A study of the He λ 10830 line emission from quiescent prominences

Observations of the He 10830 line emission in a number of quiescent prominences are presented. The line shapes are analyzed to obtain values for the Doppler widths and optical thicknesses, leading to a determination of the 2³ P – 2³ S excitation temperature of 4020 K. The results are compared with those of previous observational and theoretical research.     

Numerical simulations of the K-corona and of the λ 5303 emission line corona

More and more observations tend to prove that the lower corona is very heterogeneous and that the active regions are quite exclusively arch-structured. So, we have attempted to see what would be the result of simulations of a corona structured only with arches. In a previous work we had made the computations for both the K-corona and the 5303 emission line corona, for which we have much observational data. The complexity of computations has led us to make the comparisons with observations for the vertical intensity gradients only. A priori, it seemed impossible to obtain a simulation close to reality with a corona structured only with arches, at least as we have defined them in this paper, the important fact being a conspicuous lack of matter beyond a certain height. We have made new simulations with a different electron density distribution and for a different region. These latter calculations show us that the material can be confined in the feet of very high arches or in open structures as has already been suggested.     

Detection of langmuir solitons: implications for type III burst emission mechanisms at 2ω PE

We present the experimental verification of existing theoretical models of emission mechanisms of solar type III bursts at the second harmonic of the plasma frequency, _pe . This study is based on the detection of Langmuir and envelope solitons by the Ulysses spacecraft inside three type III burst source regions. We show that the oscillating-two-stream instability, coherent radiation by Langmuir solitons and stochastic phase mixing of the Langmuir waves in the strong turbulence regime are the appropriate emission mechanisms at 2 _pe .     

Photoelectric measurement of the coronal emission line λ 5303 by an automatic coronal photometer

A 5303 Å-photometer was constructed for the 20 cm coronagraph of the Wendelstein solar observatory. Details of the photometer, the method of measurement and an example for measured isophotes are given. The Wendelstein photometer is compared with the 5303 Å-Sac Peak photometer.Mitteilungen der Sternwarte München Bd. 2 Nr. 5.     

Precise positions of selected minor planets from the observations of 1991–1993

We present two catalogues of positions of selected asteroids in the system of the Tycho Reference Catalogue from the photographic observations carried out on Mt. Maidanak with the AFR-1 wide-field astrograph (D = 230 mm, F = 2300 mm) and in Zvenigorod with the Zeiss wide-field astrograph (D = 400 mm, F = 2000 mm) in 1991–1993. The catalogue obtained on Maidanak contains 109 positions of selected asteroids; the one obtained in Zvenigorod contains 177 asteroid positions. The two catalogues are compared to show that they are uniform. The one-position mean square errors in the Maidanak and Zvenigorod catalogues are calculated: 0.306″, 0.153″ and 0.370″, 0.219″.     

Survey of hα emission from thirty nearby dwarf galaxies

Measurements of the Hα flux from 30 neighboring dwarf galaxies are presented. After correction for absorption, these fluxes are used to estimate the star formation rate (SFR). The SFR for 18 of the galaxies according to the Hα emission are compared with estimates of the SFR from FUV magnitudes obtained with the GALEX telescope. These are in good agreement over the range log[SFR] = [ −3, 0] M_⨀ /year.     

High-resolution observations of Hα emission line from R Aquarii

We have obtained H emission line profiles from R Aquarii, a Mira variable surrounded by a complex nebulosity, using a very high-resolution Fabry-Pérot spectrometer. A new feature that was seen in our observations is the fact that the line profile shows a splitting which we interpret as due to two expanding shells surrounding the star with velocities of 5 km s^–1 and 15 km s^–1. The expansion velocities show an acceleration outwards due perhaps to the radiation pressure caused momentum transfer. Possible periodic variation of radial velocity derived from observations is discussed.     

Enhanced emission of Alfvén waves from sunspots during proton flares

Thomas (1978) has shown that, if Alfvén waves exist in a sunspot umbra, they are normally reflected so strongly by the temperature minimum as to be essentially undetectable in the upper solar atmosphere. However, it is known that in many proton flares, chromospheric emission overlies the umbra of a sunspot, indicating that the transition region (TR) between chromosphere and corona in the umbral flux tube has moved down to lower altitudes. As a result of this lowering, umbral Alfvén waves have readier access to the corona: the coronal leakage depends exponentially on the altitude of the TR. We find that the Alfvén wave flux which leaks out of the umbra into the corona can exceed 10⁷ ergs cm^-2 s^-1. A flux of this magnitude is expected to dissipate rapidly in the corona, thereby contributing to a positive feedback loop which ensures prolonged (1 hr) leakage of the umbral Alfvén waves into the corona. We propose that these Alfvén waves may contribute significantly to prolonged energization of proton flares in which umbral coverage occurs.     

