BRIGHTNESS VARIATIONS OF Mg Ib BRIGHT FEATURES     

Dara  H.C.  Koutchmy  S.  Zachariadis  Th.G.  Alissandrakis  C.E. 《Solar physics》2001,198(2):313-324

We study the temporal intensity variations of Mgib bright features and investigate the corresponding Hα velocity pattern. The network bright features are well visible in the continuum, in images averaged over the duration of the observations (130 min). We detected `flashing' bright features, which appear and disappear within two to five minutes, while the rest of the bright features undergo small variations of either their shape and/or their intensity. A power spectrum analysis reveals a 10-min oscillation for approximately half of the stable bright features. The 5-min oscillations are detected mainly at the network boundaries, where stable bright features are located, while 3-min oscillations coincide with few bright features, but are also quite intense inside the network cells. The majority of bright features are associated with Hα downflows. The downflow is very intense at the location of `flashing' bright features.  相似文献   

Trigger conditions and effective areas of imaging air Cherenkov telescopes (Astroparticle Physics 6 (1996) 77)     

C. Khler  G. Hermann  W. Hofmann  A. Konopelko  A. Plyasheshnikov 《Astroparticle Physics》1997,6(3-4):423

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A Linear Dependence between the Magnitude and the Logarithm of the Length of the Time the Quasars OJ287 and 3C345 Stay below this Magnitude     

Jin He  G.Z. Xie 《Astrophysics and Space Science》1997,254(2):223-232

We have studied the optical historical light curves of two Active Galactic Nuclei (AGNs): OJ287 and 3C345. We find a linear dependence between the magnitude and the logarithm of the length of the time the objects stay below this magnitude. The relation may originate from a fractal structure of the light curve. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Transient phenomena in the energetic behind-the-limb solar flare of september 29, 1989     

A. Bhatnagar  R. M. Jain  J. T. Burkepile  I. M. Chertok  A. Magun  H. Urbarz  P. Zlobec 《Astrophysics and Space Science》1996,243(1):209-213

The powerful cosmic ray flare of Sept. 29, 1989 occurred behind the limb and was observed over a wide spectral range. The analysis of optical, radio, and other relevant data suggest two phases of energy release. After an impulsive phase a prolonged post eruption energy release occurred in an extended region of the corona following the eruption of a large coronal mass ejection (CME). This phase is responsible for numerous coronal and interplanetary phenomena including the ground-level increase of cosmic rays.  相似文献   

Kinematics of Gas and Stars in 20 Disc Galaxies     

J.C. Vega Beltrán  W.W. Zeilinger  A. Pizzella  E.M. Corsini  F. Bertola  J.G. Funes  J.E. Beckman 《Astrophysics and Space Science》2001,276(2-4):1201-1210

In this paper we present the kinematics of the gas and/or the stars of a sample of 20 disc galaxies. We investigate whether there is any relation between the kinematics of the gas and stars and the classical morphological type of the galaxies in the sample. We deduce that, in most of the late-type spirals we have studied, the stars and the ionized gas are moving with virtually circular velocity, except when the spectroscopic slit crosses a bar region. On the other hand, we found in the central parts of early-type disc galaxies a wider variety of different behaviour of stars and gas. We find many possible factors that complicate the classification of the kinematical properties of the galaxies by their morphological type: the presence of counter-rotations (star vs. stars or star vs. gas), misalignment between the different kinematic components present in the galaxy, the presence of a bar structure and its orientation with respect to the line of nodes of the galaxy, and interactions and mergers or external accretion processes are some of the problems we find in the study of the kinematics of a galaxy.  相似文献   

VALIDATION - ANOTHER PERSPECTIVE   总被引：1，自引：0，他引：1  

C. McCombie  I. McKinley 《Ground water》1993,31(4):530-531

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The Geminid Meteor Stream Activity Profile     

Ryabova  G. O. 《Solar System Research》2001,35(2):151-157

The existence of two maxima of the activity of the Geminid meteor stream and the general shape of the stream activity (rate curve) are discussed. The data of visual and radar observations are compared to the results of mathematical simulation. The distribution of the orbits of meteoroids, which are observed on the Earth, is determined from the mathematical model. This distribution cannot as yet be confirmed or disproved because of the absence of appropriate experimental data.  相似文献   

