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Meaurements of solar flare spectra have allowed the electric field strengths in two flares to be determined, using the Inglis-Teller formula. Further, an independently estimated value for the electron density has allowed the two components of this field, that is, the interionic component and the external component that arises, for example, through plasma instabilities, to be separately extracted. External electric field strengths 0.5 kV cm–1 for a limb flare and 1.3 kV cm–1 for a white-light flare are found. Estimates of electric fields strengths generated by the resistive magnetic tearing instability indicate that this process could account for a significant part of the electric field if pre-existing magnetic field strengths in the flaring regions are characterized by a few kilogauss. Other plasma processes probably contribute measurably as well.Operated by the Association of Universities for Research in Astronomy, Inc., under contract NSF AST84-18716 with the National Science Foundation. 相似文献
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Emission-line coronagraph images of a high-latitude, nominally quiescent prominence, recorded at wavelengths of H, 6374 Å (Fex) and 5303 Å (Fe xiv), are analyzed. Over a two-day period, the coronal images, which are found to arise predominantly from coronal emission, evolve such that the emission becomes concentrated at locations corresponding to the outer regions of the prominence. This edge enhancement has similar characteristics to results inferred from EUV prominence observations. It is postulated that this coronal emission associated with the prominence results from MHD wave dissipation. Dissipation lengths for slow-mode, fast-mode and Alfvén waves are estimated for different prominence conditions. Of these, fast-mode waves appear to be the most physically realistic heating source if the prominence magnetic field is along the length of the prominence.Operated by the Association of Universities for Research in Astronomy, Inc., under contract AST 78-17292 with the National Science Foundation. 相似文献
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A. Fassia W. P. S. Meikle W. D. Vacca S. N. Kemp N. A. Walton D. L. Pollacco S. Smartt A. Oscoz A. Aragón-Salamanca S. Bennett T. G. Hawarden A. Alonso D. Alcalde A. Pedrosa J. Telting M. J. Arevalo H. J. Deeg F. Garzón A. Gómez-Roldán G. Gómez C. Gutiérrez S. López M. Rozas M. Serra-Ricart M. R. Zapatero-Osorio 《Monthly notices of the Royal Astronomical Society》2000,318(4):1093-1104
We present contemporaneous optical and infrared (IR) photometric observations of the Type IIn SN 1998S covering the period between 11 and 146 d after discovery. The IR data constitute the first ever IR light curves of a Type IIn supernova. We use blackbody and spline fits to the photometry to examine the luminosity evolution. During the first 2–3 months, the luminosity is dominated by the release of shock-deposited energy in the ejecta. After ∼100 d the luminosity is powered mostly by the deposition of radioactive decay energy from 0.15±0.05 M⊙ of 56 Ni which was produced in the explosion. We also report the discovery of an astonishingly high IR excess, K − L '=2.5, that was present at day 130. We interpret this as being due to thermal emission from dust grains in the vicinity of the supernova. We argue that to produce such a high IR luminosity so soon after the explosion, the dust must be pre-existing and so is located in the circumstellar medium of the progenitor. The dust could be heated either by the UV/optical flash (IR echo) or by the X-rays from the interaction of the ejecta with the circumstellar material. 相似文献
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M. T. Botticella A. Pastorello S. J. Smartt W. P. S. Meikle S. Benetti R. Kotak E. Cappellaro R. M. Crockett S. Mattila M. Sereno F. Patat D. Tsvetkov J. Th. Van Loon D. Abraham I. Agnoletto R. Arbour C. Benn G. Di Rico N. Elias-Rosa D. L. Gorshanov A. Harutyunyan D. Hunter V. Lorenzi F. P. Keenan K. Maguire J. Mendez M. Mobberley H. Navasardyan C. Ries V. Stanishev S. Taubenberger C. Trundle M. Turatto I. M. Volkov 《Monthly notices of the Royal Astronomical Society》2009,398(3):1041-1068
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A. Pastorello S. Mattila L. Zampieri M. Della Valle S. J. Smartt S. Valenti I. Agnoletto S. Benetti C. R. Benn D. Branch E. Cappellaro M. Dennefeld J. J. Eldridge A. Gal-Yam A. Harutyunyan I. Hunter H. Kjeldsen Y. Lipkin P. A. Mazzali P. Milne H. Navasardyan E. O. Ofek E. Pian O. Shemmer S. Spiro R. A. Stathakis S. Taubenberger M. Turatto H. Yamaoka 《Monthly notices of the Royal Astronomical Society》2008,389(1):113-130
