasi-molecular absorptions near 1600 A and 1400 A. New-ODF fluxes are expected to reproduce the ultraviolet observations of Boo stars and metal-poor A-type stars in a more realistic way than previous computations did. In this paper we compare low- and high-resolution IUE observations of Boo (HD 125162, HR 5351) with fluxes and synthetic spectra based on ATLAS9 models and new-ODFs, which were computed for (M=H) = 2:0 for all the elements, except CNO. For C, N, and O, abundances log(Nelem=Ntot) equal to 3.85, 3.99, and 3.11, respectively, were adopted. We selected Boo in order to compare results from the new-ODFs with those from Allard et al. (1998a, 1998b), who tested their semi-classical computations of the H{H and H{H + quasi-molecular absorptions on this star. The analysis of the IUE high-resolution spectrum has shown that lines of H2 are a very important source of line opacity for Boo shortward 1600 A. When both atomic and molecular lines are considered, the slope of the observed energy distribution is well reproduced in the whole region 1300{3000 A by the new-ODF model, but the H{H quasi-molecular absorption at 1600 A is computed about 10% too strong. The t of the low-resolution IUE image SWP17872 to a small grid of new-ODF models gives parameters Te = 8650 K, log g =4 :0, while the t of the high-resolution image SWP42081, rebinned at the low resolution wavelength step size, gives parameters Te = 8500 K, log g =4 :0. These last parameters are in close agreement with Te = 8550 K, log g =4 :1 obtained by tting the visible energy distribution. The dierent IUE images are discussed.

Significant influence of diurnal and interdiurnal variations of irregular movements at heights of the lower thermosphere on the frequency parameters of ionospheric sporadic E-layer, characterizing its intensity, was fount out. Common periodicities with time scales of planetary waves, having significant coherence, were revealed in variations of mesocale turbulence intensity and critical frequency foEs, blanketing frequency fbEs.

SN 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supenovae and probably the first supernova associated with a gamma-ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the AAT, UKST and the SSO 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 days after V_band maximum in comparison to well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from the observations of classical Ic SNe, we find that the evolution from the photospheric to the nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10% - 50% higher than other SNe and on day 94 emission lines are 45% broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope., 8 pages, 6 figures

It seems that the wind shear theory is accepted for the explanation of sporadic E at mid and low latitudes. Some examples from Arecibo are displayed to show this. The effect of lunar tides should then modify the wind-shear theory in a manner that yields the observed features of the lunar tide in the critical frequency foEs and the height h'Es of the sporadic E. This is shown to imply that the phase of the lunar tide in h'Es should be the same as the phase of the lunar tide in the eastward wind and that the phase of the lunar tide in foEs is three hours later. Hourly values of foEs, f bEs (the blanketing critical frequency) and h'Es from several observatories are analysed for the lunar semidiurnal tide. It is found that the phase of the tide in foEs is often about 3 hours later than for h'Es in agreement with the theory. Seasonal variations in the tide are also examined with the statistically most significant results (largest amplitudes) usually occurring in summer. After reviewing the many difficulties associated with determining the lunar tide in Es, both experimentally and theoretically, the analysed phase results are compared with what might be expected from Hagan's global scale wave model. Agreement is only fair (a success rate of 69% among the cases examined) but probably as good as might be expected.Key words. Ionosphere (ionosphere – atmosphere interactions – ionospheric irregularities), Meteorology and atmosphere dynamics (waves and tides)

Using a significantly revised non-LTE radiative transfer code that allows for the effects of line blanketing by He, C, O, Si, and Fe, we have performed a detailed analysis of the Galactic Wolf-Rayet (W-R) star HD 165763 (WR 111, WC5). Standard W-R models consistently overestimate the strength of the electron scattering wings, especially on strong lines, so we have considered models where the wind is both homogeneous and clumped. The deduced stellar parameters for HD 165763 are as follows: The stellar parameters deduced for HD 165763 are significantly different from earlier analyses. The deduced luminosity is a factor of 2 larger, and a smaller core radius is found. The smaller radius is in better agreement with expectations from stellar evolution calculations. Both of these changes can be attributed to the effects of line blanketing. The deduced C/He abundance is similar to earlier calculations, and the O/He abundance had not previously been determined. The observed iron spectrum, principally due to Fe V and Fe VI, is well reproduced using a solar iron mass fraction, although a variation of at least a factor of 2 about this value cannot be precluded. In particular, the models naturally produce the Fe V emission feature centered on 1470 A and the complex Fe emission/absorption spectrum at shorter wavelengths. Also, Fe strongly modifies the line strengths and profile shapes shortward of 1800 A and must be taken into account if we are to successfully model this region. The reddening toward HD 165763 does not follow the mean Galactic extinction law. We determine the reddening law toward HD 165763 by comparing our model continuum levels to observations. In order to simultaneously match the UV, optical, and particularly the infrared fluxes, we used the parameterized reddening law of Cardelli, Clayton, and Mathis with EB-V = 0.3 and R = 4.5, where R = AV/EB-V. Based on both observational and theoretical suggestions we have considered models in which the wind is still accelerating at large radii. In particular, we discuss models in which the velocity law can be characterized by β = 1 for r < 10R* but that undergo a substantial velocity increase (~600 km s-1) beyond 10R*. These models appear to give slightly better fits to the line profiles, but the improvements are small, and it is difficult to gauge whether observational data require such a velocity law. We cannot yet determine whether the winds of W-R stars are driven by radiation pressure, because we neglect many higher levels of iron in our model ions, and we do not include important elements such as cobalt and nickel. However, the wind problem in W-R stars is less severe than previously assumed if clumping occurs. For our clumped model, the single scattering limit is only exceeded by a factor of 10 compared to 3 times this value for a homogeneous wind. Clumping appears to be the key to explaining the apparent high mass-loss rates determined for W-R stars and is extremely important in understanding how or even whether W-R winds are driven by radiation pressure. A reduction in W-R mass-loss rates has important implications for stellar evolution calculations.

