Yuzong Zhang

Transequatorial Filament Eruption and Its Link to a Coronal Mass Ejection

We revisit the Bastille Day flare/CME Event of 2000 July 14, and demonstrate that this flare/CME event is not related to only one single active region (AR). Activation and eruption of a huge transequatorial filament are seen to precede the simultaneous filament eruption and flare in the source active region, NOAA AR 9077, and the full halo-CME in the high corona. Evidence of reconfiguration of large-scale magnetic structures related to the event is illustrated by SOHO EIT and Yohkoh SXT observations, as well as, the reconstructed 3D magnetic lines of force based on the force-free assumption. We suggest that the AR filament in AR 9077 was connected to the transequatorial filament. The large-scale magnetic composition related to the transequatorial filament and its sheared magnetic arcade appears to be an essential part of the CME parent magnetic structure. Estimations show that the filament-arcade system has enough magnetic helicity to account for the helicity carried by the related CMEs. In addition, rather global magnetic connectivity, covering almost all the visible range in longitude and a huge span in latitude on the Sun, is implied by the Nancay Radioheliograph (NRH) observations. The analysis of the Bastille Day event suggests that although the triggering of a global CME might take place in an AR, a much larger scale magnetic composition seems to be the source of the ejected magnetic flux, helicity and plasma. The Bastille Day event is the first described example in the literature, in which a transequatorial filament activity appears to play a key role in a global CME. Many tens of halo-CME are found to be associated with transequatorial filaments and their magnetic environment.

Optical spectrum of the planetary nebula M 2-24 ?

We have obtained medium-resolution, deep optical long-slit spectra of the bulge planetary nebula (PN) M 2-24. The spectrum covers the wavelength range from 3610-7330 A. Over two hundred emission lines have been detected. The spectra show a variety of optical recombination lines (ORLs) from C, N, O and Ne ions. The diagnostic diagram shows significant density and temperature variations across the nebula. Our analysis suggests that the nebula has a dense central emission core. The nebula was thus studied by dividing it into two regions: 1) a high ionization region characterized by an electron temperature of Te = 16 300 K and a density of log Ne(cm 3 ) = 6:3; and 2) a low ionization region represented by Te = 11 400 K and log Ne(cm 3 )= 3:7. A large number of ORLs from C, N, O and Ne ions have been used to determine the abundances of these elements relative to hydrogen. In general, the resultant abundances are found to be higher than the corresponding values deduced from collisionally excited lines (CELs). This bulge PN is found to have large enhancements in two-elements, magnesium and neon.

Coexisting fast and slow propagating waves of the extreme-UV intensity in solar coronal plasma structures

Context. From 06:15 UT to 08:15 UT on 2011 June 2, a toroidal filament located at the joint of two active regions, 11226 and 11227, appeared to perform two eruptions. During this phenomenon, fast and slow magnetoacoustic waves were detected to propagate simultaneously along a funnel coronal loop system of AR 11227. Aims. We aim to understand the relationship between fast and slow magnetoacoustic waves during their propagations and measure their properties, such as the propagating speed, path, amplitude, and period observed in the extreme ultraviolet (EUV) wavebands. Methods. We analyse time sequences of EUV images acquired by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. By creating time-distance maps along selected directions, we measure the speeds and localisation of EUV intensity waves in different EUV wavebands. We determine the periods of the waves with wavelet analysis. Results. The fast and slow magnetoacoustic waves, apparently propagating along the same path, are found to have different properties. Their apparent propagation speeds, travel distances, and periods are about 900 km s-1 and 100 km s-1, 145 Mm and 36 Mm, and 2 min and 3 min, respectively.

