Faculae,filigree and calcium bright points

Simultaneous observations of fine structure photospheric features at several wavelengths are described. The observations, which include regions near disk center and at the limb, were obtained using a narrow band calcium filter and selected wavelengths in Mg b₁, the red wing of H and the H continuum using the Universal Birefringent Filter of the Sacramento Peak Observatory.From the disk-center series it is concluded that bright point structures seen in calcium are cospatial with the H filigree and are related in origin.The limb photographs confirm that the calcium network is cospatial with the white light faculae. However, in regions of good seeing it is clear that even at the limb the calcium network patterns consist of individual bright points which are essentially the same as those seen near disk center.Thus it is concluded that the white light faculae, the H filigree and the calcium bright points are different manifestations of the same photospheric features.On leave from Department of Applied Mathematics, University of Sydney, Australia.The Sacramento Peak Observatory is operated by the Association of Universities for Research in Astronomy, Inc. under contract AST 78-17292 with the National Science Foundation.     

Some statistical properties of Ellerman bombs

One hundred seventy-eight Ellerman bombs were identified and studied with on- and off-band H filtergrams of two active centers, one near disk center and the other near the east limb. The photographs, taken through a 1/4 Å bandpass filter, occasionally attained resolution as fine as 0.3. The mean duration of bombs at H-2 Å was about 13 min near disk center and 11 min near the limb; these times increase slightly when we observe closer to the core of H. Eighty-six percent of the bombs in the near-limb region and 56% in the disk-center region were seen to be accompanied by ejections of dark material; the ejections were 3–30 long. The ejection length appears to be proportional to the bomb size times the bomb lifetime.     

Some observational results on moustaches

The results of new observations of moustaches in H filtergrams and in H spectra are presented and their relations to photospheric and chromospheric phenomena are studied. The main findings and conclusions are: (1) previous results on basic data (size, brightness, lifetime, etc.) are essentially confirmed; (2) limb observations located the moustaches at the base of the structured H chromosphere, just above the level of the emission of H±1 Å. At the disk moustaches are, in general, covered by absorbing and slightly Doppler-shifted chromospheric elements which determine the H core in the moustache spectrum. However, absorption-free moustaches with an H emission core revealing a pure (true) moustache spectrum have also been found; (3) moustaches have been found to coincide with continuous facular granules; it is suggested that they are an extension of facular granules into the chromosphere rather than a low-level flare-like phenomenon.Mitteilung aus dem Fraunhofer Institut, No. 114.     

Fine Structure of the Quiet Solar Chromosphere: Limb-Crossing Features

In this article we study chromospheric structures (spicules) crossing the solar limb in H images corrected for limb darkening. This correction enabled us to view structures both on the disk and beyond the limb in the same image. The observations were obtained at the Sacramento Peak Observatory at H±0.75 Å. The processed images reveal both bright and dark (relative to the local background) features crossing the limb. We also observed bushes (rosettes) crossing the limb, as well as structures indicating probably arch-shaped mottles beyond the limb.     

Resolution of the Hα double-limb controversy

The discussion of the H double limb had reached the point where the question of its existence as a real solar phenomenon could not be resolved without new observations made with the Lockheed filter and the Mount Wilson spectroheliograph. A study of the instrumental profiles had indicated that there was sufficient off-band light to produce the observed inner limb step in the Mount Wilson instrument, but this analysis was not completely satisfactory because of limitations inherent in the measurement of instrument functions with a Hg-198 source. The instrumental profile work did indicate, however, that the spectral purity of the instruments in question could be substantially improved by the use of narrow-band interference filters. An experimental program was thus launched to determine the effect of such a blocking filter on the appearance of the H limb. The results of these observations with three Halle filter systems and the Mount Wilson spectroheliograph are that the inner limb completely disappears at the center of H when a blocking filter is used to reduce unwanted light, which originates at wavelengths beyond ±0.8 Å. In addition, the contrast and visibility of the chromospheric fine structure is increased by eliminating the off-band light. Thus the experiment conclusively demonstrates that the apparent inner limb is not a solar feature but is due entirely to instrumental parasitic light.     

