Main Emission Region Research Articles

Auroral 3D structure retrieval from the Juno/UVS data

Context. Jovian auroras, the most powerful in the Solar System, result from the interaction between the magnetosphere and atmosphere of Jupiter. While the horizontal morphology of these phenomena has been widely studied, their vertical structure, determined by the penetration depth of the magnetospheric electron into the auroral regions, remains relatively unexplored. Previous observations, including those from the Hubble Space Telescope (HST), have addressed this question to a limited extent. Aims. In this study we aim to map the vertical structure of Jovian auroral emissions. Methods. Using observations from Juno’s UltraViolet Spectrograph (UVS), we examined the vertical structure of the auroral emissions. Building on a recent study of auroral energy mapping based on UVS observations that mapped the average energy of precipitating electrons in the Jovian auroral regions, we find a relationship between this average energy and the volume emission rate (VER) of H2 for two types of electron energy distributions: monoenergetic and a kappa distribution with κ = 2.5. Results. Using brightness maps, we derived the 3D VER structure of Jovian auroras in both northern and southern regions, across multiple spacecraft perijoves (PJs). By considering the example of PJ11, we find that the average altitude of the VER peak in the polar emission region is approximately ~250 km for the monoenergetic distribution case and ~190 km for kappa distribution case. In the main emission region, we find that the average altitude of the VER peak is approximately ~260 km for the case of monoenergetic distribution and ~197 km for kappa distribution case. For the other PJs, we obtained results that are very similar to those of PJ11. Conclusions. Our findings are, on average, consistent with measurements from the Galileo probe and the HST observations. This study contributes to a better understanding of the complexity of Jovian auroras and highlights the importance of using Juno observations when probing their vertical structure. Considering the variability in the κ parameter in the auroral region, we also studied the impact of this variability on the vertical structure of the auroral emission. This sensitivity study reveals that the influence of the κ parameter on our results was very weak. However, the impact of the κ variability on the VER amplitude shows that there is an influence on the thermal structure and chemical composition of the atmosphere in the auroral regions.

Modeling of Radio Supernovae: Including the Effects of Inhomogeneities and Radiative Cooling

The presence of inhomogeneities in a spatially unresolved source is often hard to establish. This limits the accuracy with which the source properties can be determined. It is shown how observed features not expected for a homogeneous model can be used to infer the properties of the inhomogeneities in radio supernovae. Furthermore, the observed consequences of radiative cooling can be seriously affected by inhomogeneities. It is shown that the deduced source properties are very sensitive to the observed value of the cooling frequency; even a lower limit is often useful to constrain its characteristics. It is argued that the main synchrotron emission region in SN 2003L has a small volume filling factor, possibly as low as a few percent. On the contrary, deviations from homogeneity are substantially smaller in SN 2002ap. The observed properties of Type Ib/c radio supernovae in general indicate the volume filling factor to remain rather constant with time for individual sources, but those peaking later at radio frequencies have lower filling factors. The conditions in the main synchrotron component in both SN 2003L and SN 2002ap are consistent with equipartition of energy between relativistic electrons and magnetic fields.

Hemispheric-wide climate response to regional COVID-19-related aerosol emission reductions: the prominent role of atmospheric circulation adjustments

