Limb observations of He I 1083 nm

Imaging spectroscopic data of the He i 1083 nm limb emission were taken on several dates in October and November 1995 with the NASA/NSO spectromagnetograph at the NSO/Kitt Peak vacuum telescope and on 9 December, 1993 with the Michigan infrared camera at the NSO/Sacramento Peak vacuum tower telescope. Emission line profiles were observed in quiet-Sun and coronal hole locations on the northern and southern solar poles and on the east solar limb. The height of the He i 1083 nm shell above the continuum limb at 1083 nm was measured to be 2.11 ± 0.12 Mm with the Kitt Peak data, and 1.74 ± 0.05 Mm with the Sacramento Peak data. The Kitt Peak data show (1) within the measurement error there is no significant difference in the height or thickness of the emission shell in coronal holes compared with the quiet Sun, (2) the 1083 nm emission intensity drops by 50% in coronal holes, (3) the line width decreases by about 2 km s^-1 in coronal holes (suggesting less inclined spicules), (4) the line width of the He i 1083 nm line jumps significantly as the line of sight crosses the solar limb (consistent with a higher temperature upper shell), (5) a quiescent prominence shows a smaller spectral line width (consistent with a cooler temperature or less velocity broadening), and (6) the entire emission shell and the prominence show a He i spectral component ratio of about 8 (suggesting optically thin emission).Operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation.     

Zenith photoelectric measurements during the annular solar eclipse of April 29, 1976

Measurement of the light intensity in the zenith, obtained during the annular solar eclipse of April 29, 1976 are given in three wavelength bands (centered on 's 4800, 5400 and 6100 Å). The observed differences in the three wavelength regions have been examined and compared with calculations taking into account limb darkening.     

Spectroscopic observations of zeta Aurigae during the 1971–72 eclipse

The chromospheric phases in the 1971–72 eclipse were observed at wavelength regions containing the K-line of ionized calcium on six nights at ingress and on eight nights at egress at the Okayama Astrophysical Observatory. The linear dispersion of the spectrograms is about 10 Å mm^?1. The spectrograms were measured for line intensities of the K-line and for radial velocities of metallic and hydrogen lines. The results are compared with those obtained in the earlier eclipses. The intensities of the chromospheric K-line during this eclipse were relatively ‘weak’ at both ingress and egress and were similar to those in the 1939–40 eclipse. It seems that the chromospheric activity of ζ Aurigae increased after 1939, reached a maximum at 1950–56, and then decreased again until 1971. The radial velocities of the chromospheric lines of hydrogen atoms, ionized calcium, and some other atoms and ions varied with phase showing almost the same characteristic features as in most earlier eclipses. Intensities and velocities were also measured for satellite lines of the K-line.     

The brightness of the helium D3 line in the undisturbed chromosphere from eclipse observations

Slitless spectra of the chromosphere, observed cinematographically at the total solar eclipse of 10 July 1972, were reduced. The surface brightness distribution of the helium D₃ line in the undisturbed chromosphere was obtained in agreement with results by other observers. The available eclipse data on the D₃ absolute brightness was analysed by means of theoretical curves of growth. Intensity data by some observers were found to be certainly too high. A trend was found that the D₃ absolute brightness in the quiet chromosphere decreases with the increasing solar activity (sunspot number). This perhaps indicates a variation of the spicule number over the solar surface during a sunspot cycle.     

Eclipse observations of coronal emission lines. I. [Fex] 6374Å profiles at the eclipse of 16 February 1980

Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm^-1. The observed line profiles from 1.1 to 1.7 R_⊙ with a spatial resolution of 10 × 22 arcsec², give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 10⁶ K. If temperature of the order of 1.3 × 10⁶ K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s^-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s^-1 to -17 km s^-1. Most of the locations have velocities less than ±5 km s^-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down.     

