Main sequence stars?

Question

how do main sequence stars get on/off and what do they do on it

Answer 1

Main sequence stars are those which are doing nuclear fusion in their cores. This is a long lasting and stable period for the star. Following a star like the sun through its lifetime will go like this:

It will start far to the bottom right: cool and dim, and below the main sequence. This is when it is a protostar and has not started fusion.

In a relatively short period of time, it will jump into the main sequence when it starts fusion hydrogen into helium. It may be any of a wide range of temperatures and sizes, but most stars like our sun lie on or near the main sequence and stay there for billions of years. The hottest and largest ones stay there for less time. The cooler ones stay there longer.

The really hot stars use up their fuel faster and go through the cycles more quickly, but eventually all of them will become red giants or supergiants. They will drift upward and to the right on the diagram.

When average stars like the sun shed their outer portions, they will leave a white dwarf behind. So now they will make a long and relatively quick trip down and to the left on the diagram, well below the main sequence and into the white range. These are white dwarfs. Because they are very small and not doing fusion, they are not nearly as bright. That's why they are so low on the diagram. Over vast periods of time, they will drift to the right and downward, as they cool.

Answer 2

A main sequence star is a star that burns hydrogen to helium in its innermost 20% of radius, which is called the core. The main sequence is the part of a star's life that follows gravitational accretion and ends when about 14% of the hydrogen has been used up in the core.

Here's an empirically curve-fit method for creating models of main sequence stars.

Choose: the mass of the star in solar masses, M.
1 solar mass = 1.99E+30 kilograms.

Q = log M
(Q is the base 10 logarithm of the star's mass in solar masses.)

If M <= 0.631 then
A = -3.346 M^2 + 4.518 M + 2.482

If 0.631 < M <= 3.981 then
A = -1.7708 Q^2 + 0.5 Q + 4.1708

If M > 3.981 then
A = 3.3023 + 0.64295 EXP(-0.048036 M)

The EXP function is the base e exponent function.

L = M^A
where L is the star's luminosity in units of the sun's luminosity, Ls = 3.826E26 Watts.

if log M <= -0.4 then
B = -0.3625 Q^2 - 0.7535 Q + 0.5078

If -0.4 < log M <= +0.4 then
B = 0.52083 Q^2 + 0.0625 Q + 0.69167

If +0.4 < log M <= +0.8 then
B = -1.5 Q^2 + 1.6 Q + 0.4

If log M > +0.8 then
B = 0.72

R = M^B
where R is the star's radius in units of the sun's radius, Rs = 6.96E+8 meters.

T = (5784K) M^(A/4 - B/2)
where T is the star's effective temperature in Kelvins.

p = (1.4105 g cm^-3) M^(1-3B)
where p is the star's average density in grams per cubic centimeter.

Mv = 4.75 - 2.5 AQ
where Mv is the star's absolute magnitude.

Lmax = 2.89776E+07 angstroms / T
where Lmax is the star's wavelength of peak power output.

Tms = 1.01E10 years M^(1-A)
where Tms is the star's lifetime on the main sequence.

K = log T
(K is the base 10 logarithm of the star's effective temperature in Kelvins.)

If K >= 3.967 then
S = -26.1452 K + 125.8483

If 3.772 < K <= 3.967 then
S = -86.1025 K + 363.7926

If 3.740 < K <= 3.772 then
S = -246.753 K + 970.494

If K <= 3.740 then
S = -66.3801 K + 296.8677

Round S to the nearest integer.
The "tens" digit of S will indicate the letter designation of the spectral type.
A zero means spectral type O.
A one means spectral type B.
A two means spectral type A.
A three means spectral type F.
A four means spectral type G.
A five means spectral type K.
A six means spectral type M.
The "ones" digit of S will indicate the numerical subtype of the spectral type, the number to follow the letter.

If K>4.009 then
B-V = 0.8332 K^2 - 7.769 K + 17.786

If 3.719 < K <= 4.009 then
B-V = 5.2593 K^2 - 43.334 K + 89.227

If 3.662 < K <= 3.719 then
B-V = 13.674 K^2 - 103.91 K + 198.13

If 3.509 < K <= 3.662 then
B-V = -24.868 K^2 + 174.54 K - 304.69

If K < 3.509 then
B-V = 27.605 K^2 - 196.65 K + 351.71

where B-V is the star's color index.

If K > 4.127 then
BC = -6.5896 K + 26.3657

If 3.924 < K <= 4.127 then
BC = -10.515 K^2 + 81.232 K - 156.98

If 3.700 < K <= 3.924 then
BC = -9.4985 K^2 + 72.637 K - 138.9

If K < 3.700 then
BC = -34.541 K^2 + 260.71 K - 491.94

where BC is the star's bolometric correction.

Rhab = (1.496E+11 meters) M^(0.5 A)
where Rhab is the distance of an Earthlike planet from the star.

Phab = (365.25 days) M^(0.75 A - 0.5)
where Phab is the orbital period of an Earthlike planet at a distance of Rhab.

diam = 2 arctan{ 0.0046524 M^(0.72 - 0.5 A) }
where diam is the angular diameter of the star from an Earthlike planet at a distance of Rhab.

Under ordinary circumstances, only stars with mass in the range of 0.8

Answer 3

Main sequence stars, also called dwarf stars, are stars that fuse hydrogen to helium in their cores. Once a protostar has collapsed to a stable size it is considered a main sequence star. A star leaves the main sequence and becomes a red giant when it has used up all the hydrogen in its core. A red giant begins by burning hydrogen in a shell around a helium core, and then fuses helium in its core. The most massive stars go on to fuse oxygen, carbon, silicon, etc.

Answer 4

Thinking a star as a human, from baby to adult to elderly. Main sequence is like adulthood where you spend more of your life. When you grow up from childhood, you get on the Main Sequence, and when you are too old to move, you get off it.

Answer 5

Any star that is in hydrostatic equilibrium between gravity and pressure is a main sequence star, including some very massive giant stars. Super giant stars are not in hydrostatic equilibrium so they are not on the main sequence once their cores collapse and the outer layers start to expand because of the cores hotter temperature and increased pressure from the core.