Magnetic field estimation in Cyg X-3's jet

Multi-wavelength photometric observations of Cygnus X-3 were carried out at 18 cm through to 450 μm, complemented by X-ray (2–10 keV) observations. The system was mildly active with cm fluxes at 150–250 mJy. We find the spectrum to be flat with a spectral index of zero. Using a modified Wolf-Rayet wind model, and assuming emission is generated in synchrotron emitting jets from the source, we find an upper-limit to the magnetic field of 20 G at a distance 5×10¹² cm is required.     

Latitudinal Distribution of Polar Faculae

The distribution of polar faculae with respect to latitude is investigated, using data obtained at the Ussuriysk Observatory during the years 1963–1994. To correct the data for the effect of visibility, a visibility function of polar faculae is derived. Corrected surface density of polar faculae is calculated as a function of latitude and time. During most part of each solar cycle, polar faculae exhibit pronounced concentrations at high latitudes with maxima of the surface density located near the poles. Such concentrations of polar faculae (below referred to as `polar condensations') are formed after a lapse of 1–2 years from the polar magnetic field reversals, and then they persist for 7–9 years, until the high-latitude magnetic fields again start to reverse. During several years after the sunspot minima, the polar condensations co-exist with the new latitudinal belts of polar faculae which appear at middle latitudes and then migrate toward the poles. To describe the evolution of the polar condensations quantitatively, the polar faculae density n at latitudes above 60° has been approximated by means of the power law nn ₀ cos^m where is polar angle. The parameters n ₀ and m both are found to vary during the course of the solar cycle, reaching maximum values near or shortly after the minimum of sunspot activity. At the minimum phase of the solar cycle, on average, the surface density of polar faculae varies as cos¹⁴. In addition to the 11-yr variation, the latitude–time distribution of polar faculae exhibits short-term variations occurring on the time scale of 2–3 years.     

Galaxy cluster Abell 98

The results of B and V photometry of 594 galaxies in the field of A98 cluster are presented. The plates were obtained with the 2.6m telescope of the Byurakan Astrophysical Observatory. The galaxy distribution, luminosity function, and color distribution constructed for A98 as a whole and A98S and A98N components show that the A98N component apparently is not an individual cluster as it was suggested earlier but only a condensation of galaxies in the cluster A98 similar to condensations in many other clusters.Published in Astrofizika, Vol. 37, No. 1, pp. 13–33, January–March, 1994.     

High energy gamma-ray emission from binaries

The current Cherenkov telescopes together with GLAST are opening up a new window into the physics at work close to black holes and rapidly rotating neutron stars with great breakthrough potential. Very high energy gamma-ray emission up to 10 TeV is now established in several binaries. The radiative output of gamma-ray binaries is in fact dominated by emission above 1–10 MeV. Most are likely powered by the rotational spindown of a young neutron star that generates a highly relativistic wind. The interaction of this pulsar wind with the companion’s stellar wind is responsible for the high energy gamma-ray emission. There are hints that microquasars, accretion-powered binaries emitting relativistic jets, also emit gamma-ray flares that may be linked to the accretion–ejection process. Studying high energy gamma-ray emission from binaries offers good prospects for the study of pulsar winds physics and may bring new insights into the link between accretion and ejection close to black holes.     

High resolution images of Cygnus X-1

The classic black hole candidate Cygnus X-1 exhibits many similarities to Galactic jet sources (micro-quasars) in soft gamma and hard X-ray rays. This has fuelled suspicions that radio jets also may be present in Cygnus X-1. The lack of radio flaring in Cygnus X-1 has been associated with the presence of continuous jets rather than multiple plasmon ejection however no evidence for this has been observed with the VLA, or with MERLIN. Recent VLBA observations at 15 GHz have detected extended emission and further multi frequency observations are required to confirm the presence of jets on a milliarcsecond level.     

