bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations of magnetic and kinetic helicity proxies
Authors: Zhang Hongqi 
Published: July 2013

AbstractThe helicity is important to present the basic topological configuration of magnetic field in solar atmosphere. The distribution of magnetic helicity in solar atmosphere is presented by means of the observational (vector) magnetograms. As the kinetic helicity in the solar subatmosphere can be inferred from the velocity field based on the technique of the helioseismology and used to compare with the magnetic helicity in the solar atmosphere, the observational helicities provide the important chance for the confirmation on the generation of magnetic fields in the subatmosphere and solar dynamo models also. In this paper, we present the observational magnetic and kinetic helicity in solar active regions and corresponding questions, except the relationship with solar eruptive phenomena.
How much more can sunspots tell us about the solar dynamo?
Authors: Norton Aimee A. , Jones Eric H. , Liu Y. , Hayashi K. , Hoeksema J. T. , Schou Jesper 
Published: July 2013

AbstractSunspot observations inspired solar dynamo theory and continue to do so. Simply counting them established the sunspot cycle and its period. Latitudinal distributions introduced the tough constraint that the source of sunspots moves equator-ward as the cycle progresses. Observations of Hale's polarity law mandated hemispheric asymmetry. How much more can sunspots tell us about the solar dynamo? We draw attention to a few outstanding questions raised by inherent sunspot properties. Namely, how to explain sunspot rotation rates, the incoherence of follower spots, the longitudinal spacing of sunspot groups, and brightness trends within a given sunspot cycle. After reviewing the first several topics, we then present new results on the brightness of sunspots in Cycle 24 as observed with the Helioseismic Magnetic Imager (HMI). We compare these results to the sunspot brightness observed in Cycle 23 with the Michelson Doppler Imager (MDI). Next, we compare the minimum intensities of five sunspots simultaneously observed by the Hinode Solar Optical Telescope Spectropolarimeter (SOT-SP) and HMI to verify that the minimum brightness of sunspot umbrae correlates well to the maximum field strength. We then examine 90 and 52 sunspots in the north and south hemisphere, respectively, from 2010 - 2012. Finally, we conclude that the average maximum field strengths of umbra 40 Carrington Rotations into Cycle 24 are 2690 Gauss, virtually indistinguishable from the 2660 Gauss value observed at a similar time in Cycle 23 with MDI.
Phase relationship between polar faculae and sunspot numbers
Authors: Deng L. H. 
Published: July 2013

AbstractLinear and nonlinear approaches are used to investigate the phase asynchrony between the polar faculae (PF) and sunspot numbers (SNs). It is found that, (1) PF show leads of 52 months relative to SNs on the average of the considered time interval; (2) the cross-wavelet transform analysis shows that they are asynchronous in both the low- and high-frequency components. These indicate that their phase relationship is not only time-dependent but also frequency-dependent.
Comparison of solar activity during last two minima on turn of Activity Cycles 22/23 and 23/24
Authors: Gryciuk Magdalena , Gburek Szymon , Siarkowski Marek , Podgorski Piotr , Sylwester Janusz , Farnik Frantisek 
Published: July 2013

AbstractThe subject of our work is the review and comparison of solar activity during the last two solar minima that occurred between recent activity cycles. We use the soft X-ray global solar corona observations covering the two nine-months long time intervals in 1997/98 and 2009. Data from RF15-I multichannel photometer are used for the penultimate minimum. For the last unusually deep and prolonged solar activity minimum in 2009 the data from SphinX spectrophotometer are used. Comparison of measurements from both minima takes place in the overlapping energy range 2–15 keV. We focus on the active region formation, evolution and flaring productivity during respective minima.
Modeling the solar cycles 12-20 with a Babcock-Leighton flux transport dynamo
Authors: Jiang Jie 
Published: July 2013

AbstractWe use a Babcock-Leighton-type of dynamo with the poloidal source based as closely as possible on the observations to model the solar cycle irregularities during the cycles 12-20. The nonlinearities in the poloidal field generation, i.e., the cycle dependence of the sunspot group tilt angles and the latitudes are included. The convective pumping dominates the transport of the surface poloidal field to the tachocline. Our results show that the modeled polar fields have a good correlation with the observed next cycle strength and the build-up of the toroidal flux at the tachocline is strongly correlated with the observed cycle strength as well. Both correlation coefficients are above 0.8. The success of the model indicates that they are the nonlinearities in the poloidal field generation which cause the solar cycle irregularities.
On the extended 23rd solar cycle
Authors: Krivodubskij Valery N. 
Published: July 2013