To assess the uncertainties in primordial helium abundance determination by nebular codes, we calculate a grid of OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. The more sophisticated stellar atmosphere models we use can differ from LTE models by as much as 40% in the ratio of He to H-ionizing photons.

We calculate a grid of spherically symmetric OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. This is done to assess the uncertainties in helium abundance determination by nebular codes due to input stellar atmosphere models. The more sophisticated stellar atmosphere models we use can differ from LTE models by as much as 40 percent in the ratio of He to H-ionizing photons.

From new high signal-to-noise ratio (S/N) 1-2.2 μm spectroscopy of nine extreme early-type stars—including O Iaf, O Iafpe and WN9 types—we determine stellar parameters from detailed atmospheric analysis and evaluate results from near-IR analogues of well-known spectral diagnostics in the optical. We conclude that accurate stellar parameters can be measured from near-IR spectroscopy alone, an analysis technique important to studies of luminous stars in the Galactic center and other galaxies. Derived stellar parameters—mass-loss rates, luminosities, surface abundances, temperatures—show good agreement between optical and near-IR analyses, provided that IR data are of sufficient spectral resolution (R>2000) and S/N (S/N>30). Wind velocities derived from He I 1.0830 μm are consistent with those from ultraviolet P Cygni profiles. Temperatures 200-1300 K systematically lower are determined from the near-IR diagnostics, a difference not significant in determining the stellar properties of these objects; which set of spectral lines provides the more accurate physical parameters—optical or IR—cannot at present be ascertained. The strength of He I 2.0581 μm is very sensitive to the extreme ultraviolet energy distribution where line blanketing by heavy elements plays an important role; this line should not on its own be considered a reliable temperature diagnostic. The three peculiar, extreme emission-line stars—the O Iafpe stars HD 152386, HD 152408, and HDE 313846—are more similar in both morphological and physical characteristics to WNL-type Wolf-Rayet stars than to normal O Iaf supergiants and should be classified as W-R. Their classification should be WN9ha, in which they remain a unique subgroup.

Until recently, a major deficiency of most spectroscopic modeling of hot stars was the neglect of line-blanketing. With the availability of new atomic data, faster computers, suitable approximations, and improved numerical techniques it is now feasible to include non-LTE line-blanketing due to CNO and iron group elements in atmospheric calculations. We highlight the capabilities of the present generation of models. New blanketing results are presented for WN and WC Wolf-Rayet stars, and for LBVs. Line-blanketing alters individual line strengths in unpredictable ways, and can significantly influence the determination of stellar parameters. We specifically highlight the UV spectral region in which the effects of Fe blanketing are directly manifested. The importance of the charge exchange reaction Fe2+ + H ⇌ Fe+ + H+ for modeling of the Fe emission lines in the extreme P-Cygni star HDE 316285 is illustrated.

Modern ionosondes make almost simultaneous measurements of the time rate of change of phase path in different directions and at different heights. By combining these 'Doppler' measurements and angles of arrival of many such radar echoes it is possible to derive reliable estimates of plasma drift velocity for a defined scattering volume. Results from both multifrequency and kinesonde-mode soundings at 3-min resolution show that the Dynasonde-derived F-region drift velocity is in good agreement with EISCAT, despite data loss during intervals of 'blanketing' by intense E-region ionisation. It is clear that the Tromsø Dynasonde, employing standard operating modes, gives a reliable indication of overall convection patterns during quiet to moderately active conditions.Key words. Auroral ionosphere · Plasma convection · Instruments and techniques

Sulfur hexafluoride (SF6) is the most potent greenhouse gas known. Its atmospheric concentration has increased by 2 orders of magnitude since industrial production started in 1953. Once released into the atmosphere, SF6 will only be removed exceedingly slowly due to its atmospheric lifetime of about 3200 yr. These features have brought SF6 into the climatic impact discussion aimed at reduction of emissions. The dominant uses of SF6 are in gas insulated switchgear (GIS) and in blanketing or degassing molten aluminum and magnesium. From 1978 onward, the rapidly growing global SF6 burden is well-documented by atmospheric observations. Concerning the SF6 applications responsible for that, a vast range of speculations is circulating. The underlying information gapwhich preempts the design of any reduction programwill be bridged for the first time. Recently reported global sales of SF6 for end-use applications form the basis of this investigation but need various revisions. The good agreement between emissions ...

We present a finite-element model for the prediction of the subsidence history and thermal evolution of extensional basins. The model takes into account the inhomogeneity of the lithosphere, and allows the space formed by lithospheric extension to be filled with sediments or water or both. Local isostatic compensation is assumed. The stability and accuracy of the algorithm are investigated. Time increments of 0.05–0.1 Ma are most appropriate for triangular elements of size 13 km 2 . For an initially old continental lithosphere (thickness: 130 km), thermal equilibrium is reached in approximately 100 Ma for a basin of initial width 100 km with a maximum β-factor of 2.0. The duration of extension for a given β-factor affects the heat flow and subsidence. For extension periods of 10 and 20 Ma, faster extension results in less subsidence and more prolonged high heat flow after the cessation of extension. If the basin is filled with sediments (as opposed to water), thermal blanketing effects are significant. The algorithm can be used to complement our understanding of the effects of thermal blanketing, lateral heat conduction, and sediment loading on the subsidence and thermal evolution of extensional basins.

Only recently has it been possible to find an effective temperature and composition for the hot DA white dwarf G191–B2B which can consistently match the optical, far-UV and EUV data simultaneously, by using new non-LTE model calculations that include the effects of line blanketing from more than 9 million (mainly Fe and Ni) transitions. However, to maintain agreement below the He ii 228-A Lyman limit requires the inclusion of additional He ii opacity in the form of photospheric, circumstellar or interstellar material. If photospheric, the homogeneous H+He structure adopted predicted a He ii 1640-A line strength well above the IUE detection limit, while an unusally high He ionization fraction was required in this particular line of sight if the material was in the local ISM. We show that, by considering the effects of a stratified H upon He photospheric structure within the heavy-element blanketed models, a lower interstellar He ii column density is obtained, leading to a more reasonable He ionization fraction for the G191–B2B line of sight. In addition, the absence of a He ii 1640-A feature in the far-UV data is consistent with the equivalent width predicted by the stratified model. However, while this alternative interpretation offers a better description of certain aspects of the G191–B2B optical-to-EUV spectra, a new problem is introduced, namely that the He ii Lyman lines are predicted to be stronger than can be comfortably accommodated by the observational data.

