L dwarfs stars

Hi

I have a small question.

After their formation, the brown and red dwarfs have spectre M. I know that the brown dwarfs become cold and evolve in brown dwarfs L, T, Y...

But why some red dwarfs become L? The temperature of the stars of main sequence must go up with time, and not go down. The red dwarfs do not seem to make exception, since at the end when some dozens one thousand one million years when they evolve in blue dwarfs (in theory).

I also hope for a paper on the dwarfs L, it would be very interessant.

Thank you.

L, T, and Y dwarfs are sub-stellar, and do not undergo the process of nuclear fusion of hydrogen into helium that main-sequence stars do. As such, their thermal evolution is different.

The primary component of 2M0746 is a L red dwarf star with 0,085 M_Sol and the secondary is a pulsating L brown dwarf (radio pulsating) with 0,06 M_Sol.

http://www.eso.org/public/news/eso0420/

VB 10:
-mass:0,0779 M_Sol;
-age:~10^9 years;
-temperature: 2600K

2M0746A:
-mass:0,085 M_Sol;
-age:~0,5-1x10^9 years;
--temperature:1800 K

WTF???

Sirius_Alpha wrote:

L, T, and Y dwarfs are sub-stellar

That is incorrect.

L dwarfs house both stars and brown dwarfs.
T dwarfs so far, only house brown dwarfs
Y dwarfs so far, do not exist as none has been found yet (good candidates, but not proven).
http://en.wikipedia.org/wiki/Stellar_classification
http://en.wikipedia.org/wiki/Stellar_classification#Class_L

Oh, interesting. Thanks for the correction.

I think that was an error. Back when L Dwarfs were assumed L stood for Lithium on the internet.

The correct thing is that L dwarf stars burn all their lithium and no lithium is detected.
While an L brown dwarf does not fuse lithium and thus lithium exist in the atmosphere.
Hence the term, "Lithium Test".
http://en.wikipedia.org/wiki/Brown_dwarf#History
Search for the word "Lithium Test" and you will see the explaination.

As for Ultracool Dwarfs, I am not sure if that proposed name became a term. I can't remember what astronomer did that term. It's in an AJ paper.
However, 2MUCD is associated to the Ultracool Dwarf term.
As 2MUCD = 2MASS UltraCool Dwarf.

I don't understand. The ultracool stars and L brown dwarfs should follow the same evolution up to the ignition of the hydrogen. It is proved that the hydrogen burning limit binary L dwarfs show very close temperatures between them.

The temperature of ignition of the lithium is very close to the temperature of ignition of the hydrogen. About its mass is, a star should not have the time to get colder between the stage of lithium and the beginning of main sequence. And even if it's case, impossible to have the same temperature as a brown dwarf of the same age, because energy was fabricated by lithium burning. If episode " L " is intercalated between the stage of fusion of the deuterium and lithium, it is in keeping with observations.

Logically the test of the Lithium should not exist for the L dwarfs.

Theory of Low-Mass Stars and Substellar Objects

The Lithium test cannot make the difference between a young star (deuterium burning or ultracool) and a brown dwarf because young stars doesn't yet destroyed Lithium. And it cannot make the difference between a star and a very massive brown dwarf (between 0,06 and 0,07M_Sol) because it is hot and compact enough to destroy lithium.

Interesting. I never knew that