The IRIS sodium cell instrument

In the framework of the IRIS programme, full-disk solar Doppler-shift measurements are made with an optical resonance sodium cell spectrophotometer, a new pattern of the instrument successfully used at the geographic South Pole 10 years ago. After many successive improvements, the IRIS version has now become a precise and reliable device, being limited only by the solar and/or by the atmospheric noise in all the frequency ranges of interest for the p-mode and the g-mode investigation. This instrument is described here in some detail, with the technical specification for each individual component being defined by comparison to the photon and the solar noise.     

Optical Response of the Atmosphere During the Caribbean Total Solar Eclipses of 26 February 1998 and of 3 February 1916 at Falcón state,Venezuela

An investigation of the optical response of the atmosphere before, during, and afterthe total solar eclipse of 26 February 1998 at the Caribbean Peninsula of Paraguaná (Falcón State) in Venezuela, was made by measuring photometrically the intensity of the sky brightness in three strategic directions: zenith, horizon anti-parallel or opposite the umbra path, and horizon perpendicular to this path. From these measurements, and by applying in an inverse way an empirical photometric model, very rough estimations of theextinction coefficient, and also of the average optical depth, were obtained in one of these particular directions. However based on meteorological measurements such as those of relative humidity and temperature, and applying a different model, a better estimation in the visual of the total global extinction coefficient of the sky (except the horizon), were made considering the contribution of each component: atmospheric aerosol, water vapour, ozone and Rayleigh scattering. It is shown that this global coefficient is mostly dependent upon aerosol extinction. In spite of the strong reduction of sky brightness photometrically observed during the totality, the results show that the sky was not dark. This is confirmed by the results obtained for the total global extinction coefficient. Additionally it is estimated that the total solar eclipse that took place also in Falcón State, Venezuela, at the beginning of the last century on 3 February 1916, was 30% darker that the 1998 eclipse, and that atmospheric aerosol played a relevant and similar role in the scattering of sunlight during the totality as it was for 1998's. Visual observations made during each event, which show that at length only one or two bright stars could be seen in the sky, support the results obtained for both eclipses.     

Diurnal Atmospheric Extinction Over Oukaïmeden Observatory using IRIS Database: 1989–1997. Comparison With The Other IRIS Sites

In this work, we use data of nine years (1989 to 1997) at all IRIS sites (Culgoora, Kumbel, Oukaïmeden, Izaña, La Silla and Stanford, devoted to the study of the solar velocity oscillation) to study of diurnal atmospheric extinction coefficient behaviour at Oukaïmeden observatory and to compare it to the others. By this study, we can conclude that the mean extinction coefficient at Oukaimeden is around 0.120 mag airmass^-1. Besides, we show that the daily extinction coefficient varies under the influence of the seasonal effect. By the comparison of Oukaïmeden to the other sites, we showed that Oukaïmeden has a good photometric sky quality and constitutes a potential site for astronomical observations in the north hemisphere.     

Martian atmospheric and indigenous components of xenon and nitrogen in the Shergotty,Nakhla, and Chassigny group meteorites

