Surface photometry of theHii regions S254–S257

The surface photometry of S254–S257 has been carried out by means of a wide range image processing technique in the reduction system. The photographic plates in the H+[NII] andV-bands are taken with the Schmidt telescope. Especially, we have obtained the calibrated map of theHii region, superposing two or more plates with different exposure times, and removing the star images. Three kinds of calibrated maps of theHii regions are drawn: (1)E-map in the (H+[NII]+continuum) (2)V-map in the continuum atV-band, (3)(E-V)-map in the (H+[NII]) line emission. The intensity profiles across the nebular centers were also obtained. Based on calibrated maps, the morphological structure and mass distribution of S255 and S257 are discussed. The location of observed nebulae on the (m _H–m _v) diagram, wherem _H andm _v denote the surface brightness, expressed in the magnitude per square arcmin, is shown together with that of some other nebulae. Some arguements on the age sequence of observedHii regions are presented.     

Hα line emission and infrared excess in Be stars

The H observations of a selected sample of bright Be stars are presented. The available infrared observations at K band (2.2 m) of these stars have been used to find the infrared excess emission. The analysis of the combined data show thatL _H, the luminosity of the H emission line, is proportional toL _IR, the luminosity of the infrared excess emission. The linear correlation betweenL _IR andL _H shows that both the infrared excess and the H line originate in a common region. It is also detected that the infrared excess emission is produced throughout the whole envelope whereas the H is emitted in some defined region of the circumstellar (CS) envelope.     

Comparison between some Hα and X-ray flares

In the present paper, H-evolutive curves of chromospheric events are compared with flux evolutive curves of X-ray events observed at the same time in different spectral regions. A correspondence between the emissions E(I _H/I _chr)'s at higher and higher H-intensity levels, and the X-ray fluxes F()'s in harder and harder -ranges is shown. Further, the present observations seem to indicate the existence of a single triggering mechanism during the flash-phase of a flare. It is also shown that these results may be in agreement with Brown's model for chromospheric flares.     

Cerenkov line emission: The Lα/Hβ, Hα/Hβ, Pα/Hα intensity ratios of quasars

We use the Cerenkov line emission mechanism to give a new explanation of the observed intensity ratios, particularly the L/H ratio, of the emission lines of quasars. We give equations that restrict the choice of the parameter values. The parameters are the characteristic energy of the relativistic electrons, the number density of neutral hydrogen and its relative level populations. With reasonable choice of the parmaeters, we can obtain calculated L/H, H/H, P/H ratios in agreement with observed values. Our estimate for the gas density in the broad line region of quasars is 10¹⁵ cm^–3, very different from previous estimates. Unlike previous theories, such a high density causes no difficulties with the Cerenkov line emission.     

On the line intensity ratios E(Hα)/E(D3) and E(Hβ)/E(D3) in prominences

The intensity ratios E(H)/E(D3) and E(H)/E(D3) in prominences depend on the total optical thickness in H of the layer. The emission of the He D3 line appears relatively enhanced in thin layers and in outer parts of the prominences.     

Hα Doppler brightening and Lyman-α Doppler dimming in moving Hα prominences

We consider the effect that coherent motion has on the observed brightness of moving clouds above the photosphere. We find that steady state clouds (constant N _e and T _e ) that are moving perpendicular to the line of sight will appear brighter in H for speeds between 8 and 100 km/sec and dimmer for speeds greater than 135 km/sec. The brightening and dimming are due to apparent Doppler shifts of the respective H absorption and the Lyman- emission profiles seen by the absorption profile of the moving cloud.We apply this analysis, along with optical depth and geometrical considerations, to the observed brightness variations of the 1 March 1969 limb eruptive prominence. We find that all of the observed brightening and dimming can be explained by the motions, and that no significant change in the prominence N _e or T _e was necessary during the observed H event. This conclusion is significant in interpreting an X-ray burst that began as the prominence velocity increased abruptly at the time of maximum H intensity. The thermal X-ray peak occurred 150 sec later when the prominence had become faint again. There was no associated flare that was visible in H. We discuss the relative brightness of H and D ₃ in a specific moving prominence knot.We note that the observed range of limb speeds (30–150 km/sec) may be due to the combined H Doppler brightening and Lyman- dimming effects. We also discuss generally the H brightness of disk surges (bright and dark) and flares, and sprays and puffs that occur at or near the limb.Now at the Dept. of Physics and Astrophysics, University of Colorado, and High Altitude Observatory (NCAR) Boulder, Colo., U.S.A.     

A prominence model based on spectral observations

Intensities and profiles of the H, H, H, K, and D₃ lines are measured in a solar prominence. From the profiles of these lines we estimate T = 6400 K and _t = 5.7 km s^–1. We construct a simple isothermal model which explains the H intensity and profile for an assumed total particle density n _T = 3 × 10¹¹ cm^–3, and a filling factor, = 1/6.From this model we find that the source function in the H line is nearly constant through the prominence. We estimate from the model that the radiative energy loss at the center of the prominence is of the order of 10⁷ erg s^–1 g^–1.     

