T Tauri wind
Encyclopedia
The T Tauri wind — so named because of the young star currently in this stage—is a phenomenon indicative of the phase of stellar development between the accretion of material from the slowing rotating material of a solar nebula
Solar nebula
In cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...

 and the ignition of the hydrogen that has agglomerated into the protostar
Protostar
A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...

.

The protostar, at first, only has about 1% of its final mass. But the envelope of the star continues to grow as infalling material is accreted. After 10,000–100,000 years http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit2/starform.html, thermonuclear fusion begins in its core, then a strong stellar wind is produced which stops the infall of new mass. The protostar is now considered a young star since its mass is fixed, and its future evolution is now set.

The evolutionary picture of low mass protostars

The T Tauri
T Tauri
T Tauri is a variable star in the constellation Taurus, the prototype of the T Tauri stars. It was discovered in October 1852 by John Russell Hind...

 stars, with masses less than twice the mass of our Sun, are thought to follow this process:
  1. very slowly rotating cloud solar nebula
    Solar nebula
    In cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...

     + trigger
  2. collapse
  3. star + protoplanetary disk
    Protoplanetary disk
    A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...

     formation
  4. slow contraction and accretion + intense stellar winds (bipolar flows)
  5. ignition of hydrogen burning and appearance of star on the main sequence.

Protostar evolution in detail

Initially there is a random amount of interstellar gaseous matter, mainly hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, containing traces of dusts (ices, carbon, rocks).
  1. initially, the clouds which collapse are thought to be very slowly rotating
  2. What happens is that the dense cores collapse faster than the less dense outer regions of the cloud. This follows from the free-fall time ~ 1/√(gxdensity). The initial collapse of the core is quite fast; time ~ 1/√(6.7×10−8×10−18 g/cm³) ~ 50,000–100,000 years or so. The lower density envelope takes longer to collapse accrete (collapse onto the protostar); time ~ millions of years or so. Roughly, speaking the Sun forms as shown here.
  3. The inside-out collapse leads to the formation of the forming star in the center of the cloud which then slowly builds up its mass by accreting the outer layers of the cloud.
  4. Another noteworthy aspect of this later stage of formation is that before the star actually gets hot enough to ignite nuclear fusion, an intense stellar wind is generated. Often because the cloud was slowly rotating, a disk of material forms around the star. The disk collimates the intense stellar wind into 2 oppositely directed beams producing what is referred to as a bipolar flow, which can cause the forming star to lose up to 0.4 mass of our Sun, and can start to disrupt the cloud.
  5. Even though it takes several millions of years for the cloud to accrete onto the protostar, because the protostars are relatively low mass, it takes even longer to slowly contract and approach starhood. For the most part, the cloud has a chance to accrete onto the protostar before the violent stages of evolution begin.

The character of accretion and stellar wind parameters of T Tauri stars

The main portion of emission continuum of Classic T Tauri Stars is formed outside the accretion shock, what means a great deal of accretion matter falls onto the star in nearly horizontal direction. This gas decelerate in turbulent layer near the star surface.

We suggest two scenarios to explain such nature of accretion: two-stream accretion (through boundary layer and magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...

) and magnetospheric accretion by way of streams, the bulk of matter in which falls onto the star in nearly horizontal direction.

Observations have provided quantitative parameters of disk wind, derived from the analysis of optical and UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 spectra of CTTS. The matter outflows observed from a disk region with an outer radius of < 0.5 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

. The outflowing matter initially moves almost along the disk until being accelerated up to V> 100 km/s and only afterwards begins to collimate. Inner region of the wind is collimated into the jet at a distance <3 AU from the disk mid plain. The Vz gas velocity component in the jet decreases with increasing distance from the jet axis. The gas temperature in the jet bottom is less than 20,000 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

s.

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