We present new spectroscopic and photometric data of the Type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal Type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf–Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf–Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a Type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous Type Ia event with some resemblance to SN 1991bg. 相似文献
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Coronal images recorded above the limb in Fexiv (530.3 nm) and Fex (637.5 nm) sometimes have localized regions of anomalously low emission, with the appearance of an abrupt gap in the background corona. These dark spaces have been previously described in the literature in the case of the 530.3 nm line and tentatively explained by reduced coronal plasma density and/or a decrease in the line intensity due to temperatures above or below the optimal ionization temperature for Fexiv. However, loops are sometimes observed spanning gaps, with diminished loop brightness over the region of the gap. It is concluded that at least some of these regions of reduced brightness are caused by absorption of the coronal emission. An analysis reveals that absorption by coronal ions is inadequate as a mechanism to explain the phenomenon. Absorption by neutral hydrogen is, however, consistent with the observations in terms of the reduced brightness of the gaps. The concentration of cool material in the coronal environment associated with large magnetic fields on the disk could explain the gaps. Hence, neutral hydrogen continuum absorption appears to provide a plausible interpretation of, at least, some coronal gaps. Based on this result and from measured intensities, the electron density in the region of a gap is derived and found to be consistent with estimates derived elsewhere. 相似文献
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Simultaneous observations obtained with the HAO/SPO coronal emission-line polarimeter and the new SPO emission-line coronagraph are compared. The polarimeter data are measured in the Fexiii (10747 Å) line and the coronagraph observations are recorded in the Fexiv (5303 Å) line. The polarimeter field-of-view is relatively coarse compared with the resolution limit of the coronagraph. Therefore, the observed coronal polarization cannot be related directly to the detailed loop structures that characterize the localized coronal distribution, but it is found that large-scale emission features have corresponding polarization signatures. Since the measured linear polarization vectors describe the projected magnetic field direction, as shown theoretically, it follows that the form of the large-scale coronal distribution describes corresponding magnetic field structures. Measured polarization values are consistent with those predicted theoretically. Interpretation of these data to obtain corresponding magnetic field directions suggests that the value usually accepted for iron abundance in the corona might be too large.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc. under contract AST 78-17292 with the National Science Foundation. 相似文献
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A preliminary discussion is presented of measurements of the polarization of the He i D3 multiplet in a quiescent prominence, observed with a wavelength-scanning Stokes polarimeter. For a series of 43 observations in the same prominence, the linear polarization of the major component of D3 lies primarily in the range 1 to 2% and of the wing component, the range 2 to 5%; the polarization vector angle lies primarily in the range 10–25° for the major component, and 25–35° for the other component. From a more limited data set, the polarization of both components is found to first increase as a function of height in the prominence, and then to decrease; the polarization angles of the major component vary in a random-like way with height, while the wing component shows a systematic change. The amount of polarization and the angle of polarization are governed by the Hanle effect. The collective effect of the group of lines at the peak of D3 evidently has a different sensitivity to the Hanle effect than does the wing component, thus yielding at least four independent measurements - two polarizations and two angles. With some redundancy, the vector magnetic field can then be established using the detailed theory of the Hanle effect. Since the wing component of D3 is a simple triplet, an initial estimate of the magnetic field strength and its horizontal orientation, 0, relative to the line of sight, is simply obtained. Examples of such calculations are presented.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc. under contract AST 78-17292 with the National Science Foundation. 相似文献