T Tauri star

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This article is about the type of variable star. For the particular variable star called "T Tauri", see T Tauri.
Artist's impression of a T Tauri star with a circumstellar accretion disc
Star formation
Object classes
Theoretical concepts

T Tauri stars (TTS) are a class of

radiative zone, or when a smaller star commences nuclear fusion on the main sequence
.

History

While T Tauri itself was discovered in 1852, the T Tauri class of stars were initially defined by Alfred Harrison Joy in 1945.[3]

Characteristics

T Tauri stars comprise the youngest visible F, G, K and M

spectral type stars (<2 M☉). Their surface temperatures are similar to those of main-sequence stars of the same mass, but they are significantly more luminous because their radii are larger. Their central temperatures are too low for hydrogen fusion. Instead, they are powered by gravitational energy released as the stars contract, while moving towards the main sequence
, which they reach after about 100 million years. They typically rotate with a period between one and twelve days, compared to a month for the Sun, and are very active and variable.

There is evidence of large areas of starspot coverage, and they have intense and variable X-ray and radio emissions (approximately 1000 times that of the Sun). Many have extremely powerful stellar winds; some eject gas in high-velocity bipolar jets. Another source of brightness variability are clumps (protoplanets and planetesimals) in the disk surrounding T Tauri stars.

The ejection of a bubble of hot gas from XZ Tauri, a binary system of T Tauri stars. The scale is much larger than that of the Solar System.

Their spectra show a higher

pre–main sequence phase of the Hayashi contraction
may be one of the main sources of energy for T Tauri stars. Rapid rotation tends to improve mixing and increase the transport of lithium into deeper layers where it is destroyed. T Tauri stars generally increase their rotation rates as they age, through contraction and spin-up, as they conserve angular momentum. This causes an increased rate of lithium loss with age. Lithium burning will also increase with higher temperatures and mass, and will last for at most a little over 100 million years.

The p-p chain for lithium burning is as follows


p
 		 + 
6
3Li
 		 → 
7
4Be
  
7
4Be
 		 + 
e−
 		 → 
7
3Li
 		 + 
ν
e

p
 		 + 
7
3Li
 		 →  8
4Be
 		   (unstable)
    8
4Be
 		 →  2 4
2He
 		 + energy

It will not occur in stars with less than sixty times the mass of Jupiter (MJ). The rate of lithium depletion can be used to calculate the age of the star.

Types

Several types of TTSs exist:[4]

  • Classical T Tauri star (CTTS)
  • Weak-line T Tauri star (WTTS)
    • Naked T Tauri star (NTTS), which is a subset of WTTS.
Protoplanetary discs in the Orion Nebula

Roughly half of T Tauri stars have

planets
.

Analogs of T Tauri stars in the higher mass range (2–8

pre–main-sequence stars, are called Herbig Ae/Be-type stars. More massive (>8 solar masses) stars in pre–main sequence stage are not observed, because they evolve very quickly: when they become visible (i.e. disperses surrounding circumstellar gas and dust cloud), the hydrogen in the center is already burning and they are main sequence
objects.

Planets

Planets around T Tauri stars include:

See also

References

  1. S2CID 118324477
    .
  2. ^ "Stellar Evolution - Cycles of Formation and Destruction; Young Stellar Objects". chandra.harvard.edu. Retrieved 2023-01-31.
  3. doi:10.1086/144749
    .
  4. ^ Scott J. Wolk (1996). "T Tauri Stars, Naked and Otherwise". Retrieved 2018-03-14.
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