AbstractAn explanation of the mystery of the extended 23rd solar cycle duration about 13 years in the frame of non-linear regime of the αΩ- dynamo model is proposed. The calculated dynamo-period of the solar cycle, T, depends (in the inverse proportion) on the intensity of the α- effect in the solar convection zone (SCZ). As well, the intensity of the α- effect in non-linear regime depends (also in the inverse proportion) on the value of toroidal magnetic field, BT (magnetic alpha-quenching). Thus, the calculated period is in direct proportion to the value of toroidal magnetic field: the stronger toroidal field BT in certain cycle, the longer dynamo-period T of this cycle. Since the toroidal field is hidden in the deep layers of the SCZ, it is necessary to know some other magnetic experimental evidence that reflects something like information about inner toroidal field. In this connection we allow for that the strong toroidal field is transported by magnetic buoyancy to the solar surface and produces here the sunspots, so they carry indirect information on BT. In this connection we took into account up-to-date observed data on the essential increase of the averaged annual module of the magnetic field of the large-scale sunspots, Bsp, in the 23rd cycle; and then we made calculation of the alpha-quenching which depends on these referred data. It is important to know only relative variations of magnetic index Bsp for calculation of the dynamo-period variation. Our estimations showed that the average solar period, which is about 11 years, must increase by a factor of 1,2; so the calculated 23rd cycle dynamo-period would be about 13 years.
Model of poleward magnetic field streams from sunspot butterflies
Authors: Zolotova Nadezhda V. , Ponyavin Dmitri I. 
Published: July 2013

AbstractThe poleward magnetic field streams on time-latitude diagram of the photospheric magnetic field of the Sun during 1975–2011 (Kitt Peak NSO, SOLIS NSO, SOHO MDI data) are modeled. We performed simulations in terms of probability density function and bipole orientation according to Joy's law and Hale's cycle. The difference between distributions of leading and trailing fluxes of bipolar sunspots defines the so-called surplus. Finally, magnetic field streams and polar field reversals are a result of meridional drift of a surplus to the poles.
Spectropolarimetric diagnostics of unresolved magnetic fields in the quiet solar photosphere
Authors: Shchukina Nataliya G. , Bueno Javier Trujillo 
Published: July 2013

AbstractA few years before the Hinode space telescope was launched, an investigation based on the Hanle effect in atomic and molecular lines indicated that the bulk of the quiet solar photosphere is significantly magnetized, due to the ubiquitous presence of an unresolved magnetic field with an average strength 〈B〉, ≈ 130 G. It was pointed out also that this “hidden” field must be much stronger in the intergranular regions of solar surface convection than in the granular regions, and it was suggested that this unresolved magnetic field could perhaps provide the clue for understanding how the outer solar atmosphere is energized. In fact, the ensuing magnetic energy density is so significant that the energy flux estimated using the typical value of 1 km/s for the convective velocity (thinking in rising magnetic loops) or the Alfvén speed (thinking in Alfvén waves generated by magnetic reconnection) turns out to be substantially larger than that required to balance the chromospheric energy losses. Here we present a brief review of the research that led to such conclusions, with emphasis on a new three-dimensional radiative transfer investigation aimed at determining the magnetization of the quiet Sun photosphere from the Hanle effect in the Sr I 4607 Å line and the Zeeman effect in Fe I lines.
Nature of the solar dynamo at small scales
Authors: Stenflo J. O. 
Published: July 2013