A newH α survey of chromospherically active binaries (II)

We have obtained CCD spectra for 30 chromospherically active binaries using the 2.16 m telescope at Beijing Observatory in 1995. Our purpose was to search for the presence ofH emission which is characteristic of stars with extreme levels of chromospheric activity. Spectra of V711 Tau, V471 Tau, HD 12545 and V833 Tau presentedH emission above the continuum in the different degree. TheH behavior of the other observed 26 active binaries, which were unknown in CABS (1993), has been discovered in this paper. TheH profiles of the most among 26 systems are partially filled-in by chromospheric emission. TheH profiles of a few systems show a pure absorption line. The results are given in Table I.supported by the National Natural Science Foundation of China     

Spectrograph,filtergraph and magnetograph observations of the two-ribbon flare of 29 July, 1973

We present high resolution detailed observations of the class 3N two-ribbon flare of 1973, July 29 (McMath 12461), which was associated with the disappearance of a large filament (disparition brusque). This flare occurred in a diffuse bipolar magnetic region completely devoid of sunspots, and was further associated with a type IV radio burst and a soft X-ray event. Extensive H filtergraph, spectrograph and magnetograph records during the main phase of the flare suggest that downfalling and streaming material is present on both ribbons for several hours during the H emission enhancement, but only at a small number of points located both on and off the ribbons. We find a poor spatial correspondence between bright emission knots in the H ribbons and the positions of the observed downward motion. We conclude that the model of infall-impact of Hyder (1967a, b) is not consistent with our filtergraph and spectrograph observations.Presently at the University of Michigan, Ann Arbor, Michigan.     

A study of the contrast of sunspots from photometric images

The thermal contrast , and the umbra-penumbraA _u/A _p, were calculated for 63 sunspots of various sizes and morphologies. Contrary to the assumptions of the PSI model, andA _u/A _p were found to be quite variable. The values of ranged from 0.1807 to 0.4266;A _u/A _p ranged from 0.0089 to 0.4899. The values of andA _u/A _p correlated well (r = 0.6018;p<0.005) and the regression for andA _u/A _p was obtained: = (0.220 ± 0.016) + (0.340 ± O.06)A _u/A _p. The values of andA _u/A _p were then compared with complexity ratings, magnetic field strength, time, and . The quantities andA _u/A _p were found to be independent of the complexity, magnetic field strength, and time factors. The correlation between andA _u/A _p lead to the proposed division of into an umbral thermal contrast _u, and a penumbral thermal contrast _p. These values were calculated from the photometric data: _u = 0.57 ± 0.01 and _p = 0.26 ± 0.006.     

Bidimensional spectroscopy of network bright points

We develop an automatic, computer controlled procedure to select and to analyze the Network Bright Points (NBPs) on solar images. These have been obtained at the Sac Peak Vacuum Tower Telescope by means of the Universal Birefringent Filter and Zeiss H filters, tuned, respectively, along the profiles of the H, Mg-b1, Na-D2, and H lines.A structure is identified as an NBP if at the wavelength H- 1.5 A its maximum intensity is greater than I + 3 and its area is greater than 1.5 arc sec² at I + 1.5, where I is the mean value and the standard deviation of the intensity distribution on the image. Each detected NBP is then searched and confirmed in all the remaining 31 images at different wavelengths.For each NBP several parameters are measured (position, area, mean and maximum contrast, Dopplergram velocity, compactness, and so on) and some identification constraints are applied.The statistical analysis of the various parameter distributions, for NBPs present within an active region and its surroundings, shows that two types of NBPs can be identified according to the value of their mean contrast C _min the H- 1.5 Å image (C _m 0.1 type I, C _m> 0.1 type II). The type I NBPs (all occurring on the boundaries of the supergranular network) appear to be much more frequent (180/26) than the type II ones.The size A of type I NBPs is less than 1.0 arc sec for H/H wings but of the order of 1.2 arc sec for Na-D2 and Mg-bl. The mean contrast C _m is around the value of 10% along the Na-D2 and Mg-bl profiles and of 20% along the H/H wings.The C _m - A scatter diagrams show, for the photospheric radiation (h < 100 km), a narrow range of variability for C _min correspondence with a wide range for A. For radiation orginated at higher levels (h > 200 km), the C _m- A scatter diagrams seem to indicate, even if with a large variance, that the highest C _m's tend to correspond to the highest A values.The mean Doppler shift is close to zero for Na-D2 and Mg-bl lines but negative (downward motion) for H and H lines.The type II NBPs tends to be preferentially located in the neighbourhood of small, compact sunspots and their detectability is almost constant through all the 4 studied line profiles. No conclusions can be derived on the mean size, contrast and Doppler shift values because their distributions are too dispersed. The only positive information is that its C _m- A scatter diagram, in H and H wings, indicates a wide range of variability for C _m in correspondence with very narrow range of variability for A.     

