فهرست مطالب

Iranian Journal of Astronomy and Astrophysic
Volume:10 Issue: 1, Spring 2023

  • تاریخ انتشار: 1402/07/24
  • تعداد عناوین: 6
  • Nasim Ildartanha, Sadollah Nasiri * Pages 1-9
    We aim to reconstruct a nonlinear force-free magnetic field by minimizing the global departure of an initial field from a force-free and solenoidal state in the presence of helicity to obtain an appropriate representation of the magnetic field compatible with the solar coronal condition. Following the Wheatland et al method we modify their functional to include the magnetic helicity using the Lagrange multiplier technique. We reconstruct the magnetic field by minimizing the new functional in a computational box whose lower side coincides with the artificial magnetogram on the photosphere while the lateral and top sides extends up to the corona and by assuming appropriate boundary conditions for the Lagrange multiplier. The artificial magnetogram is obtained by Low and Lou semi-analytical solutions. A potential field as well as a suitable ansatz is used for the initial input magnetic filed and Lagrange multiplier for the iteration procedure, respectively. The results obtained by different optimization methods are in agreement with those obtained by our approach.
    Keywords: Sun, magnetic field, Helicity, Lagrange Multiplier
  • Sima Zeighami *, Ehsan Tavabi Pages 11-60
    The Sun is a magnetically active star. It has a powerful magnetic field that shifts slightly from year to year until it reverses about every eleven years. The sun's magnetic field has many effects, the collection of which is called solar activity such as, sunspots, solar flares, and coronal mass ejections(CMEs). Currently, it is only possible to predict a magnetic storm 30 to 60 minutes before it occurs, which is a very short time. Solar flares and CMEs, massive eruptions of superheated plasma, are the two most energetic phenomenon which impulsively ejected and accelerated by releasing magnetic energy in the solar corona. Heliosphere, space weather, and the Earth are affected from transporting coronal plasma. Following the occurrence of these phenomenon in the Sun, the solar wind blows with greater speed and intensity and sends energetic charged particles into the space of the solar system. When these particles reach the Earth, their radiating electromagnetic waves interact with magnetic field of the Earth. Then various effects are observed, as shock waves and massive geomagnetic storms that disrupt satellites and power grids. Today, using the advancements of ground and space technology, the solar surface can be easily observed. Therefore, observation and prediction of solar storm will be possible more than in the past. In this paper, we review papers intended to collect comprehensive information about what has already been researched about fast solar jets and CMEs made by ground and space instruments over the last decades.
    Keywords: Solar Jets, Bright Points, CMEs, Chromosphere, Transition Region, corona
  • Neda Dadashi *, Maryam Ghiassi Pages 61-75
    Prominences are cold and dense chromospheric material suspended in the solar atmosphere with the support of coronal magnetic fields. Oscillatory behavior of a limb core prominence is studied in the AIA 171, 193, 211, 335, and 94 \AA\ passbands of AIA aboard SDO. Vertical oscillations with periods of 34.8, and 40.0 minutes with velocity amplitudesof 4.6, and 5.2 $\rm km/s$ are obtained over the prominence core structure in the all studied channels. These long period oscillation started 54 minutes before an external flare eruption starts to develop over the north side of the studied core prominence, and continued for about two hours. Wave fronts from the Flare Eruption (FE) might be the exciter of these long period oscillation over the entire core prominence. Propagating upward and Downward slow magneto-acoustic waves with velocities in the range of 11.3 to 24.2 $\rm km/s$ are observed over the upper and lower boundaries of the prominence. The multiple rapidly heating and cooling effects, with the time scales less than one minutes, are observed over the propagating peak intensities, which might be the response of the plasma before reaching to a thermal balance between the injected heating flux (through the wave fronts of the FE) and heating loss flux through conduction, radiation, and viscosity.