Abstract. The national and global restrictions in response to the COVID-19 pandemic led to a sudden, albeit temporary, emission reduction of many greenhouse gases (GHGs) and anthropogenic aerosols, whose near-term climate impact were previously found to be negligible when focusing on global- and/or annual-mean scales. Our study aims to investigate the monthly scale coupled climate-and-circulation response to regional, COVID-19-related aerosol emission reductions, using the output from 10 Earth system models participating in the Covid model intercomparison project (CovidMIP). We focus on January–February and March–May 2020, which represent the seasons of largest emission changes in sulfate (SO2) and black carbon (BC). During January–February (JF), a marked decrease in aerosol emissions over eastern China, the main emission region, resulted in a lower aerosol burden, leading to an increase in surface downwelling radiation and ensuing surface warming. Regional sea-level pressure and circulation adjustments drive a precipitation increase over the Maritime Continent, embedded in a negative Pacific Decadal Oscillation (PDO)- and/or El Niño–Southern Oscillation (ENSO)-like response over the Pacific, in turn associated with a northwestward displacement and zonal shrinking of the Indo-Pacific Walker cell. Remote climate anomalies across the Northern Hemisphere, including a weakening of the Siberian High and Aleutian Low, as well as anomalous temperature patterns in the northern mid-latitudes, arise primarily as a result of stationary Rossby wave trains generated over East Asia. The anomalous climate pattern and driving dynamical mechanism reverse polarity between JF and MAM (March–May) 2020, which is shown to be consistent with an underlying shift of the dominant region of SO2 emission reduction from eastern China in JF to India in MAM. Our findings highlight the prominent role of large-scale dynamical adjustments in generating a hemispheric-wide aerosol climate imprint even on short timescales, which are largely consistent with longer-term (decadal) trends. Furthermore, our analysis shows the sensitivity of the climate response to the geographical location of the aerosol emission region, even after relatively small, but abrupt, emission changes. Scientific advances in understanding the climate impact of regional aerosol perturbations, especially the rapidly evolving emissions over China and India, are critically needed to reduce current uncertainties in near-future climate projections and to develop scientifically informed hazard mitigation and adaptation policies.

Electron Partial Density and Temperature Over Jupiter's Main Auroral Emission Using Juno Observations

AbstractWe present a survey of electron partial densities (i.e., the portion of the total density measured between ∼0.05 and 100 keV) and temperatures in Jupiter's main auroral emission region using plasma measurements from the Jovian Auroral Distributions Experiment (JADE) on Juno. The electron partial density increases from ∼0.01 or 0.1 cm−3 near the main oval to a few cm−3 at the edge of the measurable part of the UV emission equatorward of the main oval. The electron temperature is highest near the main oval at ∼10–20 keV and decreases equatorward down to ∼0.3–2 keV. The JADE electron partial density agrees within a factor of ∼2 with the total electron densities derived from Juno‐Waves when the comparison is possible. The electron density and temperature trends are consistent for all sampled longitudes, for the north and the south, and there is no significant trend with radial distance in the range examined in this study (1.25–1.96 RJ). The electron density is anti‐correlated with the temperature and the characteristic energy. The ratio of the magnetic field strength to the electron density is maximum near the main oval.

Effect of surface topography on emission properties of hot-cathode

As a kind of influence factor, the surface topography determines the uniformity and current of peritoneal impregnated diffusion cathode (M-type dispenser cathode) emitted electrons. It can be seen from the emission characteristics of the cathode in the micro-range that the lathe tool grains at the cathode surface can affect the current uniformity, and the electron emission will be enhanced. But the distribution of the lathe tool grains is uncontrollable. Therefore to fully utilize the promoting effect of surface stripes on electron emission, the effect of surface topography onthe emission property of M-type dispenser cathode is investigated. And the simplest way to change the surface morphology of cathode surface is to fabricate a periodic stripe structure which can be divided into unidirectional stripe structure and orthogonal bidirectional stripe structure. And the orthogonal bidirectional stripe structure at the cathode surface can form micro-tip structure like the spindle cathode. To research the effect of surface topography on the emission properties of M-type dispenser cathode, the periodic stripe structures on the cathode surface with different sizes and shapes are processed by the femtosecond leaser in the fabrication of micro/nano-size microstructure. The cathodes are prepared with the same degassing and activated method. The test results of the cathodes show the periodic stripe structure on the cathode surface can effectively enhance the cathode electron emission capability. The emission current density of cathode with orthogonal bidirectional stripe is higher than that of cathode with unidirectional stripe. And with the stripe size declining, the emission capability is gradually enhanced. Also, this phenomenon occurs in the scandium-impregnated diffusion cathode. With the help of simulation of cathode surface topography, it is shown that the top of tip has a great electron emission capability for its strong electric field. When the ratio of bottom radius to height of the tip (<i>r</i>/<i>h</i>) is small, the side area is the main region of cathode electron emission. But as the <i>r</i>/<i>h</i> keeps decreasing, the main electron emission region is transferred from the side of tip to the top of tip, and the field assisted effect is the major component of the cathode electron emission.

