LOFAR Observations of Fine Spectral Structure Dynamics in Type IIIb Radio Bursts

Solar radio emission features a large number of fine structures demonstrating great variability in frequency and time. We present spatially resolved spectral radio observations of type IIIb bursts in the 30?–?80 MHz range made by the Low Frequency Array (LOFAR). The bursts show well-defined fine frequency structuring called “stria” bursts. The spatial characteristics of the stria sources are determined by the propagation effects of radio waves; their movement and expansion speeds are in the range of \((0.1\,\mbox{--}\,0.6)c\). Analysis of the dynamic spectra reveals that both the spectral bandwidth and the frequency drift rate of the striae increase with an increase of their central frequency. The striae bandwidths are in the range of \({\approx}\,(20\,\mbox{--}\,100)\) kHz and the striae drift rates vary from zero to \({\approx}\,0.3~\mbox{MHz}\,\mbox{s}^{-1}\). The observed spectral characteristics of the stria bursts are consistent with the model involving modulation of the type III burst emission mechanism by small-amplitude fluctuations of the plasma density along the electron beam path. We estimate that the relative amplitude of the density fluctuations is of \(\Delta n/n\sim10^{-3}\), their characteristic length scale is less than 1000 km, and the characteristic propagation speed is in the range of \(400\,\mbox{--}\,800~\mbox{km}\,\mbox{s}^{-1}\). These parameters indicate that the observed fine spectral structures could be produced by propagating magnetohydrodynamic waves.     

Interferometric Observations of the Quiet Sun at 20 and 25 MHz in May 2014

We present the results of solar observations at 20 and 25 MHz with the Ukrainian T-shaped Radio telescope of the second modification (UTR-2) in the interferometric session from 27 May to 2 June 2014. In this case, the different baselines 225, 450, and 675 m between the sections of the east–west and north–south arms of UTR-2 were used. On 29 May 2014, strong sporadic radio emission consisting of Type III, Type II, and Type IV bursts was observed. On other days, there was no solar radio activity in the decameter range. We discuss the observation results of the quiet Sun. Fluxes and sizes of the Sun in east–west and north–south directions were measured. The average fluxes were 1050?–?1100 Jy and 1480?–?1570 Jy at 20 and 25 MHz, respectively. The angular sizes of the quiet Sun in equatorial and polar directions were \(55'\) and \(49'\) at 20 MHz and \(50'\) and \(42'\) at 25 MHz. The brightness temperatures of the radio emission were \({T_{\mathrm{b}}} = 5.1 \times{10^{5}}~\mbox{K}\) and \({T_{\mathrm{b}}} = 5.7 \times{10^{5}}~\mbox{K}\) at 20 and 25 MHz, respectively.     

The Most Intense Electron-Scale Current Sheets in the Solar Wind

Previous analysis of magnetohydrodynamic-scale currents in high-speed solar wind near 1 AU suggests that the most intense current-carrying structures occur at electron scales and are characterized by average current densities on the order of \(1~\mbox{pA}/\mbox{cm}^{2}\). Here, this prediction is verified by examining the effects of the measurement bandwidth and/or measurement resolution on the analysis of synthetic solar wind signals. Assuming Taylor’s hypothesis holds for the energetically dominant fluctuations at kinetic scales, the results show that when \(\nu_{c}\gg \nu_{b}\), where \(\nu_{c}\) is the measurement bandwidth and \(\nu_{b} \approx 1/3~\mbox{Hz}\) is the break frequency, the average scale of the most intense fluctuations in the current density proxy is approximately \(1/\nu_{c}\), and the average peak current density is a weakly increasing function that scales approximately like \(\nu_{c}^{0.1}\).     

