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  • 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations  (12)
  • Deutschland
  • Q11
  • Astronomy
  • J24
  • 2005-2009  (17)
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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
    Format: text
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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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    La Rete Integrata Nazionale GPS (RING) dell' INGV: una infrastruttura aperta per la ricerca scientifica (2007)
    Details
    Publication Date: 2017-04-04
    Description: Since 2004, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) is investing important energies for the creation of a continuous GPS network dislocated all over the Italian territory. Data transmission will occur in real time, integrating the experiences already existing in the different INGV institutes and developing a 3-yrs strategy for the new installations. The main targets of the network are represented by active tectonics studies, including also the seismological part as strain accumulation on faults. Within a 3-yrs funding project, it is expected, to realize for the scientific community an infrastructure which is comparable to those existing in countries where advanced crustal deformation studies are carried out. Thus, INGV have co-located the classical seismological instrumentation (broad band seismometers and accelerometers) with GPS receivers to observe and quantify the whole seismic cycle. In this short paper, we describe the CGPS network, the technological choices for the monumentation and the data transmission, the data and metadata management and, finally, the data policy and the deliverables.
    Description: INGV
    Description: Unpublished
    Description: reserved
    Keywords: RING ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: report
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  • 7
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    Contemporary crustal extension in the Umbria–Marche Apennines from regional CGPS networks and comparison between geodetic and seismic deformation (2008)
    Elsevier
    Details
    Publication Date: 2020-11-16
    Description: Here we report the results of the analysis of a GPS velocity field in the Umbria–Marche Apennines (central Italy) obtained from the integration of diverse geodetic networks. The velocity field obtained shows a high degree of consistency both spatially and in terms of comparison with independent information, despite the limited time span of some GPS stations. Starting from the velocity field we derive a continuous strain rate field applying a spline interpolation technique which provide a smooth estimate of the deformation field. The main feature of the resulting strain rate field is a continuous high (N50 nanostrain/year) strain rate belt coincident with the area of largest historical and instrumental seismic release. The model directions of the principal axes agree with geological and seismological information indicating NE–SW extension. We transform the strain rate field into geodetic moment rate using the Kostrov formula to evaluate the potential seismic activity of the region and compare it with actual seismic release in the last 720 years from MwN5.5 earthquakes. This comparison highlights a large possible deficit in the seismic release with respect to the overall potential seismic activity, particularly concentrated in the northern part of the study area. This discrepancy can be resolved with either a large amount of seismicity to be released in the near future or significant aseismic slip and deformation.
    Description: Published
    Description: 3-12
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Description: reserved
    Keywords: GPS ; crustal deformation ; Northen Apennines ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Active tectonics of the Adriatic region from GPS and earthquake slip vectors (2008)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: To investigate the kinematics of the Adriatic region we integrate continuous and episodic GPS measurements and ${M_w} 〉 4.5$ earthquake slip vectors selected from the Regional Centroid Moment Tensor (RCMT) catalogue. Coherent motion of GPS sites in the Po Valley, in Apulia and in the Hyblean Plateau allows us to estimate geodetically constrained angular velocities for these regions. The predictions of the GPS-inferred angular velocities are compared with the earthquake slip vectors, showing that the seismically-expressed deformation at the microplate boundaries is consistent with the observed geodetic motion. The remarkable consistency between geodetic, seismological and geological evidence of active tectonics, suggests that active deformation in the Central Adriatic is controlled by the relative motion between the Adria and Apulia microplates. The microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses (1) that Apulia forms a single microplate with the Ionian Sea and possibly with the Hyblean region and (2) that Adria and Apulia rotate in such a way as to accommodate the Eurasia-Nubia relative motion. We suggest that the present-day microplate configuration follows a recent fragmentation of the Adriatic promontory that during the Neogene rigidly transferred the Africa motion to the orogenic belts that now surround the Adriatic region.
    Description: Published
    Description: B12413
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: Adria ; GPS ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
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    Intrusive Mechanisms at Mt. Etna Forerunning the July-August 2001 Eruption from Seismic and Ground Deformation Data (2005)
    Springer
    Details
    Publication Date: 2017-04-04
    Description: In this work we present seismological and ground deformation evidence for the phase preparing the July 18 to August 9, 2001 flank eruption at Etna. The analysis performed, through data from the permanent seismic and ground deformation networks, highlighted a strong relationship between seismic strain release at depth and surface deformation. This joint analysis provided strong constraints on the magma rising mechanisms. We show that in the last ten years, after the 1991–1993 eruption, an overall accumulation of tension has affected the volcano. Then we investigate the months preceding the 2001 eruption. In particular, we analyse the strong seismic swarm on April 20–24, 2001, comprising more than 200 events (Mmax = 3.6) with prevalent dextral shear fault mechanisms in the western flank. The swarm showed a ca. NE-SW earthquake alignment which, in agreement with previous cases, can be interpreted as the response of the medium to an intrusive process along the approximately NNW-SSE volcano-genetic trend. These mechanisms, leading to the July 18 to August 9, 2001 flank eruption, are analogous to ones observed some months before the 1991–1993 flank eruption and, more recently, in January 1998 before the February-November 1999 summit eruption.
    Description: Published
    Description: 1469-1487
    Description: partially_open
    Keywords: Ground deformation ; volcano seismology ; Mt. Etna Volcano ; intrusive mechanism ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 513 bytes
    Format: 878745 bytes
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  • 10
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    Tectonic evolution of fault-bounded continental blocks: (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We report on new paleomagnetic and anisotropy of magnetic susceptibility (AMS) data from Plio-Pleistocene sedimentary units from Corinth and Megara basins (Peloponnesus, Greece). Paleomagnetic results show that Megara basin has undergone vertical axis CW rotation since the Pliocene, while Corinth has rotated CCW during the same period of time. These results indicate that the overall deformation in central Greece has been achieved by complex interactions of mostly rigid, rotating, fault bounded crustal blocks. The comparison of paleomagnetic results and existing GPS data shows that the boundaries of the rigid blocks in central Greece have changed over time, with faulting migrating into the hanging walls, sometimes changing in orientation. The Megara basin belonged to the Beotia-Locris block in the past but has now been incorporated into the Peloponnesus block, possibly because the faulting in the Gulf of Corinth has propagated both north and east. Paleomagnetic and GPS data from Megara and Corinth basins have significant implications for the deformation style of the continental lithosphere. In areas of distributed deformation the continental lithosphere behaves instantaneously like a small number of rigid blocks with well-defined boundaries. This means that these boundaries could be detected with only few years of observations with GPS. However, on a larger time interval the block boundaries change with time as the active fault moves. Paleomagnetic studies distinguishing differential rotational domains provide a useful tool to map how block boundaries change with time.
    Description: Published
    Description: 1-15
    Description: reserved
    Keywords: Paleomagnetism ; Greece, block rotations ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 1167012 bytes
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