Comparison of Stellar Oscillations and Activity Data to Infer Internal Rotation

1993 ◽  
Vol 137 ◽  
pp. 675-678
Author(s):  
Gaetano Belvedere
Keyword(s):  
Active Regions ◽  
The Sun ◽  
Acoustic Oscillations ◽  
Activity Data ◽  
Surface Distribution ◽  
Stellar Oscillations ◽  
Mhd Dynamo ◽  
Latitude Distribution ◽  
Stellar Interiors ◽  
Angular Velocity Profile

AbstractRecently it has beeen suggested that the latitude distribution of the main surface features of solar activity is intimately related to the angular velocity profile inside the Sun through the working of a MHD dynamo in the boundary layer between the convective and the radiative zones (Belvedere et al. 1991).Although the present observational capabilities are not very encouraging, here we want to point out, in the framework of the analogy to the Sun (solar-stellar connection), that space observations of surface distribution and latitudinal migration of active regions on stellar surfaces, which could be carried out in this decade with more sophisticated techniques, may conversely allow us to infer the rotation profile, and consequently the angular momentum distribution, in stellar interiors. This methodology may in principle be considered alternate or complementary to the classical one based on observation of acoustic oscillations.

What happened with the comet 71P/Clark?

1999 ◽  
Vol 173 ◽  
pp. 259-264
Author(s):  
S. Szutowicz
Keyword(s):  
Active Regions ◽  
Discrete Source ◽  
Spin Axis ◽  
Model Parameters ◽  
The Sun ◽  
Surface Distribution ◽  
Axis Orientation ◽  
Numerical Fitting ◽  
Nongravitational Effects

AbstractDiscovered in 1973, 71P/Clark had made only five revolutions around the Sun. The motion of the comet has been subjected to a constant small deceleration between 1973 and 1989 and then a dramatic jump in the nongravitational perturbations occured. To explain the discontinuity in the comet's nongravitational effects a change in the surface distribution of active areas and a nucleus orientation was considered. The model of discrete source of out gassing was employed in the orbital calculations. From numerical fitting of the model parameters to positional observations the spin-axis orientation, localizations and outgassing areas of two active regions have been derived and the orbit successfully improved. The nucleus radius was estimated as equal to 0.76 km.

scholarly journals Helio- and asteroseismology

2008 ◽  
Vol 4 (S252) ◽  
pp. 135-147 ◽  
Author(s):  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Internal Rotation ◽  
Sound Speed ◽  
Solar Interior ◽  
The Sun ◽  
Stellar Oscillations ◽  
Stellar Interiors ◽  
Insight Into

AbstractObservations of solar and stellar oscillations are providing detailed information about stellar interiors. In the case of the Sun the set of observed frequencies is sufficiently detailed and accurate that the properties of the solar interior, such as sound speed, density and internal rotation, can be inferred with substantial precision and resolution. This allows detailed tests of solar modelling, with interesting and to some extent controversial results. Observations of solar-like oscillations in distant stars have started only recently, owing their very small amplitudes. However, developments in ground-based equipment and observations from space are revolutionizing this field, promising greatly increased insight into the structure and evolution of the stars.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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

Study of the magnetospheres of active regions on the sun by radio astronomy techniques

2017 ◽  
Vol 55 (1) ◽  
pp. 1-11
Author(s):  
V. M. Bogod ◽  
T. I. Kal’tman ◽  
N. G. Peterova ◽  
L. V. Yasnov
Keyword(s):  
Radio Astronomy ◽  
Active Regions ◽  
The Sun

scholarly journals Solar Internal Rotation, the Boundary Layer Dynamo and Latitude Distribution of Activity Belts

1991 ◽  
Vol 130 ◽  
pp. 237-240
Author(s):  
G. Belvedere ◽  
M.R.E. Proctor ◽  
G. Lanzafame
Keyword(s):  
Boundary Layer ◽  
Internal Rotation ◽  
Radial Profile ◽  
Active Regions ◽  
Dynamo Model ◽  
Main Sequence Stars ◽  
Dynamo Action ◽  
Latitude Distribution ◽  
Thin Spherical Shell ◽  
And Migration

Abstract We suggest that the latitude distribution of solar activity belts and the related equatorward or poleward migration of different tracers of the solar cycle are a natural consequence of the internal radial profile of angular velocity via the working of a dynamo in the boundary layer beneath the convection zone. This has been confirmed by the results of a non-linear dynamo model in a very thin spherical shell which show that dynamo action may reasonably take place in the boundary layer and reproduce the observed surface phenomenology.Extending the argument to late main-sequence stars, it is reasonable to think that observations of the latitude distribution and migration of stellar active regions by current sophisticated techniques may make it possible to infer their internal rotation profile in a simple and direct way.

scholarly journals A study of morfodynamic of active regions on the Sun for short-term flare prognosis

2007 ◽  
Vol 11 (3) ◽  
pp. 334-338
Author(s):  
M. Koval'chuk ◽  
M. Hirnyak
Keyword(s):  
Active Regions ◽  
The Sun ◽  
Short Term

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.

Parameters of dust jets in comet Encke’s coma

2020 ◽  
Vol 493 (4) ◽  
pp. 5499-5505
Author(s):  
Yu Chernetenko ◽  
Yu Medvedev
Keyword(s):  
Active Regions ◽  
Dust Particles ◽  
The Sun ◽  
Restricted Area ◽  
Dust Emissions

ABSTRACT Using 4412 positional observations, we compute eight single apparition orbits in the period 1993–2017. The analysis of the residuals of the orbit’s fit shows their systematic deviations around perihelia. We assume that these deviations in positional observations are a result of the dust emissions from a restricted area of the nucleus, and that the ejected dust particles contain a certain amount of ice. Additional sublimation of ice from particles causes a gas-rich effect when the comet is approaching the Sun. Another effect of the jet motion of particles is a shift of the centre of brightness in the direction of ejection. Taking these effects into account, we estimate the size of the dust particles (2–10 cm) containing $80{{\ \rm per\ cent}}$ ice, dust velocities (1.8–2.6 m s−1), and the positions of active regions on the comet’s nucleus (cometocentric latitude from 55° to 74°). These estimates are based on the data for the residuals in the positional observations before the perihelia of the 1993, 2003, 2013 and 2017 apparitions.

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