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.

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.

scholarly journals Mass-loss varying luminosity and its implication to the solar evolution

2019 ◽  
Vol 15 (S356) ◽  
pp. 403-404
Author(s):  
Negessa Tilahun Shukure ◽  
Solomon Belay Tessema ◽  
Endalkachew Mengistu
Keyword(s):  
Standard Model ◽  
Mass Loss ◽  
Main Sequence ◽  
The Sun ◽  
Solar Mass ◽  
Solar Luminosity ◽  
Solar Evolution

AbstractSeveral models of the solar luminosity, , in the evolutionary timescale, have been computed as a function of time. However, the solar mass-loss, , is one of the drivers of variation in this timescale. The purpose of this study is to model mass-loss varying solar luminosity, , and to predict the luminosity variation before it leaves the main sequence. We numerically computed the up to 4.9 Gyrs from now. We used the solution to compute the modeled . We then validated our model with the current solar standard model (SSM). The shows consistency up to 8 Gyrs. At about 8.85 Gyrs, the Sun loses 28% of its mass and its luminosity increased to 2.2. The model suggests that the total main sequence lifetime is nearly 9 Gyrs. The model explains well the stage at which the Sun exhausts its central supply of hydrogen and when it will be ready to leave the main sequence. It may also explain the fate of the Sun by making some improvements in comparison to previous models.

scholarly journals Radiation-Driven Stellar Eruptions

Galaxies ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 10 ◽  
Author(s):  
Kris Davidson
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Central Region ◽  
Massive Stars ◽  
Variable Stars ◽  
Blast Waves ◽  
Subsequent Evolution ◽  
Fundamental Causes ◽  
Radiative Output ◽  
Luminous Blue Variable

Very massive stars occasionally expel material in colossal eruptions, driven by continuum radiation pressure rather than blast waves. Some of them rival supernovae in total radiative output, and the mass loss is crucial for subsequent evolution. Some are supernova impostors, including SN precursor outbursts, while others are true SN events shrouded by material that was ejected earlier. Luminous Blue Variable stars (LBV’s) are traditionally cited in relation with giant eruptions, though this connection is not well established. After four decades of research, the fundamental causes of giant eruptions and LBV events remain elusive. This review outlines the basic relevant physics, with a brief summary of essential observational facts. Reasons are described for the spectrum and emergent radiation temperature of an opaque outflow. Proposed mechanisms are noted for instabilities in the star’s photosphere, in its iron opacity peak zones, and in its central region. Various remarks and conjectures are mentioned, some of them relatively unfamiliar in the published literature.

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 ON THE EFFECTS OF SOLAR RADIATION PRESSURE ON THE DEVIATION OF ASTEROIDS

2021 ◽  
Vol 57 (2) ◽  
pp. 279-295
Author(s):  
L. O. Marchi ◽  
D. M. Sanchez ◽  
F. C. F. Venditti ◽  
A. F. B. A. Prado ◽  
A. K. Misra
Keyword(s):  
Solar Radiation ◽  
Radiation Pressure ◽  
Scientific Research ◽  
Orbital Plane ◽  
Solar Radiation Pressure ◽  
The Sun ◽  
Mass Ratio ◽  
High Area ◽  
Planetary Defense

In this work, we study the effects of solar radiation pressure (SRP) on the problem of changing the orbit of an asteroid to support planetary defense, scientific research, or exploitation of materials. This alternative considers a tethered reflective balloon (or a set of reflective balloons) attached to the asteroid, with a high area-to-mass ratio, to use the SRP to deflect a potentially hazardous asteroid (PHA) or to approximate the target asteroid to Earth. The tether is assumed to be inextensible and massless, and the motion is described only in the orbital plane of the asteroid around the Sun. The model is then used to study the effects that the tether length, the reflectivity coefficient, and the area-to-mass ratio have on the deviation of the trajectory of the asteroid.

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
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