An isolated, bright cusp aurora at Saturn

AbstractSaturn's dayside aurora displays a number of morphological features poleward of the main emission region. We present an unusual morphology captured by the Hubble Space Telescope on 14 June 2014 (day 165), where for 2 h, Saturn's FUV aurora faded almost entirely, with the exception of a distinct emission spot at high latitude. The spot remained fixed in local time between 10 and 15 LT and moved poleward to a minimum colatitude of ~4°. It was bright and persistent, displaying intensities of up to 49 kR over a lifetime of 2 h. Interestingly, the spot constituted the entirety of the northern auroral emission, with no emissions present at any other local time—including Saturn's characteristic dawn arc, the complete absence of which is rarely observed. Solar wind parameters from propagation models, together with a Cassini magnetopause crossing and solar wind encounter, indicate that Saturn's magnetosphere was likely to have been embedded in a rarefaction region, resulting in an expanded magnetosphere configuration during the interval. We infer that the spot was sustained by reconnection either poleward of the cusp or at low latitudes under a strong component of interplanetary magnetic field transverse to the solar wind flow. The subsequent poleward motion could then arise from either reconfiguration of successive open field lines across the polar cap or convection of newly opened field lines. We also consider the possible modulation of the feature by planetary period rotating current systems.

On the Spectral Curvature of VHE Blazar 1ES 1011+496: Effect of Spatial Particle Diffusion

Abstract A detailed multi-epoch study of the broadband spectral behavior of the very high energy (VHE) source 1ES 1011+496 provides us with valuable information regarding the underlying particle distribution. Simultaneous observations of the source at optical/UV/X-ray/γ-ray during three different epochs, as obtained from Swift-UVOT/Swift-XRT/Fermi-LAT, are supplemented with the information available from the VHE telescope array, HAGAR. The long-term flux variability at the Fermi-LAT energies is clearly found to be lognormal. It is seen that the broadband spectral energy distribution of 1ES 1011+496 can be successfully reproduced by synchrotron and synchrotron self Compton emission models. Notably, the observed curvature in the photon spectrum at X-ray energies demands a smooth transition of the underlying particle distribution from a simple power law to a power law with an exponential cutoff, or a smooth broken power law distribution, which may possibly arise when the escape of the particles from the main emission region is energy dependent. Specifically, if the particle escape rate is related to its energy as E 0.5 , then the observed photon spectrum is consistent with the ones observed during the various epochs.

Auroral evidence of radial transport at Jupiter during January 2014

AbstractWe present Jovian auroral observations from the 2014 January Hubble Space Telescope (HST) campaign and investigate the auroral signatures of radial transport in the magnetosphere alongside contemporaneous radio and Hisaki EUV data. HST FUV auroral observations on day 11 show, for the first time, a significantly superrotating polar spot poleward of the main emission on the dawnside. The spot transitions from the polar to main emission region in the presence of a locally broad, bright dawnside main emission feature and two large equatorward emission features. Such a configuration of the main emission region is also unreported to date. We interpret the signatures as part of a sequence of inward radial transport processes. Hot plasma inflows from tail reconnection are thought to flow planetward and could generate the superrotating spot. The main emission feature could be the result of flow shears from prior hot inflows. Equatorward emissions are observed. These are evidence of hot plasma injections in the inner magnetosphere. The images are thought to be part of a prolonged period of reconnection. Radio emissions measured by Wind suggest that hectometric (HOM) and non‐Io decametric (DAM) signatures are associated with the sequence of auroral signatures, which implies a global magnetospheric disturbance. The reconnection and injection interval can continue for several hours.

Luminescent properties of Eu2+-doped BaGdF5 glass ceramics a potential blue phosphor for ultra-violet light-emitting diode

Eu2+ doped transparent oxyfluoride glass ceramics containing BaGdF5 nanocrystals were successfully fabricated by melt-quenching technique under a reductive atmosphere. The structure of the glass and glass ceramics were investigated by differential scanning calorimetry, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The luminescent properties were investigated by transmission, excitation, and emission spectra. The decay time of the Gd3+ ions at 312 nm excited with 275 nm were also investigated. The results of XRD and TEM indicated the existence of BaGdF5 nanocrystals in the transparent glass ceramics. The excitation spectra of Eu2+ doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED). Compared with the as-made glass, the emission of glass ceramics is much stronger by a factor of increasing energy transfer efficiency from Gd3+ to Eu2+ ions, the energy transfer efficiency from Gd3+ to Eu2+ ions was discussed. In addition, the chromaticity coordinates of glass and glass ceramics specimens were also discussed, which indicated that the Eu2+ doped BaGdF5 glass ceramics may be used as a potential blue-emitting phosphor for UV-LED.

