Molecular hydrogen line emission from the reflection nebula Parsamyan 18

The newly commissioned University of New South Wales Infrared Fabry–Perot (UNSWIRF) has been used to image molecular hydrogen emission at 2.12 and 2.25 μm in the reflection nebula Parsamyan 18. P 18 is known to exhibit low values of the (1–0)/(2–1) S(1) ratio, suggestive of UV-pumped fluorescence rather than thermal excitation by shocks. Our line ratio mapping reveals the full extent of this fluorescent emission from extended arc-like features, as well as a more concentrated thermal component in regions closer to the central exciting star. We show that the emission morphology, line fluxes and gas density are consistent with the predictions of photodissociation region (PDR) theory. Those regions with the highest intrinsic 1–0 S(1) intensities also tend to show the highest (1–0)/(2–1) S(1) line ratios. Furthermore, variations in the line ratio can be attributed to intrinsic fluctuations in the incident radiation field and/or the gas density, through the self-shielding action of H₂. An isolated knot of emission discovered just outside P 18, and having both an unusually high (1–0)/(2–1) S(1) ratio and relative velocity, provides additional evidence for an outflow source associated with P 18.     

An emission measure analysis of two sunspots observed by the UVSP instrument on the SMM spacecraft

The EUV observations from the SMM satellite of two sunspots are presented here. These observations show the sunspots (a) to be regions of lower intensity than the surrounding plage, contrary to that found by previous authors, and (b) to have line intensities which vary little over a period of several hours. An upper limit to mass flows of 2km s^-1 is derived, indicating a relatively simple energy balance for the chromosphere-corona transition zone with thermal conduction being balanced by radiative losses. Electron densities derived from Niv to Civ line ratios imply electron pressures (log N _eT_e) of 15.0 to 15.3.     

Measurements of the ambient photoelectron spectrum from atmosphere explorer: II. AE-E measurements from 300 to 1000 km during solar minimum conditions

The ambient photoelectron spectrum above 300 km has been measured for a sample of 500 AE-E orbits during the period 13 December 1975 to 24 February 1976 corresponding to solar minimum conditions. The 24 h average and maximum ΣK_p were 19 and 35, respectively. The photoelectron flux above 300 km was found to have an intensity and energy spectrum characteristic of the 250–300 km production region only when there was a low plasma density at the satellite altitude. Data taken at local times up to 3 h after sunrise were of this type and the escaping flux was observed to extend to altitudes above 900 km with very little modification, as predicted by several theoretical calculations. The flux at high altitudes was found to be extremely variable throughout the rest of the day, probably as a result of attenuation and energy loss to thermal plasma along the path of the escaping photoelectrons. This attenuation was most pronounced where the photoelectrons passed through regions of high plasma density associated with the equatorial anomaly. At altitudes of 600 km, the photoelectron fluxes ranged from severely attenuated to essentially unaltered—depending on the specific conditions, Photoelectron fluxes from conjugate regions were often less attenuated than those observed arriving from the high density regions immediately below. Comparison of the observed attenuations, photoelectron line broadening, and energy loss due to coulomb scattering from the thermal plasma with rough calculations based on stopping power and transmission coefficients of thermal plasma for fast electrons yielded order of magnitude agreement—satisfactory in view of the large number of assumptions necessary for the calculations. Overall, the impression of the high altitude photoelectron flux which emerges from this work is that the fluxes are extremely variable as a consequence of interactions with the thermal plasma whose density is in turn affected by electrodynamic and neutral wind processes in the underlying F region.     

