Active solar radio regions at metric frequencies and the interplanetary sector structures

The possible relation between type I noise active regions and the polarity distribution of the interplanetary magnetic field is examined for the period from 13 March to 21 August, 1968 (Solar Rotation Numbers 1842–1847) by using data from ground-based and satellite observations. In general four type I radio regions appeared during each solar rotation period except for Rotation No. 1842. The number of type I regions is the same as the number of sector boundaries. This result suggests that the configuration of the photospheric magnetic field extending into the interplanetary space may be related to the origin of the type I radio regions. Statistically the passage of the sector boundaries is delayed by approximately 5 days after the central meridian passage of the type I noise regions on the solar disk.The position of the source of the sector boundaries and its relation to the type I radio regions are investigated by taking into account the mean bulk velocity of solar winds as observed by space probes. A model of the large-scale structure of type I radio regions and their relation to the sector structure of the magnetic field as observed in the interplanetary space is briefly discussed.NASA Research Associate at the University of Maryland.     

On the characteristics of the solar active regions responsible for the generation of type III radio bursts at hectometric frequencies in August 1968

The RAE (Radio Astronomy Explorer) satellite observed enormous numbers of type III radio bursts at hectometric wavelengths from 13 to 25 August in 1968. The drift rate of these bursts reached a maximum around the middle of 20 August. This means that the source responsible for these bursts gradually moved on the solar disk in association with the rotation of the sun. During this period, there were two large active sunspot groups, MacMath Nos. 9593 and 9597, which were located in the southern hemisphere and adjacent to each other. By examining the observational data on solar flares, type I noise storm activity and energetic electron flux increases, it is shown that the active region, MacMath No. 9597 is responsible for the generation of these type III radio bursts. The relation between type III bursts producing electron beams and type I noise activity is briefly discussed and a model of this active region is qualitatively described.NAS-NRC Associate with NASA.     

Solar active regions at 9 and 3.5 mm wavelengths under disturbed conditions

Some properties of solar active regions at 9 and 3.5 mm wavelengths under disturbed conditions are discussed. New regions develop or weak regions intensify at millimeter wavelengths as a result of flares at distant sites. The spectra of the peak flux density of moderately strong bursts observed at 9 mm show a sharp drop toward the shorter millimeter wavelengths. The weak bursts at 3.5 mm manifest mainly as heating phenomena.     

Parameters of oscillation generation regions in open star cluster models

We determine the masses and radii of central regions of open star cluster (OCL) models with small or zero entropy production and estimate the masses of oscillation generation regions in clustermodels based on the data of the phase-space coordinates of stars. The radii of such regions are close to the core radii of the OCL models. We develop a new method for estimating the total OCL masses based on the cluster core mass, the cluster and cluster core radii, and radial distribution of stars. This method yields estimates of dynamical masses of Pleiades, Praesepe, and M67, which agree well with the estimates of the total masses of the corresponding clusters based on proper motions and spectroscopic data for cluster stars.We construct the spectra and dispersion curves of the oscillations of the field of azimuthal velocities v _φ in OCL models. Weak, low-amplitude unstable oscillations of v _φ develop in cluster models near the cluster core boundary, and weak damped oscillations of v _φ often develop at frequencies close to the frequencies of more powerful oscillations, which may reduce the non-stationarity degree in OCL models. We determine the number and parameters of such oscillations near the cores boundaries of cluster models. Such oscillations points to the possible role that gradient instability near the core of cluster models plays in the decrease of the mass of the oscillation generation regions and production of entropy in the cores of OCL models with massive extended cores.     

The physical parameters and exciting stars of six Hii regions

The radio spectra of particular radio sources (mainly Hii regions) are plotted on the same graph for comparison. Various physical parameters of these objects are obtained from the radio data through a model. Predictions about the number and the nature of the exciting stars of six Hii regions are made. A comparison with the so far identified exciting stars is also presented.     

On the physical conditions in AGN optical jets

The energy budget of all known optical jets is discussed. It is found that to power the extended radio lobes of radio galaxies, the jet bulk motion on kpc scales must be relativistic, on average. Based on various constraints, a “most probable” region centered around Γ_bulk∼7.5 and θ∼20° is found. Because of the consequent relativistic beaming, the rest frame magnetic field is lower and electron lifetimes longer. Combining the effects of time dilation and lower emission rate, the electron diffusion length becomes fully consistent with the deprojected jet length, without the need for reacceleration.     

The physical conditions in the BHR71 outflows

Highly-collimated outflows are believed to be the earliest stage in outflow evolution, so their study is essential for understanding the processes driving outflows. The BHR71 Bok globule is known to harbour such a highly-collimated outflow, which is powered by a protostar belonging to a protobinary system. Using the APEX telescope on Chajnantor, we mapped the BHR71 highly-collimated outflow in CO(3-2), and observed several bright points of the outflow in the molecular transitions CO(4-3), CO(7-6), ¹³CO(3-2), C¹⁸O(3-2), CH₃OH(7-6) and H₂CO(4-3). We use an LVG code to characterise the temperature enhancements in these regions. These observations are particularly interesting for investigating the interaction of collimated outflows with the ambient molecular cloud. In our CO(3-2) map, the second outflow driven by IRS2, which is the second source of the binary system, is completely revealed and shown to be bipolar. We also measure temperature enhancements in the lobes. The CO and methanol LVG modelling points to temperatures between 30 and 50 K in the two lobes. The methanol emission in the southern lobe bright knot is barely resolved with the APEX single-dish. ALMA will thus be a central tool to study the shock chemistry in these regions.     