Late-time emission of the type II Supernovae powered by the radioactive decay56Ni−56Co−56Fe

A one-zone model for the late time SN II energized by the radioactive decay⁵⁶Ni–⁵⁶Co–⁵⁶Fe is presented. The model succeeds in reproducing for the late time evolution of H and [Oi] 6300 emission lines in SN1970g for the reasonable set of parameters: mass of ejecta 4M , boundary velocityv ₀=4000 km s^–1 and amount of⁵⁶NiM _Ni=0.02M . However, a one-zone model does not account for the late time continuum. In the case of SN1980k the radioactive model fits H and [Oi] 6300 emissions att250 day satisfactory but fails at very late time, e.g.,t=670 day when the predicted value of the ratioL(H)/L(6300) is two orders of magnitude smaller than the observed one. We suggest that the strong H emission in SN1980k on the 670th day is due to the interaction of the supernova envelope with the pre-SN wind. The radioactive model for the late time SN II predicts strong Mgii 2800 line and detectable Hei 10830 line in emission and absorption.     

Time delay between Hα and hard X-ray emissions during impulsive solar flares

This investigation shows that statistically there are significant time delays between H and hard X-ray (HXR) emissions during solar flares; most impulsive flares produce HXR emissions up to 1 min before and up to 2 min after the onset of H emission. HXR emissions are also found to be peaked up to 2 min before the H emissions.     

On the Possible Observations of Intergalactic or Halo Clouds in Optical Emission

The discussion of the problems of observation of tenuous intergalactic and/or halo clouds in recombination emission is presented. We elaborate the possibility that clouds are illuminated only by metagalactic ultraviolet radiation flux, and assume some plausible values for the parameters determining the physical conditions in such objects. A simple, semiqualitative approach may give specific observational predictions for the two major signposts of fluorescent emission: Ly and H lines. We conclude that H detection of Lyman-limit systems at low redshift is within present observational capabilities. Open questions for further research are put in a convenient framework.     

Observational study of the ‘post’-flare loops on June 4, 1991

A limb, two-ribbon H flare on June 4, 1991, associated with a white-light flare and followed by an emission spray and post-flare loops, is studied. A region of rapidly enhanced brightness at the bottom of the H ribbon above the white-light flare is revealed. The energy released by the white-light flare at _eff = 4100 is estimated to be about 1.5 × 10²⁸ erg s^–1.     

Hα Emission Stars in the Cepheus OB3 Region

H emission objects were searched for, using the objective-prismSchmidt plates in a 36 deg² sky area covering the Cepheus OB3 association.Hundred and eight emission stars have been found, 68 of which are newfindings to our knowledge. The properties of the IRAS point sourcesidentified with H emission stars indicate that most of theH emission stars are T Tauri stars or related objects. Hemission stars associated with IRAS sources and those unassociated havedifferent distributions, suggesting an age sequence among them.Altogether, they show a ring- or shell-like surface distribution, whichalmost coincides with that of heated dusts, and these distributionsappear to be encompassed by an HI shell.     

Faint Hα emission in the solar corona: Morphological,situational and hydromagnetic analysis

Very faint H emission in the solar corona registered on over-exposed photographs made by a coronagraph and an H filter is studied. The over-exposed filtergrams have been processed by a Joyce Loebl automated microdensitometer and the two-dimensional scans have been analysed by the residual image method. A classification of the faint H emission objects, revealed on the isodensity maps, is proposed and the latitudinal distribution, the morphology, and the location with respect to the other active phenomena are analysed. Taking into account some possible plasma effects that could be caused by coronal magnetic field changes, a hydromagnetic interpretation of the faint H emission is proposed.     

Some comments on the photographic subtraction method of determining chromospheric velocities

The photographic subtraction formula expressing the Doppler signal in terms of line-of-sight velocity is rederived and the conditions governing its validity are carefully stated. By appealing to the observed profiles of individual bright and dark mottles it is shown that, in the case of H observations of the quiet chromosphere, two essential conditions are violated.An analysis based on Beckers' (1964) theoretical mottle profiles shows that, assuming the correctness of his model, the photographic subtraction method correctly maps regions of zero velocity and, provided the original photographs are taken sufficiently far from the centre of H, gives the correct signs of any line-of-sight velocities present. However, at H ± 0.25 Å the method gives inconsistent signs. Moreover, at all wavelengths in the line the magnitude of the Doppler signal depends not only on velocity but also on the source function S, optical thickness t ₀, and line broadening parameter ₀. Accordingly, there is no one-to-one correspondence between velocity and the Doppler signal since S, in particular, shows considerable variation from place to place over the quiet chromosphere.An alternative procedure which obviates these difficulties is suggested. It is also based on Beckers' model and yields a calibrated measure of the velocity in terms of ₀ (assumed constant) which is independent of spatial variations in S and t ₀.     

Measurements on the Lyman alpha corona

As a result of a collaborative rocket experiment carried out during the solar eclipse on 7 March, 1970, measurements have been made of the brightness of Lyman from the corona, at heights between 5 × 10⁴ and 5 × 10⁵ km above the limb. The emission is shown to occur primarily through the resonance scattering of chromospheric Lyman from the residual neutral hydrogen in the corona. Both the absolute value and radial fall-off of the brightness agree well with calculations based on solar density models. The Lyman emission has similar variations around the limb to the white light corona, showing in particular an equatorial enhancement.