scholarly journals KOI-256’s Magnetic Activity Under the Influence of the White Dwarf

2017 ◽  
Vol 34 ◽  
Author(s):  
Ezgi Yoldaş ◽  
Hasan Ali Dal
Keyword(s):  
White Dwarf ◽  
Active Component ◽  
Active Regions ◽  
Magnetic Activity ◽  
Activity Level ◽  
Logarithmic Scale ◽  
Flare Activity ◽  
Migration Period ◽  
Kepler Mission ◽  
Spot Activity

AbstractWe present the findings about chromospheric activity nature of KOI-256 obtained from the Kepler Mission data. First, it was found that there are some sinusoidal variations out-of-eclipses due to cool spot activity. The sinusoidal variations modelled by the spotmodel program indicate that the active component has two different active regions. Their longitudinal variation revealed that one of them has a migration period of 3.95 yrs, while the other has a migration period of 8.37 yrs. Second, 225 flares were detected from the short cadence data in total. The parameters, such as increase (Tr) and decay (Td) times, total flare time (Tt), equivalent durations (P), were calculated for each flare. The distribution of equivalent durations versus total flare times in logarithmic scale is modelled to find flare activity level. The Plateau value known as the saturation level of the active component was calculated to be 2.3121 ± 0.0964 s, and the Half-life value, which is required flare total time to reach the saturation, was computed to be 2233.6 s. In addition, the frequency of N1, which is the number of flares per an hour in the system, was found to be 0.05087 h−1, while the flare frequency N2 that the flare-equivalent duration emitting per an hour was found to be 0.00051. Contrary to the spot activity, it has been found that the flares are in tends to appear at specific phases due to the white dwarf component.

scholarly journals Detailed Chromospheric Activity Nature of KIC 9641031

2016 ◽  
Vol 33 ◽  
Author(s):  
Ezgi Yoldaş ◽  
Hasan Ali Dal
Keyword(s):  
Active Component ◽  
Active Regions ◽  
Activity Level ◽  
Light Curves ◽  
Chromospheric Activity ◽  
Rotational Modulation ◽  
Kepler Mission ◽  
Period Variations ◽  
Analytic Models ◽  
Flare Frequency

AbstractThis study depends on KIC 9641031 eclipsing binary with a chromospherically active component. There are three type variations, such as geometrical variations due to eclipses, sinusoidal variations due to the rotational modulations, and also flares, in the light curves. Taking into account results obtained from observations in the Kepler Mission Database, we discuss the details of chromospheric activity. The sinusoidal light variations due to rotational modulation and the flare events were modelled. 92 different data subsets separated using the analytic models were modelled separately to obtain the cool spot configuration. Acording to the model, there are two active regions separated by about 180° longitudinally between the latitudes of +50° and +100°. 240 flares, whose parameters were computed, were detected. Using these parameters, the OPEA model was derived, in which the Plateau value was found to be 1.232±0.069 s, and half-life parameter was found as 2291.7 s. The flare frequency N1 was found as 0.41632 h−1, while the flare frequency N2 was found as 0.00027. Considering these parameters together with the orbital period variations demonstrates that the period variations depend on chromospheric activity. Comparing the system with its analogue, the activity level of KIC 9641031 is remarkably lower than the others.

Active Regions on the Sun with Increased Flare Activity in Cycle 24

2021 ◽  
Vol 65 (6) ◽  
pp. 507-517
Author(s):  
S. A. Yazev ◽  
E. S. Isaeva ◽  
Yu. V. Ishmukhametova
Keyword(s):  
Active Regions ◽  
Flare Activity ◽  
The Sun ◽  
Cycle 24

scholarly journals CHROMOSPHERIC ACTIVITY NATURE OF KIC 6044064

2021 ◽  
Vol 57 (2) ◽  
pp. 351-361
Author(s):  
E. Yoldaş
Keyword(s):  
Primary Component ◽  
Secondary Component ◽  
Migration Period ◽  
Chromospheric Activity ◽  
Spot Group ◽  
Kepler Mission ◽  
Phase Interval

This study presents results obtained from the data of KIC 6044064 (KOI 6652). KIC 6044064 was observed by the Kepler Mission for a total of 1384.254 days. 525 minima times were determined, 264 of which were primary minima and the rest were secondary minima. The OPEA model was derived and its parameters were obtained. On the secondary component, there are two different spot bands latitudinally outstretched, consisting of three spots located with a phase interval of 0.33. The average migration period was found to be 623.063±4.870 days (1.71±0.01 years) for the first spot group, while it was 1125.514±7.305 days (3.08±0.02 years) for the second group. The spectral types of the components seem to be G7V+K9V. Their masses and radii were determined to be 0.86Mʘ and 0.89Rʘ for the primary component and 0.54Mʘ and 0.62Rʘ for the secondary component.

