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T-Tauri Phase

Jim Hurley wrote:

> I have been reading up on Chondrite formation theories lately and had > some thoughts on it. Since I don't have any real expertise in the > science involved, I have to use my imagination.
> One of the characteristics of T-Tauri stars that isn't well understood > is their sudden flaring for hours or days.
> The chondrules were probably formed at this time in the pre-solar > nebula and recent theories claim that they had to be formed by sudden > thermal shocks lasting for minutes to hours.
> It doesn't seem then that these flarings could be the cause - they > would probably vaporize any chondritic particles. Investigation into > chondrite formation does seem to suggest they underwent several melts.
> Here's my thought - could these flarings be due to a temporary H->He > fusion cause by large infalling masses. The core of the nebulae hasn't > reached the point where fusion could be sustained,
> but it's getting there. There must be some times when it is close to > that point and a sudden big shock could take it locally to that stage, > cause some H->He local fusion and then died out for lack of sustaining > energy.


Hello Jim, hello List,

While updating my METCAT database, I came across the following article
and thought it might be of interest to Jim and some of you:

METEORITICS 26-4 Dec. 1991, p.339:

Meteoritic evidence for an active early sun.

J. N. Goswami. Physical Research Laboratory, Ahmedabad-380 009, India.

The pre-main-sequence evolution of sun-like stars is dominated by an
active phase, the so-called T-Tauri phase, characterized by high
mass-outflow at the rate of about 10^-7 to 10^-8 solar mass per year.
Planetary scientists have invoked the presence of a strong T-Tauri wind
from the early Sun which presumably cleared the residual nebular gas and
dust following the formation of small objects, the precursors to the
planetesimals/planetary objects in our solar system. Even if the Sun was
magnetically active during this phase and was the source of intense
flare activity, self-shielding by the nebular gas may not allow the
solar energetic particles to effectively interact with the meteoritic
components at 2-4 AU. Recent studies have however revealed that weak
T-Tauri stars, which are not prominent in optical emission and have weak
mass-outflow, show variations in their emission in X-ray and radio-band
over short time-scales. These variabilities have been attributed to
magnetically driven intense flare-like activity in the weak T-Tauri
stars (1). If the Sun has also gone through such a stage, following the
burst of the T-Tauri wind that cleared the residual nebular gas and
dust, it will be logical to expect intense solar flare irradiation
records in meteoritic components that were exposed to an active early
Sun. Gas-rich meteorites, and the gas-rich carbonaceous chondrites in
particular, seem to be the most ideal samples to look for such records.
Several experimental approaches, both direct and indirect, have so far
been attempted to address this problem (2). The main uncertainty in
interpreting the data is our lack of proper knowledge about (i) the
exact epoch of the early irradiation of the meteoritic component and
(ii) collision-controlled evolutionary time scales of the
meteorite-parent-body surfaces. The present status of the work will be
summarized and results from some recent effort will be presented.

References:
(1) Feigelson E.D. et al. (1991) In The Sun in Time, in press.
(2) Caffee M. et al. (1991) In The Sun in Time, in press.

Regards, Bernd

P.S.: In the same issue of METEORITICS, there is an interesting abstract
by J.N. Grossman: The coevolution of chondrules and matrix in ordinary
chondrites: A new model (METEORITICS 26-4 Dec. 1991, p.340-341).

Perhaps Jeff could share his thoughts on Jim's T-Tauri subject (and
maybe also on the subtype subdivision of type 3 chondrites).