Venus EUV measurements of hydrogen and helium from Venera 11 and Venera 12

Lyman α and 58.4 nm HeI radiations resonantly scattered were observed with EUV spectrophotometers flown on Venera 11 and Venera 12. The altitude distribution of hydrogen was derived by limb observations from 250 km (exobase level) to 50,000 km. In the inner exosphere (up to ? 2,000 km of altitude) the distribution can be described by a classical exospheric distribution with T_C = 275 ± 25 K and n = 4_?2⁺³ × 10⁴ atom. cm^?3 at 250 km. The integrated number density from 250 to 110 km (the level of CO₂ absorption) is 2.1 × 10¹² atom. cm^?2, a factor of 3 to 6 lower than that predicted by aeronomical models. This number density decreases from the morning side to the afternoon side, or alternately from equatorial to polar regions. Above 2,000 km a “hot” hydrogen population dominates, which can be simulated by T = 10³K and n = 10³ atom. cm^?3 at the exobase level.The optical thickness of helium above 141 km (the level of CO₂ absorption for 58.4 nm radiation) was determined to be τ_o = 3, corresponding to a density at 150 km of 1.6 × 10⁶ cm^?3. This is about 3 times less than what was obtained with the Bus Neutral Mass Spectrometer of Pioneer Venus, and about twice less than ONMS measurements, but is in agreement with earlier EUV measurement by Mariner 10 (2 ± 1 × 10⁶ cm^?3).     

Energy conversion of the flare due to direct electric fields from the sheared reconnection

In this paper we present a new mechanism of the main energy conversion of the solar flare. Since a flare inducing prominence (flux tube) rises V_z ? 300 km s⁻¹, the plasmas below it cannot continuously eject with Alfvén speeds of V_A = 3000 km s⁻¹ but probably with V_z ≈ ±100 km s⁻¹. Plasma up and downflows with V_A will within a short duration be blocked between the chromosphere where reconnected flux tubes are piling up, and the slowly rising flux rope. Hence the Petschek slow shock mechanism is difficult to be realized as a major energy converting mechanism.     

A multiple type-II burst associated with a coronal transient and its MHD simulation

A large coronal transient took place on 8 May 1981. The transient was related to an M7.7/2B flare and was associated with at least two coronal type II bursts. The velocities of the type II bursts were in the range 1100–1800 kms^?1, in excess of the transient velocity of 500–1000 kms^?1. Two dimensional positions of the type II radio sources are available from both the Clark Lake and the Culgoora Radio Observatories. We carry out two dimensional MHD simulations of the event, taking into account the observed velocity, position, and size of the type II bursts. We simulate the multiple shocks observed during the event and their interaction, and discuss some results of the simulation.     

Acceleration theory for 5–40 keV ions at interplanetary shocks

Power-law spectra f(E)∝E^?2.7 of < 40 keV suprathermal ions within ～10⁷ km of propagating interplanetary shocks are explained by diffusive scattering near a plane shock. The theory fits the 25 November 1977 event with a mean free path perpendicular to the shock with is 0.01 AU in front of the shock and less than .0003 AU behind it, for 1 keV ions. The theory predicts a steepening spectrum at higher energies, of the form $\text{f(v)∝v}{}^{\mathrm{?4}}\text{exp(??λdv/ur)}\text{where}\text{u = (ΔV)}{}^2\text{/2V}{}_{\mathrm{W}}$ depends on the plasma velocity jump ΔV and the plasma speed V_W and mean free path λ in front of the shock     

The neutral particle impact de-excitation cross-section of the fine structure level3P1 of atomic oxygen in the thermosphere

A new upper limit value (9.9 × 10^?21cm²) of the mean equivalent de-excitation cross-section of O(³P₁) by collision with neutral particles in the thermosphere is obtained by comparing the³P₁ state de-excitation rate due to neutral practice impact with that due to electron impact. The existing data of the cross-section obtained from the aeronomic study are compared with the theoretical data, and it indicated that the former is much less than the latter.     

