Evidence of Traveling Waves in Filament Threads

High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m Solar Telescope resolve numerous very thin, thread-like structures in solar filaments. The threads are believed to represent thin magnetic flux tubes that must be longer than the observable threads. We report on evidence for small-amplitude (1 – 2 km s⁻¹) waves propagating along a number of threads with an average phase velocity of 12 km s⁻¹ and a wavelength of 4″. The oscillatory period of individual threads vary from 3 to 9 minutes. Temporal variation of the Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6 minutes) wave pattern. These short-period oscillations could possibly represent fast modes in accordance with numerical fibril models proposed by Díaz et al. (Astron. Astrophys. 379, 1083, 2001). In some cases, it is clear that the propagating waves are moving in the same direction as the mass flows.     

ROSA: A High-cadence,Synchronized Multi-camera Solar Imaging System

The Rapid Oscillations in the Solar Atmosphere (ROSA) instrument is a synchronized, six-camera high-cadence solar imaging instrument developed by Queen’s University Belfast. The system is available on the Dunn Solar Telescope at the National Solar Observatory in Sunspot, New Mexico, USA, as a common-user instrument. Consisting of six 1k × 1k Peltier-cooled frame-transfer CCD cameras with very low noise (0.02 – 15 e s⁻¹ pixel⁻¹), each ROSA camera is capable of full-chip readout speeds in excess of 30 Hz, or 200 Hz when the CCD is windowed. Combining multiple cameras and fast readout rates, ROSA will accumulate approximately 12 TB of data per 8 hours observing. Following successful commissioning during August 2008, ROSA will allow for multi-wavelength studies of the solar atmosphere at a high temporal resolution.     

Temporal Evolution of a Rapidly-Moving Umbral Dot

We performed two-dimensional spectroscopic observations of the preceding sunspot of NOAA 10905 located off disk center (S8 E36, μ≈0.81) by using the Interferometric BI-dimensional Spectrometer (IBIS) operated at the Dunn Solar Telescope (DST) of the National Solar Observatory, New Mexico. The magnetically insensitive Fe I line at 709.04 nm was scanned in wavelength repetitively at an interval of 37 s to calculate sequences of maps of the line-wing and line-core intensity, and the line-of-sight Doppler velocity at different line depths (3% to 80%). Visual inspection of movies based on speckle reconstructions computed from simultaneous broadband data and the local continuum intensity at 709.04 nm revealed an umbral dot (UD) intruding rapidly from the umbral boundary to the center of the umbra. The apparent motion of this object was particularly fast (1.3 km s⁻¹) when compared to typical UDs. The lifetime and size of the UD was 8.7 min and 240 km, respectively. The rapid UD was visible even in the line-core intensity map of Fe I 709.04 nm and was accompanied by a persistent blueshift of about 0.06 km s⁻¹.     

Umbral Three-Minute Oscillations and Running Penumbral Waves

We present results of investigations into chromospheric velocity oscillations in sunspots, carried out at the Sayan Solar Observatory. It is shown that the “chevron” structures in the space-time diagrams demonstrate wavetrain properties. Such structures are indicators of a propagating wave process and they are typical of many sunspots. In the authors’ opinion, three-minute umbral oscillations are not the source of running penumbral waves (RPW). It is very likely that umbral oscillations and RPW initially propagate along different magnetic field lines. We explain the decrease in RPW propagation velocity and frequency in the outer penumbra, as compared with the inner, by the combined action of different frequency modes. To better reveal the properties of these modes, frequency filtering was used. Our measurements of the RPW (five-minute mode) wavelength and RPW propagation velocity in different sunspots vary from 12^″ to 30^″ and from 28 to 60 – 70 km s⁻¹ correspondingly.     

