Supergranular line profile variation of Mg i λ2852

The chromospheric network is barely visible in the Mg i 2852 line. Unlike in plages, where it shows well-defined self-reversed emission structure in the core, the line is an unreversed absorption feature in the network boundaries, exhibiting only a small blue asymmetry. In the network cell interiors, the line is unreversed and symmetrical.     

Evening and morning twilight enhancement of λ5577 Å atomic oxygen line at Allahabad

A photometer for the observation of twilight airglow emissions has been fabricated. Intensity variation in morning and evening twilight of 5577 Å line of atomic oxygen has been recorded at Allahabad for one year duration from 23rd March, 1987 to 22nd March, 1988. The enhancement in the intensity of the line is found to be irregular. Out of 40 clear evenings and 25 clear mornings from 23rd March, 1987 to 15th June, 1987 enhancement is observed in 24 evenings and 15 mornings. However, no enhancement is observed during the period from 15th September, 1987 to 15th October, 1987. It is found that rise and fall of intensity is exponential during twilight period. Considering different mechanism for the excitation of atomic oxygen green line, it is concluded that none of them are able to explain enhancement. More work is needed to be carried out for the better understanding of the problem.     

Variability of the spectrum of β CrB in the region of the lithium line Li I λ6708Å

Some results of observations of the spectrum of the spectroscopic-binary Ap star CrB in the region of the lithium line Li I 6708Å are presented. The observations were made at the Crimean Astrophysical Observatory over the period 1993–1995 with the coudé spectrograph equipped with a CCD camera on the 2.6-m telescope. Several factors which can affect the behavior of the lithium blend are examined: stellar rotation, magnetic field, isotopic shift, the binary system, and blending by unidentified elements. The principal result of this work is the detection of variability of the lithium blend Li I 6708Å over the period of rotation of the star. The variations of the radial velocity V_r, and the FWHM of the lithium blend are reported here for the first time. They indicate either a nonuniform distribution of lithium or a nonuniform distribution of conditions for excitation of the lithium resonance doublet in the complex structure of the strong surface magnetic field. Similar variations are also shown by the lines of the rare-earth elements Gd II 6702.10 Å, Gd II + Ce II 6704.3Å, and Ce II + Fe I 6706.0 Å.Translated fromAstrofizika, Vol. 39, No. 1, pp. 19–30, January–March, 1996.     

Fabry-Pérot line profiles in the λ5303 å and λ6374 å coronal lines obtained during the 1983 Indonesian eclipse

During the total solar eclipse of 11 June, 1983, an imaging dual-channel Fabry-Pérot interferometer was used to obtain line profiles simultaneously in the green 5303 Å [Fe xiv] and the red 6374 Å [Fe x] coronal lines at various positions in the corona. Extensive microdensitometry followed by multi-Gaussian curve-fitting analysis has resulted in the determination of coronal temperatures and velocity separations between different pockets of coronal gas in the line of sight over a large extent of the corona. Fewer high temperature zones are to be found in the corona of 1983 compared with our similar green-line measurements of the solar maximum corona of 1980. The data are consistent with a temperature maximum occurring at 1.2 R , as found at the 1980 eclipse, but our new data are insufficient to observe farther out than this radius and so determine the position of a maximum. The velocity field in the corona at the 1983 eclipse is less structured compared with that at the 1980 eclipse and is mainly confined to the zone 20–30km s^–1.     

Intensity variation of Oi λ5577 Å line of atomic oxygen at allahabad during morning and evening twilight

Intensity variation of Oi green line observed at Allahabad (25°32 N, 81°53 E) by a laboratorymade photometer has been reported here for the period January 1988 to December 1988. During the summer period of observation, slight enhancement in the intensity of evening and morning twilight emission is observed for a short duration of 4 min. However, winter observations show less pronounced enhancement in the intensity of evening twilight, while it does not occur during morning twilight. These observations are closely in agreement with those of Schaffer (1975).     

Variations of the λ525.02 nm FeI line profile over the solar disk and observations of large-scale magnetic fields

This paper examines the question of the influence of the 525.02 nm Fei line profile (slope of its wings) variations over the solar disk upon observations of large-scale magnetic fields (LSMF) made in this line. The study has shown that depending on the position on the disk (center-limb effect) and magnetic field parameters at the place of the observation, values of magnetic field strengths determined with proper account of the real line profile and in the usual way (by calibration using the line profile at the center of the solar disk only) can differ by 25% or more, which is of crucial importance. Observations at the Solar Telescope for Operative Predictions (STOP) of the Sayan Observatory have been used to accomplish this work.     

Echelle observations of C iii λ1909 and Si iii λ1892

Profiles of C iii 1909 and Si iii 1892 obtained on and near the limb during the 1976 flight of the University of Hawaii echelle rocket spectrograph were reduced and analyzed to determine electron densities and mass motions. The electron pressure derived (N _eT_e 4 × 10¹⁵ cm^–3) agrees well with that determined by Cook and Nicolas (1979) from ATM data. Nonthermal velocities in the region of formation of Si iii 1892 on the disk were found to be 10–12 km s^–1, somewhat lower than the values obtained by Doschek et al. (1976), also from ATM spectra. However, velocities derived at and above the limb were in closer agreement, about 17 km s^–1.Geosciences Systems Department, Computer Sciences Corporation, 8728 Colesville Road, Silver Spring, Md. 20910, U.S.A.     

