A Nap- és csillagaktivitás a fotoszférától a koronáig = Solar and stellar activity from the photosphere to the corona

A Nap aktivitási jelenségek 3-dimenziós rekonstrukcióját végeztük el, űreszközök észleléseit modellezéssel kombinálva. Kimutattuk, hogy (1) a konvektív zónában levő örvények a felszálló mágneses fluxuscsövek deformációjának legfőbb okozói; (2) a nyírott mágneses terek disszipációján alapuló korona fűtési modellek jobb egyezést mutatnak az észlelésekből levont skálázási szabályokkal, mint az elektromágneses hullámok disszipációján alapuló modellek; 3) a fehér flerek esetében a koronában jelentősen magasabb a gáznyomás, mint az azonos energiát felszabadító, de fehér fényű emissziót nem produkáló flerekben; (4) az első észlelési bizonyítékot szolgáltattuk a koronalyukak határa mentén folytonos mágneses átkötődésre; (5) korona kitörésekben különböző modellek kombinált, egymást segítő működése vezet aktivitáshoz. Továbbá, úttörő munkát végeztünk a mágneses helicitás észlelésekből való meghatározására a koronában és korona kitörések során kidobott interplanetáris mágneses felhőkben, az első kvantitatív bizonyítékot szolgáltatván fizikai kapcsolatukra. A csillagaktivitás terén sikerült megvalósítani a legtöbb célkitűzésünket. Több vizsgálatot végeztünk a csillagok aktivitására vonatkozóan hosszú időskálájú fotometriai és spektroszkópiai méréseket felhasználva. Megerősítettük a csillagokra kapott legrövidebb ciklushosszakat és összefüggésüket a rotációs periódussal. Több aktív csillagon mutattunk ki differenciális rotációt Doppler leképezés és fotometriai adatok felhasználásával (UZ Lib, zeta And, LQ Hya, IL Hya). Részletesen vizsgáltuk több csillagon az aktív hosszúságok helyzetét (IM Peg, UZ Lib, FK Com). | In solar studies we carried out 3-D reconstruction of solar events based on multi-wavelength space-born data combined with modelling. We have shown, that (1) in the convective zone emerging flux tubes are deformed mainly by huge vortices; (2) coronal heating models based on dissipation of stressed magnetic fields were in better agreement with the scaling laws deduced from observations than the models based on MHD wave dissipation; (3) white-light flares have higher coronal pressure than flares of the same energy, but having no white-light emission; (4) the first observational evidence for continuous magnetic reconnection along coronal hole boundaries; (5) in coronal mass ejections (CMEs) a combination of different models lead to eruption. Furthermore, we have done pioneering work on deducing magnetic helicity from observations both in the solar corona and in interplanetary magnetic clouds (MCs), which are ejected in CMEs, providing the first quantitative evidence for the direct corrrespondence between CMEs and MCs. In active star studies, we succesfully realised most of our goals. We carried our several studies on stellar activity using long-term spectroscopic and photometric observational data. We confirmed the shortest cycle lengths of stars and their correlation with the stars' rotational periods. Differential rotation was revelaed on several stars from Doppler maps and photometric data (UZ Lib, zeta And, LQ Hya, IL Hya). We studied the location of the active longitudes on IM Peg, UZ Lib and FK Com in details

A new trigger mechanism for coronal mass ejections. The role of confined flares and photospheric motions in the formation of hot flux ropes

Context. Many previous studies have shown that the magnetic precursor of a coronal mass ejection (CME) takes the form of a magnetic flux rope, and a subset of them have become known as "hot flux ropes" due to their emission signatures in ∼10 MK plasma. Aims: We seek to identify the processes by which these hot flux ropes form, with a view of developing our understanding of CMEs and thereby improving space weather forecasts. Methods: Extreme-ultraviolet observations were used to identify five pre-eruptive hot flux ropes in the solar corona and study how they evolved. Confined flares were observed in the hours and days before each flux rope erupted, and these were used as indicators of episodic bursts of magnetic reconnection by which each flux rope formed. The evolution of the photospheric magnetic field was observed during each formation period to identify the process(es) that enabled magnetic reconnection to occur in the β < 1 corona and form the flux ropes. Results: The confined flares were found to be homologous events and suggest flux rope formation times that range from 18 hours to 5 days. Throughout these periods, fragments of photospheric magnetic flux were observed to orbit around each other in sunspots where the flux ropes had a footpoint. Active regions with right-handed (left-handed) twisted magnetic flux exhibited clockwise (anticlockwise) orbiting motions, and right-handed (left-handed) flux ropes formed. Conclusions: We infer that the orbital motions of photospheric magnetic flux fragments about each other bring magnetic flux tubes together in the corona, enabling component reconnection that forms a magnetic flux rope above a flaring arcade. This represents a novel trigger mechanism for solar eruptions and should be considered when predicting solar magnetic activity. Movies associated to Figs. 4, 8, 12, and 14 are available at http://https://www.aanda.or