Galactic kinematics from OB3 stars with distances determined from interstellar Ca II lines

Based on data for 102 OB3 stars with known proper motions and radial velocities, we have tested the distances derived by Megier et al. from interstellar Ca II spectral lines. The internal reconciliation of the distance scales using the first derivative of the angular velocity of Galactic rotation Ω′₀ and the external reconciliation with Humphreys’s distance scale for OB associations refined by Mel’nik and Dambis show that the initial distances should be reduced by ≈20%. Given this correction, the heliocentric distances of these stars lie within the range 0.6–2.6 kpc. A kinematic analysis of these stars at a fixed Galactocentric distance of the Sun, R ₀ = 8 kpc, has allowed the following parameters to be determined: (1) the solar peculiar velocity components (u _⊙, v _⊙, ω _⊙) = (8.9, 10.3, 6.8) ± (0.6, 1.0, 0.4) km s⁻¹; (2) the Galactic rotation parameters Ω₀ = −31.5 ± 0.9 km s⁻¹ kpc⁻¹, Ω′₀ = +4.49 ± 0.12 km s⁻¹ kpc⁻², Ω″₀ = −1.05 ± 0.38 km s⁻¹ kpc⁻³ (the corresponding Oort constants are A = 17.9 ± 0.5 km s⁻¹ kpc⁻¹, B = −13.6 ± 1.0 km s⁻¹ kpc⁻¹ and the circular rotation velocity of the solar neighborhood is |V ₀| = 252 ± 14 km s⁻¹); (3) the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, f _R = −12.5±1.1 km s⁻¹ and f _ϑ = 2.0 ± 1.6 km s⁻¹; the pitch angle for the two-armed spiral pattern i = −5.3° ± 0.3°, with the wavelength of the spiral density wave at the solar distance being λ = 2.3 ± 0.2 kpc; the Sun’s phase in the spiral wave x _⊙ = −91° ± 4°.     

Results of astrometrical observations of the Sun and major planets at the mountain astronomical station of the Pulkovo Observatory

A series of daytime observations of the Sun and major planets are obtained at the mountain astronomical station of the Pulkovo Observatory using the Ertel-Struve meridian instruments. A series of declinations of Solar System bodies and major planets includes 4057 positions and that of right ascensions of Solar System bodies comprising 2057 positions. Based on the joint processing of observations of the Sun, Mercury, Venus, and Mars obtained with the Ertel-Struve vertical circle and large transit instrument, the orientation elements of the DE200/LE200 dynamic coordinate system, namely, a correction for the right ascensions of FK5 stars ΔA = +0.127″ ± 0.033″, a correction for declinations of FK5 stars ΔD = +0.056″ ± 0.011″, a correction for the ecliptic inclination Δɛ = −0.044″ ± 0.012″, and a correction for the average longitude of the Sun ΔL = −0.083″±0.035″, are determined with respect to the stellar coordinate system.     

The kinematics of Trapezium-type systems

Summary In this paper the results of the research of the stars proper motions Trapezium components are reported. They are: the galactic coordinates of the solar aprx and the Sun velocity (L _⊙=43±18°,B _⊙=+28±13°,V _⊙=13±4 km s⁻¹), the dispersion of peculiar velocities in the direction of the galactic coordinates for the above mentioned stars (σ _l =±11 km s⁻¹, σ _b =±7 km s⁻¹).The attained accuracy of the proper motions (±0.005″ yr⁻¹) is shown to be insufficient to the study of internal space motions in these systems. At present the work to increase the relative proper motions accuracy for multiple system components and to improve reductions from the relative to absolute proper motions, is being carried out in the Main Astronomical Observatory (Academy of Sciences of the Ukrainian SSR). The new catalogue of the AGK3 stars is composed now in the vicinity of the galactic equator in order to improve reductions from the relative to absolute proper motions. The r.m.s. errors of the proper motions, obtained in the AGK3 system, are ±0.005″ yr⁻¹.     

Acoustic Events in the Solar Atmosphere from <Emphasis Type="Italic">Hinode</Emphasis>/SOT NFI Observations

We investigate the properties of acoustic events (AEs), defined as spatially concentrated and short duration energy flux, in the quiet Sun, using observations of a 2D field of view (FOV) with high spatial and temporal resolution provided by the Solar Optical Telescope (SOT) onboard Hinode. Line profiles of Fe i 557.6 nm were recorded by the Narrow-band Filter Imager (NFI) on a 82″×82″ FOV during 75 min with a time step of 28.75 s and 0.08″ pixel size. Vertical velocities were computed at three atmospheric levels (80, 130, and 180 km) using the bisector technique, allowing the determination of energy flux to be made in the range 3 – 10 mHz using two complementary methods (Hilbert transform and Fourier power spectrum). Horizontal velocities were computed using local correlation tracking (LCT) of continuum intensities providing divergences. We found that the net energy flux is upward. In the range 3 – 10 mHz, a full FOV space and time averaged flux of 2700 W m⁻² (lower layer 80 – 130 km) and 2000 W m⁻² (upper layer 130 – 180 km) is concentrated in less than 1 % of the solar surface in the form of narrow (0.3″) AE. Their total duration (including rise and decay) is of the order of 10³ s. Inside each AE, the mean flux is 1.6×10⁵ W m⁻² (lower layer) and 1.2×10⁵ W m⁻² (upper). Each event carries an average energy (flux integrated over space and time) of 2.5×10¹⁹ J (lower layer) to 1.9×10¹⁹ J (upper). More than 10⁶ events could exist permanently on the Sun, with a birth and decay rate of 3500 s⁻¹. Most events occur in intergranular lanes, downward velocity regions, and areas of converging motions.     