The solar coronal mass ejection of 20–21 November, 1973

The coronal transient event of 20–21 November is unusual in that its appearance is distinctly non-loop-like; rather, the transient resembles a confined ray or fan-like volume. Studies of the distribution of the coronal material with time indicate that this is a mass ejection event, involving about 1 × 10¹⁵ g of material from the lower corona. Analysis of the polarization signal of the event suggests that the event is associated with chromospheric activity in a region near longitude E68. The observed properties (distributions in brightness and polarization) of the transient are compared with the properties of a well-studied event of typical loop-like appearance, but rotated to simulate an edge-on appearance; the differences suggest that the 20–21 November event is not such an edge-on, loop-like transient, but rather is most simply described as an axisymmetric-cylindrical or conical volume, the boundaries of which remain constant over the events' lifetime. On this basis, the variation of the transient spatial density with height and the variation of density with time can be specified rather more certainly than for previously-studied coronal mass ejection events. Densities are found to range from 3 × 10^–16 g cm^–3 at 2.1 R heliocentric height early in the event to 1 × 10^–18 g cm^–3 at 4.0 R late in the event. Typical temporal variations of the ejected material (at a given heliocentric height) are found to be on the order of 10^–18 g cm^–3 s^–1. The mass and momentum balance in the event have been estimated from the observed parameters, employing a multiparameter approach. We find that a model with modest mass flux typified by material speed u ₀ 50 km s^–1 and a near balance between the event's pressure gradient force and gravity — with possibly a small hydromagnetic wave contribution to the total pressure — is consistent with the observations. The kinetic energy of the event, determined from the motion of the center of mass of the ejected material, is only about 10²⁶ ergs, and thus is the smallest for any solar mass ejection studied to date.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The Role of Giant Molecular Clouds in the Evolution of the Oort Comet Cloud

We estimated the gravitational influence of giant molecular clouds passing near the Solar system on the orbital evolution of Oort cloud comets. We performed a comparative analysis of the accuracies of the following two methods of allowance for the perturbations from giant molecular clouds: the impulse approximation and numerical integration. The impulse approximation yields fairly accurate estimates of the change in the energy of Oort cloud comets and the probability of their ejection under the influence of a molecular cloud if the path of the Solar system does not cross its boundary and if the molecular cloud may be treated as a point perturbing mass. The comet survival probability in the Oort cloud depends significantly on the internal structure of the perturbing molecular cloud and the impact parameter of the encounter. The most massive injection of comets into the planetary region and their ejection from the Oort cloud take place if the Solar system passes through a giant molecular cloud composed of several high-mass condensations. In this case, most of the comets injected into the planetary region were initially comets of the inner Oort cloud (a 10^–4 AU) with high orbital eccentricities.     

Large-scale active coronal phenomena in Yohkoh SXT images

We have found several occurrences of slowly rising giant arches inYohkoh images. These are similar to the giant post-flare arches previously discovered by SMM instruments in the 80s. However, we see them now with 3–5 times better spatial resolution and can recognize well their loop-like structure. As a rule, these arches followeruptive flares with gradual soft X-ray bursts, and rise with speeds of 1.1–2.4 km s^–1 which keep constant for >5 to 24 hours, reaching altitudes up to 250 000 km above the solar limb. These arches differ from post-flare loop systems by their (much higher) altitudes, (much longer) lifetimes, and (constant) speed of growth. One event appears to be a rise of a transequatorial interconnecting loop.In the event of 21–22 February 1992 one can see both the loop system, rising with a gradually decreasing speed to an altitude of 120 000 km, and the arch, emerging from behind the loops and continuing to rise with a constant speed for many more hours up to 240 000 km above the solar limb. In the event of 2–3 November 1991 three subsequent rising large-scale coronal systems can be recognized: first a fast one with speed increasing with altitude and ceasing to be visible at about 300 000 km. This most probably shows the X-ray signature of a coronal mass ejection (CME). A second one, with gradually decreasing speed, might represent very high rising flare loops. A third one continues to rise slowly with a constant speed up to 230 000 km (and up to 285 000 km after the speed begins to decay), and this is the giant arch. This event, including an arch revival on November 4–5, is very similar to rising giant arches observed by the SMM on 6–7 November 1980. Other events of this kind were observed on 27–28 April 1992, 15 March 1993, and 4–6 November 1993, all seen above the solar limb, where it is much easier to identify them.The temperature in the brightest part of the arch of 2–3 November 1991 was increasing with its altitude, from 2 to 4 × 10⁶ K, which seems to be an effect of slower cooling at lower densities. Under an assumption of line-of-sight thickness of 50 000 km, the emission measure indicates densities from 1.1 × 10¹⁰ cm^–3 at an altitude of 150 000 km to 1.0 × 10⁹ cm^–3 at 245 000 km 11.5 hours later. It appears that the arch is composed of plasma of widely different temperatures, and that hot plasma rises faster than the cool component. Thus the whole arch expands upward, and its density gradient increases with time, which explains whyYohkoh images show only the lowest and coolest parts of the expanding structure. The whole arch may represent an energy in excess of 10³¹ erg, and more if conduction contributes to the arch cooling.We suggest that the rise of the arch is initiated by a CME which removes the magnetic field and plasma in the upper corona, and the coronal structures remaining below this cavity begin to expand into the vacuum left behind the CME. However, we are unable to explain why the speed of rise stays constant for so many hours.     

