The relations between chromospheric features and photospheric magnetic fields

High resolution photographic magnetograms are compared with H filtergrams (both on- and off - band) for a wide variety of solar features. It is verified that H filaments overlie neutral lines or bands and that H plages always occur at magnetic field clumps. However, the brightness of H plages bear no relation to magnetic field strength or polarity, and the direction of the magnetic field with respect to threads and filaments remains obscure. Counter-examples can be found for virtually every rule that has been formulated so far.Basic questions about the usefulness and final research goal of filtergrams and magnetograms are raised. It is shown that neither filtergram or magnetogram alone is capable of furnishing a unique solution. It is suggested that the proper direction for research is to use magnetograms, together with (as yet unspecified) additional sources of data, to understand H structures.     

Association of type II solar radio bursts with coronal structures above Hα filament channels

A study of type II solar radio bursts recorded at 160 MHz by the Culgoora radioheliograph during 1980 to 1982 shows that the radio emission occurs above H filaments rather than above H flares. This suggests that the type II radio emission most probably originates from within a coronal helmet streamer overlying the filament channel.     

An Estimate of Microwave low-Brightness-Temperature Regions' Heights Obtained Measuring Their Rotation Velocity

Daily full-disk solar maps obtained at 37 GHz in the years 1979, 1980, 1981, 1982, 1987, 1988, 1989, 1990, and 1991 are analysed and compared with full-disk solar maps in H. A search for a difference in the measured angular rotation velocity for two classes of microwave low-brightness-temperature regions (LTRs), associated and not associated with H filaments, is performed. Procedures with and without statistical weights, assigned to angular rotation velocities according to the tracing time, are applied and the statistical significance of the results is discussed. A higher angular rotation velocity is measured for LTRs associated with H filaments than for the not-associated ones. This angular velocity difference is interpreted as a consequence of a height difference between these two types of LTR tracers. Changes of the solar differential rotation velocity during the activity cycle measured using LTRs as tracers are explained by the measured cycle-dependence of the association rate between LTRs and H filaments. Similarly, the north–south asymmetry in the solar rotation velocity measured tracing LTRs is explained by the measured north–south asymmetry in the association rate between LTRs and H filaments. The rotation velocity of LTRs and H filaments is on the average more rigid in comparison with sunspots.     

3.5mm Depression features associated with Hα ‘disparitions brusques’

The characteristics of 3.5 mm depression features associated with two disparition brusques observed in H are discussed. The millimeter depressions still exist, although reduced in strength, after the disappearance of the H filament. The two depressions correspond to temperatures of 600 and 450 K before and to 200 and 250 K after the H filament disappearance.     

Magnetic fields and helium-D3 spectroheliograms

Spectroheliograms, having a resolution approaching 2, have been obtained which show He-D₃ in absorption against the disk. The He-D₃ features are compared with the distribution of magnetic fields and with H structures. The brightest regions in H usually show the strongest D₃ absorption. Most H dark filaments show some D₃ absorption, but the degree of correlation varies from filament to filament. The correlation between B_II and He-D₃ absorption is rather poor and the He features are much more diffuse than the photospheric magnetic field.     

The solar filigree

As a birefringent filter is tuned from the center of H to the continuum the H bright mottles appear to break up into a network of grains. The name filigree is suggested for this bright network. Its size, shape, contrast and time evolution is described as well as its relation to the abnormal granulation, magnetic field and spicules.On leave from The University of Hawaii.     

Observations of solar filaments at 8, 15, 22 and 43 GHz

On April 3, 4, 6, and 8, 1978, solar observations were made using the Haystack 120 ft telescope at 8, 15, 22, and 43 GHz. H filtergrams obtained at the Sacramento Peak Observatory on the same days showed an average of more than 30 filaments or filament fragments (per day) on the disk. Most of these appeared as depressions in brightness temperature at 15 and 22 GHz. Because of the relatively low spatial resolution at 8 GHz, only a few appeared at that frequency, and presumably because of lower opacity in filaments at higher frequencies, few depressions were visible at 43 GHz. At 15 and 22 GHz, more depressions appeared than H filaments, but virtually all the radio depressions overlay magnetic neutral lines. Taking the data sets for each day as independent samples, we found that at 22 GHz, 46 of the 77 radio depressions were associated with H filaments; at 15 GHz the correlation was smaller; only 27 out of 48 being associated with the H filaments. The data imply that the microwave depression features are the result of absorption by filaments and perhaps also the result of other effects of the associated filament channel, but not necessarily coronal depletion. The effects of filament absorption are, statistically, about twice as effective as other phenomena (such as absorption by material invisible in H, for example) in creating the radio depression. A center-to-limb study of a single large filament clearly showed that at 15 and 22 GHz the absorption by cool hydrogen supported above the neutral line was the predominant factor in producing the observed depression at radio frequencies.     

Holes in the Hα Eruptive Prominence Structure

The eruptive prominence observed on 27 May 1999 in H at Ondejov Observatory is analyzed using image-processing techniques. To understand the physical processes behind the prominence eruption, heated structures inside the cold H prominence material are sought. Two local minima of intensity (holes), the first above and the second below the erupting H prominence, have been found in the processed H images. A comparison of H images with the SOHO/EIT and Yohkoh/SXT images showed: (a) the cold H prominence is visible as a dark feature in the EIT images, (b) the upper local minimum of intensity in the H image corresponds to a hot structure seen in EIT, (c) the lower minimum corresponds to a hot loop observed by SXT. The physical significance of the H intensity minima and their relation to the hot structures observed by EIT and SXT is discussed. The time sequence of observed processes is in favor of the prominence eruption model with the destabilization of the loop spanning the prominence. For comparison with other events the velocities of selected parts of the eruptive prominence are determined.     