The broad wing of the [O Ⅲ] λ5007 emission line in active galactic nuclei

We use a sample of type 2 active galactic nuclei(AGNs) from SDSS DR7 in which the [O III] λ5007 emission line can be modeled by two Gaussian components,a broad wing plus a narrow core,to investigate the origin of the broad wing and the connection between the velocity shift of the broad wing and the physical parameters of AGNs,as well as their host galaxies. We find that the flux of the wing components is statistically roughly equal to that of the core components. However,the velocity shift of the wing component has only weak,if any,correlations with the physical properties of AGNs and the host galaxies,such as bolometric luminosity,the Eddington ratio,the mass of supermassive black holes,D4000,HδAor stellar mass. Comparing the velocity shift from our type 2 AGN sample to that from the type 1 sample in Zhang et al.,we suggest that the [O III] broad wing originates from outflow.     

Extinction of Beamed Gamma-ray Burst Afterglows in a Dense Circumstellar Cloud

Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30 pc within the initial solid angle of the jet. Asthe jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results showthat a break appears in the light curve of optical afterglow but it extends over a factor of ～ 80 in time rather than a factor of ～ 10 in time for the case of strong dust extinction and a factor of ～ 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.     

Chromospheric oscillations observed in the line C ii λ1336 with OSO-8

Satellite observations of velocity and intensity oscillations were made of the upper chromospheric line C ii 1336. The dominant period of oscillation is 300 s, with little evidence of the power peak in the range 150–200 s which has been observed in other chromospheric lines. Peak-to-peak amplitudes are 2 km s^–1 and 8% in velocity and intensity, respectively. Tentative evidence for 900-s periodicity is presented. Relative phase measurements show that maximum intensity for the 300-s oscillation leads maximum blueshift by approximately 145 s. Comparison of line and background (scattered light) intensity variation shows upward wave propagation, with time delays between the 1800 continuum and C ii 1336 variation of 27 s and 70 s for different cases.     

Quiet Sun observations of the Ali autoionization lines λ1932 and λ1936

We present quiet Sun observations obtained during a rocket flight of the Al i autoionization lines 1932 and 1936 at solar pointings ranging from = 0.73 out to the visible limb. Absolute intensities are estimated to be accurate to approximately ±20%. These lines progressively weaken with decreasing but never go into emission before finally disappearing with the continuum just beyond the visible solar limb. The observations are compared with LTE line profiles computed through the quiet Sun atmosphere of Vernazza et al. (1976). We discuss several areas of disagreement between the synthetic and observed profiles.     

On the fine structure of the Fe I λ532.4185-nm line profile in the spectrum of the solar disk center

Based on the digital spectra taken with double monochromators of high spectral resolution, we have constructed the profile of the Fe I λ532.4185-nm line in the spectrum of the solar disk center. Basic spectrophotometric characteristics of the line profile have been determined with a high accuracy. The fine structure of the line profile is studied in detail. The profile asymmetry parameters have been determined.     

On the discovery of K I 7699 Å line strength variation during the 1982–1984 eclipse of ε Aurigae

The discovery of K I 7699 Å line strength variations during the 1982–1984 eclipse of ε Aurigae is described. The equivalent widths and radial velocities of the K I 7699 Å line derived from spectra obtained during 1981 November–1983 July with the 2.1 m Otto Struve reflector telescope of the McDonald observatory are presented.     

Structure and Evolution of the Transition Region Network Observed in he ii λ304

The length scale and life time of the transition region network cells were studied using Heii 304 filtergrams. The temporal structure function was calculated from spatially aligned Heii 304 images. The estimated life time of the network cell was about 27 hr. We compared this life time with the life time of photospheric magnetic network and of the extrapolated magnetic network. The spatial structure function was calculated from the Heii 304 filtergrams. The calculated spatial structure function saturates at 25000 km. The transition region network elements are bigger in size than the photospheric magnetic network element. The magnetic network element equals the size of the Heii 304 network element when the photospheric magnetic field is extrapolated to a height of 3000 km above the photosphere where the magnetic fluxes are deployed. The derived value of the diffusion speed of the network elements was 0.098 km s^–1.     

Observations of the limb effect in potassium λ7699

Center-to-limb observations of the Ki 7699 line made on 30 days over a five-year period using the McMath-Pierce Solar Telescope at Kitt Peak are presented. Both a relative and absolute limb effect have been derived from the data. Our determination of the limb effect in Ki 7699 shows a linear increase to the limb amounting to about 40 m s^–1.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.     