Absorption due to HeII Ly-alpha has been detected at low resolution in the spectra of four quasars between redshifts z = 2.74-3.29. We assess these observations, giving particular attention to the radiative transfer of the ionizing background radiation, cloud diffuse emission and ionization physics, and statistical fluctuations. We use high-resolution observations of HI absorption towards quasars to derive improved models for the opacity of the intergalactic medium (IGM) and use these models to calculate the HI and HeII photoionization history in both optically-thin and self-shielded clouds, and the average line-blanketing contribution to HeII absorption. The derived ionization rate at z = 2-4, Gamma(HI) = (1-3)x10^-12 s^-1, is consistent with the ionizing background intensity inferred from the proximity effect, but it remains larger than that inferred by N-body hydrodynamical simulations of the Lya absorber distribution. The HeII observations are con- sistent with line blanketing from clouds with N(HI) > 10^12 cm^-2, although a contribution from a more diffuse IGM would help to explain the observed opacity. We compute the expected HeII optical depth and examine the sizable fluc- tuations that arise from variations in the cloud numbers and ionizing radiation field. We assess how HeII absorption constrains the intensity and spectrum of the ionizing radiation and the fractional contributions of the dominant sources (quasars and starburst galaxies). Finally, we demonstrate how high-resolution UV observations can distinguish between absorption from the diffuse IGM and the Lya forest clouds and determine the source of the ionizing background.

We present detailed atmospheric analyses of two [WC10] central stars of planetary nebulae (PNe), CPD−56° 8032 and He 2-113, the results of which are compared with parameters inferred from their nebular properties. Our quantitative study is based on non-LTE modelling of diagnostic He i–II, C II–IV and O II–III lines. We find that spectroscopic similarities are reflected in the derived stellar properties: for both stars we obtain Teff∼30 kK and log L/L⊙=3.7; log (˙M/M⊙ yr−1)=−5.4 and v∞=225 km s−1 for CPD−56° 8032, while log (˙M/M⊙ yr−1)=−6.1 and v∞=160 km s−1 for He 2-113. The derived stellar properties are fairly consistent with the recent study of Leuenhagen et al., when adjusted for the different distances adopted. We find excellent agreement between our C2+ wind temperature and the independent determination by De Marco et al., supporting our assumption of radiative equilibrium. We find that both stars are highly enriched in carbon and oxygen, but with stellar hydrogen undetectable for He 2-113 (in contrast to Leuenhagen et al.). Our final abundance determinations indicate H:He:C:O mass fractions of 0:34:52:14 for CPD−56° 8032 and 0:34:54:13 for He 2-113. We confront our model flux distributions with observed nebular properties using Zanstra and photoionization techniques, and identify a major discrepancy between the observed and predicted nebular properties for these particular PNe. The hydrogen ionizing fluxes predicted by our WR non-LTE models greatly exceed those implied by nebular observations. The lack of heavy-element line blanketing in our wind models could be responsible. However, the geometry and high nebular densities of these PNe suggest that they represent poor probes of the Lyman continuum flux of their central stars.

We use a spherical non-LTE fully line blanketed model atmosphere to fit the full multi-wavelength spectrum, including the extreme ultraviolet (EUV) continuum observed by the {\it Extreme Ultraviolet Explorer}, of the B2 II star \epscma. The available spectrophotometry of \epscma\ from 350 \AA\ to 25 \micron\ is best fit with model parameters \Teff = 21750\,K, \Logg = 3.5, and an angular diameter of 0.77 mas. The close agreement between the model and the measured EUV flux from \epscma\ is a result of the higher temperatures at the formation depths of the \ion{H}{1} and \ion{He}{1} Lyman continua compared to other models. The realistic model treatment of early B giants with spherical geometry and NLTE metal line blanketing results in the prediction of significantly larger EUV fluxes compared with plane-parallel models. We find that our metal line blanketed spherical models show significantly warmer temperature structures, 1-3 kK at the formation depth of the Lyman continua, and predict stronger EUV fluxes, up to a factor of 5 in the \ion{H}{1} Lyman continuum, compared with plane-parallel atmospheres that have identical model parameters. In contrast, we find spherical and plane-parallel models that do not include metal line blanketing are nearly identical. Our \Teff = 21000 K, \Logg = 3.2, spherical NLTE model predicts more than twice as many hydrogen ionizing photons and over 200 times more neutral helium ionizing photons than a standard hydrostatic plane-parallel LTE model with the same stellar parameters.

A pall of aerosols and trace gases frequently occurs over southern Africa to a depth of ∼500 hPa, blanketing vast areas, particularly in the austral winter and spring. Large-scale offshore transport of these aerosols and trace gases in extremely large plumes from interior continental areas of the subcontinent to the Indian and Atlantic Oceans is a common occurrence. The nature of the transport plumes, their climatology, chemical composition and morphology are discussed. In the vertically integrated, surface-to-500 hPa layer, poleward of about 15° S, transport into the Indian Ocean is shown to be about 60% greater into the Indian Ocean than into the Atlantic Ocean. Recirculation of atmospheric constituents is considered and estimates of aerosol mass fluxes over central southern Africa are presented. Of the total of about 50 Mt yr -1 of aerosols being transported at the central meridian, 44% is shown to be recirculated material. The rest exits the subcontinent directly without recirculation. Preferred plume corridors of exit and entry are postulated for different localities on the east and west coasts. Two case studies of east- and west-coast plumes apparently flowing uniformly out of southern Africa are examined. The illusion of uniformity in plume structure is shown to be misleading. Both plumes are shown to be above and separated from the marine boundary layer. Each is over 1500 km in width and 3–5 km deep. Likewise, both are capped by absolutely stable layers at ∼500 hPa and exhibit a complex structure of both outflowing aerosols and trace gases and inflowing, recycled and recirculated material. Indications of the composition of the recirculated material are given and implications of the plume transports are considered.