The pair of X-ray sources across NGC 4258: Its relation to intrinsic redshifts,ejection and quantization

The chance that the pair of X-ray sources observed across NGC 4258 is accidental can be calculated as 5×10^–6. The recent confirmation as quasars, and determination of the redshifts of the pair, atz=0.40 and 0.65 by E.M. Burbidge enables the final accidental probability of the configuration to be calculated as <4×10^–7. In addition there are a number of observations which indicate the central Seyfert galaxy is ejecting material from its active nucleus.The NGC 4258 association is compared to four other examples of close association of pairs of X-ray quasars with low redshift galaxies. It is concluded that in each of these five cases the chance of accidental association is less than one in a million. The ejection speed calculated from the redshift differences of the X-ray quasars is 0.12c. This agrees with the ejection velocity of 0.1c calculated in 1968 from radio quasars associated with low redshift peaks become narrower—simultaneously strengthening the ejection origin for quasars and the quantization property of their redshift     

Ultraviolet spectra of the Cygnus loop-depletion of the heavy elements

A comparison between the observed UV spectra and detailed consistent calculations of the Cygnus Loop is presented. The results demonstrate that the spectra can be explained by supposing that the Cygnus Loop (C.L.) moves into a fully ionized gas. The [O III]/H ratio is shown to be an indicator to the fraction of He⁺⁺ in the gas entering the shock.Further results are:(a) Observed shocks of higher velocity propagation move into regions of lower density; (b) the optical and UV spectra are emitted by very close and almost overlapping shocks (c) fast shocks (v240 km s^–1) propagation in the intercloud medium produce the X-ray emission, however, they can also produce faint H on impinging interstellar clouds.We find that carbon (C_I, C_II, C_III, and C_IV) depletion relative to other heavy elements is not more than a factor 3; whereas, we confirm that all heavy elements, relative to their solar abundance, are depleted by a factor 10. Heavy elemental depletion is likely to result formation of grains, sputtering and molecules in ISM.     

The large-scale structure of FR-II radio sources

The large-scale flow produced by classical and relativistic jets in a uniform external medium is explored using a combination of general arguments and numerical simulations. We find that in both cases, jets with finite initial opening angles are recollimated by the high pressure in the cocoon and that the outer flow becomes approximately self-similar at large times. However, if the opening angle is significantly less than 20°, then there is an intermediate stage during which the working surface propagates at a constant speed, which is of the same order as that in the jet. The behaviour of the relativistic and classical jets is very similar, except that the relativistic jets generate lighter cocoons. Application of the model to Cygnus A gives estimates of the source age and advance speed which agree very well with spectral ageing observations. Quantitative estimates and general arguments suggest that the regularly spaced knots in the Cygnus A jet can be interpreted as shocks associated with reconfinement of an initially free jet, knot 3 of the Cygnus A jet being identified with the reflection point of the reconfinement shock. However, the model predicts too large an initial opening angle for the Cygnus A jets. It is possible that this discrepancy is due to our imposition of axisymmetry which allows the numerical jets to become much better collimated after the reconfinement than they would be in the three-dimensional case. Further study is needed to test this idea.     

Structure and origin of the cygnus superbubble

This paper summarizes and analyzes the results of radio optical, infrared, and X-ray observations of a large sector of the sky in the constellation Cygnus (19^h20^m-22^h, =30–50°;l ^II=65–90°, |b ^II|10°). This region is associated with an extended X-ray source referred to as the Cygnus superbubble. About a quarter of the superbubble region is occupied by the extensively investigated multicomponent thermal radio source Cyg X. The region contains eight OB-associations which, when projected on the sky, duplicate the outline of the X-ray superbubble. These associations contains 110 stars of high luminosity (about 40 Wolf-Rayet and Of stars). The observations suggest that the X-ray superbubble is not a single object. Between 50 and 75% of its X-ray emission can be ascribed to discrete sources, the rest being probably due to regions of coronal gas about 100 pc in diameter, created by stellar winds and, possibly, supernova explosions in individual associations. The objects that produce the X-ray and optical radiation of the presumed superbubble are located at distances from 0.5 to 2.5 kpc from the Sun in the Carina-Cygnus spiral arm. The eastern portion of the region presumed superbubble contains the associations Cyg OB7 and Cyg OB4 and is generally less than 1 kpc distant, while the western portion contains the associations Cyg OB1, 2, 3, 8, and 9 and is 1 to 2 kpc distant.     