Plasma Upflows Induced by Magnetic Reconnection Above an Eruptive Flux Rope

One of the major discoveries of Hinode's Extreme-ultraviolet Imaging Spectrometer (EIS) is the presence of upflows at the edges of active regions. As active regions are magnetically connected to the large-scale field of the corona, these upflows are a likely contributor to the global mass cycle in the corona. Here we examine the driving mechanism(s) of the very strong upflows with velocities in excess of 70 km s(-1), known as blue-wing asymmetries, observed during the eruption of a flux rope in AR 10977 (eruptive flare SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations combined with magnetic-field modeling to investigate the possible link between the magnetic topology of the active region and the strong upflows. A Potential Field Source Surface (PFSS) extrapolation of the large-scale field shows a quadrupolar configuration with a separator lying above the flux rope. Field lines formed by induced reconnection along the separator before and during the flux-rope eruption are spatially linked to the strongest blue-wing asymmetries in the upflow regions. The flows are driven by the pressure gradient created when the dense and hot arcade loops of the active region reconnect with the extended and tenuous loops overlying it. In view of the fact that separator reconnection is a specific form of the more general quasi-separatrix (QSL) reconnection, we conclude that the mechanism driving the strongest upflows is, in fact, the same as the one driving the persistent upflows of approximate to 10 - 20 km s(-1) observed in all active regions

Can Subphotospheric Magnetic Reconnection Change the Elemental Composition in the Solar Corona?

Within the coronae of stars, abundances of those elements with low first ionization potential (FIP) often differ from their photospheric values. The coronae of the Sun and solar-type stars mostly show enhancements of low-FIP elements (the FIP effect) while more active stars such as M dwarfs have coronae generally characterized by the inverse-FIP effect (I-FIP). Here we observe patches of I-FIP effect solar plasma in AR 12673, a highly complex βγδ active region. We argue that the umbrae of coalescing sunspots, and more specifically strong light bridges within the umbrae, are preferential locations for observing I-FIP effect plasma. Furthermore, the magnetic complexity of the active region and major episodes of fast flux emergence also lead to repetitive and intense flares. The induced evaporation of the chromospheric plasma in flare ribbons crossing umbrae enables the observation of four localized patches of I-FIP effect plasma in the corona of AR 12673. These observations can be interpreted in the context of the ponderomotive force fractionation model which predicts that plasma with I-FIP effect composition is created by the refraction of waves coming from below the chromosphere. We propose that the waves generating the I-FIP effect plasma in solar active regions are generated by subphotospheric reconnection of coalescing flux systems. Although we only glimpse signatures of I-FIP effect fractionation produced by this interaction in patches on the Sun, on highly active M stars it may be the dominant process

Evolution of the magnetic field distribution of active regions

Aims. Although the temporal evolution of active regions (ARs) is relatively well understood, the processes involved continue to be the subject of investigation. We study how the magnetic field of a series of ARs evolves with time to better characterise how ARs emerge and disperse. Methods. We examine the temporal variation in the magnetic field distribution of 37 emerging ARs. A kernel density estimation plot of the field distribution was created on a log-log scale for each AR at each time step. We found that the central portion of the distribution is typically linear and its slope was used to characterise the evolution of the magnetic field. Results. The slopes were seen to evolve with time, becoming less steep as the fragmented emerging flux coalesces. The slopes reached a maximum value of ∼ −1.5 just before the time of maximum flux before becoming steeper during the decay phase towards the quiet Sun value of ∼ −3. This behaviour differs significantly from a classical diffusion model, which produces a slope of −1. These results suggest that simple classical diffusion is not responsible for the observed changes in field distribution, but that other processes play a significant role in flux dispersion

Evolution of Plasma Composition in an Eruptive Flux Rope

Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs). However, identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer observations of sigmoidal active region (AR) 10977. We analyze the coronal plasma composition in the AR and its evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and a sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical AR coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. Hence, plasma composition observations of AR 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level

Understanding the Plasma and Magnetic Field Evolution of a Filament Using Observations and Nonlinear Force-free Field Modeling

We present observations and magnetic field models of an intermediate filament present on the Sun in 2012 August, associated with a polarit inversion line that extends from AR 11541 in the east into the quiet Su at its western end. A combination of Solar Dynamics Observator (SDO)/Atmospheric Imaging Assembly, SDO/Helioseismic and Magnetic Image (HMI), and Global Oscillation Network Group Hα data allow us to analyz the structure and evolution of the filament from 2012 August 4 23:00 U to 2012 August 6 08:00 UT when the filament was in equilibrium. B applying the flux rope insertion method, nonlinear force-free fiel models of the filament are constructed using SDO/HMI line-of-sigh magnetograms as the boundary condition at the two times given above Guided by observed filament barbs, both modeled flux ropes are spli into three sections each with a different value of axial flux t represent the nonuniform photospheric field distribution. The flux i the eastern section of the rope increases by 4 × 1020 M between the two models, which is in good agreement with the amount o flux canceled along the internal PIL of AR 11541, calculated to be 3.2 1020 Mx. This suggests that flux cancellation builds flu into the filament’s magnetic structure. Additionally, the number o field line dips increases between the two models in the locations wher flux cancellation, the formation of new filament threads, and growth o the filament is observed. This suggests that flux cancellatio associated with magnetic reconnection forms concave-up magnetic fiel that lifts plasma into the filament. During this time, the free magneti energy in the models increases by 0.2 × 1031 erg