Apparent thermal inertia and the surface heterogeneity of Mars

Thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters. Consequently, surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season. To investigate these temporal variations, we processed three Mars years of Mars Global Surveyor Thermal Emission Spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia. These maps show broad regions with diurnal and seasonal differences up to 200 J m⁻² K⁻¹s^−1/2 at mid-latitudes (60° S to 60° N) and 600 J m⁻² K⁻¹s^−1/2 or greater in the polar regions. We compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5° resolution, delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials. The thermal behavior of most regions on Mars appears to be dominated by layering, with upper layers of higher thermal inertia (e.g., duricrusts or desert pavements over fines) prevailing in mid-latitudes and upper layers of lower thermal inertia (e.g., dust-covered rock, soils with an ice table at shallow depths) prevailing in polar regions. Less common are regions dominated by horizontal mixtures, such as those containing differing proportions of rocks, sand, dust, and duricrust or surfaces with divergent local slopes. Other regions show thermal behavior that is more complex and not well-represented by two-component surface models. These results have important implications for Mars surface geology, climate modeling, landing-site selection, and other endeavors that employ thermal inertia as a tool for characterizing surface properties.     

用日全食光谱探测太阳中低层大气对局部热动平衡的偏离

在太阳大气不同层次连续光谱中叠加有丰富的发射线或吸收线,对这些谱线轮廓进行反演分析可以探测太阳大气的化学成分和物理状态.太阳大气的色球及过渡区由于其密度低难以建立热动平衡,建立相应的大气模型需要采用非局部热动平衡(Non-Local Thermodynamic Equilibrium,N-LTE)理论.根据相对偏离因子计算来研究太阳中低层大气偏离局部热动平衡(Local Thermodynamic Equilibrium,LTE)分布的情况.首先对日全食观测过程中得到色球和过渡区不同高度形成的两条光谱数据进行反演,得到确定观测谱线的参数信息,如连续谱源函数、谱线源函数、多普勒宽度和由此推出的等效动力学温度;根据这些反演出的谱线参量计算出二维视场内每个空间采样点偏离LTE状态的定量结果;其次,根据用于观测的积分视场单元光纤排布阵列重构出辐射强度、等效动力学温度和相对偏离因子二维分布.结果显示:在局部小区域,温度分布和相对偏离因子的分布存在较强相关性,而与辐射强度分布无明显相关.从两条谱线导出的等效温度和相对偏离因子分布存在明显的差异.这两种二维分布揭示出太阳大气某些小尺度区域具有较强的结构性和复杂性,为进一步理解太阳中低层大气物理提供了一种新的视角.     

Studies of clump structure of photodissociation regions at millimeter and sub-millimeter wavelengths

To interpret the millimeter and sub-millimeter line emissions of atomic and molecular species from galactic and extragalactic photodissociation regions, warm gas components and molecular clouds, generally, escape probability formalism of Tielens & Hollenbach (herein referred as TH) are employed which is based on the assumption of plane parallel geometry of infinite slab allowing photons to escape only from the front. Contrary to the assumption observationally it is found that these lines are optically thin except OI(63μ m) and low rotational transitions of CO and some other molecules. This observational evidence led us to assume that emitting regions are finite parallel plane slab in which photons are allowed to escape from both the surfaces (back and front). Therefore, in the present study escape of radiations from both sides of the homogeneous and also clumpy PDR/molecular clouds are taken into consideration for calculating the line intensities at millimeter and sub-millimeter wavelengths (hereinafter referred as QA). Results are compared with that of the TH model. It is found that thermal and chemical structures of the regions are almost similar in both the formalisms. But line intensities are modified by differing factors. Particularly at low density and low kinetic temperature and also for optically thin lines line intensities calculated from TH and QA model differ substantially. But at density higher than the critical density and also for optically thick lines TH and QA models converge to almost same values. An attempt has been made to study the physical conditions of the M17 region employing the present formalism.     