We present the first measurement of the H I Gunn-Peterson effect using the Keck 10 m telescope, observing the high-redshift QSO PKS 1937-101 (z = 3.787). The high-resolution echelle (HIRES) spectra, with FWHM ~15 km s-1 and a signal-to-noise ratio (S/N) ~50 per spectral resolution element, allows us to resolve many weak lines down to NH I = 1012 cm-2, thus reducing the line-blanketing problem compared with previous data. Based on intensity-distribution analysis, we find that a maximum likelihood best fit yields a Gunn-Peterson type of opacity τGP = 0.113 ± 0.020 in addition to a power-law Lyα absorption-line population with β of 1.7 down to NH I = 1012 cm-2. There remains systematic uncertainty in this result because of problems extrapolating the spectral continuum from the red side of the Lyα emission line. This is consistent with the previous study of the same QSO in low S/N data using weighted intensity function analysis (Fang & Crotts 1995). It indicates that this previous method succeeds in measuring the Lyα forest continuum level at low S/N, which is essential in extending the technique to possible fainter QSOs with minimum emission-line contamination for reliable continuum extrapolation. We further discuss problems of severe line blanketing, even in Keck spectra for QSOs at z ≥ 4.5, and show the effectiveness of the weighted intensity function method in measuring continuum levels in extremely crowded Lyα absorption spectra for redshifts as high as z > 5.

Extensive modifications to the non-LTE radiative transfer code of Hillier have been made in order to improve the spectroscopic analysis of stars with stellar winds. The main improvement to the code is the inclusion of blanketing due to thousands of overlapping lines. To implement this effect, we have used the idea of super levels first pioneered by Anderson. In our approach, levels with similar excitation energies and levels are grouped together. Within this group, we assume that the departure coefficients are identical. Only the population (or equivalently, the departure coefficient) of the super level need be solved in order to fully specify the populations of the levels within a super level. Our approach is a natural extension of the single-level LTE assumption, and thus LTE is recovered exactly at depth. In addition to the line blanketing modifications, the code has been improved significantly in other regards. In particular, the new code incorporates the effect of level dissolution, the influence of resonances in the photoionization cross sections, and the effect of Auger ionization. Electron scattering with a thermal redistribution can be considered, although it is normally treated coherently in the comoving frame (which still leads to redistribution in the observer's frame). Several example calculations are described to demonstrate the importance of line blanketing on spectroscopic analysis. We find that the inclusion of blanketing modifies the strengths of some optical CNO lines in Wolf-Rayet (W-R) stars by factors of 2-5. In particular, the strengths of the WC classification lines C III λ5696 and C IV λ5805 are both increased because of iron blanketing. This should help alleviate problems found with nonblanketed models, which were incapable of matching the strengths of these lines. We also find that, in the UV (1100-1800 A), the influence of Fe is readily seen in both emission and absorption. The emission is sensitive to the iron abundance and should allow, for the first time, Fe abundances to be deduced in W-R stars. The improvements made to our code should greatly facilitate the spectroscopic analysis of stars with stellar winds. We will be able to determine the importance and influence of line blanketing, as well as of several other effects that have been included in the new code. It will also allow us to better determine W-R star parameters, such as luminosity, elemental abundances, wind velocity, and mass-loss rate. With future application to related objects, such as novae and supernovae, our new code should also improve our understanding of these objects with extended outflowing atmospheres.

We have made a detailed comparison of results of spectroscopic analysis using three differents types of model atmospheres: classical non-LTE H-He models; approximate non-LTE line-blanketed models (with only a subset of Fe and Ni lines: those originating from transitions between levels with measured energies); and non-LTE fully blanketed models. The three models were applied to the sdO star BD +75°325, adopted as a test case. We demonstrate that the effects of line blanketing are very important: the best fit of the observed H and He lines is achieved for Teff = 58,000 K when using H-He models, Teff = 55,000 K for approximate non-LTE line-blanketed models, and Teff = 52,000 K for fully blanketed non-LTE models. Using the high-resolution Goddard High Resolution Spectrograph spectrum of BD +75°325 and our final fully blanketed model, we have derived reliable abundances of He, C, N, O, Si, Fe, and Ni. We find that BD +75°325 is an He-enriched star (He/H = 1 by number), whose surface exhibits CNO-cycle products, i.e., N-rich (AN = 1.5 × 10-3 by number, or 4.2 × 10-3 by mass fraction), and C and O deficient (by factor of about 100 with respect to the solar value). We also find a significant surface depletion of silicon and an enhancement of iron and nickel. We argue that these anomalous abundances reflect some mixing with processed material from the core, with subsequent modification at the surface by diffusion processes. Finally, BD +75°325 possesses a weak wind. Using a simplified description of the wind, we have derived a preliminary value of the mass loss rate: =1.5 × 10−11 M☉ yr-1.