Starburst activity in a ROSAT narrow emission-line galaxy     

Katherine F. Gunn  I. M. MHardy  O. Almaini  T. Shanks  T. J. Sumner  T. W. B. Muxlow  A. Efstathiou  L. R. Jones  S. M. Croom  J. C. Manners  A. M. Newsam  K. O. Mason  S. B. G. Serjeant  M. Rowan-Robinson 《Monthly notices of the Royal Astronomical Society》2001,324(2):305-312

We present multiwaveband photometric and optical spectropolarimetric observations of the R =15.9 narrow emission-line galaxy R117_A which lies on the edge of the error circle of the ROSAT X-ray source R117. The overall spectral energy distribution of the galaxy is well modelled by a combination of a normal spiral galaxy and a moderate-strength burst of star formation. The far-infrared and radio emission is extended along the major axis of the galaxy, indicating an extended starburst.
On positional grounds, the galaxy is a good candidate for the identification of R117, and the observed X-ray flux is very close to what would be expected from a starburst of the observed far-infrared and radio fluxes. Although an obscured high-redshift QSO cannot be entirely ruled out as contributing some fraction of the X-ray flux, we find no candidates to K =20.8 within the X-ray error box, and so conclude that R117_A is responsible for a large fraction, if not all, of the X-ray emission from R117.
Searches for indicators of an obscured AGN in R117_A have so far proven negative; deep spectropolarimetric observations show no signs of broad lines to a limit of 1 per cent and, for the observed far-infrared and radio emission, we would expect 10 times greater X-ray flux if the overall emission were powered by an AGN. We therefore conclude that the X-ray emission from R117 is dominated by starburst emission from the galaxy R117_A.  相似文献   

Nature of microstructure in pulsar radio emission     

G. Machabeli  D. Khechinashvili  G. Melikidze  D. Shapakidze 《Monthly notices of the Royal Astronomical Society》2001,327(3):984-988

We present a model for microstructure in pulsar radio emission. We propose that micropulses result from alteration of the radio wave generation region by nearly transverse drift waves propagating across the pulsar magnetic field and encircling the bundle of the open magnetic field lines. It is demonstrated that such waves can modify the curvature of the field lines significantly. This, in turn, affects strongly fulfilment of the resonance conditions necessary for the excitation of radio waves. The time-scale of micropulses is therefore determined by the wavelength of the drift waves. The main features of the microstructure are naturally explained within the framework of this model.  相似文献   

SARG: The High Resolution Spectrograph of TNG     

R. G. Gratton  G. Bonanno  P. Bruno  A. CalÍ  R. U. Claudi  R. Cosentino  S. Desidera  F. Diego  G. Farisato  G. Martorana  M. Rebeschini  S. Scuderi 《Experimental Astronomy》2001,12(2):107-143

SARG is a cross dispersed echelle spectrograph in operation since late spring 2000 at the Italian Telescopio Nazionale Galileo (TNG) 3.5 m telescope, La Palma. SARG offers both single object and long slit (up to 26 arcsec) observing modes covering a spectral range from λ = 0.37 up to1 μm, with resolution ranging from R = 29,000 up to R = 164,000. Cross dispersion is provided by means of a selection of four grisms; interference filters may be used for the long slit mode (up to 26 arcsec). A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048 × 4096 EEV CCDs (pixel size: 13.5 μm) allowing complete spectral coverage at all resolving power for λ < 0.8 μm. In order to reach a high wavelength calibration precision an iodine-absorbing cell is provided. A Distributed Active Temperature Control System (DATCS) maintains constant the temperature of all spectrograph components at a preset value. Early results show that SARG works according to original specifications in terms of wavelength coverage, efficiency (measured peak efficiency is about 13%),resolution (maximum resolution R = 164,000 using a 0.3 arcsec slit, R ∼144,000 using an image slicer), and stability (preliminary estimates of radial velocity accuracy is ∼3 m/s using the iodine cell and ±150 m/s without the iodine cell). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献