磁极性反转线附近黑子半影纤维的形态

本文对８个活动区极性反转线（中性线）附近黑子半影纤维的形态进行了分析得出：１）具有强δ磁结构的活动区，穿过主要异极性黑子间的中性线近旁半影纤维或多或少地与中性线平行（交角小于３０°），有关黑子半影呈旋涡形态；２）由新浮现发展形成的δ结构区，异级黑子在大黑子边缘或与大．黑子本影之间有一段距离，中性线两边的半影纤维有序排列，走向与中性线斜交，有关黑子呈弱的旋涡形态。３）对于较稳定的极群，Ｎ、Ｓ极性间的宽窄不一的半影稀疏区，中性线沿该区经过，两旁半影松散齿状，走向与中性线大体垂直，相反极性本影间距较远。     

On the Nature of Neutral-Line-Associated Radio Sources

A number of authors claimed that radio sources above the neutral line of the magnetic field in solar active regions are due to non-thermal emission. This study shows that the thermal mechanism explains the radio emission from such sources. Models similar to those used for interpreting cyclotron lines were used in this study. Such models account for a steep decline in the spectrum at high frequencies and a low degree of polarization. The magnetic field between the two sunspots with an anti-parallel magnetic field has a lower gradient than the field above the sunspots. This, combined with the possibly high temperature in coronal loops connecting the sunspots, leads to the following conclusions. The optical thickness of the gyroresonance layers is increased and leads to more effective radiation at a harmonic number of 4 or 5. The lower gradient of the field between the sunspots also results in more rapid growth of emission intensity with increasing wavelength in this region than in the regions immediately above the sunspots. Additionally, the spatial averaging of the source structure due to the antenna beam pattern leads to a decrease in the degree of polarization in the region between the sunspots.     

Analysis of the intensities and profiles of the spectral line Mg xii 8.42 Å in the solar X-ray spectrum

High resolution profiles of the Mg xii 8.42 Å line in the solar X-ray spectrum were recorded from the Intercosmos 7 satellite. The Mg xii line intensity provides a sensitive indicator of the hot plasma content (T ? 3 × 10⁶ K) in coronal condensations and X-ray flare volumes. The ratio of the line intensity to the intensity of the adjacent continuum has been used to compute approximate thermal models of the emitting regions. For all the investigated coronal condensations the temperature distribution of plasma has been found to be a function monotonically decreasing with temperature. But for some X-ray bursts there occurred a distinct excess of the hot plasma of temperature between 6–10 × 10⁶K. FWHM values of the Mg xii line profiles have been used to estimate ion temperature in the emitting regions.     

Thermal migration of water on the Galilean satellites

We have modeled the thermal migration of water on the Galilean satellites under the assumption of ballistic molecular trajectories. We find that water migrating owing to solar radiation on an ice-covered satellite will build up in the temperate latitudes, in general not reaching the poles. As much as 50 m of ice may have been lost by this process from the equatorial regions of Europa over the age of the solar system. The disappearance of patches of ice—for instance, the bright rays surrounding some impact craters—from the equatorial regions of Ganymede and Callisto may approach a value (the irreversible evaporation rate) three orders of magnitude larger than the net equatorial loss rate for ice-covered Europa. The presence of water ice pole caps on Ganymede extending to the latitudes at which thermal migration becomes important suggests that some process distributed an extensive, thin covering of water on the satellite, and that the equatorial regions were subsequently cleared by the thermal process.     

Infrared photometric study of dust obscured galaxies

We have collected almost all published dust obscured galaxies (DOGs) with the certain coordinate in the literature (817 DOGs in total) to investigate their infrared properties by using 2MASS (and other observations in the JHK bands), WISE, IRAS and Herschel data in this paper. Our study shows that objects with different types have different presentations for the relations between the redshift and infrared colors. It is also found that in the near infrared two-color diagram, DOGs are distributed across the blackbody line and the power law line indicative of the thermal emission from the stellar component and the star formation for some objects, and the AGN dominated for other objects in the near infrared. However, in the two-color diagrams with longer wavelengths the majority of DOGs are distributed around the power law line indicative of the central AGN dominated in the mid-infrared, far infrared, and submillimeter regions. We also compared the infrared color propertes between DOGs and ULIRGs. It is found that, statistically, ULIRGs have redder colors than that for DOGs in the near and mid- infrared region while compared with DOGs, ULIRGs are more near the blackbody line indicative of the star formation dominated in far infrared.     

