Detecting the widths of shock fronts preceding coronal mass ejections

The perturbed zones and shocks preceding coronal mass ejections (CMEs) are studied using the data of the Mark 4, LASCO C2, and LASCO C3 coronagraphs. Detection of the perturbed zone indicating the presence or absence of the shock is most reliable in a frame moving with the frontal structure of the CME. The ability to correctly measure the width δ _F of the shock front using the Mark 4 and LASCO C2 data is established. The front width δ _F observed along the streamer belt at distances R < 5 R _⊙ from the center of the Sun is of the order of the mean free path of protons. This means that the energy dissipation in the shock front is collisional at such distances. At distances R ≥ (10 − 15) R _⊙, a new discontinuity with a front δ* _F ≪ δ _F is formed in the leading portion of the front. Within the errors, δ* _F ≈ (0.1–0.2) R _⊙ is independent of the distance R and is determined by the LASCO C3 spatial resolution. Initially, the discontinuity on the scale δ* _F is weak and coexists with the front with width δ _F . The relative amplitude of this discontinuity increases and the brightness profile behind it flattens as long as the distance R increases. This transformation of the brightness profile from a front of width δ F to a discontinuity of width δ* _F ≪ δ _F is explained as a transition from a collisional to a collisionless shock.     

Some properties of the development of the perturbed zone and shock preceding a coronal mass ejection

SOHO/LASCO C2 and C3 data have been used to carry out a detailed study of the perturbed zone and shock that form as a coronal mass ejection (CME) moves away from the Sun, as a result of its interaction with the ambient solar wind. The event of January 4, 2002 is used as an example. The perturbed zone is most extensive along the direction of propagation of the CME, decreases away from this direction, and reaches its minimum values perpendicular to this direction. The mass of the perturbed zone is ≥0.1 of the total mass of the CME. The condition for the formation of a shock preceding the CME (in the direction of propagation of the CME) is V − V _SW > V _A , where V, V _SW , and V _A are the CME, solar wind, and Alfvén velocities, respectively. Perpendicular to the CME axis, at distances of ≈4–6R _⊙ fromthe center of the Sun, the condition for the formation of shock is V/2 > V _A .     

The formation of a perturbed zone and shock wave excited by a coronal mass ejection

The existence of perturbed zones ahead of coronal mass ejections (CMEs) has been confirmed, and their evolution with increasing CME velocity studied. At CME velocities that are close to or higher than the local Alfvén velocity, a discontinuity forms in the plasma density distribution ahead of the perturbed zone, which can be interpreted as a shock. Estimates testify that, at distances from the solar center of R < (15–20) R _⊙, the width of the observed shock front is probably of the order of the mean free path for proton-proton collisions.     

Possible reasons for the frequency splitting of the harmonics of type II solar radio bursts

AIA/SDO data in the 193 Å channel preceding a coronal mass ejection observed at the solar limb on June 13, 2010 are used to simultaneously identify and examine two different shock fronts. The angular size of each front relative to the CME center was about 20°, and their propagation directions differed by ≈25° (≈4° in position angle). The faster front, called the blast shock, advanced the other front, called the piston shock, by R ≈ (0.02-0.03)R⊙ (R⊙ is the solar radius) and had a maximum initial speed of V_B ≈ 850 km/s (with V_P ≈ 700 km/s for the piston shock). The appearance and motion of these shocks were accompanied by a Type II radio burst observed at the fundamental frequency F and second harmonic H. Each frequency was split into two close frequencies f₁ and f₂ separated by Δf = f₂ - f₁ ? F, H. It is concluded that the observed frequency splitting Δf of the F and H components of the Type II burst could result from the simultaneous propagation of piston and blast shocks moving with different speeds in somewhat different directions displaying different coronal-plasma densities.     