THE FORMATION AND ERUPTION OF SOLAR QUIESCENT PROMINENCES

Following the two-stage catastrophic flux rope model presented by Zhang et al., we investigate how magnetic flux emergence affects the formation and evolution of solar quiescent prominences. The magnetic properties of the flux rope are described with its toroidal magnetic flux per radian Phi(p) and poloidal flux Phi(phi), and Phi(p) is defined as the emerging strength (ES) of the magnetic flux. After the first catastrophe, the quiescent prominences are supported by the vertical current sheet and located in cavities below the curved transverse current sheet in the inner corona, for which both ES and Phi(phi) are in the certain ranges. We calculate the strength range as 0.25 < ES < 0.50 for the quadrupolar field, and obtain the equation Phi(p)Phi(phi) = const., that is, the relationship between Phi(p) and Phi(phi) of the emerging flux for which the quiescent prominences are formed in the inner corona. After the second catastrophe, the quiescent prominences would either fall down onto the solar surface or erupt as an important part of coronal mass ejections. During the eruption of the quiescent prominences, most of the magnetic energy in the flux rope is lost, and less than half of the energy loss of the rope is released in the form of Alfven waves. We argue that there would be two important conditions required for the formation and eruption of solar quiescent prominences, a complicated source region and emerging toroidal magnetic flux that exceeds a critical strength.

Properties of sunspot penumbral grains observed with Hinode

Context. Penumbral grains (PGs) are small-scale (subarcsec) bright features found in the bright penumbral filament in the outer parts of sunspots. Aims. We aim to study properties of PGs at the blue continuum (4504 A) and the G-band (4305 A) by using simultaneous seeing free data obtained by Broadband Filter Imager (BFI) on board Hinode. Methods. We use an automatic identification and tracking algorithm to identify PGs, which were observed in a period of 170 min in the blue continuum and 88 min in the G-band. Results. Our results indicate that 776 PGs were identified in the blue continuum, and 413 PGs were identified in the G-band,. A statistical study reveals that about 55% of PGs move toward the umbra, about 13‐19% of PGs move toward the surrounding granulation, and the rest are relatively static. The inward moving PGs are mostly located in the inner penumbra (up to 0.6 of the distance from the umbra to the photosphere) and outward moving PGs are located in the outer penumbra. In the blue continuum (and G band), the average lifetime, speed, and brightness of inward moving PGs are 14.7 (13.5) min, 0.71 (0.70) kms −1 and 0.89 (0.88) of the quiet Sun. For outward moving PGs, the average lifetime, speed and brightness are 8.0 (7.0) min, 0.93 (0.65) kms −1 and 0.99 (0.98) of the quiet Sun. For PGs that are relatively static, the average lifetime and brightness are 7.6 (6.0) min and 0.94 (0.91) of the quiet Sun. Moreover, our observational results show that the correlation between the temporal evolutions of the speed and brightness is complex.

Study of the first productive active region in solar cycle 24

Context. The Sun is very quiet with less sunspots and activity since the beginning of solar cycle 24. However, the active region (AR) 11045 emerged on February 5, 2010, is associated with 43 (8 M- and 35 C-class) flares, 53 coronal mass ejections (CMEs), 29 filament eruptions, 19 extreme ultraviolet (EUV) waves and abundant jets, indicating that this AR is the first productive one of solar cycle 24. Aims. We study the AR evolution and its associated activities, and also their relationships, to understand this productive AR. Methods. We used SOHO/MDI magnetograms to study the magnetic fields, STEREO/SECCHI images to explore the activities, and GOES measurements to investigate the soft X-ray flux of the AR. Results. During the AR evolution, six pairs of main magnetic fields emerged, and 93.1% flares and 82.75% filament eruption occurred in the emergence and stable phases of the magnetic flux. However, 43.4% CMEs occurred in the decaying phase, even though there were lessflares. An example isgiven to show that an event isrelated to aflare, afilament eruption, a CME and an EUV wave from inner corona to outer corona in space, and the filament eruption and EUV wave occur near the peak time of the flare. Among the 29 filament eruptions, 79.3% are associated with CMEs, as well as 58.6%, associated with flares, and 34.5%, associated with EUV waves. During the 12-day active phase, 575 jets are detected with a daily occurrence rate of 49.3. This is the first time that so many jets have been identified in one AR, implying at least 575 lower magnetic reconnection processes during the AR evolution. We statistically studied these jets along with the AR evolution, and noticed that the jets mostly occurred surrounding the emerging flux. We also investigated the spatio-temporal relationships between the jets and the flares, and find that the jets are usually rooted around the flare cores, and the soft X-ray flux is inverse correlated with the number of the jets, especially during the beginning 9 days since the AR emergence. In comparison with AR 11045, we studied the other newly emerging AR 11045, and obtained similar results. The relationships between the jets and the flares may well represent a scenario of two-step magnetic reconnection. Using schematic diagrams, we explain the remarkable magnetic field emergence, cancelation and shear motion of AR 11045, and its associated activities.