Prediction of upcoming grand episodes of solar activity

2018 ◽  
Vol 13 (S340) ◽  
pp. 325-326
Author(s):  
G. L. Jayalekshmi ◽  
P. R. Prince
Keyword(s):  
Solar Activity ◽  
Active Regions ◽  
Phase Changes ◽  
Activity Level ◽  
Time Interval ◽  
The Sun ◽  
Strong Magnetic Fields ◽  
Periodicity Analysis ◽  
Long Time ◽  
Grand Minima

AbstractSunspots are active regions on the surface of the Sun having strong magnetic fields. Activity level of the Sun shows long-time scale phenomena known as grand episodes-Grand maxima and Grand minima. Present study examines grand episodes shown by sunspot numbers (1090-2017), using methods of wavelet transform and sinusoidal regression. Time interval analysed includes two grand maxima and four grand minima. Interval in between grand episodes are regular oscillations. Phase changes found from periodicity analysis clearly show the presence of upcoming grand episodes. The forthcoming grand episodes are suggested to be two grand minima which are likely to occur between the years 2100-2160 and 2220-2300.

Chaotic modulation of the solar cycle

1994 ◽  
Vol 348 (1688) ◽  
pp. 445-447 ◽  
Keyword(s):  
Solar Cycle ◽  
Magnetic Fields ◽  
Active Regions ◽  
17Th Century ◽  
Magnetic Activity ◽  
Maunder Minimum ◽  
Magnetic Cycle ◽  
Sunspot Minimum ◽  
Proxy Records ◽  
Oriented Parallel

The Sun’s magnetic activity varies cyclically, with a well-defined mean period of about 11 years. At the beginning of a new cycle, spots appear at latitudes around ±30°; then the zones of activity expand and drift towards the equator, where they die away as the new cycle starts again at higher latitudes. Active regions are typically oriented parallel to the equator, with oppositely directed magnetic fields in leading and following regions. The sense of these fields is opposite in the two hemispheres and reverses at sunspot minimum. So the magnetic cycle has a 22-year period, with waves of activity that drift towards the equator. Sunspot records show that there was a dearth of spots in the late 17th century - the Maunder minimum - which can also be detected in proxy records.

scholarly journals First current density measurements in the ring current region using simultaneous multi-spacecraft CLUSTER-FGM data

2005 ◽  
Vol 23 (5) ◽  
pp. 1849-1865 ◽  
Author(s):  
C. Vallat ◽  
I. Dandouras ◽  
M. Dunlop ◽  
A. Balogh ◽  
E. Lucek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Ring Current ◽  
Magnetic Activity ◽  
Activity Level ◽  
Local Current Density ◽  
Magnetospheric Configuration And Dynamics ◽  
Local Current ◽  
Current Region ◽  
First Time

Abstract. The inner magnetosphere's current mapping is one of the key elements for current loop closure inside the entire magnetosphere. A method for directly computing the current is the multi-spacecraft curlometer technique, which is based on the application of Maxwell-Ampère's law. This requires the use of four-point magnetic field high resolution measurements. The FGM experiment on board the four Cluster spacecraft allows, for the first time, an instantaneous calculation of the magnetic field gradients and thus a measurement of the local current density. This technique requires, however, a careful study concerning all the factors that can affect the accuracy of the J estimate, such as the tetrahedral geometry of the four spacecraft, or the size and orientation of the current structure sampled. The first part of this paper is thus providing a detailed analysis of the method accuracy, and points out the limitations of this technique in the region of interest. The second part is an analysis of the ring current region, which reveals, for the first time, the large latitudinal extent of the ring current, for all magnetic activity levels, as well as the latitudinal evolution of the perpendicular (and parallel) components of the current along the diffuse auroral zone. Our analysis also points out the sharp transition between two distinct plasma regions, with the existence of high diamagnetic currents at the interface, as well as the filamentation of the current inside the inner plasma sheet. A statistical study over multiple perigee passes of Cluster (at about 4 RE from the Earth) reveals the azimuthal extent of the partial ring current. It also reveals that, at these distances and all along the evening sector, there isn't necessarily a strong dependence of the local current density value on the magnetic activity level. This is a direct consequence of the ring current morphology evolution, as well as the relative positioning of the spacecraft with respect to the bulk of the ring current. It also proves the existence of a substantial ring current at these distances, all over the evening and the post-midnight sector. Keywords. Magnetospheric physics (Current systems; Energetic particles, trapped; Magnetospheric configuration and dynamics)