Broad-band ultraviolet photometry from the TD-1 satellite and low dispersion spectra from the short wavelength camera of IUE have been used to investigate a long-standing proposal of Bohm-Vitense that the normal main sequence A- and early-F stars may divide into two different temperature sequences: (1) a high temperature branch (and plateau) comprised of slowly rotating convective stars, and (2) a low temperature branch populated by rapidly rotating radiative stars. We find no evidence from either dataset to support such a claim, or to confirm the existence of an "A-star gap" in the B-V color range 0.22, 40 pages, 14 figures, 1 table, AAS LaTex, to appear in The Astrophysical Journal

We present new observations of the [S III] 19 μm, [O III] 52 and 88 μm, and [N III] 57 μm lines toward 18 compact and ultracompact (UC) H II regions. These data were combined with data from the literature and high-resolution radio continuum maps to construct detailed statistical equilibrium and ionization equilibrium models of 34 compact H II regions located at galactocentric distances (DG) 0-12 kpc. Our models simultaneously fitted the observed IR fine-structure lines and high-resolution radio continuum maps. Abundance gradients are found of the form [S/H] = (-4.45 ± 0.04) - (0.063 ± 0.006) DG (kpc), [N/H] = (-3.58 ± 0.04) - (0.072 ± 0.006) DG (kpc), and [O/H] = (-2.85 ± 0.06) - (0.064 ± 0.009) DG (kpc), and we derive Te = (4560 ± 220) + (390 ± 40) DG (kpc). The Te gradient is consistent with the Te gradient determined independently via radio recombination lines (Afflerbach et al.). We observe no dependence of S/O, N/O, or Teff on DG. Gradients in N++/O++ and O++/S++ are observed in the sense of increasing ionization with increasing DG. This is entirely consistent with the decreased line blanketing with increasing DG required by the above abundance gradients. All three gradients are best fitted by a linear dependence on DG. The abundances are consistent with production of sulfur, nitrogen, and oxygen by primary nucleosynthesis. Comparison with abundances in other galaxies implies a Hubble type between Sab and Sb for our Galaxy and an unbarred or mixed galactic structure (Vila-Costas & Edmunds). Our derived Teff is 2000-10,000 K lower than Teff expected from ZAMS stars of the same Lyman continuum flux (Panagia; Vacca et al.), probably owing to uncertainties in the UV flux of stellar models for E ≥ 35.1 eV, uncertainties in the luminosity-Teff calibration, and/or ionization of H II regions by multiple stars in some sources.

A RH-560 rocket instrumented with a Langmuir Probe and two pairs of double probes was launched from SHAR (dip 14 ° N) at 2130 hr LT (1ST) on 4 October 1988 during spread-F conditions. As a part of this campaign VHF scintillations at 136.1 MHz were also recorded, using the beacon onboard the geostationary satellite ETS-II (130 ° E). A new digital ionosonde (KEL) installed at SHAR during the first week of September 1988 provided the basic ionospheric information. Ionosonde and scintillation data during this campaign (15 September–4October), along with the Langmuir probe data, are described. The occurrence of scintillations and spread-F during the campaign period was very high, with maximum hourly percentage occurrences of about 80 and 70%, respectively. Generally the onset of spread-F occurred slightly before 1900 hr LT when scintillations in the satellite signal also start appearing. This is followed soon by the range spreading on the ionosonde trace. On days with spread-F the minimum virtual height of the F-layer, h′F, rose to about 400 km in the post-sunset period while on days without spread-F it rose to only about 300–320 km. The electric field reversal, as inferred from the h′F variations, occurred around 1930 hr LT on spread-F days and around 1900 hr LT on days without spread-F. The ionograms, taken at 5 min interval on several nights, were used to determine the vertical drift velocities and these exceeded 50 m/s on spread-F days in the post-sunset period. At the time of the rocket launch, a strong blanketing type of sporadic-E with several multiple reflections appeared around 105 km. The electron density profile obtained from the Langmuir probe data also showed an extremely sharp layer at 105 km and another prominent layer at 130 km, both during the ascent and the descent. The electron density irregularities associated with spread-F were seen in different altitude regions, the most prominent being from 210 to 250 km and from 300 to 320 km. The power spectra of the electron density fluctuations have been obtained both from the in situ probe data and the scintillation data.

By dividing the total energy radiated from the photosphere of a supernovae into a large number of photon packets and then following them in their outward journey, we overcome the problem of line blanketing encountered in usual simulation work. With supporting programs providing the density and abundance distributions in the envelope, our software package can be effectively used for a study of the early spectrum of supernovae. We give an application to the observed spectrum of SN 1993J on 1993-04-13.

Context. Semi-grey atmospheric models (with one opacity for the visible and one opacity for the infrared) are useful to understand the global structure of irradiated atmospheres, their dynamics and the interior structure and evolution of planets, brown dwarfs and stars. But when compared to direct numerical radiative transfer calculations for irradiated exoplanets, these models systematically overestimate the temperatures at low optical depth, independently of the opacity parameters. We wish to understand why semi-grey models fail at low optical depths, and provide a more accurate approximation to the atmospheric structure by accounting for the variable opacity in the infrared. Our analytical irradiated non-grey model is found to provide a range of temperatures that is consistent with that obtained by numerical calculations. We find that even for slightly non-grey thermal opacities the temperature structure differs significantly from previous semi-grey models. For small values of beta (expected when lines are dominant), we find that the non-grey effects are confined to low-optical depths. However, for beta larger than 0.5 (appropriate in the presence of bands with a wavelength-dependence smaller or comparable with the width of the Planck function), we find that the temperature structure is affected even down to infrared optical depths unity and deeper as a result of the so-called blanketing effect. The expressions that we derive may be used to provide a proper functional form for algorithms that invert the atmospheric properties from spectral information. Because a full atmospheric structure can be calculated directly, these expressions should be useful for simulations of the dynamics of these atmospheres and of the thermal evolution of the planets. Finally, they should be used to test full radiative transfer models and improve their convergence., Accepted by A&A, model available at http://www.oca.eu/parmentier/nongrey

