condensed dust seeds planet formation ?

[Widdekind]

Big bright stars do not produce planetary systems. For,

 

Mean rotational velocities of main sequence stars decline steeply at about F2, where the depth of the surface convection zone increases dramatically with spectral type (Kraft 1970). This implies that low mass stars lose a substantial amount of angular momentum, in their evolution to the main sequence (Kawaler. Spin-up and Spin-down on the way to the Main Sequence).

And, this break may imply the presence of planetary systems, which covertly cache the missing angular momentum (Carroll & Ostlie. Intro. Mod. Astrophys., p.891).

 

 

Sturrock.

Physics of the Sun

, p.172

(annotated)

.

Now, metal poor stars also do not produce planetary systems (Majestic Universe (Scientific American), p.). Such suggests that metallic dust may 'seed' the planet production process.

 

CONCLUSION (?):

 

Even metal-rich massive stars do not produce planets. Er go, even when metals are present in their collapsing proto-stellar clouds, those metals do not nucleate into dust grains (which would, then, 'seed' planetesimal aggregations). Might that mean, that more massive stars' raging radiation perpetually prevents metal grains from collecting (and so seeding planet accumulation) ?

 

 

 

break in 'Kraft' curve caused by onset of CNO fusion ?

 

The break in behavior, between spectral-classes F & A, segregating small, slowly-spinning stars, from big rapidly-rotating stars,

 

Lewis.

Physics & Chemistry of the Solar System

, p.28.

coincides with the occurrence of convection, in the star's outer envelope, and ensuing star-spot cycles:

 

The Kraft curve is a plot of the minimum angular momentum of a star (since it is based on the assumption of rigid rotation in the interior) against mass. An important feature of the Kraft curve is the break which occurs just above one solar mass. Stars with masses lower than the break are observed to rotate slowly, while more massive stars are mostly rapid rotators. Indeed, the sun is well-known to rotate slowly... The break in the curve coincides closely with the appearance of surface convection zones, and with the onset of magnetic activity for stars... with masses below the break in the Kraft curve (DeMarque. Mixing due to Angular Momentum transfer in evolving sun-like stars).

And, those surface convective zones, preserved in the atmospheres of small stars, through onto the Main Sequence, are present initially, in all proto-stars:

 

Angular momentum [is lost] from pre-Main Sequence stars, between the end of the dynamical collapse phase, and the arrival on the Main Sequence. The degree of angular momentum loss is a strong function of mass, with low mass stars ([math]M < 1.3 M_{\odot}[/math]) experiencing the most angular momentum loss...

 

A smooth trend of decreasing angular momentum with mass exists, for intermediate mass main sequence stars (the "Kraft" curve). Main Sequence stars less massive than [math]1.3 M_{\odot}[/math] rotate much more slowly than this trend, suggesting that they lose angular momentum with time...

 

The angular momenta of young low mass stars would lead to rotation velocities, on the main sequence, of a few hundred km/s. However, as reflected in the break in the Kraft curve, low mass main sequence stars rotate slowly, with velocities typically less than 10 km/s. Therefore, they must have lost a significant fraction of their angular momentum, during Main Sequence evolution... While stars above [math]1.3 M_{\odot}[/math] do not have significant convection zones on the main sequence, they did while they were approaching it (Kawaler. Angular Momentum Loss in pre-Main Sequence objects, and the initial angular momentum of stars).

This transition, in turn, coincides with the occurrence of core convection, in more massive stars:

 

Green & Jones.

Introduction to the Sun & Stars

, p.181.

Perhaps, then, a different 'flavor' of fusion, in more massive stars, restructures them internally, whilst externally emitting harsher radiation, which rips apart nascent nucleating metallic dust grains in their collapsing cloud, and disk, thereby preventing planets from forming. In turn, the quenching of planet formation apparently permits more mass, and angular momentum, to transfer through the circum-stellar disk, and deposit into the central star. Indeed, planets apparently compete, with the central star, to accrete disk matter, which fact limits the largest size attainable, by 'Brown Dwarf' super-planets ([math]m < 0.01 \, M_{\odot} \approx 12 \, m_J \approx 4000 \, m_{\oplus}[/math]), to the amount of matter resident in such disks (and explaining why Jupiter possesses almost all of the Sun's 'missing angular momentum'). In sum, initially "[star] formation works the same for all stars, regardless of mass", modified only by the onset of various forms of fusion, at First Light, of the central star, which would affect the spatial extent, of the "dust-free region between [the central star] and the surrounding disk [where] the star's energy had evaporated the dust molecules closest to it", apparently pushing the 'molten metallic droplet / dust-grain condensation distance' out beyond the effective edge of the disk.

Edited April 14, 2011 by Widdekind