AbstractIt is often claimed that there is not only one, but two different types of solar dynamos: the one that is responsible for the appearance of sunspots and the 11-yr cycle, frequently referred to as the “global dynamo”, and a statistically time-invariant dynamo, generally referred to as the “local dynamo”, which is supposed to be responsible for the ubiquitous magnetic structuring observed at small scales. Here we examine the relative contributions of these two qualitatively different dynamos to the small-scale magnetic flux, with the following conclusion: The local dynamo does not play a significant role at any of the spatially resolved scales, nearly all the small-scale flux, including the flux revealed by Hinode, is supplied by the global dynamo. This conclusion is reached by careful determination of the Sun's noise-corrected basal magnetic flux density while making use of a flux cancellation function determined from Hinode data. The only allowed range where there may be substantial or even dominating contributions from a local dynamo seems to be the scales below about 10 km, as suggested by observations of the Hanle depolarization effect in atomic spectral lines. To determine the fraction of the Hanle depolarization that may be due to the action of a local dynamo, a synoptic program is being initiated at IRSOL (Istituto Ricerche Solari Locarno).
Origin of quiet-Sun magnetic fields revealed with Hinode
Authors: Ishikawa Ryohko 
Published: July 2013

AbstractQuiet-Sun magnetic fields are enigmatic in terms of their properties, and their origin is not well understood. One likely possibility is that they are a consequence of interactions with turbulent convective motions of various temporal and spatial scales. Here we investigate the relationship between small-scale magnetic fields and various convection flows. We demonstrate that in addition to granulation and supergranulation, mesogranulation also plays an important role in structuring quiet-Sun magnetic fields. We also study the vector magnetic fields in the quiet Sun, and propose that emerging granular-scale bipolar loops are major sources of the quiet-Sun magnetic fields.
Self-cancellation of solar ephemeral regions observed by SDO
Authors: Yang Shuhong , Zhang Jun , Li Ting , Liu Yang 
Published: July 2013

AbstractWe study the ephemeral regions (ERs) in the quiet Sun observed by the Solar Dynamics Observatory, and find that they can be classified into two types: normal ERs (NERs) and self-cancelled ERs (SERs). We identify 2988 ERs among which there are 190 SERs, about 6.4% of the ERs. The total self-cancelled flux is 9.8% of the total ER flux. We suggest that the self-cancellation of SERs is caused by the submergence of magnetic loops connecting the dipolar patches, without magnetic energy release.
Magnetic field generation in an accretion disk of close binary star
Authors: Bisikalo Dmitry V. , Zhilkin Andrey G. 
Published: July 2013

AbstractUsing results of 3D MHD numerical simulations we investigate the generation of the magnetic field in an accretion disk of a close binary star. Analysis of the numerical simulations shows that the magnetic field, which is mainly toroidal, is intensively generated in the accretion disk. In the disk, we can distinguish three regions: inner region of the intensive toroidal field generation due to the differential rotation; region of the current sheets; and outer region of the magnetic field dissipation. In the outer regions of the accretion disk of a magnetic close binary system two types of the dynamo may exist. One of them is the laminar dynamo that occurs as a result of the nonaxisymmetric motions. The other type is the turbulent αω-dynamo. Numerical simulations show that during the disk lifetime the dynamo effect in the outer region of the disk can be significant.
On the behavior of stellar rotation in the solar neighbourhood
Authors: de Freitas Daniel B. , De Medeiros J. R. 
Published: July 2013

AbstractRotation is a fundamental physical parameter in stellar astrophysics, playing an important role on the formation and evolution of stars. This parameter may also offer valuable information on stellar magnetism, mixing in the stellar interior, tidal interactions in close binary, as well as on angular momentum transfer and rotational breaking due to planets. The present work brings the results of an unprecedented study on the behavior of the distribution of the projected rotational velocity (v sin i) as a function of galactic position, on the basis of an unique sample of 14000 main-sequence field stars, along the spectral regions F and G. The vsini measurements used in this analyses were obtained from observations carried out with the CORAVEL spectrometers, with a precision better than about 1 km/s.
Effect of magnetic fields on Lithium depletion of solar-type stars
Authors: Li Tanda , Bi Shaolan 
Published: July 2013

AbstractTo study the effect of magnetic fields on lithium depletion and explain the characters of lithium evolution in solar-type stars, stellar models including Tayler-Spruit dynamo-type field are constructed. We compare the theoretical results with the time scales of lithium depletion suggested by Sestito & Randich (2005) and obtain very good agreements.
Fundamental properties and seismological analysis of three Kepler stars
Authors: Liu K. , Bi S. L. 
Published: July 2013