A Solar Stationary Type IV Radio Burst and Its Radiation Mechanism

A stationary Type IV (IVs) radio burst was observed on September 24, 2011. Observations from the Nançay RadioHeliograph (NRH) show that the brightness temperature (\(T_{\mathrm{B}}\)) of this burst is extremely high, over \(10^{11}\) K at 150 MHz and over \(10^{8}\) K in general. The degree of circular polarization (\(q\)) is between \(-60\% \sim -100\%\), which means that it is highly left-handed circularly polarized. The flux–frequency spectrum follows a power-law distribution, and the spectral index is considered to be roughly \(-3 \sim -4\) throughout the IVs. Radio sources of this event are located in the wake of the coronal mass ejection and are spatially dispersed. They line up to present a formation in which lower-frequency sources are higher. Based on these observations, it is suggested that the IVs was generated through electron cyclotron maser emission.     

Addendum to: Strength of the Solar Coronal Magnetic Field – A Comparison of Independent Estimates Using Contemporaneous Radio and White-Light Observations

This addendum uses an alternate fit for the electron density distribution \(N(r)\) (see Figure 1) and estimates the coronal magnetic field using the new model. We find that the estimates of the magnetic field are in close agreement using both the models.

We have fit the \(N(r)\) distribution obtained from STEREO-A/COR1 and SOHO/LASCO-C2 using a fifth-order polynomial (see Figure 1). The expression can be written as

$$\begin{aligned} N_{\text{cor}}(r) &= 1.43 \times 10^{9} r^{-5} - 1.91 \times 10^{9} r^{-4} + 1.07 \times 10^{9} r^{-3} - 2.87 \times 10^{8} r^{-2} \\ &\quad {} + 3.76 \times 10^{7} r^{-1} - 1.91 \times 10^{6} , \end{aligned}$$

(1)

where \(N_{\text{cor}}(r)\) is in units of cm^?3 and \(r\) is in units of \(\mathrm{R}_{\odot}\). The background coronal electron density is enhanced by a factor of 5.5 at 2.63 \(\mathrm{R}_{\odot}\) during the coronal mass ejection (CME). The estimated coronal magnetic field strength (\(B\)) using radio data indicates that \(B(r) \approx(0.51\text{\,--\,}0.48) \pm 0.02\ \mathrm{G}\) in the range \(r \approx2.65\text{\, --\,}2.82\ \mathrm{R}_{\odot}\). The field strengths for STEREO-A/COR1 and SOHO/LASCO-C2 are ≈?0.32 G at \(r \approx 3.11\ \mathrm{R}_{\odot}\) and ≈?0.12 G at \(r \approx 4.40\ \mathrm{R}_{\odot}\), respectively.

     

IRIS Observations of Spicules and Structures Near the Solar Limb

We have analyzed Interface Region Imaging Spectrograph (IRIS) spectral and slit-jaw observations of a quiet region near the South Pole. In this article we present an overview of the observations, the corrections, and the absolute calibration of the intensity. We focus on the average profiles of strong (Mg?ii h and k, C?ii and Si?iv), as well as of weak spectral lines in the near ultraviolet (NUV) and the far ultraviolet (FUV), including the Mg?ii triplet, thus probing the solar atmosphere from the low chromosphere to the transition region. We give the radial variation of bulk spectral parameters as well as line ratios and turbulent velocities. We present measurements of the formation height in lines and in the NUV continuum from which we find a linear relationship between the position of the limb and the intensity scale height. We also find that low forming lines, such as the Mg?ii triplet, show no temporal variations above the limb associated with spicules, suggesting that such lines are formed in a homogeneous atmospheric layer and, possibly, that spicules are formed above the height of \(2''\). We discuss the spatio-temporal structure of the atmosphere near the limb from images of intensity as a function of position and time. In these images, we identify p-mode oscillations in the cores of lines formed at low heights above the photosphere, slow-moving bright features in O?i and fast-moving bright features in C?ii. Finally, we compare the Mg?ii k and h line profiles, together with intensity values of the Balmer lines from the literature, with computations from the PROM57Mg non-LTE model, developed at the Institut d’ Astrophysique Spatiale, and estimated values of the physical parameters. We obtain electron temperatures in the range of \({\sim}\, 8000~\mbox{K}\) at small heights to \({\sim}\, 20\,000~\mbox{K}\) at large heights, electron densities from \(1.1\times 10^{11}\) to \(4\times 10^{10}~\mbox{cm}^{-3}\) and a turbulent velocity of \({\sim}\, 24~\mbox{km}\,\mbox{s}^{-1}\).     