Abstract— In a study of the isotopic signatures of trapped Xe in shock-produced glass of shergottites and in ALH 84001, we observe three components: (1) modern Martian atmospheric Xe that is isotopically mass fractionated relative to solar Xe, favoring the heavy isotopes, (2) solar-like Xe, as previously observed in Chassigny, and (3) an isotopically fractionated (possibly ancient) component with little or no radiogenic ¹²⁹Xe_rad. In situ-produced fission and spallation components are observed predominantly in the high-temperature steps. Heavy N signatures in ALH 84001, EET 79001 and Zagami reveal Martian atmospheric components. The low-temperature release of ALH 84001 shows evidence for the presence of a light N component (δ¹⁵N ≤ -21%), which is consistent with the component observed in the other Shergotty, Nakhla and Chassigny (SNC) group meteorites. The highest observed ¹²⁹Xe/¹³⁰Xe ratio of 15.60 in Zagami and EET 79001 is used here to represent the present Martian atmospheric component, and the isotopic composition of this component is compared with other solar system Xe signatures. The ¹²⁹Xe/¹³⁰Xe ratios in ALH 84001 are lower but appear to reflect varying mixing ratios with other components. The consistently high ¹²⁹Xe/¹³⁰Xe ratios in rocks of different radiometric ages suggest that Martian atmospheric Xe evolved early on. As already concluded in earlier work, only a small fission component is observed in the Martian atmospheric component. Assuming that a chondritic ²⁴⁴Pu/¹²⁹I initial ratio applies to Mars, this implies that either Pu-derived fission Xe is retained in the solid planet (in fact, in situ-produced fission Xe is observed in ALH 84001) or may reflect a very particular degassing history of the planet.     

On the instrumental and atmospheric stray-light for solar observations

From aureole measurements made with a 40 cm-Vacuum-Telescope at Izaña (Tenerife) in the wavelength region 417 nm < λ < 785 nm and from a comparison with other aureole measurements we conclude the following: (a) Within one solar radius from the limb, the aureole is mostly of instrumental origin, (b) Beyond that distance, the contribution of atmospheric stray-light becomes noticeable, (c) The atmospheric contribution to the aureole intensity is, under good conditions at mountain stations, a very slowly decreasing function, and amounts to some 10^?5 of the solar disk intensity. A procedure is given to separate the variable atmospheric component of the stray-light from the constant instrumental one.     

Determination of the solar X-ray spectrum by using the atmospheric extinction

Indications about the spectral distribution of the solar radiation below 20 Å are obtained by comparing the atmospheric extinction of the solar radiation measured by three ion chambers in the satellites SOLRAD 7 and 8.The data refer to July 5, 6 and 8, 1965 and July 23, 1966 when the satellites passed from light to darkness into or out of the earth's shadow.The spectral intensity distribution is shown for the four days, and a comparison is made between active and quiet days.     

The global oscillation network group site survey

The Global Oscillation Network Group (GONG) Project is planning to place a set of instruments around the world to observe solar oscillations as continuously as possible for at last three years. The Project has now chosen the sites that will comprise the network. This paper describes the methods of data collection and analysis that were used to make this decision.Solar irradiance data were collected with a one-minute cadence at fifteen sites around the world and analyzed to produce statistics of cloud cover, atmospheric extinction, and transparency power spectra at the individual sites. Nearly 200 reasonable six-site networks were assembled from the individual stations, and a set of statistical measures of the performance of the networks was analyzed using a principal component analysis. An accompanying paper presents the results of the survey.     

Revealing of periodicities in the variations of differential rotation of the Sun

It is presumed that a north-southern asymmetry of a solid-body rotation of large spots, depending on even and odd solar activity cycles (Gigolashvili and Khutsishvili 1 1989, 1990) may possibly be explained by the asymmetry of the appearance of large structures with strong magnetic fields in the corresponding hemispheres. Spectral analysis of the observational data shows the presence of cyclic variations of differential rotation of large- and middle-sized spots. Variations of differential rotation of small spots are either absent or overlapped by noise. It is also supposed that the discovered and most frequently realized component of the spectrum of solar differential rotation variations — a four-years periodicity — may be either a real phenomenon or the result of overlapping of multiple quasi bi-annual variations.     

The Application Of À Trous Wave Filtering And Monte Carlo Analysis On Secis 2001 Solar Eclipse Observations

Eight thousand images of the solar corona were captured during the June 2001 total solar eclipse. New software for the alignment of the images and an automated technique for detecting intensity oscillations using multi-scale wavelet analysis were developed. Large areas of the images covered by the Moon and the upper corona were scanned for oscillations and the statistical properties of the atmospheric effects were determined. The à Trous wavelet transform was used for noise reduction and Monte Carlo analysis as a significance test of the detections. The effectiveness of those techniques is discussed in detail.     

