18-05-2012, 12:40 PM
STELLAR TEMPERATURE
stellar temp.ppt (Size: 3.51 MB / Downloads: 32)
INTRODUCTION
The surface temperature of a main sequence star is determined by the rate of energy production at the core and the radius of the star and is often estimated from the stars color index.
Its normally given as the effective temperature .which is temperature of an idealized block body that radiates is energy at the same luminosity per surface area as the star
The effective temperature is only reprehensive value , however as star actually have a temperature gradient that decrease with increasing distance from the core region of a star is several millions Kelvin.
Star
More technically, a star is a body which satisfies two conditions:
It is bound by self-gravity
Spherical due to the symmetric nature of gravity
It radiates energy from an internal source
Nuclear energy released by fusion reactions in its interior
Star Power
A star is powered by nuclear fusion reactions in its core
The gravity from the star’s mass squeezes the nuclei together so that they can overcome electrostatic repulsion and fuse
Hydrogen nuclei fuse to Deuterium and then Helium, releasing about 7 Me each
The released radiation keeps the star from collapsing due to its own gravity
Star Formation
In between the stars in a galaxy, there is a lot of gas which we call the interstellar medium (ISM)
The gas exists in clouds
Small clouds support themselves against gravity using their internal pressure
Large clouds( with masses greater than typical stellar masses) have gravity which exceeds the internal pressure, so are unstable to collapse
Clouds fragment, forming multiple stars and hence star clusters
Stars are made of gas and it is no surprise that wherever we see very young stars, there is gas in the vicinity.
The other, less obvious, ingredient in star formation regions is dust. This turns out to be one of the main reasons it has been hard to unravel the mysteries of star formation.
Properties of Stars
Mass – The single most important property that determines other properties of the star.
Luminosity – The total amount of energy (light) that a star emits into space.
Temperature – surface temperature, closely related to the luminosity and color of the star.
Spectral type – closely related to the surface temperature
Size – together with temperature determine the luminosity