EFFECTS OF PHYSICAL FEATURES IN THE SOLAR ATMOSPHERE ON THE CORONAL MASS EJECTION EVOLUTION

Based on time-dependent MHD simulation, we investigate how physical features in the solar atmosphere affect the evolution of coronal mass ejections (CMEs). It is found that temperature and density play a crucial role in CME initiation. We argue that lower temperature facilitates the catastrophes occurrence, and that the CMEs which initiate in low density could gain lower velocity. In our numerical experiment, by employing different values of beta, the resulting eruptions of either slow or fast events may be obtained.

Magnetic Properties of Metric Noise Storms Associated with Coronal Mass Ejections

Using Nancay Radioheliograph (NRH) imaging observations, combined with SOHO/Michelson Doppler Imager (MDI) magnetogram observations and coronal magnetic field extrapolation, we studied the magnetic nature of metric noise storms that are associated with coronal mass ejections (CMEs). Four events are selected: the events of 2000 July 14, 2001 April 26, 2002 August 16 and 2001 March 28. The identified noise storm sources cover or partially cover the active regions (ARs), but the centers of storm sources are offset from the ARs. Using extrapolated magnetic field lines, we find that the noise storm sources trace the boundary between the open and closed field lines. We demonstrate that the disappearance of noise storm source is followed by the appearance of the burst source. The burst sources spread on the solar disk and their distributions correspond to the extent of the CME in LASCO C2 field of view. All the SOHO/Extreme Ultraviolet Imaging Telescope (EIT) dimmings associated with noise storm sources are located at the periphery of noise storms where the magnetic lines of force were previously closed and low-lying. When the closed field becomes partially or fully open, the basic configurations of noise storm sources are changed, then the noise storm sources are no longer observed. These observations provide the information that the variations of noise storms manifest the restructuring or reconfiguring of the coronal magnetic field.

A Trans-equatorial Filament and the Bastille Day Flare/CME Event

The Bastille Day Event on July 14 2000, a major solar flare and a global coronal mass ejection (CME), is not a phenomenon of a single active region. Activation and eruption of a huge trans-equatorial filament is seen to precede the simultaneous filament eruption and flare in the source active region, AR9077, and the full halo-CME in the high corona. Evidence of reconfiguration of large-scale structures, manifested by SOHO EIT and Yohkoh SXT observations, is clearly seen. The large-scale magnetic composition related to the trans-equatorial filament and its sheared magnetic arcades appears to be the essential part of the CME parent magnetic structure. Estimations show that the filament-arcade system has enough magnetic helicity to account for the helicity carried by the related CMEs.

The properties of red giant stars along the Sagittarius tidal tails

Aims. We aim to measure the metallicity distribution and velocity distribution of red giant branch (RGB) stars along the Sagittarius dwarf galaxy (Sgr) streams. Thanks to the large number of stars of the Sloan Digital Sky Survey (SDSS) sample, we can study the properties of streams as a function of the Λ ⊙ from the Sgr core. Methods. Using the ~22 000 RGB stars from the ninth data release of SDSS, we selected 1100 RGB stars belonging to the streams of the Sgr. As compared with red horizontal branch stars (, ApJ, 751, 130) the RGB stars constitute a large sample size and extend to a metal-poor component of [Fe/H] ~−3.0 dex. In particular, this RGB sample has a significant number of stars in the second wrap of the leading stream of the Sgr (leading arm 2), and thus provides a good opportunity to understand the properties of the leading stream. Results. We derive a metallicity gradient of −(2.3 ± 0.5) × 10 -3 dex deg -1 in leading arm 2 for the first time, of −(1.6 ± 0.4) × 10 -6 dex deg -1 for the leading arm 1, and of −(1.3 ± 0.3) × 10 -3 dex deg -1 for the trailing arm 1. We check the distribution of Sgr stars in phase space and find a velocity dispersion of ~21.5 km s -1 for leading arm 1. Finally, we identify a possible new branch in leading arm 1.