Interpretation of OGO-5 line shape measurements of Lyman-α emission from terrestrial exospheric hydrogen

The velocity distribution of hydrogen atoms in the terrestrial exosphere was measured as a function of radial distance (up to 7 Earth radii, E_R) with the help of a Lyman-α hydrogen absorption cell, flown in 1968 on board the OGO-5 satellite. This paper contains the final analysis of the measurements. As a basis of comparison, the theory for the calculation of projected velocity distribution along a line of sight is established for the theoretical exospheric model of Chamberlain (1963). Self-absorption of Lyman-α photons along a line of sight is included to derive Lyman-α line profiles emerging from the geocorona. The effect of the hydrogen absorption cell, measured by the reduction factor R(p) is predicted as a function of impact parameter p of the line of sight, for various values of the parameters of a Chamberlain's model, n_c (density of exobase level), T_c (temperature at the exobase level), and r_cs (satellite critical radius). This predicted reduction factor R(p) is compared to the measured R_m(p), with the following findings: the Ly-α line width decreases with radial distance, as expected from the “evaporation and escape” theory of Chamberlain; the measured temperature T_c = 1080 K is in very good agreement with the exospheric temperature prediction from satellite drag data. An upper limit of 8 × 10⁴at. cm^?3 is imposed on n_c, regardless of photometric absolute calibration. A good fit to data requires the presence of atoms in satellite orbits, distributed in a different fashion than that described by the concept of satellite critical radius. Lyman-alpha radiation pressure is thought to be the cause of this departure from the exospheric theory of Chamberlain (1963), otherwise perfectly confirmed.The same scientific rationale will be applied to exospheric hydrogen of the planets Mars and Venus in subsequent papers.     

Analysis of the X-ray emission from OB stars Ⅲ: low-resolution spectra of OB stars

This paper is the third in our series of papers devoted to the investigation of X-ray emission from OB stars.In our two previous papers,we study the high-resolution X-ray spectra of 32 O stars and 25 B stars to investigate the correlations between the properties of X-ray emission and stellar parameters.We checked if the X-ray hardness and post-shock plasma temperature grow with increasing stellar magnetic field,mass loss rate and terminal wind velocity.Our previous analysis of high-resolution spectra showed that the correlations are weak or even absent.In the present paper,we analyzed low-resolution X-ray spectra,using model-independent X-ray hardness values for checking the above mentioned dependencies.We establish that X-ray luminosities L_X weakly depend on the stellar magnetic field.At the same time,Lx ∝ M~(0.5) and L_X ∝ E_(kin)~(0.5),where M is the mass loss rate and E_(kin) is the kinetic energy of the wind.The X-ray luminosities decrease with growing magnetic confinement parameter η.We also argue that there is an additional(probably non-thermal) component contributed to the stellar X-ray emission.     

Analysis of thermal emission from the nightside of Venus at 1.51 and 1.55 μm

We present radiative transfer modelling of thermal emission from the nightside of Venus in two ‘spectral window’ regions at 1.51 and 1.55 μm. The first discovery of these windows, reported by Erard et al. [Erard, S., Drossart, P., Piccioni, G., 2009. J. Geophys. Res. Planets 114, doi:10.1029/2008JE003116. E00B27], was achieved using a principal component analysis of data from the VIRTIS instrument on Venus Express. These windows are spectrally narrow, with a full-width at half-maximum of ∼20 nm, and less bright than the well-known 1.7 and 2.3 μm spectral windows by two orders of magnitude.In this note we present the first radiative transfer analysis of these windows. We conclude that the radiation in these windows originates at an altitude of 20-35 km. As is the case for the other infrared window regions, the brightness of the windows is affected primarily by the optical depth of the overlying clouds; in addition, the 1.51 μm radiance shows a very weak sensitivity to water vapour abundance.     

Detection of the spectroscopic binary (SB2) nature of BD-6°1178 = IRAS 05238-0626

The star BD-6°1178, which is identified with the IRAS 05238-0626 source, is shown for the first time to be a spectroscopic binary (SB2) by analyzing the high-resolution spectra taken with the NES echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The components of the binary have close spectral types and luminosity classes: F5 IV–III and F3V. The heliocentric radial velocities are measured for both components at four time moments in 2004–2005. The two stars have close rotation velocities, which are equal to 24 and 19 km/s. We do not confirm the classification of BD-6°1178 as a supergiant in the state of becoming a planetary nebula. BD-6°1178 probably is a young pre-MS stars. It is possibly a member of the 1c subgroup of the OriOB1 association.     

Is the GeV-TeV emission of PKS 0447-439 from the proton synchrotron radiation?