The optical emission lines of type 1 X-ray bright Active Galactic Nuclei

A strong X-ray emission is one of the defining signatures of nuclear activity in galaxies. According to the Unified Model for Active Galactic Nuclei (AGN), both the X-ray radiation and the prominent broad emission lines, characterizing the optical and UV spectra of Type 1 AGNs, are originated in the innermost regions of the sources, close to the Super Massive Black Holes (SMBH), which power the central engine. Since the emission is concentrated in a very compact region (with typical size r?0.1$r?0.1$ pc) and it is not possible to obtain resolved images of the source, spectroscopic studies of this radiation represent the only valuable key to constrain the physical properties of matter and its structure in the center of active galaxies. Based on previous studies on the physics of the Broad Line Region (BLR) and on the X-ray spectra of broad (FWHM_Hβ ? 2000 km s⁻¹) and narrow line (1000 km s⁻¹ ?FWHM_Hβ ? 2000 km s⁻¹) emitting objects, it has been observed that the kinematic and ionization properties of matter close to the SMBHs are related together, and, in particular, that ionization is higher in narrow line sources. Here we report on the study of the optical and X-ray spectra of a sample of Type 1 AGNs, selected from the Sloan Digital Sky Survey (SDSS) database, within an upper redshift limit of z=0.35$z=0.35$, and detected at X-ray energies. We present analysis of the broad emission line fluxes and profiles, as well as the properties of the X-ray continuum and Fe Kα emission and we use these parameters to assess the consistency of our current AGN understanding.     

Equatorial vertical E × B drift velocities inferred from ionosonde measurements over Ouagadougou and the IRI-2007 vertical ion drift model

F-region vertical plasma drift velocities were deduced from the hourly hmF2 values acquired from ionogram data over a near dip equatorial station Ouagadougou (12.4°N, 358.5°E, dip angle 5.9°N) in Africa. Our results are compared against the global empirical model of Scherliess and Fejer (1999) incorporated in the IRI model (IRI-2007) for 1600 to 0800 LT from 1 year of data during sunspot maximum year of 1989 (yearly average solar flux intensity, F10.7 = 192) corresponding to the peak phase of solar cycle 22, under magnetically quiet conditions. The drifts are entirely downward between 2000 and 0500 LT bin for both techniques and the root mean square error (RMSE) between the modeled and the ionosonde vertical plasma drifts during these periods is 3.80, 4.37, and 4.74 m/s for June solstice, December solstice and equinox, respectively. Ouagadougou average vertical drifts show evening prereversal enhancement (PRE) velocity peaks (V_ZP) of about 16, 14, and 17 m/s in June solstice, December solstice, and equinox, respectively, at 1900–2000 LT; whereas global empirical model average drifts indicate V_ZP of approximately 33 m/s (June solstice), 29 m/s (December solstice), and 50 m/s (equinox) at 1800 LT. We find very weak and positive correlation (+0.10376) between modeled V_ZP versus F10.7, while ionosonde V_ZP against F10.7 gives worst and opposite correlation (−0.05799). The results also show that modeled V_ZP–Ap indicates good and positive correlation (+0.64289), but ionosonde V_ZP–Ap exhibits poor and negative correlation (−0.22477).     

Multiple wavelength observations of flaring active regions

We present observations of flaring active regions with the Very Large Array (V.L.A. at 6 cm and 20 cm wavelengths) and the Westerbork Synthesis Radio Telescope (W.S.R.T. at 6 cm wavelength). These are compared with photospheric magnetograms (Meudon) and with Hα and offband Hα photographs (Big Bear and Ottawa River Solar Observatories). The 6 cm radiation of these active regions marks the legs of dipolar loops which have their footpoints in lower-lying sunspots. The intense, million degree radiation at 6 cm lies above sunspot umbrae in coronal regions where the longitudinal magnetic field strength H_? = 600 Gauss and the height above the sunspot umbrae h = 3.5±0.5 × 10⁹ cm. Circularly polarized horseshoe structures at 6 cm ring the sunspot umbrae. The high degree of circular polarization (?_c = 95%) of the horseshoes is attributed to gyroresonant emission above sunspot^? penumbrae. The 20 cm radiation of these active regions exhibits looplike coronal structures which extend across regions of opposite magnetic polarity in the underlying photosphere. The 20 cm loops are the radio wavelength counterparts of the X-ray coronal loops. We infer semilengths L = 5 × 10⁹ cm, maximum electron temperatures T_e(max) = 3 × 10⁶ K, emission measures ∫N_e²d$\text{l}$ = 10²⁸ cm^?5, and electron densities N_e = 10⁹ cm^?3 (or pressures p = 1 dyn cm^?2) for the 20 cm bremsstrahlung. A total of eight solar bursts were observed at 6 cm or 20 cm wavelength with second-of-arc angular resolution. The regions of burst energy were all resolved with angular sizes between 5″ and 30″, brightness temperatures between 2 × 10⁷ K and 2 × 10⁸ K, and degrees of circular polarization between 10% and 90%. The impulsive phase of the radio bursts are located near the magnetic neutral lines of the active regions, and between the flaring Hα kernels which mark the footpoints of magnetic loops. In one case there was preburst heating in the coronal loop in which a burst occurred. Snapshot maps at 10 s intervals reveal interesting burst evolution including rapid changes of circular polarization and an impulsive burst which was physically separated from both the preburst radio emission and the gradual decay phase of the burst.     

