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1.
Following the work of Garcia et al. (2001a) (GFCB), we compute the thermal properties and ionization structure of magnetically-driven disk winds. The original model's dominant heating function along the jet, ambipolar diffusion, is augmented by a mechanical heating term supposed to arise from weak shocks, as used by (Shang et al., 2002). We add this mechanical heating function to a cold disk wind model and calculate its effect on the jet as a whole. The temperature and ionization of the flow are calculated in the case of cold jet solutions consistent with the underlying accretion disk (Ferreira, 1997). These solutions are compared to those of (GFCB) in order to quantitatively determine the effect of the mechanical heating on the flow. We then use the computed thermal and ionization structures to calculate jet synthetic observations. We find that the addition of mechanical heating leads to higher electron fractions, in turn leading to increased line fluxes and line ratios approaching observed values.  相似文献   

2.
Imaging and spectroscopy of the solar corona, coupled with polarimetry, are the only tools available at present to capture signatures of physical processes responsible for coronal heating and solar wind acceleration within the first few solar radii above the solar limb. With the recent advent of improved detector technology and image processing techniques, broad-band white light and narrow-band multi-wavelength observations of coronal forbidden lines, made during total solar eclipses, have started to yield new views about the thermodynamic and magnetic properties of coronal structures. This paper outlines these unique capabilities, which until present, have been feasible primarily with observations during natural total solar eclipses. This work also draws attention to the exciting possibility of greatly increasing the frequency and duration of solar eclipse observations with Moon orbiting observatories utilizing lunar limb occultation of the solar disk for coronal measurements.  相似文献   

3.
The fate of interstellar gas heated by energetic radiation and far from the galactic plane is considered. It is shown that for plausible heating rates a very hot corona forms, separated from the cooler gas in the disk by a conductive boundary layer. For heating rates exceeding a critical value a galactic wind is set up, as first shown by Mathews and Baker for elliptical galaxies. Such winds may fill the intracluster space in clusters of galaxies; further heating may drive a cluster wind, as shown by Yahil and Ostriker. It is believed that the flow problem of intracluster gas in the presence of intercluster gas is not yet adequately solved. A variety of observations at X-ray and ultraviolet wavelengths are needed to resolve these questions.  相似文献   

4.
Obtaining reliable measurements of plasma parameters in the Sun’s corona remains an important challenge for solar physics. We previously presented a method for producing maps of electron temperature and speed of the solar corona using K-corona brightness measurements made through four color filters in visible light, which were tested for their accuracies using models of a structured, yet steady corona. In this article we test the same technique using a coronal model of the Bastille Day (14 July 2000) coronal mass ejection, which also contains quiet areas and streamers. We use the coronal electron density, temperature, and flow speed contained in the model to determine two K-coronal brightness ratios at (410.3, 390.0 nm) and (423.3, 398.7 nm) along more than 4000 lines of sight. Now assuming that for real observations, the only information we have for each line of sight are these two K-coronal brightness ratios, we use a spherically symmetric model of the corona that contains no structures to interpret these two ratios for electron temperature and speed. We then compare the interpreted (or measured) values for each line of sight with the true values from the model at the plane of the sky for that same line of sight to determine the magnitude of the errors. We show that the measured values closely match the true values in quiet areas. However, in locations of coronal structures, the measured values are predictably underestimated or overestimated compared to the true values, but can nevertheless be used to determine the positions of the structures with respect to the plane of the sky, in front or behind. Based on our results, we propose that future white-light coronagraphs be equipped to image the corona using four color filters in order to routinely create coronal maps of electron density, temperature, and flow speed.  相似文献   

5.
Spectroscopic diagnostics for the Nev and Mgv solar ions have been investigated. The theoretical forbidden line ratios from these ions are presented for estimating the Ne/Mg variation in different solar structures. Calculations for density and temperature line diagnostics of these ions are given for the several spectral line ratios and their applications are discussed with the help of available solar observations in space. Future observations from the CDS and the SUMER experiments aboard the SOHO satellite are also discussed.  相似文献   