We explore the properties of Type II-Plateau (II-P) supernovae (SNe) together with their red-supergiant (RSG) star progenitors. Using MESA STAR, we modulate the parameters (e.g., mixing length, overshoot, rotation, metallicity) that control the evolution of a 15Msun main-sequence star to produce a variety of physical pre-SN models and SN II-P ejecta. We extend previous modeling of SN II-P radiation to include photospheric and nebular phases, as well as multi-band light curves and spectra. Our treatment does not assume local thermodynamic equilibrium, is time dependent, treats explicitly the effects of line blanketing, and incorporates non-thermal processes. We find that the color properties of SNe II-P require large model atoms for FeI and FeII, much larger than adopted in Dessart & Hillier (2011). The color properties also imply RSG progenitors of limited extent (~500Rsun) --- larger progenitor stars produce a SN II-P radiation that remains too blue for too long. This finding calls for a reduction of RSG radii, perhaps through a strengthening of convective energy transport in RSG envelopes. Increased overshoot and rotation reduce the ratio of ejecta to helium-core mass, similarly to an increase in main-sequence mass, and thus complicate the inference ofprogenitor masses. In contrast to the great sensitivity on progenitor radius, SN II-P color evolution appears insensitive to variations in explosion energy. Finally, we document the numerous SN II-P signatures that vary with progenitor metallicity, revealing their potential for metallicity determinations in the nearby and distant Universe., Paper accepted to MNRAS

This paper investigates the nitrogen blanketing front during the dead-ended anode (DEA) operation of a PEM fuel cell. It is found that the dynamic evolution of nitrogen accumulation in the DEA of a PEM fuel cell eventually arrives to a steady-state, which suggests the existence of equilibrium. We use a multi-component model of the two-phase, one-dimensional (along-channel) system to analyze this phenomenon. Specifically, the model is first verified with experimental observations, and then utilized to show the evolution toward equilibrium. The full order model is reduced to a second-order partial differential equation (PDE) with one state, which can be used to predict and analyze the observed steady state DEA behavior. The parametric study is performed focusing on the influence of the cathode pressure on the existence of equilibrium in the DEA condition.

The model atmosphere programs FASTWIND and CMFGEN are both elegantly designed to perform non-LTE analyses of the spectra of hot massive stars, and include sphericity and mass-loss. The two codes differ primarily in their approach towards line blanketing, with CMFGEN treating all of the lines in the co-moving frame and FASTWIND taking an approximate approach which speeds up execution times considerably. Although both have been extensively used to model the spectra of O-type stars, no studies have used the codes to independently model the same spectra of the same stars and compare the derived physical properties. We perform this task on ten O-type stars in the Magellanic Clouds. For the late-type O supergiants, both CMFGEN and FASTWIND have trouble fitting some of the He I lines, and we discuss causes and cures. We find that there is no difference in the average effective temperatures found by the two codes for the stars in our sample, although the dispersion is large, due primarily to the various difficulties each code has with He I. The surface gravities determined using FASTWIND are systematically lower by 0.12 dex compared to CMFGEN, a result we attribute to the better treatment of electron scattering by CMFGEN. This has implications for the interpretation of the origin of the so-called mass discrepancy, as the masses derived by FASTWIND are on average lower than inferred from stellar evolutionary models, while those found by CMFGEN are in better agreement., Accepted by the Astrophysical Journal

We present non-LTE time-dependent radiative-transfer simulations of pair-instability supernovae (PISNe) stemming from red-supergiant (RSG), blue-supergiant (BSG) and Wolf-Rayet (WR) star rotation-free progenitors born in the mass range 160-230Msun, at 10^-4 Zsun. Although subject to uncertainties in convection and stellar mass-loss rates, our initial conditions come from physically-consistent models that treat evolution from the main-sequence, the onset of the pair-production instability, and the explosion phase. With our set of input models characterized by large 56Ni and ejecta masses, and large kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar, and Ib/c light-curve morphologies, although they have larger peak bolometric luminosities (~10^9 to 10^10 Lsun) and a longer duration (~200d). We discuss the spectral properties for each model during the photospheric and nebular phases, including Balmer lines in II-P and II-pec at early times, the dominance of lines from intermediate-mass-elements (IMEs) near the bolometric maximum, and the strengthening of metal line blanketing thereafter. Having similar He-core properties, all models exhibit similar post-peak spectra that are strongly blanketed by FeII and FeI lines, characterized by red colors, and that arise from photospheres/ejecta with a temperature of, accepted to MNRAS

The coalescence of compact objects are a promising astrophysical sources of gravitational wave (GW) signals. The ejection of r-process material from such mergers may lead to a radioactively-powered electromagnetic counterpart which, if discovered, would enhance the science return of a GW detection. As very little is known about the optical properties of heavy r-process elements, previous light curve models have adopted opacities similar to those of iron group elements. Here we report that the presence of heavier elements, particularly the lanthanides, increase the ejecta opacity by several orders of magnitude. We include these higher opacities in time dependent, multi-wavelength radiative transport calculations to predict the broadband light curves of one-dimensional models over a range of parameters (ejecta masses from 0.001 to 0.1 solar masses and velocities from 0.1 to 0.3c). We find that the higher opacities lead to much longer duration light curves which can last a week or more. The emission is shifted toward the infrared bands due to strong optical line blanketing, and the colors at later times are representative of a blackbody near the recombination temperature of the lanthanides (T ~ 2500K). We further consider the case in which a second mass outflow, composed of 56Ni, is ejected from a disk wind, and show that the net result is a distinctive two component spectral energy distribution, with a bright optical peak due to 56Ni and an infrared peak due to r-process ejecta. We briefly consider the prospects for detection and identification of these transients., Comment: submitted to ApJ

The Southwest Research Institute’s John Spencer delves into the oceans of ice and water blanketing the outer moons, with a focus on Saturn’s dramatic erupting satellite Enceladus. Beyond Saturn, we survey moons of the other outer worlds, where water or other liquids might be hidden, or might once have been hidden, beneath their hard-frozen surfaces.

The star G191-B2B is one of a number of hot DA white dwarfs whose atmospheres have been found to contain significant quantities of heavy elements, including C, N, O, Si, Fe, and Ni. Several earlier studies have measured their abundances using IUE echelle data in conjunction with synthetic spectra derived from theoretical model atmosphere calculations of varying degrees of sophistication. However, predictions of the EUV spectrum based on these observations failed completely to match either its shape or absolute flux level. We present here the results of new non-LTE model calculations including the effects of line blanketing from more than 9 million (mainly Fe and Ni) transitions. For the first time, we are able to find an effective temperature and composition that can consistently match the optical, FUV and EUV data. However, to maintain this agreement below the He ii Λ228 Lyman limit, it is necessary to incorporate additional He ii opacity in the form of photospheric, circumstellar or interstellar material.