On the spectrum of granular and intergranular regions

A very high quality wiggly-line spectrogram was analyzed by making high-resolution spectral scans of numerous small solar features. An attempt from the line profiles to detect a magnetic field difference between the granular and intergranular regions, resulted in a field increase of 20 ± 15 G in the darker regions of the granular field. Line width increases apparently due to small-scale turbulent velocities are seen in the darker regions. It is postulated that in general darker regions show increased turbulent velocities. Conspicuous asymmetries in line profiles are seen in dark intergranular regions. It is suggested that these are the result of velocity gradients in the downward flow of material. An ionized Cr line showed a conspicuous increase in equivalent width in the darker regions of the granular field, thus indicating a decrease in electron pressure in these areas.     

New interstellar masers in nonmetastable ammonia

We report the astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high s 1090 K above the ground state. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km s-1) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containing compact H II regions and strong infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.     

Magnetic field and flares of the large sunspot group of April–May 1978

From magnetograms of the active region 15266 obtained at Yunnan observatory we found that 1) an inverted field configuration and a twisted neutral line are both closely correlated with high-energy flare eruptions. After the flares, the field configuration and the neutral line revert to more stable states. 2) Most of the flares of the present region occurred away from the neutral line; those near the line occurred either in regions of high field gradient or in the vicinity of Severny's “neutral points”.     

Thermal instability of coronal neutral sheets and the formation of quiescent prominences

It is argued that the quiscent prominences are a natural consequence of the formation and thermal instability of current sheets in the corona. Thus observation and theory of prominences can give vital information on the presence of currents and the topology of magnetic fields in the corona. Conversely by developing the theory of the structure and evolution of current sheets under coronal conditions we can attempt to gain a comprehensive understanding of the structure, evolution, and mass and energy balance of quiescent prominences. A stability analysis for coronal material permeated by a vertical magnetic field rooted in the photosphere, indicates that a condensation will take the form of a thin vertical wedge of cool matter. The development of a finite condensation is followed and it is shown that photospheric line tying is only important in the initial stages. A perturbation analysis of vertical motions at the neutral sheet shows that thermal instability can lead to overstable oscillations. Cooling of coronal material can lead to both upward and downward mass motions, and gravitational energy release is important to the thermal balance of prominences. Relevant optical and radio observations are discussed. Synoptic observations of the development of active regions and magnetic fields are needed to test the basic hypothesis of the formation of prominences from neutral sheets.     

A review of diagnostic emission line ratios in the Narrow Line Region of Active Galactic Nuclei

The availability of new observing facilities both from ground and space such as the Keck 10m telescope and the Hubble Space Telescope is casting new light on the spectroscopic investigation of emission line galaxies. In particular, it is now possible to detect spectra with a significantly improved signal to noise ratio in a very wide wavelength range, from the ultraviolet to the near infrared (HST, Keck) and beyond (ISO is unveiling the far infrared domain). As we move to high redshifts, however, it is more likely that the observed spectra are given by the contribution of different components in the galaxy: in particular, this may be the case if an Active Galactic Nucleus (AGN hereafter) emitting a power-law continuum is surrounded by regions with strong star formation activity. The identification of the source which ionizes the line emitting regions is then complicated by the fact that we are observing the integrated spectrum from regions which are ionized by different sources. In this paper we wish to review which line ratios may be used in order to discriminate between photoionization by young stars and power-law continuum in the wavelength range from 1200 Å to 100 μm. To this aim we used the photoionization code Cloudy (Ferland 1996) to present a series of diagnostic diagrams showing the dependence of emission line ratios on the main input parameters of photoionization models in the case of one component models with gaseous clouds ionized by (1) a stellar continuum typical of an HII region and (2) a power-law continuum typical of an AGN: these line ratios are plotted as isoratio maps for different values of the hydrogen density, ionization parameter and slope of the power-law continuum. We then show how the results may be affected by more realistic assumptions about the environment of the ionized gas: to this aim, we show the effects on selected line ratios of (a) the presence of two populations of clouds with different densities and (b) an AGN surrounded by regions with strong star formation activity.     