ALMA capabilities for observations of spectral line emission

The Atacama Large Millimeter/submillimeter Array (ALMA) (The Enhanced Atacama Large Millimeter/submillimeter Array (known as ALMA) is an international astronomy facility. ALMA is a partnership between North America, Europe, and Japan/Taiwan, in cooperation with the Republic of Chile, and is funded in Europe by the European Southern Observatory (ESO) and Spain, in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC), and in Japan by the National Institutes of Natural Sciences (NINS) in cooperation with the Academia Sinica in Taiwan. ALMA construction and operations are led on behalf of Japan/Taiwan by the National Astronomical Observatory of Japan (NAOJ), on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI), and on behalf of Europe by ESO) combines large collecting area and location on a high dry site to provide it with unparalleled potential for sensitive millimeter/submillimeter spectral line observations. Its wide frequency coverage, superb receivers and flexible spectrometer will ensure that its potential is met. Since the 1999 meeting on ALMA Science (Wootten, ASP Conf. Ser. 235, 2001), the ALMA team has substantially enhanced its capability for line observations. ALMA’s sensitivity increased when Japan joined the project, bringing the 16 antennas of the Atacama Compcat Array (ACA), equivalent to eight additional 12 m telescopes. The first four receiver cartridges for the baseline ALMA (Japan’s entry has brought two additional bands to ALMA’s receiver retinue) have been accepted, with performance above the already-challenging specifications. ALMA’s flexibility has increased with the enhancement of the baseline correlator with additional channels and flexibility, and with the addition of a separate correlator for the ACA. As an example of the increased flexibility, ALMA is now capable of multi-spectral-region and multi-resolution modes. With the former, one might observe e.g. four separate transitions anywhere within a 2 GHz band with a high resolution bandwidth. With the latter, one might simultaneously observe with low spectral resolution over a wide bandwidth and with high spectral resolution over a narrow bandwidth; this mode could be useful for observations of pressure-broadened lines with narrow cores, for example. Several science examples illustrate ALMA’s potential for transforming millimeter and submillimeter astronomy.     

White light and monochromatic observations of the corona during the 1980 February 16 eclipse. I. The quiet parts

This paper describes the photographic observations of the corona in white light and in four monochromatic lights (4700 A, 5303 A, 6000 A, 6374 A) at the 1980 February 16 eclipse in Yunnan with particular emphasis on the quiet parts of the corona. The following results are presented: the white light isophotes and ellipticities, the positions of coronal holes and coronal condensations, the variations of the monochromatic intensities with the radial distance along several chosen directions, the derived coefficients in the empirical corona formula in these directions and the variation of the electron density with the radial distance and the electron temperature.     

Radio observations of the 1968 September solar eclipse

This paper summarizes the analysis of the radio observations of the solar eclipse at wavelengths 3.2, 11.1 and 21 cm in Xinjiang, on 1968 Sept. 22. From the observations, we have determined the flux densities, angular diameters and heights of the localized radio sources on the solar disk, circumstances of the radio eclipse, equivalent radius of the radio Sun and certain features of a small radio burst that occurred during the eclipse. We have also investigated the correlation between the flux density of the localized sources and the activity of the active regions, as measured by the integrated brightness of plages and the sunspot area.     

Coronagraphic observations of an enhanced coronal region: I,Fexii and Nixv emission line data

Nine coronal emission lines representing five stages of Fe ionization and one stage of Ni were observed in an enhanced coronal region. The data from these observations are presented along with a density model of the enhanced region obtained from the FeXIII and NiXV emission line ratios as a function of position angle. The electron densities obtained from FeXIII lines range from N _e = 10⁸ to 10⁹ cm^–3, and are slightly lower for NiXV line data. Estimates of the variation of temperature over the enhanced region are inferred from the observed line intensities.     

16–40 Å coronal X-ray emission during the 12 November 1966 eclipse

The solar eclipse of 12 November 1966 was used to study the coronal emission near the limbs in selected emission lines between 16 and 40 Å. Eight fixed-wavelength, curved crystal spectrometers were carried in each of 3 rocket launches to an altitude of 290 km and monitored the flux in each of eight narrow-wavelength intervals encompassing the principal emission lines from the hydrogen-like and helium-like ions of C, N, and O. At totality the emissions dropped to background levels of 1% or less of the full sun values, showing that on the solar limbs on that day there was very little emission above 17000 km in these lines.Work performed under the auspices of the U.S. Atomic Energy Commission.     

On the variation of the direct solar radiation during the annular solar eclipse of April 29, 1976

Measurements of the direct solar radiation during the annular solar eclipse of April 29, 1976 are given in three wavelength bands (centered on 800, 680, and 450 nm). A decrease of the solar radiation after the last contact was observed, especially in the red and infrared. This is considered in connection with the results of other direct light and zenith light measurements.     

Sunspot and stray light observations during the 1971, February 25 partial solar eclipse

Observations of a sunspot during and after a partial solar eclipse are described. The amount of scattered light confirms the existence of a spread function component with a half width of 10″. The observations also indicate the possibility of severely underestimating this component by aureole measurements. Umbral continuum intensities of 0.10 I _⊙ in the red spectral region were directly measured, the correction for scattered light amounts to 0.02 I _⊙. Intensities calculated with four umbral models are larger than the observed values, indicating this sunspot to be cooler by some 100 K. The wings of two strong Ca i lines are equally explained by the models of Henoux, Kneer, and Stellmacher/Wiehr. Yun's model can be ruled out because of too high a temperature.     