Timing irregularities of PSR J1705–1906

Timing analysis of PSR J1705–1906 using data from Nanshan 25-m and Parkes 64-m radio telescopes, which span over fourteen years, shows that the pulsar exhibits significant proper motion, and rotation instability. We updated the astrometry parameters and the spin parameters of the pulsar. In order to minimize the effect of timing irregularities on measuring its position, we employ the Cholesky method to analyse the timing noise. We obtain the proper motion of \(-77(3)\) mas?yr^?1 in right ascension and \(-38(29)\) mas?yr^?1 in declination. The power spectrum of timing noise is analyzed for the first time, which gives the spectral exponent \(\alpha =-5.2\) for the power-law model indicating that the fluctuations in spin frequency and spin-down rate dominate the red noise. We detect two small glitches from this pulsar with fractional jump in spin frequency of \(\Delta \nu /\nu \sim 2.9 \times 10^{-10}\) around MJD 55199 and \(\Delta \nu /\nu \sim 2.7\times 10^{-10}\) around MJD 55953. Investigations of pulse profile at different time segments suggest no significant changes in the pulse profiles around the two glitches.     

The global modulation of Galactic and Jovian electrons in the heliosphere

A full three-dimensional, numerical model is used to study the modulation of Jovian and Galactic electrons from 1 MeV to 50 GeV, and from the Earth into the heliosheath. For this purpose the very local interstellar spectrum and the Jovian electron source spectrum are revisited. It is possible to compute the former with confidence at kinetic energies \(E < 50~\mbox{MeV}\) since Voyager 1 crossed the heliopause in 2012 at \(\sim 122~\mbox{AU}\), measuring Galactic electrons at these energies. Modeling results are compared with Voyager 1 observations in the outer heliosphere, including the heliosheath, as well as observations at or near the Earth from the ISSE3 mission, and in particular the solar minimum spectrum from the PAMELA space mission for 2009, also including data from Ulysses for 1991 and 1992, and observations above 1 MeV from SOHO/EPHIN. Making use of the observations at or near the Earth and the two newly derived input functions for the Jovian and Galactic electrons respectively, the energy range over which the Jovian electrons dominate the Galactic electrons is determined so that the intensity of Galactic electrons at Earth below 100 MeV is calculated. The differential intensity for the Galactic electrons at Earth for \(E = 1~\mbox{MeV}\) is \(\sim 4\) electrons \(\mbox{m}^{-2}\,\mbox{s}^{-1}\,\mbox{sr}^{-1}\,\mbox{MeV}^{-1}\), whereas for Jovian electrons it is \(\sim 350\) electrons \(\mbox{m}^{-2}\,\mbox{s}^{-1}\,\mbox{sr}^{-1}\,\mbox{MeV}^{-1}\). At \(E = 30~\mbox{MeV}\) the two intensities are the same; above this energy the Jovian electron intensity quickly subsides so that the Galactic intensity completely dominates. At 6 MeV, in the equatorial plane the Jovian electrons dominate but beyond \(\sim 15~\mbox{AU}\) the Galactic intensity begins to exceed the Jovian intensity significantly.     