Modeling of EIS Spectrum Drift from Instrumental Temperatures

An empirical model has been developed to reproduce the drift of the spectrum recorded by the EIS on Hinode using instrumental temperatures and relative motion of the spacecraft. The EIS spectrum shows an artificial drift in wavelength dimension in sync with the revolution of the spacecraft, which is caused by temperature variations inside the spectrometer. The drift amounts to 70 km s⁻¹ in Doppler velocity and introduces difficulties in velocity measurements. An artificial neural network is incorporated to establish a relationship between the instrumental temperatures and the spectral drift. This empirical model reproduces observed spectrum shift with an rms error of 4.4 km s⁻¹. This procedure is robust and applicable to any spectrum obtained with EIS, regardless of the observing field. In addition, spectral curvatures and spatial offset in the north – south direction are determined to compensate for instrumental effects.     

Recent work on CNO in dwarfs and subdwarfs

The recent results on CNO in dwarfs and subdwarfs are discussed. The value of [O/Fe] ≃ 0.0 at solar abundances but gradually increases with decreasing [Fe/H]. The value of [C/Fe] is constant at ≃ 0.0 ₋₂ ⁺¹ as [Fe/H] declines from + 0.5 to −2.0; for [Fe/H] < − 2.0, [C/Fe] increases somewhat reaching a mean value near + 0.2 or + 0.3 dex. All the investigations agree that N has a strong primary component.     

The EVE Doppler Sensitivity and Flare Observations

The Extreme-ultraviolet Variability Experiment (EVE; see Woods et al., 2009) obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity of the EVE data. We find that the 30.4 nm line of He ii has a random Doppler error below 0.001 nm (1 pm, better than 10 km s⁻¹ as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE’s optical layout, which (as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we find the line centroid to have a redshift of 16.8 ± 5.9 km s⁻¹ relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as Fe xxiv 19.2 nm, have well-determined Doppler components for major flares, with decreasing apparent blueshifts as expected from chromospheric evaporation flows.     

Characteristics of CMEs associated with solar flares and DH type II radio bursts based on source position

We studied the characteristics of Coronal Mass Ejections (CMEs) associated with solar flares and Deca-Hectometric (DH) type II radio bursts, based on source position during 23rd solar cycle (1997–2007). We classified these CME events into three groups using solar flare locations as, (i) disk events (0–30^∘); (ii) intermediate events (31–60^∘) and (iii) limb events (61–90^∘). Main results from this studies are, (i) the number of CMEs associated with solar flares and DH-type IIs decreases as the source position approaches from disk to limb, (ii) most of the DH CMEs are halo (72%) in disk events and the number of occurrence of halo CMEs decreases from disk to limb, (iii) the average width and speed of limb events (164^∘ and 1447 km s⁻¹) are higher than those of disk events (134^∘ and 1035 km s⁻¹) and intermediate events (146^∘ and 1170 km s⁻¹) and (iv) the average accelerations for disk, intermediate and limb events are −8.2 m s⁻², −10.3 m s⁻² and −4.5 m s⁻² respectively. These analysis of CMEs properties show more dependency on longitude and it gives strong evidence for projection effect.     

Periodic Motion Along Solar Filaments

We present observations of four filaments that exhibit large-amplitude periodic mass motion. Observations are obtained using the high resolution (2″) and high cadence (1 min) Hα telescope system at the Big Bear Solar Observatory (BBSO). The motions found in these events are along the axis of the filaments, and are associated with the activity of a nearby flare or filament. The most characteristic properties of these motions are long period (≥ q80 min), large distance (≥ q 4 × 10⁴ km) of mass transport at much higher velocity (≥ q 30 km s⁻¹) than ever detected from filament motions. The velocity, period, dimension and damping timescale measured for these motions are presented, and discussed to identify the most plausible restoring force and damping mechanism.     