AbstractThe lithium abundance of KIC 11395018 and KIC 10920273 are not compatible with their age, which is deduced by asteroseismology. To explain this phenomenon, we investigate the possible evolutionary status and perform seismological analysis of the three stars KIC 11395018, KIC 10273246 and KIC 10920273. Using the Yale Rotating Stellar Evolution Code (YREC), we constructed a grid of evolutionary tracks with different input physics and rotation rates. In addition to the conventional observed properties, we added two observed constraints: lithium abundance and rotational period. As a result, the lithium abundance of our rotation models agrees well with the observation. Meanwhile, we obtained a set of more accurate stellar fundamental parameters than previous studies.
Chromospheric activity of late-type stars based on Guoshoujing Telescope
Authors: Zhang Liyun , Shi Jianrong , Zhao Jingkun , Luo Ali , Zhang Guoyin , Pi Qingfeng ,   for the Guoshoujing Telescope Collaboration
Published: July 2013

AbstractWe introduced our preliminary results of chromospheric activity of late-type stars based on the stellar spectrum of the pilot survey of the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST, also called Guo Shou Jing telescope). We have found 1151 active M stars from 17471 M samples using the chromospheric active indicator of the Hα line.
Galactic spiral patterns and dynamo action
Authors: Chamandy Luke , Subramanian Kandaswamy , Shukurov Anvar 
Published: July 2013

AbstractThe theory of mean-field galactic dynamos is generalized by allowing for a finite response time of the mean electromotive force (emf) to variations in the mean magnetic field and small-scale turbulence. A non-axisymmetric forcing of the dynamo by a spiral pattern (either stationary or transient) is invoked. The resulting magnetic spiral arms are phase-shifted from the spiral arms of the pattern by an angle 15°–40°, opposite to the sense of galactic rotation. Our findings may help to explain the phase shift between material and magnetic arms observed in NGC 6946 and other galaxies.
Growth rate of magnetic field during starburst phase in a galaxy
Authors: Ko Chung-Ming 
Published: July 2013

AbstractDuring an active star formation phase, it is conceivable that the turbulent level of a galaxy increases and consequently an increase in magnetic field by turbulent dynamo process. We point out that the thickness of the dynamo region is sensitive to the turbulent level. We examine the linear growth rate of three different dynamos, namely, αω, α2ω and α2 dynamos. We find that the dependence of the growth rate on turbulent level is quite different for different dynamos. Moreover, the growth rate is not necessary monotonic to turbulence level even in the linear regime.
Astrophysical MHD turbulence: confluence of observations, simulations, and theory
Authors: Burkhart Blakesley , Lazarian Alex 
Published: July 2013

AbstractMagnetohydrodynamic (MHD) turbulence is a critical component of the current paradigms of star formation, dynamo theory, particle transport, magnetic reconnection and evolution of the ISM. In order to gain understanding of how MHD turbulence regulates processes in the Galaxy, a confluence of numerics, observations and theory must be imployed. In these proceedings we review recent progress that has been made on the connections between theoretical, numerical, and observational understanding of MHD turbulence as it applies to both the neutral and ionized interstellar medium.
Turbulence and dynamo interlinks
Authors: de Gouveia Dal Pino E. M. , Santos-Lima R. , Kowal G. , Falceta-Gonçalves D. 
Published: July 2013

AbstractThe role of turbulence in astrophysical environments and its interplay with magnetic fields is still highly debated. In this lecture, we will discuss this issue in the framework of dynamo processes. We will first present a very brief summary of turbulent dynamo theories, then will focus on small scale turbulent dynamos and their particular relevance on the origin and maintenance of magnetic fields in the intra-cluster media (ICM) of galaxies. In these environments, the very low density of the flow requires a collisionless-MHD treatment. We will show the implications of this approach in the turbulent amplification of the magnetic fields in these environments. To finalize, we will also briefly address the connection between MHD turbulence and fast magnetic reconnection and its possible implications in the diffusion of magnetic flux in the dynamo process.
Saturation of the magnetorotational instability by stable magnetoacoustic modes
Authors: Liverts Edward , Shtemler Yuri , Mond Michael , Umurhan Orkan M. , Bisikalo Dmitry V. 
Published: July 2013