A Major Geoeffective CME from NOAA 12371: Initiation,CME–CME Interactions,and Interplanetary Consequences

In this article, we present a multi-wavelength and multi-instrument investigation of a halo coronal mass ejection (CME) from active region NOAA 12371 on 21 June 2015 that led to a major geomagnetic storm of minimum \(\mathrm{Dst} = -204\) nT. The observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot EUV channel of 94 Å confirm the CME to be associated with a coronal sigmoid that displayed an intense emission (\(T \sim6\) MK) from its core before the onset of the eruption. Multi-wavelength observations of the source active region suggest tether-cutting reconnection to be the primary triggering mechanism of the flux rope eruption. Interestingly, the flux rope eruption exhibited a two-phase evolution during which the “standard” large-scale flare reconnection process originated two composite M-class flares. The eruption of the flux rope is followed by the coronagraphic observation of a fast, halo CME with linear projected speed of 1366 km?s^?1. The dynamic radio spectrum in the decameter-hectometer frequency range reveals multiple continuum-like enhancements in type II radio emission which imply the interaction of the CME with other preceding slow speed CMEs in the corona within \(\approx10\)?–?\(90~\mbox{R} _{\odot}\). The scenario of CME–CME interaction in the corona and interplanetary medium is further confirmed by the height–time plots of the CMEs occurring during 19?–?21 June. In situ measurements of solar wind magnetic field and plasma parameters at 1 AU exhibit two distinct magnetic clouds, separated by a magnetic hole. Synthesis of near-Sun observations, interplanetary radio emissions, and in situ measurements at 1 AU reveal complex processes of CME–CME interactions right from the source active region to the corona and interplanetary medium that have played a crucial role towards the large enhancement of the geoeffectiveness of the halo CME on 21 June 2015.     

Formation of Thorne–Żytkow objects in close binaries

Thorne–?ytkow objects (T?Os), originally proposed by Thorne and ?ytkow, may form as a result of unstable mass transfer in a massive X-ray binary after a neutron star (NS) is engulfed in the envelope of its companion star. Using a rapid binary evolution program and the Monte Carlo method, we simulated the formation of T?Os in close binary stars. The Galactic birth rate of T?Os is about \(1.5\times 10^{-4}~\hbox {yr}^{-1}\). Their progenitors may be composed of a NS and a main-sequence star, a star in the Hertzsprung gap or a core-helium burning, or a naked helium star. The birth rates of T?Os via the above different progenitors are \(1.7\times 10^{-5}\), \(1.2\times 10^{-4}\), \(0.7\times 10^{-5}\), \(0.6\times 10^{-5}~\hbox {yr}^{-1}\), respectively. These progenitors may be massive X-ray binaries. We found that the observational properties of three massive X-ray binaries (SMC X-1, Cen X-3 and LMC X-4) in which the companions of NSs may fill their Roche robes were consistent with those of their progenitors.     

Spatial Distribution of Element Abundances and Ionization States in Solar Energetic-Particle Events

We have studied the spatial and temporal distribution of abundances of chemical elements in large “gradual” solar energetic-particle (SEP) events, and especially the source plasma temperatures, derived from those abundances, using measurements from the Wind and Solar TErrestrial RElations Observatory (STEREO) spacecraft, widely separated in solar longitude. A power-law relationship between abundance enhancements and mass-to-charge ratios [\(A/Q\)] of the ions can be used to determine \(Q\)-values and source plasma temperatures at remote spacecraft with instruments that were not designed for charge-state measurements. We search for possible source variations along the accelerating shock wave, finding one clear case where the accelerating shock wave appears to dispatch ions from \(3.2\pm 0.8~\mbox{MK}\) plasma toward one spacecraft and those from \(1.6\pm 0.2~\mbox{MK}\) plasma toward another, 116^° away. The difference persists for three days and then fades away. Three other SEP events show less-extreme variation in source temperatures at different spacecraft, in one case observed over 222^° in longitude. This initial study shows how the power-law relation between abundance enhancements and ion \(A/Q\)-values provides a new technique to determine \(Q\) and plasma temperatures in the seed population of SEP ions over a broad region of space using remote spacecraft with instruments that were not originally designed for measurements of ionization states.     