Mapping the electron energy in Jupiter's aurora: Hubble spectral observations

AbstractFar ultraviolet spectral observations have been made with the Hubble Space Telescope in the time‐tag mode using the Space Telescope Imaging Spectrograph (STIS) long slit. The telescope was slewed in such a way that the slit projection scanned from above the polar limb down to midlatitudes, allowing us to build up the first spectral maps of the FUV Jovian aurora. The shorter wavelengths are partly absorbed by the methane layer overlying part of the auroral emission layer. The long‐wavelength intensity directly reflects the precipitated energy flux carried by the auroral electrons. Maps of the intensity ratio of the two spectral regions have been obtained by combining spectral emissions in two wavelength ranges. They show that the amount of absorption by methane varies significantly between the different components of the aurora and inside the main emission region. Some of the polar emissions are associated with the hardest precipitation, although the auroral regions of strong electron precipitation do not necessarily coincide with the highest electron energies. Outputs from an electron transport model are used to create maps of the distribution of the characteristic electron energies. Using model atmospheres adapted to auroral conditions, we conclude that electron energies range between a few tens to several hundred keV. Comparisons of derived energies are in general agreement with those calculated from magnetosphere‐ionosphere coupling models, with values locally exceeding the standard model predictions. These results will provide useful input for three‐dimensional modeling of the distribution of particle heat sources into the high‐latitude Jovian upper atmosphere.

Optimizing laser produced plasmas for efficient extreme ultraviolet and soft X-ray light sources

Photon sources produced by laser beams with moderate laser intensities, up to 1014 W/cm2, are being developed for many industrial applications. The performance requirements for high volume manufacture devices necessitate extensive experimental research supported by theoretical plasma analysis and modeling predictions. We simulated laser produced plasma sources currently being developed for several applications such as extreme ultraviolet lithography using 13.5% ± 1% nm bandwidth, possibly beyond extreme ultraviolet lithography using 6.× nm wavelengths, and water-window microscopy utilizing 2.48 nm (La-α) and 2.88 nm (He-α) emission. We comprehensively modeled plasma evolution from solid/liquid tin, gadolinium, and nitrogen targets as three promising materials for the above described sources, respectively. Results of our analysis for plasma characteristics during the entire course of plasma evolution showed the dependence of source conversion efficiency (CE), i.e., laser energy to photons at the desired wavelength, on plasma electron density gradient. Our results showed that utilizing laser intensities which produce hotter plasma than the optimum emission temperatures allows increasing CE for all considered sources that, however, restricted by the reabsorption processes around the main emission region and this restriction is especially actual for the 6.× nm sources.

Synthesis and luminescence properties of glass ceramics containing MSiO 3:Eu 2+ (M=Ca, Sr, Ba) phosphors for white LED

Eu 2+ doped silicate glasses were prepared of the system 52SiO 2–48MO: xEu 2+(in molar ratio, M=Ca, Sr, Ba; x=1, 3, 5, 7, 9) by a high temperature melt-quenching method in a reducing atmosphere. Glass ceramics containing MSiO 3:Eu 2+(M=Ca, Sr, Ba) nano-phosphors were obtained after the heat treatment of the glass samples. The excitation, emission spectra and lifetime decay curves of 4f 65d 1→4f 7 of Eu 2+ were measured and interpreted with respect to their crystal structures and multi-site occupations of divalent europium in the hosts. Their excitation bands mainly extend from 450 to 250 nm, which is adaptable to the main emission region of the UV LED chip. With UV light excitation, the Eu 2+ emission in CaSiO 3, SrSiO 3 and BaSiO 3 shows blue, green and yellow colors centered at 440, 505 and 555 nm, respectively. The critical Eu 2+concentration was studied and determined to be x=5 for both CaSiO 3 and SrSiO 3 and x=7 for BaSiO 3 phosphors. The results show that the Eu 2+ doped glass ceramic phosphors containing MSiO 3 (M=Ca, Sr, Ba) nano-crystals can be used as potential matrix materials for a high power white LED pumped by the UV LED chip.