Expanding shells of young pulsars as sources of high-energy neutrinos

The initial power outputs P_o of pulsars are not yet well known, but these seem to follow approximately a distribution law N(> P_o) ∝ P_o⁻ⁿ where 0.5 ≤ n ≤ 1.0. It seems likely that P_o ≥ 10³⁸ ergs/sec. With these assumptions, we estimate that the DUMAND detector can record ≥ 10³ high-energy (> 4 TeV) neutrino events in a four-month period per Galactic supernova; (in our Galaxy, these are estimated to occur at the rate of about 8 per century.) Neutrinos from supernova shells in the Virgo supercluster would be marginally detectable (one very bright supernova per decade at about 20 Mpc) if N(> P_o) ∝ P_o^−0.5, but undetectable if N(> P_o) ∝ P_o⁻¹. The diffuse flux summed over distant extragalactic supernovae is likely to be well below the detection threshold.     

Variability of foE in the equatorial ionosphere with solar activity

This research examined the variability of f_oE in the equatorial ionosphere with solar activity within the equatorial ionospheric anomaly region. Ionosonde data recorded at Ouagadougou (lat. 12.4°N, long. 1.5°W and magnetic dip 1.43°N) were engaged to study the transient variations of the critical frequency of the E-layer (f_oE) and its dependence on solar activity. The study revealed that f_oE increases with the increase in solar intensity of the sun. The variability of the f_oE decreases with increases in the solar activity. The maximum value of the f_oE is at local noon when the ionosphere is stable; the variability at this local time is minimal. The minimum value of the f_oE is at sunrise and sunset, at this period on local time the equatorial ionosphere recorded its maxima variability. Irrespective of the degree of solar activity, f_oE is observed to be maximum in June solstice, followed by the equinoxes and minimum in December solstice. Equinoctial asymmetry occurred in the variation of the relative standard deviation of f_oE with maximum in September/March equinox for low/high solar activity.     

Classification and quantification of solar wind driver gases leading to intense geomagnetic storms

Classification and quantification of the interplanetary structures causing intense geomagnetic storms (Dst?≤??100?nT) that occurred during 1997–2016 are studied. The subject of this consists of solar wind parameters of seventy-three intense storms that are associated with the southward interplanetary magnetic field. About 30.14% of the storms were driven by a combination of the sheath and ejecta (S?+?E), magnetic clouds (MC) and sheath field (S) are 26% each, 10.96% by combined sheath and MCs (S?+?C), while 5.48% of the storms were driven by ejecta (E) alone. Therefore, we want to aver that for storms driven by: (1) S?+?E. The Bz is high (≥10?nT), high density (ρ) (>10?N/cm³), high plasma beta (β) (>0.8), and unspecified (i.e. high or low) structure of the plasma temperature (T) and the flow speed (V); (2) MC. The Bz is ≥10?nT, low temperature (T?≤?400,000?K), low ρ (≤10?N/cm³), high V (≥450?km), and low β (≤0.8); (3) The structures of S?+?C are similar to that of MC except that the V is low (V?≤?450?km); (4) S. The Bz is high, low T, high ρ, unspecified V, and low β; and (5) E. Is when the structures are directly opposite of the one driven by MCs except for high V. Although, westward ring current indicates intense storms, but the large intensity of geomagnetic storms is determined by the intense nature of the electric field strength and the Bz. Therefore, great storms (i.e. Dst?≤??200?nT) are manifestation of high electric field strength (≥13?mV/m).     