Counterstreaming in a Large Polar Crown Filament

The motion of small-scale structures is well resolved in high-resolution filament images that were observed on 19 June 1998 with the Swedish Vacuum Solar Telescope, La Palma. The filament was between 80 000 and 100 000 km high. The study is based on two hours of narrow-band observations at three wavelength positions in Hα. Velocities along the line of sight and in the transverse direction, respectively, V _los and V _tr, were measured for a large number of individual small-scale filament structures. Small features are all moving along nearly parallel threads, some in one direction along the threads and the remainder in the other direction, a pattern of motion known as counterstreaming. The net flow velocities in the two directions are about 8 km s⁻¹ and both are tilted by an angle δ≃16° relative to the plane of the sky. This angle is less than expected, by factors between 2.0 and 2.5, relative to the local horizontal plane. We believe that V _los is underestimated by these factors due to a line-shift reducing effect by the underlying Hα absorption line of the chromosphere. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1026150809598     

Solar Wind Quasi-invariant for Slow and Fast Magnetic Clouds

The solar wind quasi-invariant (QI) has been defined by Osherovich, Fainberg, and Stone (Geophys. Res. Lett. 26, 2597, 1999) as the ratio of magnetic energy density and the energy density of the solar wind flow. In the regular solar wind QI is a rather small number, since the energy of the flow is almost two orders of magnitude greater than the magnetic energy. However, in magnetic clouds, QI is the order of unity (less than 1) and thus magnetic clouds can be viewed as a great anomaly in comparison with its value in the background solar wind. We study the duration, extent, and amplitude of this anomaly for two groups of isolated magnetic clouds: slow clouds (360<v<450 km s⁻¹) and fast clouds (450≤v<720 km s⁻¹). By applying the technique of superposition of epochs to 12 slow and 12 fast clouds from the catalog of Richardson and Cane (Solar Phys. 264, 189, 2010), we create an average slow cloud and an average fast cloud observed at 1 AU. From our analysis of these average clouds, we obtain cloud boundaries in both time and space as well as differences in QI amplitude and other parameters characterizing the solar wind state. Interplanetary magnetic clouds are known to cause major magnetic storms at the Earth, especially those clouds which travel from the sun to the Earth at high speeds. Characterizing each magnetic cloud by its QI value and extent may help in understanding the role of those disturbances in producing geomagnetic activity.     

1.3 mm Plateau de Bure Observations of IRC+10216

The Plateau de Bure millimeter-wave interferometer has been used at 1.3 mm wavelength to observe the prototype carbon-star IRC+10216 in the continuum and in the v = 1, J = 13 − 11 transition of SiS at 234.8 GHz. The 3 mm continuum and the v = (0, 2⁰, 2), J = 1 − 0 HCN transition were simultaneously observed. The source of vibrationally excited SiS appears resolved, and a source size of ∼ 0.4″ or 7 10¹⁴cm (10 stellar radii) is derived, in agreement with a crude model of line formation. This revised version was published online in September 2006 with corrections to the Cover Date.     

FESTIVAL: A Multiscale Visualization Tool for Solar Imaging Data

Since 4 December 2006, the SECCHI instrument suites onboard the two STEREO A and B probes have been imaging the solar corona and the heliosphere on a wide range of angular scales. The EUVI telescopes have a plate scale of 1.7 arcseconds pixel⁻¹, while that of the HI2 wide-angle cameras is 2.15 arcminutes pixel⁻¹, i.e. 75 times larger, with the COR1 and COR2 coronagraphs having intermediate plate scales. These very different instruments, aimed at studying Coronal Mass Ejections and their propagation in the heliosphere, create a data visualization challenge. This paper presents FESTIVAL, a SolarSoftware package originally developed to be able to map the SECCHI data into dynamic composite images of the sky as seen by the STEREO and SOHO probes. Data from other imaging instruments can also be displayed. Using the mouse, the user can quickly and easily zoom in and out and pan through these composite images to explore all spatial scales from EUVI to HI2 while keeping the native resolution of the original data. A large variety of numerical filters can be applied, and additional data (i.e. coordinate grids, stars catalogs, etc.) can be overlaid on the images. The architecture of FESTIVAL is such that it is easy to add support for other instruments and these new data immediately benefit from the already existing capabilities. Also, because its mapping engine is fully 3D, FESTIVAL provides a convenient environment to display images from future out-of-the-Ecliptic solar missions, such as Solar Orbiter or Solar Probe.     