Spectral analysis of a novel Eu 2+ activated SiO 2–BaO glass ceramics phosphor under UV-LED excitation

A novel Eu 2+ activated 60SiO 2–40BaO (mol%) glass ceramics phosphor was prepared and the optical properties were investigated. X-ray diffraction (XRD) and Raman spectra confirmed the formation of Ba 2Si 3O 8 nano-crystals in the glass matrix. The Eu 2+ activated glass ceramics exhibited broad emission band centered at 518 nm due to the 4f 65d 1→4f 7 transition of Eu 2+. Compared with the glass, the emission intensity of Eu 2+ activated glass ceramics was much stronger, and the peak wavelength shifted toward shorter wavelength. The photoluminescence excitation (PLE) spectra of the glass ceramics showed an overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED). According to the photoluminescence (PL) spectra, the CIE chromaticity coordinates of the Eu 2+ activated glass and glass ceramics were calculated. The results indicated that the Eu 2+ activated glass ceramics containing Ba 2Si 3O 8 nano-crystals can be used as a potential green emitting phosphor under UV-LED excitation.

Hydrides in young stellar objects: Radiation tracers in a protostar-disk-outflow system

Context: Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays. Aims: We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation. Methods: W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep integration (about 2500 s) in 8 spectral regions. Results: The target lines including CH, NH, H3O+, and the new molecules SH+, H2O+, and OH+ are detected. The H2O+ and OH+ J=1-0 lines are found mostly in absorption, but also appear to exhibit weak emission (P-Cyg-like). Emission requires high density, thus originates most likely near the protostar. This is corroborated by the absence of line shifts relative to the young stellar object (YSO). In addition, H2O+ and OH+ also contain strong absorption components at a velocity shifted relative to W3 IRS5, which are attributed to foreground clouds. Conclusions: The molecular column densities derived from observations correlate well with the predictions of a model that assumes the main emission region is in outflow walls, heated and irradiated by protostellar UV radiation.

Eu2+‐Doped Glass Ceramics Containing BaF2 Nanocrystals as a Potential Blue Phosphor for UV‐LED

The Eu2+‐doped glass ceramics containing BaF2 nanocrystals were prepared and their luminescence properties were investigated. The excitation spectra of Eu2+‐doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light‐emitting diode (UV‐LED) centered at 380 nm. The 450 nm emission of Eu2+ in glass ceramics under the 385 nm excitation was much stronger than that in glass. The Eu2+‐doped glass ceramics containing BaF2 nanocrystals may be used as a potential blue‐emitting phosphor for UV‐LED.

Deep SAURON spectral imaging of the diffuse Lyman α halo LAB1 in SSA 22

We have used the SAURON panoramic integral field spectrograph to study the structure of the Lya emission-line halo, LAB1, surrounding the submillimetre galaxy SMM J221726+0013. This emission-line halo was discovered during a narrow-band imaging survey of the z = 3.1 large-scale structure in the SSA 22 region. Our observations trace the emission halo out to almost 100 kpc from the submillimetre source and identify two distinct Lya 'mini-haloes' around the nearby Lyman-break galaxies. The main emission region has a broad line profile, with variations in the line profile seeming chaotic and lacking evidence for a coherent velocity structure. The data also suggest that Lya emission is suppressed around the submillimetre source. Interpretation of the line structure needs care because Lya may be resonantly scattered, leading to complex radiative transfer effects, and we suggest that the suppression in this region arises because of such effects. We compare the structure of the central emission-line halo with local counterparts, and find that the emission-line halo around NGC 1275 in the Perseus cluster may be a good local analogue, although the high-redshift halo is factor of ∼100 more luminous and appears to have higher velocity broadening. Around the Lyman-break galaxy C15, the emission line is narrower, and a clear shear in the emission wavelength is seen. A plausible explanation for the line profile is that the emission gas is expelled from C15 in a bipolar outflow, similar to that seen in M82.