Observations and interpretation of solar flares at microwave frequencies

The physical processes responsible for microwave emission in solar flares are outlined, and examples of how microwave observations have been interpreted in terms of physical parameters are described. Selected results obtained during Solar Cycle 21 with the microwave observatories dedicated to synoptic observations of the Sun are summarized. The status and future plans for these facilities at Bern and in Japan are presented. Also discussed are the instrument capabilities required at microwave frequencies to achieve the objectives of a future facility for high-energy solar physics.     

On periodic orbits of the second generation and regions of stability

A part of the familyh of retrograde periodic orbits of the restricted problem (μ=0.5) is examined in relation to the families of periodic orbits of the second generation branching from it. Many such families are determined and the significance of the configuration of their characteristics for the determination of the boundary of the stability region around this part ofh is discussed.     

Global photometric observations and physical properties ofHii regions in the small magellanic cloud

Integrated photoelectric measurements of the equivalent widthW _H, the [Oiii]/H ratio and the H emission line flux were obtained for 30Hii regions in the SMC. Physical properties of theHii regions and their ionizing stellar associations were derived. Some aspects of the recent star formation in the SMC and the evolution ofHii regions are discussed.     

Mass-luminosity distribution and physical conditions of ionized gas in NGC 4575

Photographic photometry and spectroscopic observations of NGC 4575 suggest it to be a galaxy of reduced dimensionsD×d=14.4×13.5 kpc and of high luminosityM=–20.7. The rotation curve was also determined. Assuming a model of three homogeneous similar spheroids, we derived the density and mass distribution, and their total mass was found to be _T =2.33 × 10¹⁰.The mass luminosity ratio does not vary withinr=24, indicating that the stellar composition is similar within it, and the ratio _T / _T 1 suggests that this object contains a high proportion of young stars. From the emission lines it is found that the electronic density Ne100 cm^–3 is relatively low in the HII regions. The abundance ratiosN(N)/N(S) andN(N)/N(H) for the nucleus and two emission regions were also derived.     

On physical conditions in the chromosphere above sunspot umbrae

By means of an inversion of H and K Ca ii line profiles the temperature and electron density in the chromosphere above the umbrae of two sunspots have been estimated. The temperature gradient 5 K km^–1 exceeds the corresponding values in both quiet regions and plages. At a height of about 1500 km the umbra becomes hotter than the quiet region. At a temperature of about 10000 K the temperature gradient increases sharply. The electron density at 1500 km is approximately the same as that in the quiet chromosphere at the same height.     

Solar micro-bursts at 22.2 GHz and their relationship to events observed at lower frequencies

Observations of McMath region 10433 at 22 GHz using a telescope with a 4 beam during July 1974 revealed the existence events or microbursts with intensities below the sensitivity limit of normal solar patrol instruments. Many of these events were simply the high frequency counterpart of more intense bursts observed at lower frequencies. This note considers the small number of events which suggest that the gyro-synchrotron mechanism alone is incapable of explaining the observations and indicates that a thermal mechanism is needed to explain the high frequency event.On leave of absence from Department of Physics, University of Surrey, Guildford, U.K.     

Magnetic field versus gas density,in different physical conditions

A search is made here for possible variations in the behavior of magnetic field valuesB at various gas density valuesn, when comparing low density gas versus high density gas, and when comparing compressed gas versus quiescent gas.

1. For thequiescent microturbulent interstellar gas (e.g., clouds, interclumps — see TableI), the statistical relationB ~n ^k yieldsk = 0.46 ± 0.07 forhigh gas densityn > 100 cm^?3, andk = 0.17 ± 0.03 forlow gas densityn < 100 cm^?3 (see Figure 1).
2. For thecompressed macroturbulent interstellar gas (e.g., masers, expanding shells — see Table II), the statistical relationB ~n ^K yieldsK = 0.61 ± 0.09 forhigh gas densityn > 100 cm^?3, andK = 0.37 ± 0.2 forlow gas densityn < 100 cm^?3 (see Figure 2).
3. The separation betweenlow density gas andhigh density gas is statistically significant. The 2 different physical behaviors (below and above the break at 100 cm^?3) are confirmed statistically (about 2 to 4 sigma away for the quiescent gas alone; about 3 to 6 sigma away for the combined quiescent plus compressed gas).
4. The separation betweencompressed gas andquiescent gas is not statistically significant now (see Figure 3). Atn > 100 cm^?3, a comparison of quiescent gas versus compressed gas shows no statistically significant differences in behavior (they are only about 1 sigma away). Atn < 100 cm^?3, a comparison of quiescent versus compressed gas also shows no statistically significant differences in behavior (less than 1 sigma away).
5. A relation between the densityn and the galactic-wide Star Formation Rate (SFR) can be made for galactic magnetic fields, i.e.: (SFR) ~n ⁿ . For galactic-wide parameters using quiescent, low densityn < 100 cm^?3, and the known relationshipsB ~n ^k/j withk = 0.17,B ~ (SFR) ^j withj = 0.13, then one gets here a lawSFR ~n ^k/j with an exponentk/j = 1.3. This is in rough accord with known data for the Milky Way and for NGC6946.