Photometric elements,apsidal motion,and the third body in the eclipsing binary V974 Cyg

We have derived the first photoelectric light curve of the eclipsing binary V974 Cyg from our own photoelectric observations. Analysis of the light curve has yielded the system’s photometric elements (r ₁ ≈ r ₂ = 0.1192, e = 0.058, L ₁ ≈ L ₂ = 0.486, and L ₃ = 0.028) and absolute parameters (M ₁ ≈ M ₂ = 2.2M _⊙, T _eff,1 ≈ T _eff,2 = 9500 K, a = 15.0R _⊙, distance d = 1.29 kpc, age log t = 8.0, t/tMS = 0.11). We have detected apsidal motion with the period U _obs = (1140 ± 170) yrs, and the presence of a third body in the system. The orbital parameters derived for the third body are P ₃ = 26.5 yrs, e ₃ = 0.78, and a ₃ sin i ₃ = 1.5 AU; and the lower limit for its mass is M ₃ > 0.58M _⊙. The observed apsidal-motion rate is higher than is expected theoretically by a factor of 1.5. The axial rotation of the system’s components is not yet synchronized with the orbital motion, probably because V974 Cyg is relatively young and detached.     

On the Ratios between Elastic Modulus and Uniaxial Compressive Strength of Heterogeneous Carbonate Rocks

The ratios M _R = E/σ _c for 11 heterogeneous carbonate (dolomites, limestones and chalks) rock formations collected from different regions of Israel were examined. Sixty-eight uniaxial compressive tests were conducted on weak-to-strong (5 MPa < σ _c < 100 MPa) and very strong (σ _c > 100 MPa) rock samples exhibiting wide ranges of elastic modulus (E = 6100–82300 MPa), uniaxial compressive strength (σ _c = 14–273.9 MPa), Poisson's ratio (ν = 0.13–0.49), and dry bulk density (ρ = 1.7–2.7 g/cm³). The observed range of M _R = 60.9–1011.4 and mean value of M _R = 380.5 are compared with the results obtained by Deere (Rock mechanics in engineering practice, Wiley, London, pp 1–20, 1968) for limestones and dolomites, and the statistical analysis of M _R distribution is performed. Mutual relations between E, σ _c, ρ, M _R for all studied rocks, and separately for concrete rock formations are revealed. Linear multiple correlations between E on the one hand and σ _c and ρ on the other for Nekorot and Bina limestone and Aminadav dolomite are obtained. It is established that the elastic modulus and M _R in very strong carbonate samples are more correlated with ρ−σ _c combination and ε _a max, respectively, than in weak to strong samples. The relation between M _R and maximum axial strain (ε _a max) for all studied rock samples (weak-to-strong and very strong) is discussed.     

First experimental studies of a perturbed zone preceding the front of a coronal mass ejection

The first experimental evidence for a perturbed zone that is likely filled with fast magnetoacoustic oscillations and precedes a coronal mass ejection is presented. When the speed of the coronal mass ejection exceeds the Alfven speed, an outward-moving discontinuity of the plasma density is observed in front of the perturbed zone, on scales comparable to the mean-free path for proton-proton collisions. This suggests that this discontinuity should be interpreted as a collisional shock at distances of R < 30 R _⊙ (where R _⊙ is the solar radius).     

The influence of the decay of OB associations on the evolution of dwarf galaxies

The ejection of stars from spheroidal and disk dwarf galaxies resulting from the decay of OB associations is studied. This has substantial observational consequences for disk galaxies with escape velocities up to 20 km/s, or dynamical masses up to 10⁸ M _⊙. The ejection of stars can (i) reduce the abundances of the products of Type Ia supernovae and, to a lesser degree, Type II supernovae, in disk stars, (ii) chemically enrich the galactic halo and intergalactic medium, (iii) lead to the loss of 50% of the stellar mass in galaxies with masses ∼10⁷ M _⊙ and the loss of all stars in systems with masses ≲10⁵ M _⊙, (iv) increase the mass-to-luminosity ratio of the galaxy.     

Blast-wave and piston shocks connected with the formation and propagation of a coronal mass ejection

The solar coronal mass ejection observed on November 3, 2010 is analyzed using AIA/SDO data (images in the 193 and 211 Å channels) and white-corona images obtained with the SOHO LASCO C2 and C3 coronographs. We have succeeded in revealing both piston and blast-wave shocks attributed to the formation and propagation of a coronal mass ejection. Both of these types of shocks could be responsible for type II radio bursts propagating in front of each shock.     