6.
Chiuderi Drago  F.  Landi  E. 《Solar physics》2002,206(2):315-332
The ratio between the Extreme Ultraviolet emission of the prominence–corona transition region and that of the quiet Sun (QS) transition region is measured using observations from the CDS and SUMER instruments on board the SOHO Satellite. These results are compared with those obtained in an earlier paper, analysing the same prominence as a filament on the disk. Theoretical models predict a difference in the emission of the prominence–corona transition region when it is observed at the limb and on the disk as a filament; the aim of the present work is to provide an observational check of this difference. SUMER and CDS data provide fairly good agreement if the prominence intensity measured by SUMER is compared with the average quiet-Sun intensity, measured near the disk center; the prominence intensity relative to the average quiet-Sun level measured on the same rasters results in disagreement with CDS, due to the smaller size of the disk portion and to the very strong limb brightening present in SUMER rasters. The relative prominence to quiet-Sun intensity ratio varies from 0.2 to 0.4, depending on the line formation temperature. This value leads to a discrepancy with the results obtained in a previous study when the same prominence was observed as a filament. This discrepancy indicates that the prominence–corona transition region emission is different when emitted by different sides of the prominence.  相似文献   

7.
We present a first analysis of 2.4-45μm spectra of NGC 1068 obtained with the Short Wavelength Spectrometer SWS on board the Infrared Space Observatory ISO. The measured fine-structure line fluxes can be fit successfully by a simple photoionization model invoking an EUV bump in the ionizing continuum, similar to the case of the Circinus galaxy. Difference are observed between the [OIV] 26μm NLR line profile and optical NLR line profiles which may indicate significant extinction to part of the NLR. We detect pure rotational transitions of molecular hydrogen that must be emitted by molecular gas spanning a wide range of temperatures. The unusual strength of the fundamental S(0) 28μm rotational transition is evidence for a large (> 1.5 × 109 M⊙) gas mass at temperatures nea r 100 K. Either most of the gas in the circumnuclear region of NGC 1068 is warm or previous molecular mass estimates based on CO observations were too low. Strong mid-infrared continuum from the circumnuclear warm dust is prominent in our spectrum. The weak PAH emission detected at the edges of the 9.7μm silicate absorption should be considered in interpretations of the silicate feature. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
Helium-like resonance, intercombination, and forbidden transitions of Ca, Si, and S were observed during the 3b solar flare of 16 November 1967, by means of the NRL Bragg crystal spectrometers aboard OSO-4. During the decay of this flare, the forbidden lines became enhanced relative to the intercombination and resonance lines. Comparisons of the observed line ratios are made with theory and mechanisms are proposed to explain the observations.  相似文献   

9.
In Part IV of the series of papers about the analysis of the INTERCOSMOS 16 ADP spectra a method is developed to evaluate plasma densities from measured resonance, intercombination, and forbidden helium-like Mg xi line intensities, using plots of the so-called G and R ratios. The density is close to the low-density limit. For the active region McMath 14352 a correlation between mean plasma density and electron temperature has been found, in agreement with earlier results. In an appendix systematic differences between measured and calculated line fluxes in all bands A to F are discussed.  相似文献   

10.
We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied black hole binaries, we take the mass flow rates derived from a fit of the advection-dominated accretion flow (ADAF) model to the observed spectra (for a review, see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare this with the observed location of the inner disk edge, as estimated from the maximum velocity of the Halpha emission line. We find that the transition caused by evaporation agrees with this determination in stellar disks. We also show that the ADAF and the "thin outer disk + corona" are compatible in terms of the physics in the transition region.  相似文献   

11.
We present meterwave maps of the solar corona made with the Clark Lake Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation. We compare and contrast them with optical data: 10830 Å maps, white-light coronagraph images (SOLWIND and Mauna Loa K coronameter) and forbidden line scans. Most of the sources in the radio maps persist for two days or more, and appear to rotate approximately with the solar rate. A coronal hole seen against the disk at all three frequencies shows interesting similarities and significant differences with the optical signatures of the hole. Elongated features of the 50 MHz corona correspond rather well to the azimuthal position of white light streamers seen in SOLWIND images. Synoptic charts made from the radio maps show overall similarities to synoptic charts constructed from (limb) coronagraph data. Some of the differences may result from the different weightings given by the radio and optical data to density and temperature, or by the different sensitivities to non-radial geometries. We show that the combined use of meter wave and optical images provide considerable new insights into the three-dimensional structure of the low to middle corona.  相似文献   

