The Hβ Chromospheric Magnetic Field in a Quiescent Filament

We observed the line-of-sight magnetic field in the chromosphereand photosphere of a large quiescent filament on the solar disk on September 6, 2001 using the Solar Magnetic Field Telescope in Huairou Solar Observing Station. The chromospheric and photospheric magnetograms together with Hβ filtergrams of the filament were examined. The filament was located on the neutral line of the large scale longitudinal magnetic field in the photosphere and the chromosphere. The lateral feet of the filament were found to be related to magnetic structures with opposite polarities. Two small lateral feet are linked to weak parasitic polarity. There is a negative magnetic structure in the photosphere under a break of the filament. At the location corresponding to the filament in the chromospheric magnetograms, the magnetic strength is found to be about 40-70 Gauss (measuring error about 39 Gauss). The magnetic signal indicates the amplitude and orientation of the internal magnetic field in the filament. We discuss several possible causes which may produce such a measured signal. A twisted magnetic configuration inside the filament is suggested .

MHD Seismology of a loop-like filament tube by observed kink waves

We report and analyze observational evidence of global kink oscillations in a solar filament as observed in Ha by instruments administered by National Solar Observatory （NSO）/Global Oscillation Network Group （GONG）. An M1.1-class flare in active region （AR） 11692 occurred on 2013 March 15 and induced a global kink mode in the filament lying towards the southwest of AR 11692. We find periods of about 61-67 minutes and damping times of 92-117 minutes at positions of three ver- tical slices chosen in and around the filament apex. We find that the waves are damped. From the observed period of the global kink mode and damping timescale using the theory of resonant absorption, we perform prominence seismology. We estimate a lower cut-off value for the inhomogeneity length scale to be around 0.34-0.44 times the radius of the filament cross-section.

A time series of filament eruptions observed by three eyes from space:from failed to successful eruptions

We present stereoscopic observations of six sequential eruptions of a filament in the active region NOAA 11045 on 2010 Feb 8, with the advantage of the STEREO twin viewpoints in combination with Earth＇s viewpoint from SOHO instruments and ground-based telescopes. The last one of the six eruptions is a coronal mass ejection, but the others are not. The flare in this successful one is more intense than in the others. Moreover, the velocity of filament material in the successful one is also the largest among them. Interestingly, all the filament velocities are found to be proportional to the power of their flares. We calculate magnetic field intensity at low altitude, the decay indexes of the external field above the filament, and the asymmetry properties of the overlying fields before and after the failed eruptions and find little difference between them, indicating the same coronal confinement exists for both the failed and successful eruptions. The results suggest that, besides the confinement of the coronal magnetic field, the energy released in the low corona should be another crucial element affecting a failed or successful filament eruption. That is, a coronal mass ejection can only be launched if the energy released exceeds some critical value, given the same initial coronal conditions.

A comparison study of a solar active-region eruptive filament and a neighboring non-eruptive filament

Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE-MHD-NLFFF code reveals that two magnetic flux ropes （MFRs） exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface （BPSS） co- spatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament （with a length of about 200 Mm）, the eruptive MFR/filament is much smaller （with a length of about 20 Mm）, but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.

The surge-like eruption of a miniature filament

We report on the rare eruption of a miniature Hα filament that took the form of a surge. The filament first underwent a full development within 46 min and then began to erupt 9 min later, followed by a compact, impulsive X-ray class M2.2 flare with a two-ribbon nature only at the early eruption phase. During the eruption, its top rose, whereas the two legs remained rooted in the chromosphere and showed little swelling perpendicular to the rising direction. This led to a surge-like eruption with a narrow angular extent. Similar to the recent observations for standard and blowout X- ray jets by Moore et al., we thus define it as a ＂blowout Hα surge.＂ Furthermore, our observations showed that the eruption was associated with （1） a coronal mass ejection guided by a pre-existing streamer, （2） abrupt, significant, and persistent changes in the photospheric magnetic field around the filament, and （3） a sudden disappearance of a small pore. These observations thus provide evidence that a blowout surge is a small- scale version of a large-scale filament eruption in many aspects. Our observations further suggest that at least part of the Hα surges belong to blowout-type cases, and the exact distinction between the standard and blowout Hα surges is important in understanding their different origins and associated eruptive phenomena.

Coupling of small-and large-scale filament eruptions

We present observations of the eruption of a large-scale quiescent filament （LF） that is associated with the formation and eruption of a miniature filament （MF）. As a result of convergence and subsequent cancelation of opposite-polarity magnetic flux, MF was formed just below the spine of the LF＇s right seg- ment. Probably triggered by a nearby newly emerging flux, MF underwent a failed eruption immediately after its full development, which first ejected away from the spine of LF and then drained back to the Sun. This eruption no sooner started than the overlying LF＇s right segment began to rise slowly and the LF＇s other parts were also disturbed, and eventually the whole LF erupted bodily and quickly. These observa- tions suggest that the MF can serve as an intermediary that links the photospheric small-scale magnetic-field activities to the eruption of the overlying large filament. It appears that, rather than directly interacting with the supporting magnetic field of LF, small-scale flux cancelation and emergence in the LF＇s channel can manifest themselves as the formation and eruption of MF and so indirectly affect the stability of LE

Preface: Frontiers in Astrophysics(Ⅱ)——A special issue dedicated to the 20th anniversary of RAA(2001–2020)

On the arrival of the 20 th anniversary of the journal,Research in Astronomy and Astrophysics(RAA),we see rapid progress in the frontiers of astronomy and astrophysics.To celebrate the birth and growth of RAA,a special issue consisting of 11 invited reviews from more than 30 authors,mainly from China,has been organized.This is the second volume of the special issues entitled Frontiers in Astrophysics published in RAA.The publication aims at evaluating the current status and key progress in some frontier areas of astronomy and astrophysics with a spirit of guiding future studies.