LASCO White-Light Observations of Eruptive Current Sheets Trailing CMEs

Many models of eruptive flares or coronal mass ejections (CMEs) involve formation of a current sheet connecting the ejecting CME flux rope with a magnetic loop arcade. However, there is very limited observational information on the properties and evolution of these structures, hindering progress in understanding eruptive activity from the Sun. In white-light images, narrow coaxial rays trailing the outward-moving CME have been interpreted as current sheets. Here, we undertake the most comprehensive statistical study of CME-rays to date. We use SOHO/LASCO data, which have a higher cadence, larger field of view, and better sensitivity than any previous coronagraph. We compare our results to a previous study of Solar Maximum Mission (SMM) CMEs, in 1984?–?1989, having candidate magnetic disconnection features at the CME base, about half of which were followed by coaxial bright rays. We examine all LASCO CMEs during two periods of minimum and maximum activity in Solar Cycle 23, resulting in many more events, \(\sim130\) CME-rays, than during SMM. Important results include: The occurrence rate of the rays is \(\sim11~\%\) of all CMEs during solar minimum, but decreases to \(\sim7~\%\) at solar maximum; this is most likely related to the more complex coronal background. The rays appear on average 3?–?4 hours after the CME core, and are typically visible for three-fourths of a day. The mean observed current sheet length over the ray lifetime is \(\sim12~R_{\odot}\), with the longest current sheet of \(18.5~R_{\odot}\). The mean CS growth rates are \(188~\mbox{km}\,\mathrm{s}^{-1}\) at minimum and \(324~\mbox{km}\,\mathrm{s}^{-1}\) at maximum. Outward-moving blobs within several rays, which are indicative of reconnection outflows, have average velocities of \(\sim350~\mbox{km}\,\mathrm{s}^{-1}\) with small positive accelerations. A pre-existing streamer is blown out in most of the CME-ray events, but half of these are observed to reform within \(\sim1\) day. The long lifetime and long lengths of the CME-rays challenge our current understanding of the evolution of the magnetic field in the aftermath of CMEs.     

Markarian galaxies in UV and multiwavelength studies

The UV properties of 1152 Markarian galaxies have been investigated based on GALEX data. These objects have been investigated also in other available wavelengths using multi-wavelength data from X-ray to radio. Using our classification for activity types for 779 Markarian galaxies based on SDSS spectroscopy, we have investigated these objects on the GALEX, 2MASS and WISE color-magnitude and color-color diagrams by the location of objects of different activity types and have revealed a number of loci. UV contours overplotted on the optical images revealed additional structures, particularly spiral arms of a number of Markarian galaxies. UV (FUV and NUV) and optical absolute magnitudes and luminosities have been calculated showing graduate transition from AGN to Composites, HIIs and Absorption line galaxies from (average \(M\)) \(-17.56^{m}\) to \(-15.20^{m}\) in FUV, from \(-18.07^{m}\) to \(-15.71^{m}\) in NUV and from AGN to Composites, Absorption line galaxies and HII from \(-21.14^{m}\) to \(-19.42^{m}\) in optical wavelengths and from (average \(L\)) \(7\times10^{9}\) to \(4 \times 10^{8}\) in FUV, from \(1\times 10^{10}\) to \(5\times10^{8}\) in NUV and from AGN to Composites, Absorption line galaxies and HII from \(7\times10^{10}\) to \(1\times10^{10}\) in optical wavelengths.     

