The quantitative properties of three soft X-ray flare kernels observed with the AS&E X-ray telescope on Skylab

The physical parameters for the kernels of three solar X-ray flare events have been deduced using photographic data from the S-054 X-ray telescope on Skylab as the primary data source and 1–8 and 8–20 Å fluxes from Solrad 9 as the secondary data source. The kernels had diameters of 5–7 and in two cases electron densities at least as high as 3 × 10¹¹ cm^–3. The lifetimes of the kernels were 5–10 min. The presence of thermal conduction during the decay phases is used to argue: (1) that kernels are entire, not small portions of, coronal loop structures, and (2) that flare heating must continue during the decay phase.We suggest a simple geometric model to explain the role of kernels in flares in which kernels are identified with emerging flux regions. The flare is triggered at the neutral sheet between the EFR and a larger loop structure. We associate the X-ray kernels with H kernels, which previously associated (incorrectly, we believe) with the nonthermal impulsive phases of flares.Most of this work was completed while the author was a Visiting Scientist at the Center for Astrophysics, Cambridge, Massachusetts 02138.     

Long transequatorial interconnecting loops of the new solar cycle

We study two long transequatorial loops connecting high-latitude regions of the new solar cycle. These loops (with lengths of 47 and 61 heliographic degrees) provide evidence that the upper length limit of 37° found by Chase et al. (1976) from Skylab data was determined simply by the typical distances between northern and southern active regions during the period of Skylab observations. We find strong support for the idea that these long interconnecting loops originate through reconnection of field lines extending from the two active regions towards and beyond the equator, and confirm the earlier finding by Canfield, Pevtsov, and McClymont (1996) that only field lines from active regions with the same chirality reconnect. As we are not aware of any longitudinal (E–W) loops of comparable lengths, we suggest that it is mainly the solar differential rotation which drives the reconnection of latitudinal (N–S) field lines.     

Planets in 47 Tuc

We consider the survivability of planetary systems in the globular cluster 47 Tucanae. We compute the cross-sections for the breakup of planetary systems via encounters with single stars and binaries. We also compute the cross-sections to leave planets on eccentric orbits. We find that wider planetary systems ( d ≳0.3 au) are likely to be broken up in the central regions of 47 Tucanae (within the half-mass radius of the cluster). However, tighter systems and those in less-dense regions may survive. Tight systems will certainly survive in less-dense clusters where subsequent surveys should be conducted.     

The Green Corona Index and Soft X-Ray Flux

We present the behaviour of the coronal index (CI) of solar activity over the period 1986–(May) 1996. These data are not only a good tool for studying the activity of the Sun as a star, but they also represent an invaluable source of information in our quest to understand the properties of the heliosphere as a whole. Having compared the variations of CI and of the solar 0.05–0.8 nm soft X-ray flux over the period 1986–1995 we did not find any significant correlation between the two quantities. This favours a scenario in which the sources of the soft X-ray flux are small-scale regions of the corona, and processes of both ionization and recombination do not occur in the same volume of the solar corona as for the green corona.     

Surface photometry of simpleHii regions

We have carried out surface photometry of six simpleHii regions which are characterized by the existence of an exciting star earlier than B0, and a nearly round shape. On the basis of on balibrated image data and adopting a spherical model, we derive the distributions of gas and dust densities in theHii regions.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.On leave from the Bosscha Observatory, Institute of Technology Bandung, Indonesia.     

Solar energetic particle events at the rise phase of the 23rd solar activity cycle registered aboard the spacecraft &;#x201C;INTERBALL-2&;#x201D;

The experiment with 10K-80 aboard the INTER-BALL-2 (which detects protons with energies > 7, 27–41, 41–58, 58–88, 88–180 and 180–300 MeV) registered six events of the solar energetic particle (SEP) increase. These events are during the initial rise phase of the 23rd solar activity cycle. Solar flares with the SEP generation are accompanied by coronal mass ejection (CME). Here we analyze the dynamics of the differential energy spectrum at different phases of the SEP increase.     