Possible scenarios for the formation of Ap/Bp stars

Possible paths for the formation of Ap/Bp stars—massive main-sequence stars with strong magnetic fields—are analyzed based on modern theories for the evolution of single and binary stars. Assuming that the strong magnetic fields of these stars are the main reason for their comparatively slow axial rotation and the observed anomalies in the chemical compositions of their atmospheres, possible origins for these high magnetic fields are considered. Analysis of several possible scenarios for the formation of these stars leads to the conclusion that their surface magnetic fields are probably generated in the convective envelopes of the precursor stars. These precursors may be young, single stars with masses 1.5–3 M _⊙ that formed at the peripheries of forming star clusters and ended their accretion at the Hayashi boundary, or alternatively close binaries whose components have convective envelopes, whose merger leads to the formation of an Ap/Bp star. Arguments are presented supporting the view that the merger of close binaries is the main channel for the formation of Ap/Bp stars, and a detailed analysis of this scenario is presented. The initial major axes of the merging binary systems must be in the range 6–12 R _⊙, and the masses of their components in the range 0.7–1.5 M _⊙. When the merging components possess developed convective envelopes and fairly strong initial magnetic fields, these can generate powerful magnetic fields “inherited” by the products of the merger—Ap/Bp stars. The reason the components of the close binaries merge is a loss of angular momentum via the magnetic stellar winds of the components.     

Evolution of the velocity ellipsoids in the thin disk of the Galaxy and the radial migration of stars

Data from the revised Geneva-Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative metallicity gradient in the thin disk, are responsible for the observed negative correlation between the metallicities and angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do not depend on either age or metallicity. The velocity components of the Sun relative to the Local Standard of Rest derived using data for stars born at the solar Galactocentric distance are (U _⊙, V _⊙, W _⊙) _LSR = (5.1 ± 0.4, 7.9 ± 0.5, 7.7 ± 0.2) km/s. The two coordinates of the apex of the solar motion remain equal to 〈l _⊙〉 = 70° ± 7° and 〈b _⊙〉 = 41° ± 2°, within the errors. The indices for the power-law age dependences of them ajor, middle, and minor semi-axes become 0.26±0.04, 0.32±0.03, and 0.07±0.03, respectively. As a result, with age, the velocity ellipsoid for thin-disk stars born at the solar Galactocentric distance increases only in the plane of the disk, remaining virtually constant in the perpendicular direction. Its shape remains far from equilibrium, and the direction of the major axis does not change with age: the ellipsoid vertex deviation remains constant and equal to zero within the errors (〈L〉 = 0.7° ± 0.6°, 〈B〉 = 1.9° ± 1.1°). Such a small increase in the velocity dispersion perpendicular to the Galactic plane with age can probably be explained by “heating” of the stellar system purely by spiral density waves, without a contribution from giant molecular clouds.     

Diffuse and concentrated recharge evaluation using physical and tracer techniques: results from a semiarid carbonate massif aquifer in southeastern Spain

In the high-permeability, semiarid carbonate aquifer in the Sierra de Gádor Mountains (southeastern Spain), some local springs draining shallow perched aquifers were of assistance in assessing applicability of the atmospheric chloride mass balance (CMB) for quantifying total yearly recharge (R _T) by rainfall. Two contrasting hydrological years (October through September) were selected to evaluate the influence of climate on recharge: the average rainfall year 2003–2004, and the unusually dry 2004–2005. Results at small catchment scale were calibrated with estimated daily stand-scale R _T obtained by means of a soil water balance (SWB) of rainfall, using the actual evapotranspiration measured by the eddy covariance (EC) technique. R _T ranged from 0.35 to 0.40 of rainfall in the year, with less than a 5% difference between the CMB and SWB methods in 2003–2004. R _T varied from less than 0.05 of rainfall at mid-elevation to 0.20 at high elevation in 2004–2005, with a similar difference between the methods. Diffuse recharge (R _D) by rainfall was quantified from daily soil water content field data to split R _T into R _D and the expected concentrated recharge (R _C) at catchment scale in both hydrological years. R _D was 0.16 of rainfall in 2003–2004 and 0.01 in 2004–2005. Under common 1- to 3-day rainfall events, the hydraulic effect of R _D is delayed from 1 day to 1 week, while R _C is not delayed. This study shows that the CMB method is a suitable tool for yearly values complementing and extending the more widely used SWB in ungauged mountain carbonate aquifers with negligible runoff. The slight difference between R _T rates at small catchment and stand scales enables results to be validated and provides new estimates to parameterize R _T with rainfall depth after checking the weight of diffuse and concentrated mechanisms on R _T during moderate rainfall periods and episodes of marked climatic aridity.     