Comparative Study of the Three-Dimensional Thermodynamical Structure of the Inner Corona of Solar Minimum Carrington Rotations 1915 and 2081

Using differential emission measure tomography (DEMT) based on time series of EUV images, we carry out a quantitative comparative analysis of the three-dimensional (3D) structure of the electron density and temperature of the inner corona (\(r<1.25\,\mathrm{R}_{\odot}\)) between two specific rotations selected from the last two solar minima, namely Carrington Rotations (CR)1915 and CR-2081. The analysis places error bars on the results because of the systematic uncertainty of the sources. While the results for CR-2081 are characterized by a remarkable north–south symmetry, the southern hemisphere for CR-1915 exhibits higher densities and temperatures than the northern hemisphere. The core region of the streamer belt in both rotations is found to be populated by structures whose temperature decreases with height (called “down loops” in our previous articles). They are characterized by plasma \(\beta\gtrsim1\), and may be the result of the efficient dissipation of Alfvén waves at low coronal heights. The comparative analysis reveals that the low latitudes of the equatorial streamer belt of CR-1915 exhibit higher densities than for CR-2081. This cannot be explained by the systematic uncertainties. In addition, the southern hemisphere of the streamer belt of CR-1915 is characterized by higher temperatures and density scale heights than for CR-2081. On the other hand, the coronal hole region of CR-1915 shows lower temperatures than for CR-2081. The reported differences are in the range \({\approx}\,10\,\mbox{--}\,25\%\), depending on the specific physical quantity and region that is compared, as fully detailed in the analysis. For other regions and/or physical quantities, the uncertainties do not allow assessing the thermodynamical differences between the two rotations. Future investigation will involve a DEMT analysis of other Carrington rotations selected from both epochs, and also a comparison of their tomographic reconstructions with magnetohydrodynamical simulations of the inner corona.     

Heights of Coronal Mass Ejections and Shocks Inferred from Metric and DH Type II Radio Bursts

A set of 27 continuous events that showed extension of metric Type-II radio bursts (m-Type IIs) into the deca–hectometric (DH) domain is considered. The coronal mass ejections (CMEs) associated with this type of continuous event supply more energy to produce space-weather effects than the CMEs that produce Type-II bursts in any one region. Since the heights of shock formation at the start of m-Type IIs were not available from observations, they were estimated using kinematic modeling in previous studies. In the present study, the heights of shock formation during metric and DH Type-II bursts are determined using two methods: i) the CME leading-edge method and ii) a method employing known electron-density models and start/end frequencies. In the first method, assuming that the shocks are generated by the associated CMEs at the leading edge, the height of the CME leading edge (LE) is calculated at the onset and end of m-Type IIs using the kinematic equation with constant acceleration or constant speed. The LE heights of CMEs that are assumed to be the heights of shock formation/end of nearly 79% of m-Type IIs are found to be within the acceptable range of \(1\,\mbox{--}\,3~\mbox{R}_{\odot}\). For other events, the heights are beyond this range, for which the shocks might either have been generated at the CME flanks/flare-blast waves, or the initial CME height might have been different. The CME/shock height at the onset and end of 17 DH Type IIs are found to be in the range of \(2\,\mbox{--}\,6~\mbox{R}_{\odot}\) and within \(30~\mbox{R}_{\odot}\), respectively. In addition, the CME LE heights from observations at the onset and end of metric/DH Type IIs are compared with the heights corresponding to the observed frequency that is determined using the known electron-density models, and they are in agreement with the model results. The heights are also estimated using the space speed available for 15 halo CMEs, and it is found that the difference is smaller at the m-Type II start/end (0.02 to \(0.66~\mbox{R}_{\odot}\)) and slightly greater at the DH Type II end (0.19 to \(1.94~\mbox{R}_{\odot}\)). Finally, the possibility of CME–streamer interactions at the start of DH Type IIs is checked, and it is found that many of the events with streamers have lower start frequencies. In addition, these results are discussed in comparison with the values reported in the literature. This study will be useful to find the source region of metric and DH Type IIs and to understand the CME-shock propagation.     

