Probing the nature of IGR J16493−4348: spectral and temporal analysis of the 1–100 keV emission     

A. B. Hill  A. J. Dean  R. Landi  V. A. McBride  A. De Rosa  A. J. Bird  A. Bazzano  V. Sguera 《Monthly notices of the Royal Astronomical Society》2008,385(1):423-429

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A spatter-forming, large-scale paroxysm at Stromboli Volcano (Aeolian Islands, Italy): insight into magma evolution and eruption dynamics     

Sonia La Felice  Patrizia Landi 《Bulletin of Volcanology》2011,73(9):1393-1406

This study focuses on a pyroclastic sequence related to a large-scale paroxysm that occurred during the seventeenth century ad and which can be considered one of the most powerful and hazardous explosive events at the volcano in the past few centuries. Paroxysms are energetic, short-lived explosions which sporadically interrupt normal Strombolian activity at Stromboli and commonly erupt a deep-derived, volatile-rich crystal-poor high-potassium basalt (“low porphyricity” (LP)), together with a shallow, degassed crystal-rich high-potassium to shoshonitic basalt (“high porphyricity” (HP)), which feed normal activity at the volcano. The studied deposit, crops out along the flanks of Sciara del Fuoco and, from base to top, consists of: (1) a layer of HP and LP ash and lapilli; (2) an unwelded layer of coarse HP lapilli and flattened dark scoriae; (3) weakly welded spatter made up of dense HP pyroclasts at the base, overlain by strongly vesicular LP clasts. The textural and chemical zoning of minerals and the glass chemistry of the LP products record repeated mafic recharge events, mixing with an old mushy body and episodes of rapid crystallization due to sudden degassing. Collapse of a foam layer originated by deep degassing probably triggered this large-scale, spatter-forming paroxysm. Decompression induced rapid degassing and vesiculation of the deep volatile-rich magma. The rapid ascent of the foamy magma blob pushed the shallow HP magma out and finally produced a fire fountain that emplaced the LP portion of the spatter.  相似文献   

A Simulation Method for Semicollisional Plasmas     

Filippo Pantellini  Simone Landi 《Astrophysics and Space Science》2001,277(1-2):149-152

We present a one dimensional kinetic simulation model which can be used to simulate the stationary state of a semicollisional plasma. Results of a simple simulation are presented and compared to Fokker-Planck calculations. The model is particularly well suited for the diluted solar atmosphere. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Soho Cds–nis in-flight intensity calibration using a plasma diagnostic method     

E. Landi  M. Landini  C. D. Pike  H. E. Mason 《Solar physics》1997,175(2):553-570

The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) – Normal Incidence Spectrometer (NIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the CDS–NIS 1 and NIS 2 windows in a solar active region is analysed in order to determine the intensity calibration curve for both channels. The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the preliminary CDS–NIS internal intensity calibration curves and the determination of the relative calibration between NIS 1 and NIS 2. A further correction factor of approximately three is found to be necessary for a correct intercalibration of the two wavelength windows. Also the NIS 2 second-order sensitivity is measured. The Arcetri diagnostic method proves to be a powerful tool for intensity calibration studies.  相似文献   

Net circular polarization in magnetic spectral lines produced by velocity gradients: Some analytical results     

M. Landolfi  E. Landi Degl'innocenti 《Solar physics》1996,164(1-2):191-202

The net circular polarization in a spectral line due to the combined effect of magnetic fields and velocity gradients is analyzed for a few schematic situations. In some particular cases, its dependence on the magnetic field, velocity field and line parameters can be expressed analytically.On leave from Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italia  相似文献   

Micro-structured magnetic atmospheres     

J. Sánchez Almeida  E. Landi Degl'innogenti 《Solar physics》1996,164(1-2):203-210

Asymmetrical Stokes profiles are produced if the photospheric magnetic and velocity fields are structured on scales smaller than the mean-free-path of the photons. Here we put forward a compact analytical expression for the radiative transfer equation in this case. Explicitly, micro-variations of the magnetic field strength and the velocity are considered. The existence of micro-structures might have serious implications on the techniques currently used to measure solar magnetic fields. For example, we show the failure of the relationship employed to calibrate magnetographs.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy  相似文献   

Correction to: CrystalMom: a new model for the evolution of crystal size distributions in magmas with the quadrature-based method of moments     

Simone?ColucciEmail authorView author&#;s OrcID profile  Mattia?de’?Michieli Vitturi  Patrizia?Landi 《Contributions to Mineralogy and Petrology》2018,173(4):32

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INTEGRAL observations of active galactic nuclei obscured by the Galactic plane     

M. Molina  A. Malizia  L. Bassani  A. J. Bird  A. J. Dean  R. Landi  A. De Rosa  R. Walter  E. J. Barlow  D. J. Clark  A. B. Hill  V. Sguera 《Monthly notices of the Royal Astronomical Society》2006,371(2):821-828

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Polarization in spectral lines     

E. Landi Degl'innocenti 《Solar physics》1983,85(1):3-31

A unifying theoretical approach is presented to derive from the general principles of Quantum Electrodynamics both the radiative transfer equations for polarized radiation and the statistical equilibrium equations for an atomic system interacting with a polarized radiation field. The radiation field is described by means of Stokes parameters while the atomic system is described in terms of its density-matrix operator. The non-diagonal terms of the density matrix are fully accounted for so that this formalism can be suitably employed to describe a wide variety of physical phenomena like resonance scattering, the Hanle effect and the Zeeman effect, either in optically thin or optically thick atmospheres, together with all the possible intermediate situations.The general formulae derived in the first sections of the paper are subsequently particularized introducing the dipole approximation in the relevant matrix elements describing the interaction between the atomic system and the radiation field. The final equations assume a quite compact expression by the introduction of suitable spherical tensors connected with the components of the polarization unit vectors associated with each direction of the radiation field. The general expressions and the main properties of these tensors are discussed in the Appendix.  相似文献   

Vector magnetic fields in prominences     

R. Grant Athay  Charles W. Querfeld  Raymond N. Smartt  Egidio Landi Degl'innocenti  Veronique Bommier 《Solar physics》1983,89(1):3-30

Observations of linear polarization in two resolved components of HeI D₃ are interpreted using the Hanle effect to determine vector magnetic fields in thirteen prominences. As in all vector magnetic field measurements, there is a two-fold ambiguity in field direction that is symmetric to a 180° rotation about the line-of-sight. The polar angles of the fields show a pronounced preference to be close to 90° from the local solar radius, i.e., the field direction is close to horizontal. Azimuth angles show internal consistency from point to point in a given prominences, but because of the rotational symmetry, the fields may be interpreted, in most cases, as crossing the prominence either in the same sense as the underlying photospheric fields or in the opposite sense. An exceptionally well observed large prominence of approximately planar geometry exhibits no measurable change in the vector magnetic field either with height or with location along the prominence axis. A second well observed large prominence overlying a sharply curved magnetic neutral line, when interpreted assuming that the prominence field has the same sense as the photospheric field, shows a rotation in the azimuth angle of the field relative to the observer by about 150° and relative to the local plane of the prominence by about 65°. In the alternative interpretation in which the prominence field has the opposite sense of the photospheric field, the field still rotates by 150° relative to the observer but remains essentially constant with respect to the plane of the prominence. This prominence erupted shortly after the extended observations. One good quality observation during the course of the eruption gives a vector field fully consistent with the pre-eruption field in the same segment of the prominence.  相似文献