Electron density distributions and bonded interactions for the fibrous zeolites natrolite, mesolite and scolecite and related materials

 For the fibrous zeolites natrolite, Na₂[Al₂Si₃O₁₀]·2H₂O, mesolite, Na₂Ca₂[Al₂Si₃O₁₀]₃·8H₂O, and scolecite, Ca[Al₂Si₃O₁₀]·3H₂O, with topologically identical aluminosilicate framework structures, accurate single-crystal X-ray diffraction data have been analyzed by least-squares refinements using generalized scattering factor (GSF) models. The final agreement indices were R(F ) = 0.0061, 0.0165, and 0.0073, respectively. Ensuing calculations of static deformation [Δρ(r)], and total, [ρ(r)], model electron density distributions served to study chemical bonding, in particular by topological electron density analyses yielding bond critical point (bcp) properties and in situ cation electronegativities. The results for 32 SiO, 24 AlO, 14 CaO, and 12 NaO unique bonds are compiled and analyzed in terms of both mean values and correlations between bond lengths, bonded oxygen radii, bcp densities, curvatures at the bcps, and electronegativities. Comparison with recent literature data obtained from both experimental electron density studies on minerals and model calculations for geometry-optimized molecules shows that the majority of the present findings conforms well with chemical expectation and with the trends observed from molecular modeling. For the SiO bond, the shared interaction is indicated to increase with decreasing bond length, whereas the AlO bond is of distinctly more polar nature, as is the NaO bond compared to CaO. Also, the observed ranges of the Si and Al in situ electronegativities and their mean electronegativities agree well with both Pauling's values and model calculation results, and statistically significant correlations are obtained which are consistent with trends described for oxide and nitride molecules. Received: 10 May 1999 / Revised, accepted: 14 September 1999     

Gas dynamics of a central collision of two galaxies: Merger, disruption, passage, and the formation of a new galaxy

Results of numerical simulations of a collision of the gaseous components of two identical disk galaxies during a head-on collision of the galaxies in the polar direction are presented. When the relative velocity of the galaxy collision is small, their gaseous components merge. At high relative velocities (100–500 km/s), the massive stellar components of the galaxies (M _g = 10⁹ M _⊙) pass through each other nearly freely, leaving behind the gaseous components, which are decelerated and heated by the collision. If the overall gaseous component of the colliding galaxies is able to cool to the virial temperature during the collision, a new galaxy forms. At velocities V ≥ 500 km/s, the gaseous component does not have time to cool, and the gas is scattered into intergalactic space, supplying it with heavy elements produced in supernovae in the colliding galaxies. High-velocity (V ≥ 100 km/s) collisions of identical low-mass galaxies (M _g ≤ 10⁹ M _⊙) whose mass is dominated by the mass of gas lead to the disruption of their stellar components. The overall gaseous component forms a new galaxy when V ≤ 500 km/s, and is scattered into intergalactic space if the velocity becomes higher than this. A galaxy collision increases the star-formation rates in the disk galaxies by nearly a factor of 100. Rotation of the colliding galaxies in the same direction increases the changes of the disruption of both the stellar and gaseous components of the galaxies. The merger of galaxies during their collision can explain the presence of gaseous disks rotating opposite to the rotation of the stellar component in some ordinary elliptical galaxies. Moreover, galaxy mergers can help explain the origin of a comparatively young stellar population in some elliptical galaxies.     