Decameter Type IV Burst Associated with a Behind-the-limb CME Observed on 7 November 2013

We report on the results of observations of a type IV burst made by the Ukrainian Radio interferometer of the Academy of Sciences (URAN-2) in the frequency range 22?–?33 MHz. The burst is associated with a coronal mass ejection (CME) initiated by a behind-the-limb active region (N05E151) and was also observed by the Nançay Decameter Array (NDA) radio telescope in the frequency band 30?–?60 MHz. The purpose of the article is the determination of the source of this type IV burst. After analysis of the observational data obtained with the URAN-2, the NDA, the Solar-Terrestrial Relations Observatory (STEREO) A and B spacecraft, and the Solar and Heliospheric Observatory (SOHO) spacecraft, we come to the conclusion that the source of the burst is the core of a behind-the-limb CME. We conclude that the radio emission can escape the center of the CME core at a frequency of 60 MHz and originates from the periphery of the core at a frequency of 30 MHz that is due to occultation by the solar corona at the corresponding frequencies. We find plasma densities in these regions assuming the plasma mechanism of radio emission. We show that the frequency drift of the start of the type IV burst is governed by an expansion of the CME core. The type III bursts that were observed against this type IV burst are shown to be generated by fast electrons propagating through the CME core plasma. A type II burst was registered at frequencies of 44?–?64 MHz and 3?–?16 MHz and was radiated by a shock with velocities of about \(1000~\mbox{km}\,\mbox{s}^{-1}\) and \(800~\mbox{km}\,\mbox{s}^{-1}\), respectively.     

Linear Polarization Features in the Quiet-Sun Photosphere: Structure and Dynamics

We present detailed characteristics of linear polarization features (LPFs) in the quiet-Sun photosphere from high-resolution observations obtained with Sunrise/IMaX. We explore differently treated data with various noise levels in linear polarization signals, from which structure and dynamics of the LPFs are studied. Physical properties of the detected LPFs are also obtained from the results of Stokes inversions. The number of LPFs and their sizes and polarization signals are found to be strongly dependent on the noise level and on the spatial resolution. While the linear polarization with a signal-to-noise ratio \(\geq4.5\) covers about 26% of the entire area in the least noisy data in our study (with a noise level of \(1.7\times10^{-4}\) in the unit of Stokes \(I\) continuum), the detected (spatially resolved) LPFs cover about 10% of the area at any given time, with an occurrence rate on the order of \(8\times10^{-3}\mbox{ s}^{-1}\)?arcsec^?2. The LPFs were found to be short lived (in the range of 30?–?300 s), relatively small structures (radii of \(\approx0.1\)?–?1.5 arcsec), highly inclined, posing hG fields, and they move with an average horizontal speed of 1.2 km?s^?1. The LPFs were observed (almost) equally on both upflow and downflow regions, with an intensity contrast always larger than that of the average quiet Sun.     

The Na <Emphasis Type="SmallCaps">i</Emphasis> and Sr <Emphasis Type="SmallCaps">ii</Emphasis> Resonance Lines in Solar Prominences

We estimate the electron density, \(n_{\mathrm{e}}\), and its spatial variation in quiescent prominences from the observed emission ratio of the resonance lines Na?i?5890 Å (D₂) and Sr?ii?4078 Å. For a bright prominence (\(\tau_{\alpha}\approx25\)) we obtain a mean \(n_{\mathrm{e}}\approx2\times10^{10}~\mbox{cm}^{-3}\); for a faint one (\(\tau _{\alpha }\approx4\)) \(n_{\mathrm{e}}\approx4\times10^{10}~\mbox{cm}^{-3}\) on two consecutive days with moderate internal fluctuation and no systematic variation with height above the solar limb. The thermal and non-thermal contributions to the line broadening, \(T_{\mathrm{kin}}\) and \(V_{\mathrm{nth}}\), required to deduce \(n_{\mathrm{e}}\) from the emission ratio Na?i/Sr?ii cannot be unambiguously determined from observed widths of lines from atoms of different mass. The reduced widths, \(\Delta\lambda_{\mathrm{D}}/\lambda_{0}\), of Sr?ii?4078 Å show an excess over those from Na?D₂ and \(\mbox{H}\delta\,4101\) Å, assuming the same \(T_{\mathrm{kin}}\) and \(V_{\mathrm{nth}}\). We attribute this excess broadening to higher non-thermal broadening induced by interaction of ions with the prominence magnetic field. This is suggested by the finding of higher macro-shifts of Sr?ii?4078 Å as compared to those from Na?D₂.     