The metallicity of galactic populations and the history of star formation

The metal abundance distribution (the metallicity function, MF) of stars and globular clusters is studied. It is found to have three gaps, near [Fe/H]=–1.0, –0.5 and –0.1. The gaps are shown to be statistically significant practically at the 100% confidence level. They divide the galactic population into four metallicity groups with the average [Fe/H] of about –1.5, –0.8, –0.25 and +0.10 (groups I, II, III and IV, respectively). The main contribution into the scatter of metallicity within the groups (apart from group I) comes from random errors in abundance measurements. So we infer that the actual MF must be essentially discrete. These results substantiate the ones obtained in our previous Papers I–IV; they support our idea on active phases in the evolution of the Galaxy, which imply the intermittent enrichment and star formation.We find that the kinematics and metallicity of groups III and IV of F and G dwarfs show a paradox: the metal-rich group (group IV) of G dwarfs turns out to be kinematically older than the group III of F dwarfs with half the metal abundance. The implication of this result for star formation is discussed. Also we show that the portion of metal poor disk population F dwarfs (group III) is the same or even larger than that of G dwarfs. This fact disagrees with the conventional idea that the young kinematics of F dwarfs owes to the absence of old F dwarfs, which are supposed to be evolved into red giants.     

S-Component Sources at 21 cm Wavelength in the Rising Phase of Cycle 23

The Synthesis Radio Telescope at the Dominion Radio Astrophysical Observatory is being used to make a long-term study of the relationship between sources of the slowly-varying component at 21-cm wavelength and the active regions with which they are associated. Although the arc-minute angular resolution of the radio telescope is insufficient to map individual active regions, the unique capability of this radio telescope to map the whole solar disc in a single operation makes it useful for identifying and measuring sources of the slowly-varying component, which at this wavelength are largely due to free–free thermal emission from plasma concentrations trapped in active region magnetic fields. The brightness temperatures of the emission are higher in large, complex active regions, suggesting the plasma slab producing the emission is thicker and/or denser in such regions. We find also that the relationship between the brightness temperature and the size and complexity of the host region is a function of the phase of the 10–13-year solar activity cycle.     

Spectrophotometric Variability of Mira

Data from the Pulkovo spectrophotometric data base on the absolute quasimonochromatic fluxes from oCet in the 320–1080 nm range are used to determine the physical parameters of this star in different phases of its light curve. The continuum emission layer is found to expand between the phases of the cycle corresponding to the rising and falling branches of the light curve. The average expansion velocity is 32 km/s. By the time the star’s brightness has fallen by roughly three magnitudes, its radius has increased by almost a factor of three. Over this same time the temperature of the layer has fallen from 3000 K to 2200 K. For this expansion velocity, the calculated mass rate loss is ⊙ M /year.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 175–189 (May 2005).     

Tracing the Electron Density from the Corona to 1 au

We derive the electron density distribution in the ecliptic plane, from the corona to 1 AU, using observations from 13.8 MHz to a few kHz by the radio experiment WAVES aboard the spacecraft Wind. We concentrate on type III bursts whose trajectories intersect the spacecraft, as determined by the presence of burst-associated Langmuir waves, or by energetic electrons observed by the 3-D Plasma experiment. For these bursts we are able to determine the mode of emission, fundamental or harmonic, the electron density at 1 AU, the distance of emission regions along the spiral, and the time spent by the beams as they proceed from the low corona to 1 AU. For all of the bursts considered, the emission mode at burst onset was the fundamental; by contrast, in deriving many previous models, harmonic emission was assumed.By measuring the onset time of the burst at each frequency we are able to derive an electron density model all along the trajectory of the burst. Our density model, after normalizing the density at 1 AU to be ne(215 R0)=7.2 cm–3 (the average value at the minimum of solar activity when our measurements were made), is ne=3.3×105 r–2+4.1×106 r–4+8.0×107 r–6 cm–3, with r in units of R0. For other densities at 1 AU our result implies that the coefficients in the equation need to be multiplied by n _e (1 AU)/7.2.We compare this with existing models and those derived from direct, in-situ measurements (normalized to the same density at 1 AU) and find that it agrees very well with in-situ measurements and poorly with radio models based on apparent source positions or assumptions of the emission mode. One implication of our results is that isolated type III bursts do not usually propagate in dense regions of the corona and solar wind, as it is still sometimes assumed.     

Fine structure superimposed on millimeter-wavelength (23–18 GHz) spectra of solar active regions

A millimeter-wavelength (23–18 GHz) variable frequency radiometer with frequency resolution of 1 GHz and time resolution of 0.1–16 s has been developed in conjunction with a 13.7 m-diameter antenna. In this paper we describe briefly this new instrument, and its use to observe active regions.Spectra of four active regions show that: (i) spectra of the quiet-Sun region and those of the active region were of the same nature and the spectral index of both varied between –0.4 and +0.3; (ii) for two cases the spectra of the active region remained almost flat during the observing period of about one hour; (iii) spectra of the two other active regions exhibited frequency fine structures similar to the trough and crest type with a width of the order of 2 GHz in frequency and lasting about 40 to 90 min.The spectra of the quiet-Sun region and those of the active regions are attributed to bremsstrahlung emission. Fine structures in frequency type crest and trough are attributed to the radio signatures of the temperature plateau in the chromosphere.     

