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  • 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry  (10)
  • Deutschland
  • Q11
  • Astronomy
  • J24
  • 2005-2009  (15)
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  • 1
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    Effects of Dust Growth and Settling in T Tauri Disks (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We presented self-consistent disk models of T Tauri stars that include a parameterized treatment of dust settling and grain growth, building on techniques developed in a series of papers by D'Alessio et al. The models incorporate depleted distributions of dust in upper disk layers along with larger sized particles near the disk midplane, which are expected theoretically and, as we suggested earlier, are necessary to account for millimeter-wave emission, SEDs, scattered light images, and silicate emission features simultaneously. By comparing the models with recent mid- and near-IR observations, we find that the dust-to-gas mass ratio of small grains at the upper layers should be less than 10% of the standard value. The grains that have disappeared from the upper layers increase the dust-to-gas mass ratio of the disk interior; if those grains grow to maximum sizes of the order of millimeters during the settling process, then both the millimeter-wave fluxes and spectral slopes can be consistently explained. Depletion and growth of grains can also enhance the ionization of upper layers, increasing the possibility of the magnetorotational instability for driving disk accretion.
    Keywords: Astronomy
    Type: The Astrophysical Journal; 638; 1; 314-335
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  • 2
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    Why Do T Tauri Disks Accrete? (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks scales roughly with the square of the central stellar mass. No dependence of accretion rate on stellar mass is predicted by the simplest version of the Gammie layered disk model, in which nonthermal ionization of upper disk layers allows accretion to occur via the magnetorotational instability. We show that a minor modification of Gaminie's model to include heating by irradiation from the central star yields a modest dependence of accretion on the mass of the central star. A purely viscous disk model could provide a strong dependence of accretion rate on stellar mass if the initial disk radius (before much viscous evolution has occurred) has a strong dependence on stellar mass. However, it is far from clear that at least the most massive pre-main-sequence disks can be totally magnetically activated by X-rays or cosmic rays. We suggest that a combination of effects are responsible for the observed dependence, with the lowest mass stars having the lowest mass disks, which can be thoroughly magnetically active, while the higher mass stars have higher mass disks that have layered accret,ion and relatively inactive or "dead" central zones at some radii. In such dead zones, we suggest that gravitational instabilities may play a role in allowing accretion to proceed. In this connection, we emphasize the uncertainty in disk masses derived from dust emission and argue that T Tauri disk masses have been systematically underestimated by conventional analyses. Furtlier study of accretion rates, especially in the lowest mass stars, would help to clarify the mechanisms of accretion in T Tauri stars.
    Keywords: Astronomy
    Type: The Astrophysical Journal; 648; 1; 484-490
    Format: text
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  • 3
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    Disks in Transition in the Taurus Population: Spitzer IRS Spectra of GM Aurigae and DM Tauri (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We presented Spitzer Infrared Spectrograph (IRS) observations of two objects of the Taurus population that show unambiguous signs of clea,ring in their inner disks. In one of the objects, DM Tau, the outer disk is truncated at 3 AU; this object is akin to another recently reported in Taurus, CoKu Tau/4, in that the inner disk region is free of small dust. Unlike CoKu Tau/4, however, this star is still accreting, so optically thin gas should still remain in the inner disk region. The other object, GM Aur, also accreting, has about 0.02 lunar masses of small dust in the inner disk region within about 5 AU, consistent with previous reports. However, the IRS spectrum clearly shows that the optically thick outer disk has an inner truncation at a much larger radius than previously suggested, of order 24 AU. These observations provide strong evidence for the presence of gaps in protoplanetary disks.
    Keywords: Astronomy
    Type: The Astrophysical Journal; 630; 2; L185 - L188
    Format: text
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  • 4
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    The Accretion Disk of the Lithium-Depleted Young Binary St 34 (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We presented the infrared spectrum of the young binary system St 34 obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The IRS spectrum clearly shows excess dust emission, consistent with the suggestion of White & Hillenbrand that St 34 is accreting from a circumbinary disk. The disk emission of St 34 is low in comparison with the levels observed in typical T Tauri stars; silicate features at 10 and 20 microns are much weaker than typically seen in T Tauri stars; and excess emission is nearly absent at the shortest wavelengths observed. These features of the infrared spectrum suggest substantial grain growth (to eliminate silicate features) and possible settling of dust to the disk midplane (to reduce the continuum excess emission levels), along with a relatively evacuated inner disk, as expected due to gravitational perturbations by the binary system. Although the position of St 34 in the H-R diagram suggests an age of 8f Myr, assuming that it lies at the distance of the Taurus-Auriga molecular clouds, White & Hillenbrand could not detect any Li I absorption, which would indicate a Li depletion age of roughly 25 Myr or more. We suggest that St 34 is closer than the Taurus clouds by about 30-40 pc and has an age roughly consistent with Li depletion models. Such an advanced age would make St 34 the oldest known low-mass pre-main-sequence object with a dusty accretion disk. The persistence of optically thick dust emission well outside the binary orbit may indicate a failure to make giant planets that could effectively remove dust particles.
