Spectral class temperature range

[snorkack]

What are the temperature ranges of the spectral classes?
Oh Be A Fine Girl, Kiss Me Like That Y?
Note that L, T and Y are added after M. Nothing is added before O. So O class... The O9-B0 border is somewhere around 30 000 K. Does lack of earlier class mean that O class starts from infinity? What is the temperature of an O0 star? What spectral class are Magnificent 7?
B class spans from about 30 000 K to the B9-A0 border around 10 000 K. This makes a temperature ratio of about 3.
A class starts from 10 000 K and A9-F0 border is around 7300 K. This makes a temperature ratio of about 1,37.
F class starts from 7300 K and F9-G0 border is around 6000 K. This makes a temperature ratio of about 1,22.
G class starts from 6000 K and G9-K0 border is around 5300 K. This makes a temperature ratio of about 1,13.
K class starts from 5300 K and K9-M0 border is around 3900 K. This makes a temperature ratio of about 1,36.
M class starts from 3900 K, and M9-L0 border is around 2300 K. This makes a temperature ratio of about 1,7.
L class starts around 2300 K, and L9-T0 border seems to be around 1500 K. This makes a temperature ratio of about 1,53.
T class starts about 1500 K, and T9-Y0 border seems to be around 620 K. This makes a temperature ratio of about 2,4.
Y class starts about 620 K and goes to where? Zero? What is the temperature of a Y9 object?

 

[mathman]

Temp. too low - not a star. Very high temp. - fast burnout.

 

[snorkack]

Temp. too low - not a star.

Is a star-planet boundary defined by temperature or something else, like mass?

 

[mathman]

Mass is the main determinant, Look it up in wikipedia. https://en.wikipedia.org/wiki/Stellar_mass

 

[Drakkith]

Is a star-planet boundary defined by temperature or something else, like mass?

It is defined by the ability to fuse hydrogen (protium) in its core, which is dependent on the mass of the body. Objects that cannot fuse anything are planets, those that can fuse deuterium but not protium are brown dwarfs ('failed stars'), those that can fuse protium are stars.

 

[snorkack]

Very high temp. - fast burnout.

The hottest stars are the compact ones. Which do cool down, but do not burn.

 

[Drakkith]

The hottest stars are the compact ones. Which do cool down, but do not burn.

Are you referring to white dwarfs and neutron stars?

 

[snorkack]

Are you referring to white dwarfs and neutron stars?

Yes.
Hot white dwarfs include the cores of planetary nebulae. And neutron stars include the Magnificent 7 I mentioned - nerby young neutron stars that are not pulsars and are seen in thermal radiation.

 

[Drakkith]

Okay. Just trying to avoid confusion with the term 'star'.

 

[Ken G]

Yes, the simple fact is there is no widely accepted definition of the term "star." For example, you should hardly do better than use the glossary of terms in Sky and Telescope, yet this is what you get for star: "A massive ball of gas that generates prodigious amounts of energy (including light) from nuclear fusion in its hot, dense core." It takes two seconds to see the flaws in that definition if it is regarded as a way to distinguish what is a star from what is not a star, like what is a sandwich from what is not a sandwich!

Personally I think we should not think of scientific definitions as strictly inclusive boxes (especially not "star" or "planet"), but instead think of them as signposts, meant to refer to everything close, but the associations simply get more vague farther away, rather than a line in the sand. So a white dwarf is a star, a red giant is a star, a pre-main-sequence star is a star, etc., because they are studied by stellar astronomers in close association with other more obvious examples of stars. (Similarly for planets.) And a brown dwarf is a star when it is studied by people who want to connect it to other stars, and it is a gas giant planet when studied by people who want to connect it with other gas giant planets. That's just how they are going to do it, after all, you really can't stop them!