Among the well-imaged small satellites and asteroids, Deimos displays a unique surface: very smooth with global-scale albedo features. We have examined the disk-resolved photometry of Deimos using Viking Orbiter images for clues to its distinctive appearance. Hapke parameters were fit to characterize the phase behavior and to compute normal reflectance. The opposition surge amplitude (B0) is smaller for Deimos than for Phobos. Outside the range of the opposition effect the two martian satellites have similarly shaped phase curves, but Deimos is about 20–30% brighter than Phobos from 10°–80° phase. The calculated mean normal reflectance of Deimos (λeff= 0.54 μm) is 0.068 ± 0.007. The brighter and darker areas on Deimos exhibit constant contrast between 0.6° and 81° phase; this characteristic allows a calculation of the range of normal reflectances over most of its surface, nearly all of which values are between 0.06 and 0.09. The trailing side of Deimos has a larger relative distribution of the brighter material, and is on average about 10% brighter than the leading side. The mean normal reflectance cannot be formally distinguished from that of Phobos (0.071 ± 0.012; Simonelli, D. P., M. Wisz, A. Switala, D. Adinolfi, J. Veverka, P. C. Thomas, and P. Helfenstein 1996. Submitted toIcarus). Although the statistical distribution of normal reflectances on the two satellites is similar, the geography of the albedo variations is very different. Deimos has gradational changes in albedo downslope from ridge crests, primarily manifested in long albedo “streamers.” On Phobos there is a more patchy global distribution of albedos, apparently related to ejecta from the large crater Stickney. Because of the similarity of mean density, spectral properties, mean normal reflectance, the range of normal reflectance, and phase function outside the opposition effect, Deimos appears to be made of materials with compositions very similar to those on Phobos, although the apparent wider distribution of ejecta on Deimos has been cited as indicating a greater role for strength scaling in cratering on Deimos (Lee, S. W., P. Thomas, and J. Veverka 1986.Icarus68, 77–86). Simple modeling of the formation of the albedo patterns by gardening, creep, and “weathering” of bright material from crater rims suggests that impact gardening contributes very little to the motion of the material downslope, and that vertical mixing and/or “weathering” must be important in addition to an unspecified creep process. The distinction of Deimos is primarily in the smooth surface that allows a particularly large scale of downslope movement of regolith on very gentle slopes. This smoothness is most easily explained by the effects from impact formation of a 10-km concavity at high southern latitudes in the latter half of Deimos' surface history. This impact scar is relatively much larger than is the crater Stickney on Phobos. The effects of this large impact probably include blanketing by an average of nearly 200 m of ejecta, but also may include seismic erasing of craters similar to that proposed for Ida by Asphauget al. (Asphaug, E., J. M. Moore, D. Morrison, W. Benz, and R. A. Sullivan 1996.Icarus120, 158–184).

We briefly review the state-of-the-art in non-LTE modeling of hot star atmospheres. During the last decade, the development of a new class of radiation transfer methods, based on the Accelerated Lambda Iteration method, have brought considerable progress in this field. Severe limitations of the size of model atoms used in non-LTE model atmospheres have been removed, so that realistic model atoms can now be considered. In recent years, the problem of non-LTE line blanketing, which aims to include the influence of thousands to millions of lines on the atmospheric structure, has been attacked, and first non-LTE line-blanketed models have been calculated. We illustrate the importance of non-LTE line blanketing with the example of a hot subdwarf, BD +75° 325. As a consequence of these developments, there is a need for extensive radiative and collisional atomic databases to build non-LTE models. Recent projects, like the Opacity Project, provide a substantial quantity of the necessary data. We discuss the current needs of atomic data for the purpose of building reliable non-LTE line-blanketed model atmospheres. A critical evaluation of the quality of such extensive sets of atomic data is essential. Finally, we present a new, IDL-based, graphic tool intended to facilitate the manipulation of large amounts of data needed to build the realistic model atoms that we use.

The deposition of cold sedimerlts, called thermal blanketing, is studied when the sedimentary basin is considered as part of the lithosphere. A general one‐dimensional temperature equation is obtained which accounts for blanketing, the movement of the lower boundary of the lithosphere, and the eventual stretching of the sediments and the lithosphere. These processes appear explicitly as convective terms in the model, which is a generalization of a previous temperature equation. The description of these processes b!‐means of convective terms is a major result in the paper; it makes these processes more amenable to quantitative investigations. The temperature equation is studied in two different settings; one where the lithosphere remains unstretched, and another where the lithosphere is subjected to constant strain rate stretching. The parameter controlling thermal blanketing in these models is the Peclet number. The transient period towards a stationary state, and the stationary state representing maximal blanketing are studied. Analytical expressions for various stationary states are obtained. When the lithosphere remains unstretched it is concluded that a necessary condition for strong blanketing is a sedimentation rate of the order of 250mMyr‐1. Where the sediments contribute to the heat flow by decay of radioactive isotopes, the radioactive heat production divided by the sedimentation rate should be at least 10‐9 (Wm‐3)/(mMyr‐1) for the heat production to compete with blanketing. During stretching of the lithosphere it is shown that for stretching factors (p) larger than 2, the convective effect of stretching the sediments contributes more to the reduction of the heat flow than the blanketing effect. Blanketing counteracts the increased heat flow caused by the stretching of the lithosphere, and the upwelling hot asthenosphere. With sedimentation rates inferred from isostatic calculations it is found that the strain rate times the initial crust thickness should be more than 0.25 km Myr‐1 for the blanketing effect to be noticeable. It is also shown that sediment infill which follows thermal subsidence, after a period of stretching, is not capable of blanketing.