Localization of the source of flare X-ray emission during the eclipse of 7 March, 1970

An occultation of X-ray emission from a solar flare occurred during the eclipse of 7 March, 1970 and was observed by an NRL instrument aboard the OSO-5 satellite. Ionization chamber photometers covering the wavelength ranges 0.5–3 Å, 1–8 Å, and 8–16 Å provided flux measurements once every 15 s providing a spatial resolution of 20 arc sec at the solar surface. Within this limitation the X-ray flare was observed to be confined within a region 136 000 km in one dimension.However, the measurements indicate the existence of a denser core 54 000 km wide in the direction of advance of the Moon's limb. Comparison of these results with X-ray photographs of flare regions are made and a model for the development of the soft X-ray flare is proposed.     

Photoelectric measurements of the green coronal line during the eclipse of November 12, 1966

A line to continuum ratio of the green line equal to 2.1 Å was measured above the West limb at the height p = 1.75 solar radii during the eclipse. The lower limit to the abundance of iron relative to hydrogen obtained from these measurements is 4 × 10^–5.     

Solar corona photometry by electropolarimetric and CCD observations during the eclipse of July 11, 1991

The observational data of the solar corona obtained during the solar eclipse of July 11, 1993, using both a electropolarimeter (EP) and a CCD matrix were processed. Using these data the photometry of the solar corona was carried out. The results of EP data were compared with those of the CCD data. It must be noticed here that the CCD data give us only the characteristics of the inner corona, while the EP data show the features of both the inner and the middle corona up to 4 solar radii. The standard flattening index ϵ was evaluated from both data. The dependence of ϵ on the distance from the solar limb was investigated. Three-dimensional images of the coronal intensity distribution for different spectral lines are shown. Isophotes in Na and Ca lines with unusual features are plotted. Based on these data some ideas and conclusions on the type of the solar corona and the physical conditions in it are presented.     

Chromospheric synoptic charts for the solar eclipse of November 3, 1994

The synoptic charts of the filaments and active regions near the solar limb are given for the eclipse of November 3, 1994, along with the positions of the prominences. A table helps to associate coronal and chromospheric structures.     

Simulation of Io’s auroral emission: Constraints on the atmosphere in eclipse

We study the morphology of Io’s aurora by comparing simulation results of a three-dimensional (3D) two-fluid plasma model to observations by the high-resolution Long-Range Reconnaissance Imager (LORRI) on-board the New Horizons spacecraft and by the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS). In 2007, Io’s auroral emission in eclipse has been observed simultaneously by LORRI and ACS and the observations revealed detailed features of the aurora, such as a huge glowing plume at the Tvashtar paterae close to the North pole. The auroral radiation is generated in Io’s atmosphere by collisions between impinging magnetospheric electrons and various neutral gas components. We calculate the interaction of the magnetospheric plasma with Io’s atmosphere-ionosphere and simulate the auroral emission. Our aurora model takes into account not only the direct influence of the atmospheric distribution on the morphology and intensity of the emission, but also the indirect influence of the atmosphere on the plasma environment and thus on the exciting electrons. We find that the observed morphology in eclipse can be explained by a smooth (non-patchy) equatorial atmosphere with a vertical column density that corresponds to ∼10% of the column density of the sunlit atmosphere. The atmosphere is asymmetric with two times higher density and extension on the downstream hemisphere. The auroral emission from the Tvashtar volcano enables us to constrain the plume gas content for the first time. According to our model, the observed intensity of the Tvashtar plume implies a mean column density of ∼5 × 10¹⁵ cm⁻² for the plume region.     

Microwave observations of the 4 January, 1973 solar eclipse

The eclipse was observed at two microwave frequencies, 7 GHz and 22.2 GHz, and has shown the presence of polarized regions, suggesting also excess of left-handed polarized radiation from the solar northern hemisphere. Difference in eclipsing times at the two frequencies for an active center near the limb is discussed.     

Some newly discovered coronal emission lines from high altitude infrared observations of the 7 March, 1970, solar eclipse

A survey of the infrared coronal spectrum between 1 and 3 was made from a high altitude aircraft during the 7 March, 1970, solar eclipse. The observations were made with a Fourier transform spectrometer and were confined to the outer chromosphere and inner corona. In addition to well known chromospheric lines of Hi and Hei, nine additional lines were seen. Evidence is presented for the tentative assignment of these lines to forbidden transitions in highly ionized atoms of magnesium, aluminum, silicon, sulphur, and chromium.