    Keywords: Astronomy
    Type: The Astrophysical Journal; 628; 2; L147 - L150
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  • 5
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    Disk Evolution in Cep OB2: Results from the Spitzer Space Telescope (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We presented the results of an infrared imaging survey of Tr 37 and NGC 7160 using the IRAC and MIPS instruments on board the Spitzer Space Telescope. Our observations cover the wavelength range from 3.6 to 24 microns, allowing us to detect disk emission over a typical range of radii 0.1 to 20 AU from the central star. In Tr 37, with an age of about 4 Myr, about 48% of the low-mass stars exhibit detectable disk emission in the IRAC bands. Roughly 10% of the stars with disks may be "transition" objects, with essentially photospheric fluxes at wavelengths i 4.5 microns but with excesses at longer wavelengths, indicating an optically thin inner disk. The median optically thick disk emission in Tr 37 is lower than the corresponding median for stars in the younger Taurus region; the decrease in infrared excess is larger at 6-8 microns than at 24 microns, suggesting that grain growth and/or dust settling has proceeded faster at smaller disk radii, as expected on general theoretical grounds. Only about 4% of the low-mass stars in the 10 Myr old cluster NGC 7160 show detectable infrared disk emission. We also find evidence for 24 micron excesses around a few intermediate-mass stars, which may represent so-called "debris disk" systems. Our observations provided new constraints on disk evolution through an important age range.
    Keywords: Astronomy
    Type: The Astrophysical Journal; 638; 897-919
    Format: text
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  • 6
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    Wollastonite- anorthite- gehlenite-, and fassaite-bearing rocks: Igneous petrological oddity or paralavas? (2006)
    Details
    Publication Date: 2020-12-14
    Description: We brieß y review the petrological and geochemical features, and physical characteristics, of the Colle Fabbri and Ricetto rocks to discuss their possible paramagmatic origin, i.e., derived from complete melting, after devolatilization, of marly protoliths, without any orthomagmatic, ultimately mantle-derived, chemical or thermal input. Contrary to the various comments that have been made, the overall mineralogical, petrological, and geochemical data provided in the literature well agree with this Þ nding.
    Description: Published
    Description: 1926- 1933
    Description: partially_open
    Keywords: Wollastonite ; gehlenite ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 489 bytes
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  • 7
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    Mineralogic and bulk rock composition of Italian wollastonite- and melilite-bearing paralava and clinker: Further evidence of their pyrometamorphic nature (2006)
    Mineralogical Society of America
    Details
    Publication Date: 2020-12-14
    Description: Two small outcrops of wollastonite- and melilite-bearing paralavas, with a pyrometamorphic genesis, have been found along the Apennine chain, in Central Italy, at the localities of Colle Fabbri and Ricetto. Recent papers added new data strengthening the hypothesis that the Ricetto wollastonite- and melilite-bearing rocks were produced by pyrometamorphism of carbonate-rich siliciclastic sedimentary rocks. In addition, these new papers depicted the Ricetto paralavas as having wide mineralogical and compositional variations due to liquid immiscibility and/or carbonate devolatilization, paralleling the trend observed for other paralavas (e.g., Colle Fabbri, Italy; British Columbia, Canada; Wyoming, U.S.A.; etc.). The source of heat for inducing pyrometamorphism was not investigated in the original paper, which was the subject of the comment. Capitanio et al. (2004), on the basis of 14C age determination and of a mineralogical study, argued convincingly that heat was supplied to the Ricetto rocks by wood-combustion for charcoal production.