A new investigation on neutralino dark matter: relic density and detection rates

The main properties of the neutralino dark matter are revisited in the light of the new theoretical developments in Susy theories and of the recent constraints from accelerators and underground experiments. The neutralino relic abundance and the detection rates relevant for direct and indirect searches are evaluated in the minimal supersymmetric standard model (MSSM) with the full inclusion of the (one-loop) radiative corrections, both to the Higgs masses and to the trilinear Higgs self-coupling. The relevance of these corrections for the neutralino-neutralino annihilation cross-section, and thus for the relic density, is discussed in detail. Large regions of the parameter space are considered, including those where the neutralino only provides a fraction of the local dark matter density; in these domains the standard value for the local density is appropriately scaled down. Some general properties of the detection rates as functions of the MSSM parameters are also elucidated; in particular it is shown that in the regions of the parameter space where scaling of the local density occurs, the rates are largely independent of two of the model free parameters. The relevance of the Kamiokande upper bounds to the upgoing muon fluxes is discussed in connection with the possible neutrino outputs from the Earth and from the Sun due to neutralino accumulation and annihilation in these macroscopic bodies. Finally, the complementarity between the search for neutralino dark matter and the discovery potential of future accelerators is discussed.     

The Medusae Fossae-Elysium region,Mars: geologic characteristics of the depression of epithermal-neutron flux based on HEND measurements onboard the Mars Odyssey spacecraft

We studied the geological structure and characteristics of fluxes of fast and epithermal neutrons from the area of Mars within 50°S–50° N and 120°–240° W, the Medusae Fossae-Elysium region. The study area does not show any anomalies in the energy spectrum of fast neutrons, indicating that a thin (10–20 cm) subsurface layer in the equatorial region is characterized by quite a uniform distribution of hydrogen-containing phases. At the same time, the studied region is characterized by a distinct depression in the epithermal-neutron flux, which is outlined by a 0.150–0.170 counts/s contour line and does not show any seasonal changes in its shape, depth, and latitudinal position. This suggests that the depression is not associated with the short-term (seasonal) variations of the temperature regime and that it represents an aggregation of hydrogen-containing phases with longer lifetimes. The position of the epithermal-neutron-flux depression does not correlate with regional geology, and none of the geological units can be responsible for its appearance. To a rather greater degree, the flux of epithermal neutrons correlates with the amount of dust material on the surface. This indicates that the dust material presumably played a major role in the formation of the neutron-flux depression within the Medusae Fossae-Elysium region. The depression of the epithermal-neutron flux presumably has a polygenic nature. It can be related both to the primary accumulation of water-bearing material and to the later blowing of this material by wind and transportation of the dust fraction with its simultaneous enrichment in hydrogen-containing phases (most likely, in water-bearing minerals).Translated from Astronomicheskii Vestnik, Vol. 39, No. 1, 2005, pp. 3–25. Original Russian Text Copyright © 2005 by Ivanov, Kozyrev, Litvak, Mitrofanov.     

What is the closest black hole to the Sun?

We examine the distance of the two galactic microquasars GRO J1655–40 and A 0620–00 which are potentially the two closest black holes to the Sun. We aim to provide a picture as wide and complete as possible of the problem of measuring the distance of microquasars in our Galaxy. The purpose of this work is to fairly and critically review in great detail every distance method used for these two microquasars in order to show that the distances of probably all microquasars in our Galaxy are much more uncertain than currently admitted. Moreover, we show that many confirmations of quantitative results are often entangled and rely on very uncertain measurements. We also present a new determination of the maximum distance of GRO J1655–40 using red clump giant stars, and show that it confirms our earlier result of a distance less than 2 kpc instead of 3.2 kpc. Because, it then becomes more likely that GRO J1655–40 could originate from the stellar cluster NGC 6242, located at 1.0 kpc, we review the distance estimations of A 0620–00, which is so far the closest black hole with an average distance of about 1.0 kpc. We show that the distance methods used for A 0620–00 are also problematic. Finally, we present a new analysis of spectroscopic and astrometric archival data on this microquasar, and apply the maximum distance method of Foellmi et al. [Foellmi, C., Depagne, E., Dall, T.H., Mirabel, I.F., 2006b. A&A 457, 249]. It appears that A 0620–00 could indeed be even closer to the Sun than currently estimated, and consequently would be the closest known black hole to the Sun.     