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.     

Comparison of Prominences in Hα and He II 304 Å

In this letter, we bring attention to prominences which show different morphology in H and Heii 304 Å, as observed simultaneously by BBSO and EIT on board SOHO. Those two lines have been thought to represent similar chromospheric structures although they are formed at significantly different temperatures. We give two examples representing two kinds of anomaly: (1) prominences showing strong H emissions in the lower part and strong Heii emissions in the upper part, and (2) erupting prominences showing extensive Heii emission, but nothing in H. Our results indicate that a part or the whole of a prominence may be too hot to emit H radiation, possibly due to heating or thermal instability. Please note that these are not just two isolated cases, many other prominences show the similar differences in H and Heii 304 Å.     

Interferometric study of the Milky Way between Carina and Aquila

Large field H observations of the Milky Way between Carina and Aquila were made through a narrow interference filter 15 wide. Characteristic large-scale features of the observed region are extended emission areas in Carina, Norma-Scorpius and Scutum-Sagittarius and some weak isolated nebulosities near the Coal Sac, Centauri and Normae. H photographs, a chart mapping the emission, and a list of identified emission regions are given.     

Observations of prominences at 3.5 millimeter wavelength

At 3.5 mm wavelength absorption features are observed in correspondence with H dark filaments on the disk; beyond the limb the prominences correspond to emissive regions. The absorption features are larger (2–3 arc) than the corresponding H dark filaments; the emissive regions at the limb have similar angular sizes. The emissive regions at the limb have electron temperatures of 5500±500 K; the amount of absorption observed on the disk leads to mean electron densities of about 5 × 10¹⁰ per cm³.     

Spatial correlation of Hα filaments and photospheric velocity

The location of H filaments is compared with maps of the photospheric line of sight velocity V and the magnetic field H . It is found that (1) H filaments are associated with regions of ¦V ¦ 300m s^–1, (2) always both positive as well as negative velocities are present under H structures, (3) stable (long lasting) portion of filaments frequently occur at the position of H = 0 as well as V = 0 lines, (4) this association remains valid for the longitudes less than 50° from central meridian.     

Synoptic Hα Full-Disk Observations of the Sun from Big Bear Solar Observatory – I. Instrumentation,Image Processing,Data Products,and First Results

The Big Bear Solar Observatory (BBSO) has a long tradition of synoptic full-disk observations. Synoptic observations of contrast enhanced full-disk images in the Caii K-line have been used with great success to reproduce the Hi L irradiance variability observed with the Upper Atmosphere Research Satellite (UARS). Recent improvements in data calibration procedures and image- processing techniques enable us now to provide contrast enhanced H full-disk images with a spatial resolution of approximately 2 and a temporal resolution of up to 3 frames min–1.In this first paper in a series, we describe the instruments, the data calibration procedures, and the image-processing techniques used to obtain our daily H full-disk observations. We also present the final data products such as low- and high-contrast images, and Carrington rotation charts. A time series of an erupting mini- filament further illustrates the quality of our H full-disk observations and motivate one of the future research projects. This lays a solid foundation for our subsequent studies of solar activity and chromospheric fine structures. The high quality and the sunrise- to-sunset operation of the H full-disk observations presented in this paper make them an ideal choice to study statistical properties of mini-filament eruptions, chromospheric differential rotation, and meridional flows within the chromosphere, as well as the evolution of active regions, filaments, flares, and prominences.     

Fine structure of the Solar Chromosphere: Arch-Shaped Mottles

We analyze a time series of high resolution observations near the solar limb, obtained in H and the Mg b1 line. We identified arch-shaped dark mottles, which are thin, faint H structures observable under very good seeing conditions, best seen in H +0.75 Å. Their mean length is about 15, their mean height about 6 and indicative lifetimes is of the order of 5 min. They show negative (away from the observer) line-of-sight velocities. A possible interpretation is that material flows from the apex towards the feet of the arches.     

On the size of the structure elements in the solar chromosphere

Photometric reductions of the spectrograms obtained during the third flight of the Soviet Stratopsheric Solar Station are discussed. A comparison of photometric scans in H and its far wings near to the continuum leads to the conclusion that chromospheric mottles are at least several times broader than photospheric granules. The optimum size of mottles is about 0.8–1.1. The H profiles of mottles are practically the same as those obtained from the ground observations. The broadening of mottles is considered as an effect of expansion of magnetic arcs growing up to chromospheric levels.     

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.     

Rapid simultaneous observations of Feii and Balmer emission lines of X Oph

Sudden brightening of FeII and Balmer (H and H) lines of X Oph was observed on 28–29 May, 1986. Equivalent width of FeII and H lines increased by a factor of two and that for H line by a factor of four, during the brigtening phase of the star. This brightening phenomena has been explained in the framework of Coronal Radiative Instability.     

Study of alpha component dynamics in the solar wind using the Prognoz satellite

The analysis of solar wind He⁺⁺ and H⁺ ion distribution functions, collected over five months by the satellite Prognoz 1, shows that these are in general maxwellian but that often tails appear at higher speeds. The existing relation V-T, the observation of ratios of T/Tp 3.83 and V/Vp 1.035 give evidence of preferential He⁺⁺ ion heating and acceleration. The criteria for heating by dissipation of hydromagnetic waves proposed by Barnes and Hung (1973) are tested experimentally. Finally, multifluid models are likely to predict certain observations such as dependence of the velocity ratio V/Vp on the solar wind flux.     

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.