Planetary Sciences American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on Planetary Sciences (1991) / Chapter Skim
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1. The Properties and Environment of Primitive Solar Nebulae as Deduced from Observations of Solar-Type Pre-Main Sequence Stars
1. The Properties and Environment of Primitive Solar Nebulae as Deduced from Observations of Solar-Type Pre-Main Sequence Stars
Pages 1-16
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The time scales for disk survival as massive (M ~ 0.01 to 0.1 Me) , optically thick structures appear to lie in the range t << 3 x 106 years to t ~ 107 years.
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They exhibit infrared spectral energy distributions, AF>, vs. A, which are a)
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(by A plot of the observed spectral energy distribution for the continuum + ~rnrnission T Taun star, HL Tau. Near-infrared images of HL Tau suggest that this YSO is surrounded by a flattened distribution of circumstellar dust.
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1988~. Radiation from the boundary layer overwhelms that from the cool PMS star photosphere.
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What is the range in time scales for disk evolution in the inner and outer disks, and how do these time scales compare with those inferred for our solar system from meteoritic and primitive body studies, and theoretical modeling of the early solar nebula? In what fraction of star/disk systems can the gas in the outer disk regions survive removal by energetic winds long enough to be assembled into analogs of the giant planets?
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In order to account for the fact that these IR-luminous YSOs are visible at optical wavelengths, it is necessary to assume that the observed far-IR radiation arises in an optically thick but phy~cabty dour circumstellar envelope: a disk If the heated circumstellar dust responsible for the observed far-infrared radiation intercepted a large solid angle, the
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Because material in this disk must be in Keplerian motion about a central PMS star, absorption lines formed in the disk reflect the local rotational velocity. High spectral resolution observations show that lines formed in the outer, cooler regions of the disk are narrower than absorption features formed in the inner, hotter, more rapidly rotating disk regions (Hartmann and Kenyon 1987a,b; Welty et al.
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Frequency of Disk Occurrence What fraction of stars are surrounded by disks of distributed gas and dust at birth? If excess infrared and mm-wave continuum emission is produced by heated dust in disks, then all continuum + emission, T Tauri, and Herbig emission stars must be surrounded by disks.
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It does not appear as if NUTS as a class lack infrared excesses.
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This somewhat surprising result implies that circumstellar envelopes of mass > 10-4 Me and of dimension 10 to 100 AU are present even in close binary systems. Disk Evolutionary Time Scales On what time scales do disks evolve from massive "primitive" to low mass, perhaps "post planet-building" disks?
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Note the small near-infrared excess and relatively large mid- to far-infrared excesses for several of the NTIS. A spectral energy distribution of this character might be produced by a circumstellar disk in which the optical depth of emitting material in the inner disk is small, while that in the outer disk is large.
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Fewer than 10% of PMS stars older than 107 years show AK > al. If excess near-IA emission arises in the warm, inner regions of circumstellar disks, then we can use these statistics to discuss the range of time scales for disks to evolve from massive, optically thick structures (with large K values)
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Our data suggests that the time scales for evolving from a massive, optically thick disk to a low mass, tenuous disk must range from ~ 3 X 106 to 107 years. This range represents the best available astrophysical constraint on the time scale for planet building.
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largely equatorial mass outflows obliquely shocking gas located at the raised surface of a slightly flaring disk (Hartmann and Raymond 1988~. Knowledge of the wind geometry is necessary if we are to derive more accurate estimates of PMS star mass loss rates from [O I]
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Many of the arguments developed here have been sharpened and improved following consultation with Steven Beckwith, Robert ~ Brown, Belva Campbell, Luis Carrasco, H Melvin Dyck, Galy Grasdalen, Lee Hartmann, S
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Stencel (eds.~. Proceedings of the Fifth Cambridge Cool Star Workshop.
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