The center-to-limb behavior of Ca i λ6573 and [Ca ii] λ7324

Center-to-limb measurements of the Ca i 6573 intercombination line and the Ca ii 7324 forbidden line are compared with synthetic profiles based on a simple representation of the non-LTE Ca-Ca⁺ ionization equilibrium. The effects of photoionizations from low lying excited states of neutral calcium are found to reduce the sensitivity of the 6573 center-to-limb behavior as a thermal structure diagnostic. The synthetic center-to-limb behavior is also sensitive to uncertainties in the nonthermal broadening. Nevertheless, the measured center-to-limb behavior of 6573 favors a cool photospheric model similar to the Vernazza, Avrett, and Loeser model M over hotter models based on the Ca ii K wings. The non-LTE calcium abundance obtained from the disk center equivalent widths of 6573 and 7324 using the best fit model is A _Ca2.1±0.2 × 10^-6 (by number relative to hydrogen). Applications of these lines as diagnostics of the Ca-Ca⁺ ionization equilibrium in other stars are briefly discussed.Visiting Astronomer, Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.     

UBVRI photometry of the eclipsing symbiotic system CI Cygni in 1996–1999

The UBVRI photometry of the eclipsing symbiotic star CI Cyg in 1996–1999 is presented. The system continued to be in quiescence during this period. The shape of the minima in its light curves attributable to eclipses of the compact star with an accretion disk by the red giant is the same as that in 1988–1995. An analysis of our observations and those of other researchers, which span a total of 27 years, has revealed a cyclic variability of the out-of-eclipse photometric properties of CI Cyg on a time scale of about 10.7±0.6 years with the clearest manifestation in the U-B color. The fact that the system’s out-of-eclipse light variations in U, on the one hand, and in BVRI, on the other, occur in antiphase suggests that the titanium red giant plays a significant role in this cyclic process. However, with its contribution to the total U flux being no larger than 10%, the observed light fluctuations of CI Cyg in this band must be caused not only by variability of the giant but also by light variations of the hot component. The presence of a 10.7-year cycle in the system’s active and quiescent states suggests that some precession phenomenon is responsible for it. Precession of the accretion disk, which would cause both the observed brightness of the primary component and the effect of its radiation on the titanium red giant to vary, can serve as an example of such a phenomenon.     

Nova Cygni 1975 (V1500 Cyg) in 2000–2009 and the nature of its synodic period

Multicolor photometric data are presented for the asynchronous polar V1500 Cyg during 2000–2009, i.e., 23–35 years after its outburst. Some examples of individual light curves of the system are shown. An analysis of these reveals large variations in its brightness and color with the phase of the orbital period owing to a “reflection effect” caused by reradiation from the side of the red dwarf facing the hot white dwarf and heated by its hard ultraviolet radiation. The variations in the O-C residuals and in the maximum intensity with the phase of the synodic period are illustrated. It is found that the amplitude A of the orbital fluctuations increases in proportion to the intensity I at a rate dA/dI=0.64. This behavior of V1500 Cyg is most likely caused by periodic shading of the illuminated part of the red dwarf, where the degree of shading depends on the phase of the synodic cycle.     

Alfvén turbulence and the time dependence of non-thermal line broadening in flares

Alfvén wave turbulence is considered as the source of the non-thermal line broadenings observed in soft X-rays in solar flares. The waves are assumed to lose energy to particle acceleration and the temporal development for the case of Fermi acceleration,W(k)k ^–2, is investigated. The decay of the wave energy density is compared to that of the non-thermal velocity for the event of 1980 June 29. The wave energy densities required to explain the degree of non-thermal broadening and its temporal characteristics are consistent with those typically inferred from-ray observations. A relationship between the degree of non-thermal broadening and-ray fluxes is predicted. In general, the larger the-ray flux the shorter the time scales for the decay of the wave energy.     

Changes of the CaI λ6102.7 Å line profile and the magnetic field structure during the August 12, 1981 solar flare

We study the changes of the CaI λ6102.7 Å line profile and the magnetic field structure during the 1B/M2.2 while-light flare of August 12, 1981. The two brightest flare knots located in the penumbra of a sunspot with a δ configuration are investigated. The 1 ± V line profiles are analyzed. The reduction and analysis of our observations have yielded the following results. (1) The line profiles changed significantly during the flare, especially at the time of optical continuum emission observed near the flare maximum. In addition to the significant decrease in the depth, a narrow polarized emission whose Zeeman splitting corresponded to a longitudinal magnetic field strength of 3600 Gs was observed. This is much larger than the magnetic field strength in the underlying sunspot determined from the Zeeman splitting of absorption lines. (2) The largest changes of the CaI λ6102.7 Å line profile observed during the flare can lead to an underestimation of the longitudinal magnetic field strength measured with a video magnetograph by a factor of 4.5, but they cannot be responsible for the polarity reversal. (3) A sharp short-term displacement of the neutral line occurred at a time close to the flare maximum, which gave rise to a reversed-polarity magnetic field on a small area of the active region, i.e., a magnetic transient. This can be interpreted as a change in the inclination of the magnetic field lines to the line of sight during the flare. The short-term depolarization of the CaI λ6102.7 Å line emission observed at the other flare knot can also be the result of a change in the magnetic field structure. (4) These fast dynamic changes of the magnetic field lines occurred after the maximum of the impulsive flare phase and were close in time to the appearance of type II radio emission.