IR photometry and dust-shell models for two carbon stars

We present JHKLM photometry of the carbon stars ST And and T Lyn acquired in 2000–2010. Along with brightness variations due to pulsations, changes on timescales of 2000–3000 days are also observed. Our combined light curves can be satisfactorily represented with light elements derived from visual observations, but the maxima are delayed relative to the calculated times. A color-index analysis demonstrates that the dust shell of ST And is fairly weak, and is manifest only episodically, while the presence of hot dust was always detected for T Lyn. These results confirm models of spherically symmetric stellar dust shells based on mean-flux data, supplemented with observations in the intermediate IR from the IRAS and AKARI satellites. The visual optical depth of the relatively cool dust shell of ST And assuming a dust temperature at the inner edge of T ₁ = 510 K is very low: τ _V = 0.047. The dust shell of T Lyn is considerably hotter (T ₁ = 940 K), with τ _V = 0.95. We estimate the mass-loss rate to be 1.8 × 10⁻⁷ M _⊙/year for ST And and 3.7 × 10⁻⁷ M _⊙/year for T Lyn.     

IR photometry and models of dust shells for two RCB stars

We present JHKLM photometry obtained in 1984–2009 for the RCB stars UV Cas and SU Tau. No major fadings characteristic of RCB stars were detected during the observations of UV Cas, while two events of this kind occurred for SU Tau. The observed flux and color-index variations can be explained with a changing dust concentration in the line of sight, and possibly variations of the stellar temperature. We use the measured fluxes, supplemented with observations in the intermediate IR, to compute spherically symmetric dust-shell models for the stars. The mass-loss rate is estimated to be 1.7 × 10⁻⁶ M _⊙ yr⁻¹ for UV Cas and 4.1 × 10⁻⁶ M _⊙ yr⁻¹ for SU Tau.     

Phosphorus – an omnipresent minor element in garnet of diverse textural types from leucocratic granitic rocks

Summary Elevated P contents of up to 0.086 apfu (1.21 wt.% P₂O₅) were found in garnet from leucocratic granitic rocks (orthogneisses, granites, barren to highly evolved pegmatites) in the Moldanubicum and Silesicum, Czech Republic, and in complex granitic pegmatites from southern California, USA, and Australia. Minor concentrations (0.15–0.55 wt.% P₂O₅) appear ubiquitous in garnet from leucocratic granitic rocks of different origins and degrees of fractionation. Concentrations of P are not related to Mn/(Mn + Fe) that vary from 0.12–0.86 and to textural types of garnet (i.e., isolated anhedral to euhedral grains and nodules, graphic and random garnet–quartz aggregates, subsolidus veins of fine-grained garnet). Garnet compositions exhibit negative correlations for P/Si and P/R²⁺ where R²⁺ = Fe + Mn + Mg + Ca, while Al is constant at ∼2.05 apfu. Concentrations of Na are largely below 0.02 apfu but positively correlate with P. The main substitution may involve A-site vacancy and/or the presence of some light element(s) in the crystal structure. The substitution □P₂ R²⁺ ₋₁Si₋₂ and/or alluaudite-type Na□P₃ R²⁺ ₋₁Si₋₃ seem the most likely P-incorporating mechanisms. The partitioning of P among garnet and associated minerals in granitic systems remains unclear; however, it directly affects the distribution of Y and REEs.     

Evidence for shock generation in the solar corona in the absence of coronal mass ejections

The solar event SOL2012–10–23T03:13, which was associated with a X1.8 flare without an accompanying coronal mass ejection (CME) and with a Type II radio burst, is analyzed. A method for constructing the spatial and temporal profiles of the difference brightness detected in the AIA/SDOUVand EUV channels is used together with the analysis of the Type II radio burst. The formation and propagation of a region of compression preceded by a collisional shock detected at distances R < 1.3R _⊙ from the center of the Sun is observed in this event (R _⊙ is the solar radius). Comparison with a similar event studied earlier, SOL2011–02–28T07:34 [1], suggests that the region of compression and shock could be due to a transient (impulsive) action exerted on the surrounding plasma by an eruptive, high-temperature magnetic rope. The initial instability and eruption of this rope could be initiated by emerging magnetic flux, and its heating from magnetic reconnection. The cessation of the eruption of the rope could result from its interaction with surrounding magnetic structures (coronal loops).