STEREO observations of hybrid stars V775 Tau and V483 Tau

In this study, pulsational and physical characteristics of two \(\delta\) Scuti stars, V775?Tau and V483?Tau, are analysed by using four-year high-precision photometric data of the STEREO satellite. Thus, it is aimed to gain new insights into behaviours of these pulsators and evolution of \(\delta\) Scuti, \(\gamma\) Dor and Am type stars. The data are taken between 2007–2011 and examined with the help of the Lomb–Scargle method. The detection precision in the four-year combined data is around \(10^{-5}\) cd^?1 in frequency and \(10^{-5}\) mag in amplitude. It is revealed that V775?Tau exhibits weak pulsation characteristic which is interpreted as the existence of the interaction between the helium loss in the partial ionization zone and pulsation intensities. It is also considered that the absence of strong pulsations is also related to the evolution status of the star. Further, its periodogram shows low-frequency peaks. If these oscillations are g-modes, V775?Tau can be thought to be one of the rare stars that show all \(\gamma\) Dor, \(\delta\) Scuti and Am type variations. V483?Tau is comparatively more luminous, hotter and has higher rotational velocity. Therefore, although it shares the same region with V775?Tau in the H–R diagram, it is not considered to be an Am star. Yet, it exactly overlaps with the \(\gamma\) Dor stars. These clues as well as g-modes detected in its periodogram indicate that V483?Tau is a hybrid star. Finally, both V775?Tau and V483?Tau display period changes whose rates are between \(10^{-3}\) and \(10^{-4}\) yr^?1. Considering the \(\delta\) Scuti nature, it may be speculated that these changes are non-evolutionary.     

Density variation effect on multi-ions with kinetic Alfven wave around cusp region—a kinetic approach

The kinetic Alfven waves in the presence of homogeneous magnetic field plasma with multi-ions effect are investigated. The dispersion relation and normalised damping rate are derived for low-\(\beta\) plasma using kinetic theory. The effect of density variation of \(\text{H}^{+}\), \(\text{He}^{+}\) and \(\text{O}^{+}\) ions is observed on frequency and damping rate of the wave. The variation of frequency (\(\omega\)) and normalised damping rate (\(\gamma / \varOmega_{H^{ +}} \)) of the wave are studied with respect to \(k_{ \bot} \rho_{j}\), where \(k_{ \bot} \) is the perpendicular wave number, \(\rho_{j}\) is the ion gyroradius and \(j \) denotes \(\text{H}^{+}\), \(\text{He}^{+}\) and \(\text{O}^{+}\) ions. The variation with \(k_{ \bot} \rho_{j}\) is considered over wide range. The parameters appropriate to cusp region are used for the explanation of results. It is found that with hydrogen and helium ions gyration, the frequency of wave is influenced by the density variation of \(\text{H}^{+}\) and \(\text{He}^{+}\) ions but remains insensitive to the change in density of \(\text{O}^{+}\) ions. For oxygen ion gyration, the frequency of wave varies over a short range only for \(\text{O}^{+}\) ion density variation. The wave shows damping at lower altitude due to variation in density of lighter \(\text{H}^{+}\) and \(\text{He}^{+}\) ions whereas at higher altitude only heavy \(\text{O}^{+}\) ions contribute in wave damping. The damping of wave may be due to landau damping or energy transfer from wave to particles. The present study signifies that the both lighter and heavier ions dominate differently to change the characteristics of kinetic Alfven wave and density variation is also an important parameter to understand wave phenomena in cusp region.