Correlations between environment and other properties of galaxies from the Sloan Digital Sky Survey at fixed color

From the volume-limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6), we construct three samples with g–r color bins , labeled S1–S3, to investigate how other properties of galaxies depend on environment at fixed color. For each sample, we measure the local three-dimensional galaxy density in a comoving sphere with radius equal to the distance to the 5th nearest galaxy for each galaxy, select about 5% galaxies and construct the two subsamples at both extremes of density. Our study suggests that the environmental dependence of luminosity is mainly due to the environmental dependence of galaxy color and the correlation between color and luminosity. In addition, we preferentially conclude that concentration index and morphologies are not strongly correlated with local density at fixed color, and that galaxy color is a galaxy property very predictive of the local environment. Because SDSS spectroscopy is incomplete for bright galaxies at very low redshifts, we also use a volume-limited Main galaxy sample with a lower redshift limit z = 0.05, which contains 94,954 galaxies at 0.05 < z < 0.089 with −22.40 < M_r < −20.16, and reach the same conclusions.Due to the bimodality of the u–r color distribution, we classify galaxies as ‘red’ and ‘blue’, respectively, and further subdivide the samples into star-forming galaxies and passive ones using Hα equivalent width, W₀(Hα). Results show that color and star formation activity of galaxies are galaxy properties very predictive of the local environment.     

Collisional excitation of interstellar molecules due to H2: Linear molecules CO,OCS, SiO,HCN and HC3N in1Σstate

Using a normalized perturbative, semi-classical approach, collision-induced rotational excitation rates of CO, OCS, SiO, HCN, HC₃N due to H₂ are computed. The calculated excitation rates for CO–H₂ and OCS–H₂ systems at 100 K are in good agreement with the results of close coupling approximation at low values ofJ, whereJ is the rotational quantum number. The rates are found to be very sensitive with respect to ortho and para states of H₂.     

Nir spectroscopy and molecular shocks in Herbig-Haro 1

Near Infrared spectroscopic observations (1.2–2.4µm) of two condensations (HH 1A & HH 1G) of Herbig-Haro object 1 are used to explore the nature of its molecular shocks and extinction. The H₂ emission lines display a more complex behaviour than that accounted for C or J type shock models. The extinction, determined from the ratio of [Fe II] 1.257 & 1.644µm, is higher than what is expected from optical [S II] measurements, and it may indicate real discrepancies between the optical and IR regions of the ISM extinction curve.     

Reconstruction of past decades sea level using thermosteric sea level, tide gauge, satellite altimetry and ocean reanalysis data

This study investigates past sea level reconstruction (over 1950–2003) based on tide gauge records and EOF spatial patterns from different 2-D fields. In a first step, we test the influence on the reconstructed signal of the 2-D fields temporal coverage. For that purpose we use global grids of thermosteric sea level data, available over 1950–2003. Different time spans (in the range 10–50 yr) for the EOF spatial patterns, and different geographical distributions for the 1-D thermosteric sea level time series (interpolated at specific locations from the 2-D grids), are successively used to reconstruct the 54-year long thermosteric sea level signal. In each case we compare the reconstructed trend map with the reference. The simulation indicates that the longer the time span covered by the spatial EOFs, the closer to the reference the reconstructed thermosteric sea level trends. In a second step, we apply the method to reconstructing 2-D sea level data over 1950–2003, combining sparse tide gauge records available since 1950, with EOF spatial patterns from different sources: (1) thermosteric sea level grids over 1955–2003, (2) sea level grids from Topex/Poseidon satellite altimetry over 1993–2003, and (3) dynamic height grids from the SODA reanalysis over 1958–2001. The reconstructed global mean sea level trend based on thermosteric EOFs (case 1) is significantly lower than the observed trend, while the interannual/decadal sea level fluctuations are well reproduced. Case 2 (Topex/Poseidon EOFs over 1993–2003) leads to a global mean sea level trend over the 54-year time interval very close to the observed trend. But the spatial trends of the reconstruction over 1950–2003 are significantly different from those obtained with thermosteric EOFs. Case 3 (SODA EOFs over 1958–2001) provides a reconstruction trend map over 1950–2003 that differs significantly from the previous two cases. We discuss possible causes for such differences. For the three cases, on the other hand, reconstructed spatial trends over 1993–2003 agree well with the regional sea level trends observed by Topex/Poseidon.     