Study of the post-flare loops on 29 July 1973

Bright and dark curvilinear structures observed between the two major chromospheric ribbons during the flare of 29 July 1973 on films from the Big Bear Solar Observatory are interpreted as a typical system of coronal loops joining the inner boundaries of the separating flare ribbons. These observations, made through a 0.25 Å H filter, only show small segments of the loops having Doppler shifts within approximately ± 22 km s^–1 relative to the filter passband centered at H, H -0.5 Å or H +0.5 Å. However, from our knowledge of the typical behavior of such loop systems observed at the limb in H and at 5303 Å, it has been possible to reconstruct an appoximate model of the probable development of the loops of the 29 July flare as they would have been viewed at the limb relative to the position of a prominence which began to erupt a few minutes before the start of the flare. It is seen that the loops ascended through the space previously occupied by the filament. On the assumption that H fine structures parallel the magnetic field, we can conclude that a dramatic reorientation of the direction of the magnetic field in the corona occurred early in the flare, subsequent to the start of the eruption of the filament and prior to the time that the H loops ascended through the space previously occupied by the filament.     

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.     

Solar bright points in 3840 Å and Hα

Analysis of bright features in 3840 Å and H shows that forevery Ellerman bomb (H-0.9 Å) there is a cospatial brightening in the 3840 Å network. We give properties of these bright points in both wavelengths as well as describe: (1) the appearance, and subsequent separation, of new elements in the 3840 Å network and (2) the direct transition from a 3840 Å bright point to a new sunspot.     

Observations of Ellerman bombs in H α

A developing active region near the center of the solar disk was observed for 80 min at the center and the wings of H. Ellerman bombs lying both below an Arch Filament System and near sunspots were studied at H - 1.0 Å and H - 0.75 Å. We determined their average contrast, lifetime, size and we studied their flux as a function of time. We found evidence that the size of Ellerman bombs increases with height. The time curves of flux provide evidence for both impulsive and gradual energy release. Under the AFS the Ellerman bombs form a cellular pattern with a characteristic size of 3.1 × 10³ km. Fifty percent of the bombs appear and disappear in pairs, possibly associated with bipolar emerging magnetic flux tubes.     

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.     

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.     

New observational results for the solar chromosphere

High resolution photographs of the solar chromosphere have been obtained with the 40-cm refractor of the Athens Observatory and a 0.5 Å Halle H filter. Our best photographs show a resolution of 0.6, which is comparable with the theoretical resolving limit of 0.4, at H. The achieved resolution permitted us to secure some excellent observations of the fine structure of the chromosphere on the disk as well as on the limb. The study of these observations leads to the following results: (a) the bright filaments of the disturbed chromosphere as well as the penumbral ones appear to consist of knots, (b) inside the cells of the chromospheric network of the quiet chromosphere, bright roundish granule-like formations are present, their mean size being of the order of 2500 km. (c) the bright fine mottles seem to lie at the root of the elongated dark ones, each pair of them giving rise to a spicule.     

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.     

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.     

Study of Hα Jets on the Quiet Sun

High-speed jets of solar quiet regions have been observed at Big Bear Solar Observatory in H–1.0 Ú, and compared with high-resolution magnetograms. Over the whole Sun, the birthrate of the H–1.0 Ú jets is about 19±3 events s^–1, which is much lower than the birthrate of spicules. The average lifetime of these jets is 2±1 min. H–1.0 Ú jets are very different from spicules, in the sense of birthrate, lifetime, and shape. Jets tend to recur in the same sites, always located in boundaries of supergranules. Under the best observing conditions, we found that 80% of the major jet sites are associated with converging magnetic dipoles – mainly the sites where intranetwork elements are canceling with opposite polarity network elements. In order to establish a possible relationship between the disk H jets and limb macrospicules, we have also obtained time sequences of H center-line images at the limb. These images are enhanced by median filtering so that jet structures over the limb are easily studied. We found that these limb H jets (above the spicule forest) repeatedly occur in the same sites, which is the property shared by the disk H–1.0 Ú jets. However, their mean lifetime is 10 min, substantially longer than that of disk jets. Comparison with simultaneous SOHO/EIT Heii 304 Ú images shows that every Heii 304 Ú jet over the limb coincides with an H jet, although Heii 304 Ú jets extend much farther out. Some H jets do not have associated He jets, probably due to the difference in image resolutions. H spectra of selected jets are analyzed, and we found that jets are not simply blue-shifted; instead, the line profiles are broadened with significantly larger broadening on the blue side. Two-component fitting finds that the velocity of the blue-shifted component (an optically-thin component) is around 20 to 40 km s^–1.     

