When a star "goes off the main-sequence" it generally means the star has run out of hydrogen fuel and is beginning the post-main-sequence or its end of life phase. The main sequence of a star is the time where it is no longer just a proto-star but is burning hydrogen as a primary source of fuel.
Sirius is not a single star but a binary star system consisting of a white main sequence star and a white dwarf.
Chort, also known as Omicron1 Tauri, is a binary star system located in the constellation Taurus. The primary star is a yellow-white F-type main-sequence star, while the companion star is a smaller K-type main-sequence star.
Main sequence stars are bigger.
Achernar is a type B star, specifically a B6 V star. It is a hot, blue-white main sequence star located in the constellation Eridanus.
No, a white dwarf is not considered a main sequence star. A main sequence star is a star that is still fusing hydrogen in its core. A white dwarf is the remnant of a low to medium mass star in which fusion has stopped.
When star goes out of main sequence then they starts to die.
No. Red giants are not on the main sequence.
In that case, the star gets its energy from hydrogen fusion - that is, it converts hydrogen-1 to helium-4.
A red main sequence star would be a red dwarf or a branch red giant. To be on the main sequence, you have to have hydrogen nuclear fusion.
The sun is a main sequence star, so 1 AU.
Main-Sequence star
None of those is a main sequence star.
Sirius is not a single star but a binary star system consisting of a white main sequence star and a white dwarf.
The defining characteristic of a main sequence star burns hydrogen to helium in its core.
Most stars are on the main sequence; that includes red dwarves. Specifically, in this case, the closest known star - Proxima Centauri - is also the closest main-sequence star.
Algol is a blue main-sequence star in the constellation Perseus
Any star that it fusing hydrogen into helium is classed as a main sequence star.