12.
Images taken in the band centered at 30.4 nm are routinely used to map the radiance of the He?ii Ly?α line on the solar disk. That line is one of the strongest, if not the strongest, line in the EUV observed in the solar spectrum, and one of the few lines in that wavelength range providing information on the upper chromosphere or lower transition region. However, when observing the off-limb corona, the contribution from the nearby Si?xi 30.3 nm line can become significant. In this work we aim at estimating the relative contribution of those two lines in the solar corona around the minimum of solar activity. We combine measurements from CDS taken in August 2008 with temperature and density profiles from semiempirical models of the corona to compute the radiances of the two lines, and of other representative coronal lines (e.g. Mg?x 62.5 nm, Si?xii 52.1 nm). Considering both diagnosed quantities from line ratios (temperatures and densities) and line radiances in absolute units, we obtain a good overall match between observations and models. We find that the Si?xi line dominates the He?ii line from just above the limb up to ≈?2?R ⊙ in streamers, while its contribution to narrowband imaging in the 30.4 nm band is expected to become smaller, even negligible in the corona beyond ≈?2?–?3?R ⊙, the precise value being strongly dependent on the coronal temperature profile.  相似文献   

13.
We have developed three types of mathematical models to describe the mechanisms of plasma heating in the corona by intense heat fluxes from a super-hot (T e ? 108 K) reconnecting current layer in connection with the problem of energy transport in solar flares. We show that the heat fluxes calculated within the framework of self-similar solutions using Fourier’s classical law exceed considerably the real energy fluxes known from present-day multi-wavelength observations of flares. This is because the conditions for the applicability of ordinary heat conduction due to Coulomb collisions of thermal plasma electrons are violated. Introducing anomalous heat conduction due to the interaction of thermal runaway electrons with ion-acoustic turbulence does not give a simple solution of the problem, because it produces unstable temperature profiles. Themodels incorporating the effect of collisional heat flux relaxation describe better the heat transport in flares than Fourier’s law and anomalous heat conduction.  相似文献   

14.
Spectroscopic studies of the solar corona, using the high spatial and spectral resolution 25-cm coronagraph at the Norikura Solar Observatory for equatorial off-limb observations, indicated that the variation of radiance and line width with height is different for different temperature lines. The line width of the forbidden red emission line [Fe x] 6374 Å was found to increase with height, and that of the green emission line [Fe xiv] 5303 Å decreased with height. This had been interpreted in terms of the interaction between different temperature plasmas but needed to be confirmed. Further observations were made on several days during 2004, in two emission lines simultaneously covering the mid-latitude and polar regions to investigate the existence of the observed variation in other parts of the solar corona. In this study, we have analysed several raster scans that cover mid- and high-latitude regions of the off-limb corona in all four bright emission lines [Fe x] 6374 Å, [Fe xi] 7892 Å, [Fe xiii] 10747 Å, and [Fe xiv] 5303 Å. We find that the FWHM of the red line increases with height and that of the green line decreases with height, similar to the observations in the equatorial regions. The line widths are higher in the polar regions for all of the observed emission lines except the green line. Higher values of FWHM in polar regions may imply higher non-thermal velocities, which could be further linked to a non-thermal source powering the solar-wind acceleration, but the reason for the behaviour of the green emission line remains to be explored.  相似文献   

15.
Pierrard  Viviane  Lamy  Hervé 《Solar physics》2003,216(1-2):47-58
Due to their different mass and varying charge states, heavy solar ions provide invaluable information on the physical mechanisms responsible for the heating of the corona and the solar wind acceleration. It is shown in the present work that some key characteristics observed in the corona are straightforward features predicted by the velocity filtration effect. This mechanism originally proposed by Scudder (1992a,b) accounts for the heating of the corona by just assuming that the velocity distribution functions have enhanced supra-thermal tails. The apparent `heating' is then a natural consequence of the increasing ratio of supra thermal over thermal particles as a function of altitude. Applied to the minor ions, it offers a natural explanation for the high temperatures of the heavy ions compared to the protons. The kinetic filtration theory predicts temperatures more than proportional to the mass of the ions, with a small correction for the charge state. With sufficiently high temperatures, the ions flow faster than the protons. These characteristics are in good agreement with the most recent spectroscopic and in-situ solar wind observations.  相似文献   

16.
The Sun is a mysterious star. The high temperature of the chromosphere and corona present one of the most puzzling problems of solar physics. Observations show that the solar coronal heating problem is highly complex with many different facts. It is likely that different heating mechanisms are at work in solar corona. Recent observations show that Magnetic Carpet is a potential candidate for solar coronal heating.  相似文献   