     

The physical conditions in the shells of type I supernovae

Two models of the origin of the spectrum of type I supernovae are analysed: (I) the photosphere of the ‘central remnant’ and the expanding shell are separated by a density cavity; (II) the ‘photosphere’ (the layer which produces the continuous spectrum) is the inner part of the expanding shell. The arguments are given in favour of model I. Opacity of the shell close to light maximum for λ>4000 Å is mostly due to Thomson scattering; soon after light maximum (and it may be already at light maximum) the shell becomes completely transparent in this region of the spectrum. The problem of the origin of the very large width and of the relatively high central residual intensities of the absorption lines in the spectra of type I supernovae are analysed. A very noticeable dispersion in the velocities of the radial gas motions in the shell is the principal cause of the large equivalent width of the absorption lines in the spectra of these supernovae. The role played by the inhomogeneities in the shell is also discussed. The depth of the strong absorption lines produced by a very inhomogeneous shell may be equal to the filling factor of the medium. From the analysis of the spectra of supernova 1972e a lower limit for the mass of the shell is obtained (M>10³¹ g). Then from the fact of absence of a detectable H-absorption line and a simultaneous presence of strong Siii absorption lines (6347, 6371 Å) in the spectrum of supernova 1972e it follows that the ratio Si/H is at least two or three orders greater than that for the ‘normal’ stars.     

Long-Term and Medium-Term Variations of Solar Radio Emissions at Different frequencies

Plots of 12-month moving averages of the radio emission values for 1947–2002 indicated that the ratios (maximum/minimum) of the solar cycles 19–23 were low (∼ 1.2) in the upper chromosphere and lower corona (frequencies near 15 000 MHz), rose to maximum levels of ∼ 3.5 in the middle corona (frequencies ∼ 2000±500 MHz), and dropped thereafter to ∼ 2.5. In some cycles, there were two maxima separated by about 2 years. In cycles 20 and 23, mostly the second maximum was larger than the first maximum, but in cycles 21 and 22, some parameters showed the first maximum larger while others showed the second maximum larger. There was no systematic shift from first maximum to second maximum, with frequency or temperature (or altitude).     

Spikes in solar radio bursts at frequencies near 3 GHz

Many solar microwave bursts presenting fine structures were recorded at high temporal resolution (8 ms) by the 2.6–3.8 GHz spectrometer of National Astronomical Observatories of China (NAOC). Here we present data that were recorded on 15 April 1998. After data processing, more than one hundred spikes were detected in the interval 07:59:29.622–07:59:50.362 UT. Some of the spikes were single, while others were grouped in clusters. We report the observational characteristics including lifetime, frequency bandwidth, drift rate and polarization degree, as well as duration of spike clusters. Afterwards we discuss the difference between the lifetime of the spikes presented here (near 3 GHz) and those reported formerly at frequency up to 1 GHz, the probable source density and dimension, the brightness temperature and some other characteristics.     

Effect of oblateness and radiation pressure on angular frequencies at collinear points

In the three-dimensional restricted three-body problem, by considering the more massive primary as an oblate spheroid with its equatorial plane coincident with the plane of motion as well as source of radiation, it is found that the collinear point L ₁ comes nearer to the primaries with the increase in oblateness and radiation pressure, while L ₂ and L ₃ move away from the more massive primary with the increase in oblateness and come nearer to it with the increase in radiation pressure. It is noted that the angular frequency s ₁ at L ₁ increases with oblateness as well as with radiation pressure. s ₂ increases with oblateness and decreases with radiation pressure and s ₃ decreases with oblateness and increases with radiation pressure. A study on the norms of the characteristic roots λ and s at L ₁, L ₂ and L ₃ is carried out. It is established that for certain oblateness and radiation pressure parameters there is a one-to-one commensurability at the collinear points L ₂, L ₃ between the planar angular frequencies (s _2,3) and the corresponding angular frequency (s _z ) in the z-direction, and that at L ₁ no such commensurability exists. At L ₂ and L ₃, the value of oblateness parameter providing the commensurability decreases with the increase in the radiation pressure. However, the commensurable angular frequencies and eccentricity of the periodic orbits decrease at L ₂ and increase at L ₃, with the increase in the radiation pressure.     

Molecule searches in Comet Kohoutek (1973f) at microwave frequencies

Nine transitions of the possible parent molecules H₂O, NH₃, CH₃OH and N₂O as well as the OH radical were searched for in Comet Kohoutek (1973f) in the frequency range 22.2–25.2 GHz. These molecules were not detected, but the upper limits for the optical depth, mean column density and the production rate are derived for each of the molecules. These results are discussed and compared with the reported detections of HCN and CH₃CN emission and OH absorption.