    Description: Published
    Description: 1940-1944
    Description: partially_open
    Keywords: rock composition ; Italian wollastonite ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 489 bytes
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  • 8
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    Serpentine and brucite of ultramafic clasts from the South Chamorro Seamount (Ocean Drilling Program Leg 195, Site 1200): inferences for the serpentinization of the Mariana forearc mantle (2006)
    Mineralogical Society
    Details
    Publication Date: 2017-04-04
    Description: Serpentine minerals and brucite in ultramafic rocks from the South Chamorro Seamount were characterized chemically to investigate the serpentinization of the Mariana forearc mantle. Relict primary minerals of the serpentinites are olivine, enstatite and minor Cr-spinel and diopside. The secondary minerals are mostly serpentine and brucite with minor magnetite. The serpentine minerals, mostly lizardite and chrysotile, display large compositional variations. Al2O3 and Cr2O3 contents depend generally upon the nature of the primary mineral from which the serpentine was derived. Both serpentine minerals and brucite exhibit wide Mg, Fe and Mn substitution: the Mg# ranges are 95.1 77.2 and 88.9 60.8, respectively. These mineralogical and chemical features allowed us to estimate an upper temperature limit for serpentinization of ~200 300ºC, in agreement with recent thermal models which suggest that the serpentinized mantle wedge of the Izu-Bonin-Mariana subduction zone is cold. The high degree of serpentinization (40 100%, average 〉75%), and the serpentine + brucite paragenesis of these ultramafics imply that the Mariana forearc mantle has a significantly reduced density and strength down to ~30 km, which provides a driving mechanism for serpentinite diapirism. Pervasive serpentinization of the forearc by fluids released from the de´collement zone also explains the low seismicity of the Izu-Bonin-Mariana subduction zone.
    Description: Published
    Description: 887–904
    Description: partially_open
    Keywords: serpentinization ; mineral chemistry ; serpentine mud volcano ; Ocean Drilling Program ; forearc mantle ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 441 bytes
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  • 9
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    Data report: electron microprobe investigation of primary minerals in basalts from the west philippine sea basin (ocean drilling program leg 195, site 1201) (2006)
    Details
    Publication Date: 2017-04-04
    Description: The basement cored at Site 1201 (west Philippine Basin) during Ocean Drilling Program Leg 195 consists of a 91-m-thick sequence of basalts, mostly pillow lavas and perhaps one sheet lava flow, with a few intercalations of hyaloclastite and interpillow sedimentary material. Hydrothermal alteration pervasively affected the basalt sequence, giving rise to a variety of secondary minerals such as K-Fe-Mg-clay minerals, oxyhydroxides and clay minerals mixtures, natrolite group zeolites, analcite, alkali feldspar, and carbonate. The primary minerals of pillow and sheet basalts that survived the intense hydrothermal alteration were investigated by electron microprobe with the aim of characterizing their chemical composition and variability. The primary minerals are mostly plagioclase, ranging in composition from bytownite through labradorite to andesine, chromian-magnesian-diopside, and spinels, both Ti magnetite (partially maghemitized) and chromian spinel. Overall, the chemical features of the primary minerals of Site 1201 basalts correspond to the primitive character of the bulk rocks, suggesting that the parent magma of these basalts was a mafic tholeiitic magma that most likely only suffered limited fractional crystallization and crystallized at high temperatures (slightly below 1200°C) and under increasing ƒO2 conditions. The major element composition of clinopyroxene suggests a backarc affinity of the mantle source of Site 1201 basement.
    Description: Published
    Description: 1-24
    Description: open
    Keywords: Data report ; basalt sequence ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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  • 10
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    Hydrothermal alteration of oceanic crust in the West Philichemistry investigationppine Sea Basin(Ocean Drilling Program Leg 195,Site 1201): inferences from a mineral (2006)
    Springer
    Details
    Publication Date: 2017-04-04
    Description: Secondary minerals of a 91 meters-thick sequence of pillow basalts cored during ODP Leg 195 (Site 1201, West Philippine Basin) were investigated to reconstruct the hydrothermal alteration history and regime. The basement was first buried by red clays, and then by a thick turbidite sequence, thereby isolating it from seawater. The basalts are primitive to moderately fractionated, texturally variable from hypocrystalline and spherulitic to intersertal, sub-ophitic and intergranular. Relic primary minerals are plagioclase, clinopyroxene and opaques. Hydrothermal alteration pervasively affected the basalts, generating secondary clay minerals (mostly glauconite, minor Al-saponite and Fe-beidellite, Na-zeolites, minor alkali-feldspar and calcite. The secondary mineral paragenesis and mutual relationships suggest that the hydrothermal alteration occurred under zeolite-facies conditions, at temperatures 100-150 C. The main phase of alteration occurred under oxidizing conditions, with a high seawater rock ratio, in an open-circulation regime, at temperatures of 30-60 C, with precipitation of abundant glauconite and iddingsite. A later stage of alteration occurred at ca. 70 C, with precipitation of abundant Na-zeolites and minor calcite, in a more restricted circulation regime as a consequence of basement burial under the sedimentary cover, which supplied an altered, Ca-rich and Magma-sulfate-poor water causing precipitation of almost pure calcite.
    Description: Published
    Description: 87-112
    Description: open
    Keywords: west Philippine ; Mineral chemistry ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 478 bytes
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