17.
M.R. Sanad 《New Astronomy》2011,16(2):114-121
We present low-resolution UV spectra of the dwarf novae SS Cyg and WX Hyi in both quiescence and outburst states from observations taken by the International Ultraviolet Explorer (IUE) during the period between 1978–1994 and 1979–1993 for two systems respectively. Both SS Cyg and WX Hyi are characterized by emission lines in quiescence physical states and absorption lines in states of outburst. We concentrated on calculating the line fluxes and line widths of the C IV 1550 Å emission line arising from the disk around the white dwarf of SS Cyg and WX Hyi. We found that there is spectral variability for these physical parameters at different times, similar to that known for their light curves (Voloshina and Khruzina, 2006, Kuulkers et al., 1991). We attribute it to the variations of both density and temperature as a result of changing the mass transfer rate (Long et al., 2005, Patterson, 1984, Meyer and Meyer-Hofmeister, 1994, Cannizzo, 2001, Schwope et al., 2002). Also we found that both line fluxes and line widths of SS Cyg are greater than the line fluxes and line widths of WX Hyi.  相似文献   

18.
We present ultraviolet spectra of two eclipsing interacting binary systems, W Ser and UX Mon, with good coverage over the 14.16-day and 5.9-day orbital periods, respectively, using observations taken by the International Ultraviolet Explorer (IUE) during the period between 1978–1993 and 1981–1991. Two profiles of W Ser and UX Mon showing variations of line fluxes at two orbital phases are presented. This paper focuses on the N V emission line at 1240 Å, C II emission line at 1336 Å, C IV emission line at 1550 Å, O III emission line at 1666 Å and the Si III emission line at 1892 Å, produced in an extended gaseous envelope around the mass-gaining component by calculating spectral line fluxes. Our results show that there are variations of line fluxes with time, similar to the light curves found for both W Ser and UX Mon. We attribute these spectral variations to eclipse effects and to variations in the mass transfer rate. These results from the IUE observations support the thick disk model around the primary star in which variations of mass transfer affect the observed radiation from the gaseous envelope around the hot star. Future, high-resolution imaging is recommended to confirm the inferred asymmetrical circumstellar envelopes.  相似文献   

19.
We analyze eight XMM-Newton observations of the bright Narrow Line Seyfert 1 galaxy Arakelian 564(Ark 564). These observations, separated bye~6 days, allow us to look for correlations between the simultaneous ultraviolet(UV) emission(from th Optical Monitor) with not only the X-ray flux but also with different X-ray spectral parameters. The X-ray spectra from all the observations are found to be adequately fitted by a double Comptonization model where the soft excess and the hard X-ray power law are represented by thermal Comptonization in a low temperature plasma and hot corona, respectively. Apart from the fluxes of each component, the hard X-ray power law index is found to be variable. These results suggest that the variability is associated with changes in the geometry of the inner region. The UV emission is found to be variable and well correlated with the high energy index while the correlations with the fluxes of each component are found to be weaker. Using viscous timescale arguments we rule out the possibility that the UV variation is due to the fluctuating accretion rate in the outer disk. If the UV variation is driven by X-ray reprocessing, then our results indicate that the strength of the X-ray reprocessing depends more on the geometry of the X-ray producing inner region rather than on the X-ray luminosity alone.  相似文献   

20.
We present the results of spectroscopic observations of three S0-Sa galaxies: NGC 338, NGC 3245, and NGC 5440 at the SAO RAS 6-m BTA telescope. The radial distributions of the line-ofsight velocities and radial velocity dispersions of stars and ionized gas were obtained, and rotation curves of galaxies were computed. We construct the numerical dynamic N-body galaxy models with N ?? 106 points. The models include three components: a ??live?? bulge, a collisionless disk, dynamically evolving to the marginally stable state, and a pseudo-isothermal dark halo. The estimates of radial velocities and velocity dispersions of stars obtained from observations are compared with model estimates, projected onto the line of sight. We show that the disks of NGC 5440 and the outer regions of NGC 338 are dynamically overheated. Taking into account the previously obtained observations, we conclude that the dynamic heating of the disk is present in a large number of early-type disk galaxies, and it seems to ensue from the external effects. The estimates of the disk mass and relative mass of the dark halo are given, as well as the disk mass-to-luminosity ratio for seven galaxies, observed at the BTA.  相似文献   

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