A Nap és csillagdinamók éves időskálájú változásai = The yearly time-scale variability of the solar and stellar dynamos

A csillagaktivitás motorja a mágneses dinamó, mely a differenciális rotáció és a konvektív burok következménye, és több időskálán is ciklikusságot mutat. A Napon rövidebb, 1-2 éves periodicitásokat találtunk különböző aktivitási indikátorokban. Kimutattuk, hogy a Nap hosszú, Gleissberg ciklusa az utóbbi 500 évben folytonosan változik. 20 aktív csillag ~20-50 év hosszú adatsorát egy új módszerrel analizálva azt találtuk, hogy a ciklusok általában többszörösek és az időben változnak. Több aktív csillag felszínén spektroszkópiai módszerekkel - Doppler leképezés - differenciális rotációt mutattunk ki, illetve csillagfelszínen meridionális áramlásokat is találtunk. Kidolgoztuk és alkalmaztuk a torzult felületű csillagok Doppler leképezését. Kidolgoztunk egy új modellt a koronakitöréseknek a napkoronában való fejlődésére. A koronakitörések táguló mágneses ``buborékok'', és a Nap koronája tele van különféle orientációjú mágneses terekkel, és a koronakitörések kölcsönhatnak és mágnesesen átkötődnek, ha ellentétes irányú mágneses erővonalakkal találkoznak tágulásuk során. A fél nap körüli periódussal pulzáló RR Lyr csillagok körében nagyszámú méréseink szerint a pulzációjuk amplitúdóját és fázisát változtató csillagok aránya lényegesen több, mint amit az irodalomból ismerünk. A legrövidebb Blazhko-periódust a mi méréseinkből ismerjük. A jelenség okaként felmerült a mágneses dinamó is, bár az egyéb megközelítések jelenleg megalapozottabbnak tűnnek. | The driving force of stellar activity is the magnetic dynamo resulting from the differential rotation and convective envelopes of stars, showing cycles on several timescales. In the Sun we found shorter, 1-2 years periodicities in different activity indicators. We demonstrated that the long, Gleissberg cycle of the Sun is continuously changing during the last 500 years. Using a new approach we studied the datasets of 20 stars and found that the cycles are generally multiple and variable. On the surface of a few active stars using spectroscopic methods - Doppler imaging - we found differential rotation and meridional flows. We constructed and applied a Doppler imaging method for non-spherical stellar surfaces. We prepared a model for the development of the mass ejections in the solar corona. The coronal mass ejections are expanding magnetic 'bubbles', the solar corona is full of magnetic fields of different orientations, and the coronal mass ejections counteract and magnetically reconnect when they meet magnetic field lines of different polarities during their expansion. According to our vast number of measurements, among the RR Lyrae star which pulsate around half day period, the number of objects whose amplitudes and phases are changing, is much higher than is known from the literature. The shortest Blazhko-period is revealed from our measurements. As cause of this phenomenon the magnetic dynamo raised up, but at present other approaches have firmer grounds

FIP Bias Evolution in a Decaying Active Region

Solar coronal plasma composition is typically characterized by first ionization potential (FIP) bias. Using spectra obtained by Hinode's EUV Imaging Spectrometer instrument, we present a series of large-scale, spatially resolved composition maps of active region (AR)11389. The composition maps show how FIP bias evolves within the decaying AR during the period 2012 January 4--6. Globally, FIP bias decreases throughout the AR. We analyzed areas of significant plasma composition changes within the decaying AR and found that small-scale evolution in the photospheric magnetic field is closely linked to the FIP bias evolution observed in the corona. During the AR's decay phase, small bipoles emerging within supergranular cells reconnect with the pre-existing AR field, creating a pathway along which photospheric and coronal plasmas can mix. The mixing timescales are shorter than those of plasma enrichment processes. Eruptive activity also results in shifting the FIP bias closer to photospheric in the affected areas. Finally, the FIP bias still remains dominantly coronal only in a part of the AR's high-flux density core. We conclude that in the decay phase of an AR's lifetime, the FIP bias is becoming increasingly modulated by episodes of small-scale flux emergence, i.e., decreasing the AR's overall FIP bias. Our results show that magnetic field evolution plays an important role in compositional changes during AR development, revealing a more complex relationship than expected from previous well-known Skylab results showing that FIP bias increases almost linearly with age in young ARs