    Keywords: The Sun: corona, The Sun: oscillations, The Sun: filaments, prominences
  • Mohsen Javaherian *, Zahra Eskandari Pages 75-109
    With the exponential growth in data volume, especially in recent decades, the demand for data processing has surged across all scientific fields. Within astronomical datasets, the combination of solar space missions and ground-based telescopes has yielded high spatial and temporal resolutions for observing the Sun, thus fueling an increase in the utilization of automatic image processing approaches. Image processing methodologies play a pivotal role in analyzing solar data, a critical component in comprehending the Sun's behavior and its influence on Earth. This paper provides an overview of the utilization of diverse processing techniques applied to images captured from the solar photosphere. The introduction of our manuscript furnishes a description of the solar photosphere along with its primary characteristics. Subsequently, we endeavor to outline the significance of preprocessing photospheric images, a crucial prerequisite before engaging in any form of analysis. The subsequent section delves into an examination of numerous reputable sources that have employed image processing methodologies in their research pertaining to the Sun's surface. This section also encompasses discussions concerning recent advancements in image processing techniques for solar data analysis and their potential implications for future solar research. The final section deliberates on post-processing procedures as supplementary steps that are essential for deriving meaningful results from raw data. Effectively, this paper imparts vital information, offering concise explanations regarding the Sun's surface, the application of image processing techniques to various types of photospheric images, indispensable image preprocessing stages, and post-processing procedures aimed at transforming raw data into coherent and comprehensive insights.
    Keywords: Sun: photosphere, Sun: activity, Sun: magnetic fields, Sun: granulation, Sun: sunspots, Techniques: image processing
  • Hashem Hamedivafa * Pages 111-120
    We use spectro-polarimetric data recorded by Hinode to analyze the magnetic field configuration of a part of a sunspot (AR10923) where a bundle of penumbral filaments are intruding into its umbra. We want to explore the role of the sunspot magnetic configuration in the formation and kinematics of the fine-structures, such as umbral dots and light bridges, inside the sunspot umbra. Both direct inferences from polarization Stokes profiles and the inversion results using the SIR code imply a well-arranged magnetic field configuration in the umbra where moving umbral dots are easily formed at the leading edges of the rapidly intruding penumbral filaments. We suggest that the magnetic field topology is rearranged via magnetic reconnection process by which a part of the magnetic energy is converted into thermal and kinetic energy, leading to the orderly aligned magnetic field lines. This new configuration causes the umbral fine-structures to form easily and more frequent.
    Keywords: Sun: sunspot, fine-structures, magnetic structure
  • Ehsan Tavabi, Azam Mollatayefeh * Pages 121-135
    The similarities between Ca and x-ray jets suggest that their formation mechanism should be the same. Surges are almost cool plasma jets and are usually observed in Hα at ground-based observation, space observations also detect Surges. The structure and movement of the observed surges and jets necessitate a reconnection framework in which magnetic tension and the release of twisted energy contribute significantly. Convincing indications of reconnection are offered by whip-like movements, and the rotational behavior of the surges arises as an outcome of the relaxation of reestablished magnetic twist. The IRIS spectra spicules to determine one of the factors affecting the production and feeding of solar winds. Jets and spicules have been considered by examining several raster frames from the regions of the Sun. The characteristics of spicules, such as the rotational velocity of each spicule concerning the central axis of the spectrum , were computed using the output of the Doppler map. Then, using the Mg II spectrum simultaneously, Doppler maps for specific index samples were created at various speeds. Based on the results, a speed of 30 km/s was demonstrated.Our investigation into spicules unveiled a distinctive type that deviates from prior observations regarding speed, angle, and direction of movement. These spicules appear to result from vortical movements, which could also contribute to the propagation of Alfvén rotational waves and the transfer of energy to the Sun's upper atmosphere. In this study, it is essential to recognize that rotating spicules represent minute structures observable in exceedingly high-resolution imaging.
    Keywords: Sun, Chromosphere, jets, Transition Region