The Effect of Collisional Line Broadening on the Spectrum and Fluxes of Thermal Radiation in the Lower Atmosphere of Venus

The absorption spectrum and thermal radiation fluxes are calculated for the lower atmosphere of Venus in the far-wing approximation based on the theory of the collisional broadening of spectral lines. The results are in good agreement with the available experimental data. An outgoing thermal radiation flux is about 2.6 W/m² near the planetary surface. This indicates that free convection significantly contributes to the thermal balance of the lower troposphere. The fluxes obtained in this study were compared to those calculated on the basis of empirical models of the spectral line profile. It was shown that the far wings of the CO₂ lines considerably affect the radiative transfer in the transparency windows. This effect becomes weaker when the contribution of the absorption of minor constituents, primarily water vapor, increases. The profiles of absorption lines of minor constituents do not influence the thermal radiation fluxes.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 3, 2005, pp. 214–226.Original Russian Text Copyright © 2005 by Afanasenko, Rodin.     

A measurement of the helium D3 profile with a birefringent filter

The D₃ line profile in plages on the disk is measured using a birefringent filter. The best fit Gaussian has a 1/e width of 0.4 Å, with negligible instrumental contribution. The D₃ opacity is produced in regions with thermal linewidth -0.1 Å; the much larger observed width indicates large non-thermal motions in the chromosphere.     

Detection of Departure from Thermal Dynamic Equilibrium in the Solar Middle and Lower Atmosphere UsingTotal Solar Eclipse Data

There are abundant emission and absorption lines superimposed on the continuum spectra of the different solar atmospheric layers. The chemical composition and physical state of the solar atmosphere can be probed by the inversion of the profiles of these spectral lines. Due to the low density and large temperature difference in the chromosphere and transition region of the Sun, it is hard to establish the thermal dynamic equilibrium. It is necessary to adopt the theory of Non-Local Thermodynamic Equilibrium (N-LTE) to construct the corresponding atmospheric model. In this paper, the departure from the Local Thermodynamic Equilibrium (LTE) in the middle and lower atmosphere of the sun is investigated with the well-defined relative departure factor and the relevant calculations. We first make an inversion of the spectral lines formed at the different heights in the chromosphere and transition region during a total solar eclipse, to obtain the parameters of the observed spectral lines, such as the continuum source function, line source function, Doppler width, and thus the equivalent kinetic temperature. According to these line parameters obtained by the inversion, we calculate the quantitative results about the departure from the LTE at each space sampling point in the 2D field of view. Secondly, we reconstruct the 2D distributions of the radiation intensity, equivalent kinetic temperature, and relative departure factor according to the alignment of the optical fiber array in the integrated field unit (IFU) used by the telescope. The results show that there is a stronger correlation in the distributions of the temperature and relative departure factor existed in local small regions, but without evident correlation with the distribution of radiation intensity. There is an obvious difference between the distributions of the equivalent temperature and relative departure factor derived from two spectral lines, which shows a strong structurization and complexity existed in some local small regions of the solar atmosphere, and provides a new perspective for us to further understand the physics of the middle and lower atmosphere of the Sun.     

Study of the nature of He II nebular emission in the spectra of low-metallicity H II regions from the Sloan Digital Sky Survey

We studied a sample of galaxies from the Sloan Digital Sky Survey Data Release 7 that exhibited the He II λ 468.6 nm nebular line (an indicator of hard radiation in H II regions) in their spectra. The intensity of this line in the spectra of H II regions from our sample increased with decreasing metallicity, thus confirming the results of earlier studies. However, the theoretical models of population synthesis predict that the He II line intensity must decrease with decreasing metallicity. A possible connection between hard UV radiation and Wolf-Rayet stars was investigated. Only 30% of spectra from our sample exhibited both the nebular emission and the broad He II emission of Wolf-Rayet stars. This fact does not rule out the possibility that Wolf-Rayet stars serve as sources of hard ionizing radiation in some H II regions. However, other possible sources, such as the fast radiative shock waves, seem to be more likely to produce this hard ionizing radiation.