Recent infrared observations of comets with UKIRT and IRAS

A preliminary analysis of infrared observations of comets P/Crommelin and P/Tempel 1 is presented. Comet P/Crommelin was observed from UKIRT over the range 1–20 micron, using standard filters. From the shape of the thermal emission spectrum, the temperature of the dust grains is estimated (T = 314 ± ₃₃⁴⁴K) and also the dust production rate (1.3 × 10⁵gs^?1). Comet P/Tempel 1 was observed with the Infrared Astronomical Satellite (IRAS). The emission is found to be considerably extended and there is also evidence for temperature variation of the dust grains as indicated by the 12 to 25 micron flux ratio.     

Spectral analysis of time-integrated Konus–Wind GRBs: Implication on radiative mechanisms

We have analysed a sample of 328 time-integrated GRB prompt emission spectra taken via the Konus instrument on board the US GGS-Wind spacecraft between 2002 and 2004 using a couple of two-components models, Cut-off Power Law (CPL) + Power Law (PL) and blackbody (BB) + PL. The spectra show clear deviation from the Band function. The PL term is interpreted as the low energy tail of a nonthermal emission mechanism. The distributions of corresponding index β give values β < −2/3 consistent with synchrotron and synchrotron self-Compton mechanisms. The distribution of low energy index α associated with the CPL term shows clear discordance with synchrotron models for 31.4% of the analysed GRBs with values exceeding that for the line of death, α = −2/3. Then, a set of nonthermal radiation mechanisms producing harder slopes, i.e., α > −2/3, are presented and discussed. For the remaining majority (68.6%) of GRBs with CPL index α < −2/3, we show that optically thin synchrotron produced by a power law electron distribution of type, N(γ) ∼ γ^−p, γ₁ < γ < γ₂, for finite energy range (γ₂ ≠ ∞) is a likely emission mechanism with α ∼−(p + 1)/2 in the frequency range ν₁ ? ν ? ν₂ (where ν₂ = η²ν₁ with η = γ₂/γ₁), such that for p > 1/3, one gets α < −2/3. We also show that corresponding spectra in terms of F_ν and νF_ν functions are peaked around frequency ν₂ instead of ν₁, respectively for p < 1 and p < 3. Besides, thermal emission is examined taking a single Planck function for fitting the low energy range. It can be interpreted as an early emission from the GRB fireball photosphere with observed mean temperature, kT′ ∼ 16.8 keV. Furthermore, we have performed a statistical comparison between the CPL + PL and BB + PL models finding comparable χ²-values for an important fraction of GRBs, which makes it difficult to distinguish which model and specific radiation mechanism (possible thermal or nonthermal γ-ray emissions) are best suitable for describing the reported data. Therefore, additional information for those bursts, such as γ-ray polarization, would be highly desirable in future determinations of GRBs observational data.     

Atomic oxygen concentrations in the lower auroral thermosphere

Atomic oxygen concentrations derived from the nightglow components of O₂(b¹Σ_g⁺ ? X³Σ_g^?) (0-0) Atmospheric Band emission profiles obtained during two rocket-borne photometer measurements of aurora are presented. The peak atomic oxygen concentrations of 2–3 × 10¹¹ cm^?3 are in better agreement with those of the MSIS-83 model than the CIRA 1972 mean reference atmosphere, although the shapes of the two derived profiles differ considerably from that of MSIS-83. The derived concentrations do not contradict the suggestion made by some investigators that the atomic oxygen concentrations in the auroral zone are depleted relative to their mid-latitude values.     

Obscured QSOs and the X-ray Background

The question of whether there exists a large population of dust obscured QSOs is currently very controversial. In favour of this hypothesis are models for the origin of the X-ray Background (XRB) and also the Unified Model of AGN which both invoke large populations of obscured QSOs. For example, Madau et al. (1994) suggest a population of QSOs with N_H ∼ 10²⁴ cm⁻² or A_V = 1000^m to improve the fit to the XRB between 1 < E < 100 keV. Arguments contradicting this theory include those of Boyle & di Matteo (1995) who claim that the tight X-ray/optical flux ratio relation for QSOs precludes the existence of a large population of objects obscured by significant amounts of intrinsic dust. Here, we follow Madau et al. (1994) and Comastri et al. (1995) to make fits to the XRB using obscured QSO populations and investigate whether selection effects may allow a tight distribution of X-ray/optical ratios to be maintained. We find that even for a flat distribution of absorbing columns, reasonable fits to the XRB can be obtained while both optical and X-ray absorption combine to produce the tight observed X-ray/optical correlation.     