The dynamics of the Orion Nebula

A model is constructed of a spherically symmetric self-gravitating condensation of neutral hydrogen immersed in anHii region. The structure of the condensation is represented by the isothermal gas sphere at a temperature of 100°K. Typical parameters of such a condensation compatible with the estimated ultra-violet radiation field in the central regions of the Orion Nebula are, mass 1M ; radius 10¹⁶ cm; mean density 10^–15 gm cm^–3. The condensations are not static configurations but evolve because of mass loss by ionization from their surfaces. Perhaps 5% become gravitationally unstable and collapse. The remainder act as sources of ionized gas which flows into the surrounding nebula.     

Solar wind velocity and normalized scintillation index from single-station IPS observations

The recently refurbished Ooty Radio Telescope in southern India was used in a two-month campaign of interplanetary scintillation (IPS) observations in collaboration with the Cambridge IPS array in England during April–May 1992. The unique feature of this campaign was that, for the first time, scintillation enhancements were predicted in real time by observing solar events on 7–8 May, 1992 and then detected at both Ooty and Cambridge. Also, for the first time, high spatial resolution ( 100 sources sr^–1) solar wind all-sky velocity maps were obtained at Ooty. Good consistency is found between the IPS observations from both observatories andin-situ shocks detected at Earth by IMP-8.Yohkoh soft X-ray images were used to infer the generation of a coronal mass ejection on 7 May, 1992.     

Brightness distribution of diffuse soft X-rays

The brightness distribution of diffuse soft X-rays in the pulse height range 0.15–0.3 keV (L-band) and 0.5–0.8 keV (M-band) are obtained over a quarter of the sky centered at the galactic anticenter with 1.5 m polypropylene window proportional counters on board a sounding rocket. In theL-band three enhanced regions are noticed on the map. They coincide with the northern and southern Hi holes and the inner part of the galactic radio Loop II.In the northern Hi hole theN _H dependence of theL-band flux and the hardness ratioM/L can be fitted with a local hot plasma model with the absorption by a low velocity neutral hydrogen gas (|V|<25 km s^–1) along the line of sight. The X-ray feature of Loop II is similar to that of Loop I. In the lowN _H region (<3×10²⁰ H atoms cm^–2) theM/L value is lower than 0.3, whereas it varies in the range 0.1–0.4 at low latitudes (|b|<30⁰). This fact seems to be interpreted in terms of a model that a number of hot plasma clouds contribute to X-ray emission.     

Ion-Sound Model of Microwave Spikes with Fast Shocks in the Reconnection Region

A new model for solar spike bursts is considered based on the interaction of Langmuir waves with ion-sound waves: l+st. Such a mechanism can operate in shock fronts, propagating from a magnetic reconnection region. New observations of microwave millisecond spikes are discussed. They have been observed in two events: 4 November 1997 between 05:52–06:10 UT and 28 November 1997 between 05:00–05:10 UT using the multichannel spectrograph in the range 2.6–3.8 GHz of Beijing AO. Yohkoh/SXT images in the AR and SOHO EIT images testify to a reconstruction of bright loops after the escape of a CME. A fast shock front might be manifested as a very bright line in T _e SXT maps (up to 20 MK) above dense structures in emission measure (EM) maps. Moreover one can see at the moment of spike emission (for the 28 November 1997 event) an additional maximum at the loop top on the HXR map in the AR as principal evidence of fast shock propagation. The model gives the ordinary mode of spike emission. Sometimes we observed a different polarization of microwave spikes that might be connected with the depolarization of the emission in the transverse magnetic field and rather in the vanishing magnetic field in the middle of the QT region. Duration and frequency band of isolated spikes are connected with parameters of fast particle beams and shock front. Millisecond microwave spikes are probably a unique manifestation of flare fast shocks in the radio emission.