AbstractThe magnetorotational instability (MRI) of thin, vertically-isothermal Keplerian discs, under the influence of an axial magnetic field is investigated near the instability threshold. The nonlinear interaction of Alfven-Coriolis (MRI) modes with stable magnetoacoustic waves is considered. The transition of the Alfven-Coriolis modes to instability occurs when the linearized system has zero eigenvalue of multiplicity two. As a result the nonlinear ordinary differential equation that describes the evolution of the amplitude of the MRI mode near the threshold is of second order. Solutions of that amplitude equation reveal that the MRI is saturated to bursty periodical oscillations due to the transfer of energy to the stable magnetosonic modes.
Modelling grand minima of solar activity using a flux transport dynamo model
Authors: Karak Bidya Binay , Choudhuri Arnab Rai 
Published: July 2013

AbstractThe occurrence of grand minima like the Maunder minimum is an intriguing aspect of the sunspot cycle. We use the flux transport dynamo model to explain the grand minima, showing that they arise when either the poloidal field or the meridional circulation falls to a sufficiently low value due to fluctuations. Assuming these fluctuations to be Gaussian and determining the various parameters from the data of the last 28 cycles, we carry on a dynamo simulation with both these fluctuations. The results are remarkably close to the observational data.
Observational methods for stellar magnetism: from detection to cartography
Authors: Strassmeier Klaus G. , Carroll Thorsten A. , Ilyin Ilya , Järvinen Silva 
Published: July 2013

AbstractWe review some of the currently used techniques to detect stellar magnetic fields on cool stars. Emphasis is put on spectropolarimetry with high-resolution spectrographs and its related data de-noising techniques and multi-line inverse modeling. Detections and results from Zeeman splittings and broadenings are briefly mentioned. We discuss some of our most recent Zeeman Doppler Imaging (ZDI) results and present a comparison of ZDI maps of the K-type WTTS V410 Tauri and the planet-hosting F8 star HD 179949 with results from other groups.
Prospect on intergalactic magnetic field measurements with gamma-ray instruments
Authors: Sol Hélène , Zech Andreas , Boisson Catherine , Krawczynski Henric , Fallon Lisa , de Gouveia Dal Pino Elisabete , Hinton Jim , Inoue Susumu , Neronov Andrii , White Richard 
Published: July 2013

AbstractObserving high-energy gamma-rays from Active Galactic Nuclei (AGN) offers a unique potential to probe extremely tiny values of the intergalactic magnetic field (IGMF), a long standing question of astrophysics, astroparticle physics and cosmology. Very high energy (VHE) photons from blazars propagating along the line of sight interact with the extragalactic background light (EBL) and produce e+e− pairs. Through inverse-Compton interaction, mainly on the cosmic microwave background (CMB), these pairs generate secondary GeV-TeV components accompanying the primary VHE signal. Such secondary components would be detected in the gamma-ray range as delayed “pair echos” for very weak IGMF (B < 10−16G), while they should result in a spatially extended gamma-ray emission around the source for higher IGMF values (B > 10−16G). Coordinated observations with space (i.e. Fermi) and ground-based gamma-ray instruments, such as the present Cherenkov experiments H.E.S.S., MAGIC and VERITAS, the future Cherenkov Telescope Array (CTA) Observatory, and the wide-field detectors such as HAWC and LHAASO, should allow to analyze and finally detect such echos, extended emission or pair halos, and to further characterize the IGMF.
How the planetary research helps to the stellar dynamo understanding
Authors: Boisse I. , Oshagh M. , Lovis C. , Santos N. C. , Dumusque X. , Bonfils X. , Montalto M. , Boué G. 
Published: July 2013

AbstractMost of the exoplanet science is dependent on the stellar knowledge. One of them that has to be understood is the magnetic activity when we search for planets with radial velocity or photometry measurements. The main shape of stellar activity and spots properties have to be understood, for example, to choose the best targets to search for low-mass planets in the habitable zone or to derive the accurate parameters of a planetary system. With that aim, we show in this presentation how these studies lead to give clues on spots latitudes and on the long term variation of stellar activity. The properties of magnetic activity on the low rotators solar-type stars are not easily reachable by other techniques (spectropolarimetry or Doppler imaging) and these studies should be used to constrain theories of stellar dynamo.