Spectroscopy and polarimetry of the AM Herculis system RX J1313.32−3259

We present polarimetric and spectroscopic observations of the ROSAT source RX J1313.32−3259, recently identified as a polar. Circular polarization is modulated over the orbital period with an amplitude of ∼10 per cent. A brief reversal in circular polarization is detected at phase ∼0.0, when the main accretion region is seen face on to the observer. We deduce that the main cyclotron emission is absorbed by the accretion shock and/or stream at this phase, allowing a second accretion shock, located at the opposite ends of the field lines that feed the main pole, to be seen. Linear polarization is also detected with possible linear pulses at orbital phases where the accretion region is expected to be on the limb of the white dwarf. The general morphology of the photopolarimetry arises as a result of a combination of the absorption of cyclotron radiation by the accretion shock/stream and projection/cyclotron beaming effects of a main cyclotron emission region as the white dwarf rotates. The main cyclotron emission region remains on the visible hemisphere of the white dwarf throughout the orbit. Doppler maps of the emission lines show emission at or near the expected location of the secondary star and an extended arc-like feature coincident with the ballistic and possibly the magnetically confined accretion stream.

Stokes imaging of the AM Her system ST LMi

The Stokes imaging technique of Potter, Hakala & Cropper is applied to the polarized emission from the AM Her system ST LMi. For the first time, the cyclotron emission region on the surface of the white dwarf is mapped in terms of optical depth/density in an analytical and objective manner. The region is found to consist of a less dense region leading a higher density region in orbital phase. It is demonstrated that the emission region needs to have a multi-temperature structure in order to explain the spectral slope and the general morphology of the cyclotron humps observed in the IR during the bright phase in ST LMi. Furthermore, it is shown that a secondary emission region, fed by the same magnetic field lines that feed the main emission region, could be responsible for the positive circular polarization in the IR, the position angle variation and the excess flux during the faint phase of the white light observations which cannot be accounted for with a single emission region.

The magnetic field configurations of AM Herculis binaries

We have considered equilibrium configurations of a white dwarf and a red dwarf companion in AM Herculis type binary system where the red dwarf is assumed to have an intrinsic centered dipole field, and the white dwarf an offset dipole or a centered dipole plus a quadrupole field, and the interaction is purely magnetic. The restoring torque, due to the system being perturbed from its stable equilibrium configuration, is compared with the accretion torque. The results are used to show that the observed alignment of the main cyclotron emission region relative to the red star can be explained quite simply by these models without having to invoke gravitational torques. We also provide a possible explanation of the observation that the more strongly accreting pole has the weaker field strength in the few systems where fields have been determined at both poles.

Gravity wave‐driven fluctuations in OH nightglow from an extended, dissipative emission region

The theory of gravity wave‐driven fluctuations in the OH nightglow from an extended source region is generalized to account for effects of eddy kinematic viscosity ν and eddy thermal diffusivity κ. In the nondiffusive case, the amplitudes and phases of vertically integrated normalized intensity 〈δI〉/〈Ī〉 and temperature perturbations and vertically integrated Krassovsky's ratio 〈η〉 as functions of period are influenced by the upper limit of vertical integration of the extended source, especially at long periods when vertical wavelengths λυ are small. The effects, which include oscillations in 〈δT〉/〈Ī〉, , and 〈η〉, particularly at long periods, are due to constructive and destructive interference of nightglow signals from vertically separated levels of the OH emitting region that occur when λυ is comparable to or smaller than the thickness of the main emission region. The sensitivity of these ratios to the upper limit of vertical integration occurs because of the relatively small rate of decay of the intensity of OH emission with height above the peak emission level and the exponential growth with altitude of nondissipative gravity waves. Because eddy diffusion increases λυ, especially at long periods, and reduces wave growth with height compared with the case ν = κ = 0, inclusion of eddy diffusion removes the sensitivity of 〈η〉 and the other ratios to the maximum height of vertical integration. It is essential to account for both eddy diffusion and emission from the entire vertically extended emission region to correctly predict 〈η〉, 〈δI〉/〈Ī〉, and at long gravity wave periods. Observations of Krassovsky's ratio are consistent with theoretical predictions of 〈η〉 for horizontal wavelengths larger than about 500 km, provided diffusion and emission from an extended region are both taken into account.