We study the multi-wavelength emission features of PKS 0447-439 in the frame of the one-zone homogeneous lepto-hadronic model. In this model, we assumed that the steady power-laws with exponential cut-offs distributions of protons and electrons are injected into the source. The non-linear time-dependent kinematic equations, describing the evolution of protons, electrons and photons, are defined; these equations self-consistently involve synchrotron radiation of protons, photon-photon interaction, synchrotron radiation of electron/positron pairs, inverse Compton scattering and synchrotron self-absorption. The model is applied to reproduce the multi-wavelength spectrum of PKS 0447-439. Our results indicate that the spectral energy distribution (SED) of PKS 0447-439 can be reproduced well by the model. In particular, the GeV-TeV emission is produced by the synchrotron radiation of relativistic protons. The physically plausible solutions require the magnetic strength \(10~\text{G}\lesssim B \lesssim 100~\text{G}\). We found that the observed spectrum of PKS 0447-439 can be reproduced well by the model whether \(z = 0.16\) or \(z = 0.2\), and the acceptable upper limit of redshift is \(z=0.343\).     

A survey of 10-μm silicate emission from dust around young sun-like stars

We obtained low resolution (R=100) mid-infrared (8–13 μm wavelengths) spectra of 8 nearby young main sequence stars with the Keck 1 telescope and Long-Wavelength Spectrometer (LWS) to search for 10 μm silicate (Si–O stretch) emission from circumstellar dust. No stars exhibited readily apparent emission: Spectra were then analyzed by least-squares fitting of a template based on a spectrum of Comet Hale-Bopp. Using this technique, we were able to constrain the level of silicate emission to a threshold 10 times below what was previously possible from space. We found one star, HD 17925, with a spectrum statistically different from its calibrator and consistent with a silicate emission peak of 7% of the photosphere at a wavelength of 10 μm. Excess emission at 60 μm from this star has already been reported.     

CH3CN J = 8 − 7 and CS J = 3 − 2 emission in orion KL

The data of the line series CH₃CN 8(K) – 7(K) K = 0 – 7 and line CS J = 3 – 2 were taken simultaneously. At beam size of 16 the emissions of CH₃CN and CS have a common center position located near IRc2 with deviations -8 and 5. The observed data show that in Orion KL core the integrated intensities of the two species have double peaks separated by a space of 14. The 2-dimension Gaussian fitting plots (FWHM) are ellipses ofD _maj = 26 andD _min = 22 for CH₃CN 8(K) – 7(K) K = 3 – 6 andD_maj = 39 D_min = 31 for CS J = 3 – 2 at a distance about 450 pc. Towards the multiple line emission region of CH₃CN 8(K) – 7(K) K = 3 – 6, using a simplified very large velocity gradient model to solve the statistical equilibrium and radiative transfer equations, we find to fit the observed results, the optimum physical parameters and kinetic temperatureT _k 120 K, densityn(H _a) 1.2 × 10⁵ cm^–3, velocity gradientV _gr 92 km s^–1 pc^–1 and the local abundance of CH₃CNF _ab 3 × 10^–8. However towards the region of single line emission of CS J = 3 – 2 we have to use LTE and the optical thin approximation on the assumption ofT _k= 120 K to obtain the lower limits of column density and then, an averaged abundance of CS of 6 × 10^–8.     

Thermal emission spectroscopy (5.2-38 μm) of three Trojan asteroids with the Spitzer Space Telescope: Detection of fine-grained silicates

We present thermal emission spectra (5.2-38 μm) of the Trojan asteroids 624 Hektor, 911 Agamemnon, and 1172 Aneas. The observations used the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. Emissivity spectra are created by dividing the measured Spectral Energy Distribution (SED) by a model of the thermal continuum. We employ the Standard Thermal Model (STM), allowing physical parameters (e.g., radius and albedo) to vary in order to find the best thermal continuum fit to the SED. The best-fit effective radius (R) and visible geometric albedo (pv) for Hektor (R=110.0±7.3, ) and Aneas (R=69.1±5.1, ) agree very well with previous estimates, and for Agamemnon (R=71.5±5.2, ) we find slightly a smaller size and higher albedo than previously derived. Other thermal models (e.g., thermophysical) result in estimates of R and pv that vary a few percent from the STM, but the resulting emissivity spectra are identical. The emissivity spectra of all three asteroids display an emissivity plateau near 10-μm and another broader rise from ∼18 to 28 μm. We interpret these as indications of fine-grained silicates on the surfaces of these asteroids. The emissivity spectra more closely resemble emission spectra from cometary comae than those from solid surfaces and measured in the laboratory for powdered meteorites and regolith analogs. We hypothesize that the coma-like emission from the solid surfaces of trojans may be due to small silicate grains being imbedded in a relatively transparent matrix, or to a very under-dense (fairy-castle) surface structure. These hypotheses need to be tested by further laboratory and theoretical scattering work as well as continued thermal emission observations of asteroids.