Hi,molecular/Hii shells from 1 to 2000 pc diameter: Wind-driven or supernova remnants?

Deep H+[Nii] photographs of five giant shell-like nebulae in the LMC are compared to 21 cm Hi maps, Schmidt photographs showing the O and B associations and the UV sources from 1200 to 1600 Å. The formation of all shell-like nebulae which do not appear to be supernova remnants and which have diameters between 1 pc and 1900 pc is discussed.     

High dispersion spectroscopic study of quiescent prominences

The utility of very high dispersion spectra (5–11 mm/Å) for the study of line profile and velocity structure in quiescent prominences is demonstrated by observations, taken with the spectregraphic slit positioned normal to the limb in H 6563 Å, He D₃ 5876 Å, and Ca⁺K 3933 Å. The emission profiles of both H and the K line often show a central reversal (absorption). Emission structures in the K-line can be complex with details as narrow as 0.04 Å. Frequently this structure consists of two distinct components: a central, strong, rather narrow line, and an often displaced, weak feature of undefined profile appearing as fuzz. It is suggested that this fuzz indicates an exchange of matter between the prominence and the corona.Visiting Astronomer, Institute for Theoretical Astrophysics, Oslo, Norway.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Solar Photospheric and Chromospheric Observations using a Lithium Niobate Fabry-Perot Etalon

We have made a narrow band tunable filter for solar observations using a Lithium Niobate Fabry-Perot etalon. The 60 mm aperture etalon with a free spectral range of 4.22 Å and finesse of 26 at = 6122 Å has been procured from CSIRO, Australia. The wavelength tuning is achieved by applying high voltage to the etalon substrate at the rate of 0.45 Å per 1000 Volts. The filter is being used for imaging the sun in H line and obtaining Doppler- and Magnetogram in CaI 6122 Å line. In this paper, we present some initial observations carried out with this filter at Udaipur Solar Observatory.     

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.     

Multi-wavelength observations of the 1998 September 27 flare spray

We report on observations of a large eruptive event associated with a flare that occurred on 27 September 1998 made with the Richard B. Dunn Solar Telescope at Sacramento Peak Observatory (several wave bands including off-line-center H), in soft and hard X-rays (GOES and BATSE), and in several TRACE wave bands (including Feix/x 171 Å, Fexii 195 Å, and Civ 1550 Å). The flare initiation is signaled by two H foot-point brightenings which are closely followed by a hard X-ray burst and a subsequent gradual increase in other wavelengths. The flare light curves show a complicated, three-component structure which includes two minor maxima before the main GOES class C5.2 peak after which there is a characteristic exponential decline. During the initial stages, a large spray event is observed within seconds of the hard X-ray burst which can be directly associated with a two-ribbon flare in H. The emission returns to pre-flare levels after about 35 min, by which time a set of bright post-flare loops have begun to form at temperatures of about 1.0–1.5 MK. Part of the flare plasma also intrudes into the penumbra of a large sunspot, generally a characteristic of very powerful flares, but the flare importance in GOES soft X-rays is in fact relatively modest. Much of the energy appears to be in the form of a second ejection which is observed in optical and ultraviolet bands, traveling out via several magnetic flux tubes from the main flare site (about 60° from Sun center) to beyond the limb.