Physics of large-scale star formation: The GAS-Dynamic aspect

The subject of the review is the nature of regions of large-scale starbursts in galaxies. Theoretical investigations are presented and discussed, for the most part. Principal attention is devoted to the gas-dynamic approach to the problem. The review has the following plan. First we give a brief summary of empirical data on superassociations as regions of collective star formation on the largest scale in disk and irregular galaxies (Sec. 2); we then describe one possible gas-dynamic scenario for the origin of these objects (Sec. 3); the key physical mechanism on which the scenario is based — a collision of shock waves — is studied on the basis of general considerations (Sec. 4), as well as using computer simulation (Sec. 5) and laboratory experiments with shock waves (Sec. 6); the possibilities for the occurrence of this process under the specific conditions of the interstellar medium in disk and irregular galaxies are discussed in Sec. 7; in Sec. 8 we then consider features of large-scale collective star formation in barred galaxies; the evolution of spiral shocks that can initiate this process is the subject of Sec. 9; possible means of generation of large-scale regions of star formation like superassociations at the center of a bar (Sec. 10) and near its ends (Sec. 11) are then described; a brief conclusion is given in Sec. 12.In memory of Victor Amazaspovich AmbartsumianTranslated from Astrofizika, Vol. 39, No. 4, pp. 627–663, October–December, 1996.     

UV Observations with the Transition Region and Coronal Explorer

The Transition Region and Coronal Explorer is a space-borne solar telescope featuring high spatial and temporal resolution. TRACE images emission from solar plasmas in three extreme-ultraviolet (EUV) wavelengths and several ultraviolet (UV) wavelengths, covering selected ion temperatures from 6000 K to 1 MK. The TRACE UV channel employs special optics to collect high-resolution solar images of the H i L line at 1216 Å, the C iv resonance doublet at 1548 and 1550 Å, the UV continuum near 1550 Å, and also a white-light image covering the spectrum from 2000–8000 Å.We present an analytical technique for creating photometrically accurate images of the C iv resonance lines from the data products collected by the TRACE UV channel. We use solar spectra from several space-borne instruments to represent a variety of solar conditions ranging from quiet Sun to active regions to derive a method, using a linear combination of filtered UV images, to generate an image of solar C iv 1550 Å emission. Systematic and statistical error estimates are also presented. This work indicates that C iv measurements will be reliable for intensities greater than 1014 photons s–1 cm–2 sr–1. This suggests that C iv 1550 Å images will be feasible with statistical error below 20% in the magnetic network, bright points, active regions, flares and other features bright in C iv. Below this intensity the derived image is dominated by systematic error and read noise from the CCD.     

Coronal survey in X-rays of O vii and Ne ix

We report some results of a rocket experiment flown on 29 April, 1971. A survey of the solar corona was carried out with a pair of collimated Bragg spectrometers to study the resonance, intersystem and forbidden line emission from the helium-like ions O vii (22 Å) and Ne ix (13 Å). In the direction of dispersion the collimator provided a field of view of 1.7. Also, the continuum radiation near 3 Å was monitored by a collimated proportional counter within a view angle of 4.2. The observed X-ray emission came from the general corona, seven plage regions, and one dynamic feature- the late stage of a small flare. From the intensity of the O vii and Ne ix resonance lines the electron temperature and emission measure of the individual emitting regions are derived on the basis of two models, one (a) in which the region is assumed to be isothermal and another (b) in which the emission measure decreases exponentially with increasing temperature. The latter model, which is the most adequate of the two, yields for the electron temperature of the time-varying feature 2–3 × 10⁶ K, for the other active regions 1.5–2.5 × 10⁶ K, and for the general corona 1.3–1.7 × 10⁶ K. The Ne ix emitting regions are about 1.5 times as hot as the O vii regions. The emission measure ranges from 0.4–2.3 × 10⁴⁸ cm^–3 for all active regions and is about 2 × 10⁴⁹ cm^–3 for one hemisphere of the general corona above 10⁶ K. From an analysis of the ratio, R, of the forbidden and intersystem lines of O vii we conclude that none of the regions producing these lines at the time of the rocket flight had electron densities exceeding about 3 × 10⁹ cm^–3. Our data demonstrate a dependence of R upon temperature in agreement with the theory of Blumenthal et al. (1971). The wavelengths for the intersystem, the 1s ²2s ² S ^e–1s2p2s ² P ⁰ satellite, and the forbidden transition show in the case of Ne ix improved agreement with predictions. The observed strength of the satellite lines for both O vii and Ne ix agrees with the predictions of Gabriel's (1972) theory, which attributes their formation to dielectronic recombination.We are saddened to report the death of A. J. Meyerott on 13 November, 1971.     