Sharp Changes of Solar Wind Ion Flux and Density Within and Outside Current Sheets

Analysis of the Interball-1 spacecraft data (1995 – 2000) has shown that the solar wind ion flux sometimes increases or decreases abruptly by more than 20% over a time period of several seconds or minutes. Typically, the amplitude of such sharp changes in the solar wind ion flux (SCIFs) is larger than 0.5×10⁸ cm⁻² s⁻¹. These sudden changes of the ion flux were also observed by the Solar Wind Experiment (SWE), on board the Wind spacecraft, as the solar wind density increases and decreases with negligible changes in the solar wind velocity. SCIFs occur irregularly at 1 AU, when plasma flows with specific properties come to the Earth’s orbit. SCIFs are usually observed in slow, turbulent solar wind with increased density and interplanetary magnetic field strength. The number of times SCIFs occur during a day is simulated using the solar wind density, magnetic field, and their standard deviations as input parameters for a period of five years. A correlation coefficient of ∼0.7 is obtained between the modelled and the experimental data. It is found that SCIFs are not associated with coronal mass ejections (CMEs), corotating interaction regions (CIRs), or interplanetary shocks; however, 85% of the sector boundaries are surrounded by SCIFs. The properties of the solar wind plasma for days with five or more SCIF observations are the same as those of the solar wind plasma at the sector boundaries. One possible explanation for the occurrence of SCIFs (near sector boundaries) is magnetic reconnection at the heliospheric current sheet or local current sheets. Other probable causes of SCIFs (inside sectors) are turbulent processes in the slow solar wind and at the crossings of flux tubes.     

Streamer Belt and Chains as the Main Sources of Quasi-Stationary Slow Solar Wind

Synoptic maps of white-light coronal brightness from SOHO/LASCO C2 and distributions of solar wind velocity obtained from interplanetary scintillation are studied. Regions with velocity V≈300 – 450 km s⁻¹ and increased density N>10 cm⁻³, typical of the “slow” solar wind originating from the belt and chains of streamers, are shown to exist at Earth’s orbit, between the fast solar wind flows (with a maximum velocity V _max≈450 – 800 km s⁻¹). The belt and chains of streamers are the main sources of the “slow” solar wind. As the sources of “slow” solar wind, the contribution from the chains of streamers may be comparable to that from the streamer belt.     

Stokes Diagnostics of 2D MHD-Simulated Solar Magnetogranulation

The properties of solar magnetic fields on scales less than the spatial resolution of solar telescopes are studied. A synthetic infrared spectropolarimetric diagnostic based on a 2D MHD simulation of magnetoconvection is used for this. Analyzed are two time sequences of snapshots that likely represent two regions of the network fields with their immediate surroundings on the solar surface with unsigned magnetic flux densities of 300 and 140 G. In the first region from the probability density functions of the magnetic field strength it is found that the most probable field strength at log τ ₅=0 is equal to 250 G. Weak fields (B<500 G) occupy about 70% of the surface, whereas stronger fields (B>1000 G) occupy only 9.7% of the surface. The magnetic flux is −28 G and its imbalance is −0.04. In the second region, these parameters are correspondingly equal to 150 G, 93.3%, 0.3%, −40 G, and −0.10. The distribution of line-of-sight velocities on the surface of log τ ₅=−1 is estimated. The mean velocity is equal to 0.4 km s⁻¹ in the first simulated region. The average velocity in the granules is −1.2 km s⁻¹ and in the intergranules it is 2.5 km s⁻¹. In the second region, the corresponding values of the mean velocities are equal to 0, −1.8, and 1.5 km s⁻¹. In addition the asymmetry of synthetic Stokes V profiles of the Fe i 1564.8 nm line is analyzed. The mean values of the amplitude and area asymmetry do not exceed 1%. The spatially smoothed amplitude asymmetry is increased to 10% whereas the area asymmetry is only slightly varied.