Mass spectrometric measurements of stratospheric ions

Recent in situ measurements with balloon borne quadrupole mass spectrometers, between 20 and 45 km altitude, are reviewed and discussed.The major stratospheric positive ions observed are proton hydrates [H⁺(H₂O)_n] and non proton hydrates of the form H⁺X_m(H₂O)₂. The data analysis allows a derivation of the vertical mixing ratio profile of X (most probably CH₃CN), which is compared with recent model calculations. From negative ion composition data, showing the presence of NO₃^? and HSO₄^? cluster ions, the density of sulfuric acid in the stratosphere is deduced. The implications of these findings on our understanding of the sulfur chemistry is briefly treated.Finally some other aspects such as contamination, cluster break up and the use of stratospheric ion mass spectra for determination of thermochemical data and other minor constituents are discussed.     

An automatic quality factor for Autoscala foF2 values

We propose a new parameter for quality evaluation of ionogram traces reconstructed by Autoscala. This parameter efficiently assesses the reliability of the automatic interpretation of ionospheric characteristics. Based on an extensive analysis of the data, the parameter values are statistically associated with the accuracy of f_oF2 data automatically scaled by Autoscala. Therefore, Autoscala will be improved by providing f_oF2 accuracy as supplementary output information.     

Stellar β-decay rates of iron isotopes and its implications in astrophysics

β-Decay and positron decay are believed to play a consequential role during the late phases of stellar evolution of a massive star culminating in a supernova explosion. The β-decay contributes in maintaining a respectable lepton-to-baryon ratio, Y_e, of the core prior to collapse which results in a larger shock energy to produce the explosion. The positron decay acts in the opposite direction and tends to decrease the ratio. The structure of the presupernova star is altered both by the changes in Y_e and the entropy of the core material. Recently the microscopic calculation of weak interaction mediated rates on key isotopes of iron was introduced using the proton–neutron quasiparticle random phase approximation (pn-QRPA) theory with improved model parameters. Here I discuss in detail the improved calculation of β^±-decay rates for iron isotopes (^54,55,56Fe) in stellar environment. The pn-QRPA theory allows a microscopic “state-by-state” calculation of stellar rates as explained later in text. Excited state Gamow–Teller distributions are much different from ground state and a microscopic calculation of decay rates from these excited states greatly increases the reliability of the total decay rate calculation specially during the late stages of stellar evolution. The reported decay rates are also compared with earlier calculations. The positron decay rates are in reasonable agreement with the large-scale shell model calculation. The main finding of this work includes that the stellar β-decay rates of ^54,55,56Fe are around 3–5 orders of magnitude smaller than previously assumed and hence irrelevant for the determination of the evolution of Y_e during the presupernova phase of massive stars. The current work discourages the inclusion of ^55,56Fe in the list of key stellar β-decay nuclei as suggested by former simulation results.     

Observed relation between solar luminosity and radius

We compile measurements of the total solar irradiance S_o made in the period 1967 to 1983 from balloons, rockets, and spacecrafts. These data, when corrected for atmospheric and calibration differences, suggest a systematic increase in S_o of about 0.025% per year. In 1979 and after the ACRIM/SMM and the ERB/NIMBUS data reveal a systematic decrease of about the same magnitude. The period of the early apparent increase embraces a full solar activity cycle of 11 years: hence the effect cannot be that of simple sunspot blocking. This trend of a slow increase followed by a similar decrease is compared with solar diameter measurements obtained from daily meridian transit timings of the Sun made during the same period at the Royal Greenwich Observatory and at the U.S. Naval Observatory. We find in both of these data sets an apparent increase in solar diameter of about 0.03″arc per year during the period of increasing solar irradiance and a weaker suggestion of a similar, subsequent decline. If the apparent trends in diameter and luminosity are real they allow us to estimate the empirical relationship between the two quantities. For this period we find W=ΔlogR/ΔlogL=0.078±0.026.