scholarly journals Radio Flare Activity of RS CVn Stars

1980 ◽  
Vol 88 ◽  
pp. 403-403
Author(s):  
Paul A. Feldman
Keyword(s):  
Binary Star ◽  
Quantitative Model ◽  
Magnetic Activity ◽  
Flare Activity ◽  
Radio Observatory ◽  
X Ray ◽  
Rs Cvn Stars ◽  
Solar Magnetic Activity ◽  
Radio Flare ◽  
Systematic Program

For several years, a systematic program to observe RS CVn and similar binaries has been undertaken with the 46-m telescope of the Algonquin Radio Observatory. A number of large radio outbursts at 2.8 cm wavelength has been found from HR 1099, AR Lac, SZ Psc, UX Ari, and HR 5110. In several cases, simultaneous, or nearly simultaneous, observations of these stars were made by cooperating observers at (other) radio, optical, UV, and X-ray wavelengths. It is now clearly established that the mechanism responsible for the cm-wavelength radio emission is nonthermal gyrosynchrotron radiation in a volume whose characteristic dimension is comparable with the binary star separation. More generally, a semi-quantitative model for the radio flare activity of these stars seems to be possible using greatly scaled-up analogues of solar magnetic activity.

scholarly journals Chromospheric variation in cool supergiant stars

1996 ◽  
Vol 176 ◽  
pp. 415-422
Author(s):  
J. A. Eaton ◽  
G. W. Henry
Keyword(s):  
Main Sequence ◽  
Active Regions ◽  
Magnetic Activity ◽  
Hybrid Stars ◽  
Magnetic Phenomena ◽  
Dividing Line

Stars close to the main sequence, if they rotate rapidly enough, show magnetic activity in the form of spots, active regions, and strong chromospheres. With the exception of the hybrid stars, stars cooler and more luminous than the so-called Linsky-Haisch dividing line, in contrast, are not known to have any of these phenomena. In fact, it is not clear such stars, even though rotating and convective, show any magnetic phenomena at all. We discuss (1) photometry used to search for spots in the hybrid stars, which we have not found, and (2) evidence for chromospheric variation in K supergiants that takes the form of enhanced winds, but which may be analogous to the activity of stars closer to the main sequence.

scholarly journals Super-active regions in solar cycle 24

2015 ◽  
Vol 11 (S320) ◽  
pp. 309-314 ◽  
Author(s):  
Anqin Chen ◽  
Jingxiu Wang
Keyword(s):  
Solar Cycle ◽  
Active Regions ◽  
Total Solar Irradiance ◽  
Flare Activity ◽  
Solar Cycles ◽  
Solar Cycle 24 ◽  
Satisfactory Account ◽  
Current Cycle ◽  
Flare Index ◽  
Cycle 24

AbstractComparing with solar cycles 21-23, the level of solar activity in the current cycle is very low. So far, there have been only five SARs and 45 X class flares. The monthly smoothed total solar irradiance decreased sharply by 0.09% from the maximum of cycle 23 to the minima between cycles 23 and 24. In this contribution, we present new studies on SARs in Cycle 24. The SARs in the current cycle have relatively smaller flare index (Iflare) and composite vector field index (Icom) comparing with the SARs in cycles 22 and 23. There is a clearly linear relationship between Iflare and Icom. The emphasis of this contribution is put on the similarity and different behaviors of vector magnetic fields of the SARs in the current solar cycle and the previous ones. We try to get a satisfactory account for the general characteristics and relatively lower level of solar flare activity in Cycle 24.

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