Longitudinal variation of radial growth at Alaska's northern treeline—recent changes and possible scenarios for the 21st century

The northern treeline is generally limited by available warmth. However, in recent years, more and more studies have identified drought stress as an additional limiting factor for tree growth in northern boreal forests and at treelines. Three growth responses to warming have been identified: increase in growth, decrease in growth, and nonsignificant correlation of tree growth with climate. Here we investigate the effect of drought stress on radial growth of white spruce at northern treelines along a longitudinal gradient spanning the entire Brooks Range in Alaska. We systematically sampled 687 white spruce at seven treeline sites. Where possible, we sampled three site types at a given site: high-density forest, low-density forest, and floodplain forest. We investigated the relationship of site and site type to tree growth responses. In the western part of our study area, we found very high numbers of trees responding with increase in growth to recent warming; while in the eastern part, trees responding with decrease in growth to recent warming are predominant. Within a given site, more trees reacting positively to warming grow on site types characterized by low tree density. These patterns coincide with precipitation decreases from west to east and local water availability gradients, therefore pointing to drought stress as the controlling factor for the distribution of trees responding with increase or decrease in growth to recent warming. Compared to 20th century climate, we project a 25–50% basal area (BA) increase in the western region for the 21st century due to climate warming as projected by five general circulation models, 4–11% in the central region and decreases (+1 to −11%) in the eastern region. The overall net change in projected 21st century BA increase at each site seems to be controlled by the relative proportion of responder groups. If these are similar, differences in the magnitude of increase versus decrease in growth control BA projections for that site. This study highlights the importance of regional-scale investigations of biosphere–climate interactions, since our results indicate a substantial gain in aboveground biomass as a result of future warming only in the western regions; while in the eastern regions, climate warming will decrease overall wood production and therefore carbon uptake potential.     

Structure and Cyclic Variations of Open Magnetic Fields in the sun

The structure and variations of open field regions (OFRs) are analyzed against the solar cycle for the time interval of 1970–1996. The cycle of the large-scale magnetic field (LSMF) begins in the vicinity of maximum Wolf numbers, i.e. during the polar field reversal. At the beginning of the LSMF cycle, the polar and mid-latitude magnetic field systems are connected by a narrow bridge, but later they evolve independently. The polar field at the latitudes above 60° has a completely open configuration and fills the whole area of the polar caps near the cycle minimum of local fields. At this time, essentially all of the open solar flux is from the polar caps. The mid-latitude open field regions (OFRs) occur at a latitude of 30–40° away from solar minimum and drift slowly towards the equator to form a typical 'butterfly diagram' at the periphery of the local field zone. This supports the concept of a single complex – 'large-scale magnetic field – active region – coronal hole'. The rotation characteristics of OFRs have been analyzed to reveal a near solid-body rotation, much more rigid than in the case of sunspots. The rotation characteristics are shown to depend on the phase of the solar cycle.     

Numerical Exploration of Chermnykh’s Problem

We study the equilibrium points and the zero-velocity curves of Chermnykh’s problem when the angular velocity ω varies continuously and the value of the mass parameter is fixed. The planar symmetric simple-periodic orbits are determined numerically and they are presented for three values of the parameter ω. The stability of the periodic orbits of all the families is computed. Particularly, we explore the network of the families when the angular velocity has the critical value ω = 2√2 at which the triangular equilibria disappear by coalescing with the collinear equilibrium point L₁. The analytic determination of the initial conditions of the family which emanate from the Lagrangian libration point L₁ in this case, is given. Non-periodic orbits, as points on a surface of section, providing an outlook of the stability regions, chaotic and escape motions as well as multiple-periodic orbits, are also computed. Non-linear stability zones of the triangular Lagrangian points are computed numerically for the Earth–Moon and Sun–Jupiter mass distribution when the angular velocity varies.