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.

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 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.

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.

scholarly journals Rate of mass loss by stars of different classes

1959 ◽  
Vol 10 ◽  
pp. 125-127
Author(s):  
E. R. Mustel
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Active Regions ◽  
Present Knowledge ◽  
Thermal Dissipation ◽  
The Sun ◽  
Present Communication ◽  
Rapid Rotation ◽  
Loss Of Mass

The present communication contains mainly the discussion of the problem of mass loss by stars of early classes. The investigations show that the loss of mass by the Sun may proceed in different ways. In the atmospheres of O stars different mechanisms of ejection of gases must also exist: thermal dissipation of gases, the ejection of prominences (electromagnetic mechanisms), the ejection of atoms by radiation pressure, the ejection of atoms from active regions which may exist in the atmospheres of O-Stars, a very rapid rotation of stars etc. However our present knowledge on the mechanisms of ejection of gases from the surface of stars of early types is extremely scanty. Therefore it seems that there exists only one way to estimate the rate of mass loss by O-stars. This is the investigation of those effects which can be produced by gases ejected from the star.

Correlated Bursts at Distant Sources on the Sun

1969 ◽  
Vol 1 (5) ◽  
pp. 186-188 ◽  
Author(s):  
K. Kai
Keyword(s):  
Time Delay ◽  
High Resolution ◽  
Active Regions ◽  
Solar Observatory ◽  
The Sun ◽  
Quiet Period ◽  
Fast Electrons ◽  
Different Sources ◽  
Large Flare

Since the start of high-resolution observations with the radioheliograph at the Culgoora Solar Observatory it has been noted that some bursts which occur from separate active regions could be physically correlated. It was suggested that the time delay between the correlated bursts is of the order of seconds, and that fast electrons provide the trigger. Wild found that shortly before a large flare weak bursts, stronelv polarized in the same sense, appeared simultaneously in different sources after a quiet period and he discussed the phenomenon in the light of flare mechanisms.

scholarly journals Solar active regions in Mg II light

1968 ◽  
Vol 35 ◽  
pp. 299-303
Author(s):  
Kerstin Fredga
Keyword(s):  
Active Regions ◽  
The Sun ◽  
Reversal Effect ◽  
Negative Results ◽  
Important Observation ◽  
Solar Active Regions

During 1965 two rockets were launched in order to obtain monochromatic pictures of the Sun in the Mg II line at 2802·7 Å. The Mg II filterheliograms have been compared with simultaneous Hα and Ca II K spectroheliograms. An important observation from both flights concerns the relative intensities of different active regions. In the Hα pictures there are old fairly faint active regions and newly formed more intense regions. In the Mg II pictures, however, the older regions appear more intense than the younger regions.Different explanations for this intensity-reversal effect have been considered. The effect has also been looked for in broadband Ca II H filterheliograms, with negative results, however.

Sign in / Sign up

Export Citation Format

Share Document