Extensive experience with the refilling of the Amersham Mk IV 1.85 PBq uranium pots has shown that helium-3 resident in the uranium matrix causes `blanketing` of the metal surface and subsequent operational problems. This paper reviews the operational procedures and results observed at Ontario Hydro`s dispensing facilities. Experimental work performed to investigate the effect of this helium-3 on the reuse of the Amersham Mk IV pots demonstrated the necessity of an operational ability to evacuate the uranium pot at stages during the tritium transfer, without affecting the quantitative transfer measurement. 2 refs., 3 figs.

The re-oxidation of low-pressure methanol synthesis catalyst was followed by means of DSC, with the aim of contributing to a better understanding of the processes taking place during catalyst blanketing, stabilization and re-oxidation. The investigations were carried out with previously hydrogen-reduced samples, and their successive re-oxidation was performed with different oxygen contents in the oxygen/nitrogen gas mixtures. A procedure for catalyst stabilization and/or catalyst discharge is proposed.

Here we present the study of daytime scintillation due to E region irregularities at low latitudes from a set of simultaneous observations on June 3, 1993. The effects of these irregularities are clearly seen on (1) the 103 MHz signal of the radio star 3C 196 recorded at Rajkot and at Thaltej (near Ahmedabad, India), (2) the 244-MHz radio beacon of Fleetsat satellite (73°E) recorded at Ahmedabad, and (3) the ionosonde being operated at Ahmedabad. These observations provide an estimate of the irregularity patch with a spatial extent of around 400 km east-west and 80 km north-south. As the subionospheric points of the radio source and satellite observations are quite far apart, a study on the dynamics of these irregularities is also possible which indicates a southward movement of the patch. The drift speed of ∼ 60 m/sec is calculated from the upper frequency roll off of the scintillation spectrum at 103 MHz. This is found to be consistent with earlier investigations of blanketing Es near magnetic equator.

In the present study, ionospheric phenomena caused by earthquakes of magnitudes M >4.0 were investigated. Night-time observations of the spreading of sporadic E-layers (Es-spread) performed every 15 min by the Dushanbe and Petropavlovsk-Kamchatsky (middle Asia) vertical sounding stations were studied. The mean relative occurrence frequency of Esspread at different values of the blanketing frequency fbEs was considered, and the dependence of Es-spread on the season as well as on the year through an 11-yr solar activity cycle were studied. The fbEs characterizes the maximum plasma density of the Es-layer. The analysis shows that 1- 3 days before seismic shocks in the Earth crust at depths of h

The delayed-detonation explosion mechanism applied to a Chandrasekhar-mass white dwarf offers a very attractive model to explain the inferred characteristics of Type Ia supernovae (SNe Ia). The resulting ejecta are chemically stratified, have the same mass and roughly the same asymptotic kinetic energy, but exhibit a range in 56Ni mass. We investigate the contemporaneous photometric and spectroscopic properties of a sequence of delayed-detonation models, characterized by 56Ni masses between 0.18 and 0.81 Msun. Starting at 1d after explosion, we perform the full non-LTE, time-dependent radiative transfer with the code CMFGEN, with an accurate treatment of line blanketing, and compare our results to SNe Ia at bolometric maximum. Despite the 1D treatment, our approach delivers an excellent agreement to observations. We recover the range of SN Ia luminosities, colours, and spectral characteristics from the near-UV to 1 micron, for standard as well as low-luminosity 91bg-like SNe Ia. Our models predict an increase in rise time to peak with increasing 56Ni mass, from ~15 to ~21d, yield peak bolometric luminosities that match Arnett's rule to within 10%, and reproduce the much smaller scatter in near-IR magnitudes compared to the optical. We reproduce the morphology of individual spectral features, the stiff dependence of the R(Si) spectroscopic ratio on 56Ni mass, and the onset of blanketing from TiII/ScII in low-luminosity SNe Ia with a 56Ni mass, 25 pages, 16 figures; accepted for publication in MNRAS

[1] In order to understand the early history of telluric interiors and atmospheres during the ocean magma stage, a coupled interior-atmosphere-escape model is being developed. This paper describes the atmospheric part and its first preliminary results. A unidimensional, radiative-convective, H2O-CO2 atmosphere is modeled following a vertical T(z) profile similar to Kasting (1988) and Abe and Matsui (1988). Opacities in the thermal IR are then computed using a k-correlated code (KSPECTRUM), tabulated continuum opacities for H2O-H2O and CO2-CO2 absorption, and water or sulphuric acid clouds in the moist convective zone (whenever present). The first results show the existence of two regimes depending on the relative value of the surface temperature Ts compared to a threshold temperature Tc depending on the total gaseous inventory. For Ts Tc, the blanketing is not efficient enough to prevent large radiative heat loss to space through a hot, cloudless atmosphere. Our current calculations may underestimate the thermal flux in the case of hot surfaces with little gaseous content in the atmosphere.

Results from geodynamic models for lithospheric extension that includes one or two large-scale upper crustal faults are presented. The study does not address the origin of these faults, but the consequences if they exist. Model components include a solid mechanical lithosphere composed of thermoelastic-plastic material with viscous creep that is subject to extension, buoyant supporting forces and sedimentary loads, and a coincident, but thicker, thermal lithosphere that includes the effect of sediment blanketing and radiogenic heating. We have chosen for comparison purposes a “standard” reference model which minimizes creep in the crust; consequently, our results depend strongly on plastic deformation. Our models show that large faults can control the position and growth history of the mantle instabilities that can lead to rupture. We observe that these instabilities have secondary, “normal mode”-like character. Models with two faults show that the normal mode behavior can interact and create an enhancement to the necking process, provided the faults are an ideal distance apart. We compare models with two rates of extension, 1.2 cm yr−1 (“fast”) and 0.038 cm yr−1 (“slow”), which show remarkably little difference. We compare our reference model with models using “wet” and “dry” rheologies and observe that flow in the crust can attenuate the propagation effect created by the faults.