Solar astrometry by photolithography

Observed temporal variations of shape and size of the solar disk as viewed from Earth may act as constraints for theories of the interior of the Sun. In addition to existing programs of solar diameter measurements we investigate a ground-based photographic method.The solar limb profile is recorded on a photoresist-coated substrate over a 20 radial length simultaneously all along the circonference as a three-dimensional 21 mm diameter, 0.0015mm thick permanent object available for inspection by interferometric methods. The exposure time is long enough for filtering much of the atmospheric turbulence, whereas the slope of the observed solar limb should help to locate a standard solar limb. The first results of February 1989 at large zenith distance and low altitude are a set of differential measurements of the position of a solar limb around a circle with, after taking into account the 3.7 atmospheric differential refraction, a 0.34r.m.s. dispersion of the residuals for a fit to a circular solar disk.We estimate that this method of accuracy comparable to other ground-based methods, with potentially more than 600 independent simultaneous measurements along the circonference, could help to discriminate between terrestrial and solar causes for variations of shape and size of the solar disk.We note that operation outside the Earth's atmosphere would provide access not only to undisturbed images but also to UV wavelengths, i.e., to a better definition of the solar limb.     

Loss of water from Mars:: Implications for the oxidation of the soil

The evolution of the martian atmosphere with regard to its H₂O inventory is influenced by thermal loss processes of H, H₂, nonthermal atmospheric loss processes of H⁺, H₂⁺, O, O⁺, CO₂, and O₂⁺ into space, as well as by chemical weathering of the surface soil. The evolution of thermal and nonthermal escape processes depend on the history of the intensity of the solar XUV radiation and the solar wind density. Thus, we use actual data from the observation of solar proxies with different ages from the Sun in Time program for reconstructing the Sun's radiation and particle environment from the present to 3.5 Gyr ago. The correlation between mass loss and X-ray surface flux of solar proxies follows a power law relationship, which indicates a solar wind density up to 1000 times higher at the beginning of the Sun's main sequence lifetime. For the study of various atmospheric escape processes we used a gas dynamic test particle model for the estimation of the pick up ion loss rates and considered pick up ion sputtering, as well as dissociative recombination. The loss of H₂O from Mars over the last 3.5 Gyr was estimated to be equivalent to a global martian H₂O ocean with a depth of about 12 m, which is smaller than the values reported by previous studies. If ion momentum transport, a process studied in detail by Mars Express is significant on Mars, the water loss may be enhanced by a factor of about 2. In our investigation we found that the sum of thermal and nonthermal atmospheric loss rates of H and all nonthermal escape processes of O to space are not compatible with a ratio of 2:1, and is currently close to about 20:1. Escape to space cannot therefore be the only sink for oxygen on Mars. Our results suggest that the missing oxygen (needed for the validation of the 2:1 ratio between H and O) can be explained by the incorporation into the martian surface by chemical weathering processes since the onset of intense oxidation about 2 Gyr ago. Based on the evolution of the atmosphere-surface-interaction on Mars, an overall global surface sink of about 2×10⁴² oxygen particles in the regolith can be expected. Because of the intense oxidation of inorganic matter, this process may have led to the formation of considerable amounts of sulfates and ferric oxides on Mars. To model this effect we consider several factors: (1) the amount of incorporated oxygen, (2) the inorganic composition of the martian soil and (3) meteoritic gardening. We show that the oxygen incorporation has also implications for the oxidant extinction depth, which is an important parameter to determine required sampling depths on Mars aimed at finding putative organic material. We found that the oxidant extinction depth is expected to lie in a range between 2 and 5 m for global mean values.     

Observation of global 160-min infrared (differential) intensity variation of the Sun

The method developed and the instrument designed for detecting variations of the solar limb darkening at the atmospheric transparency window of the solar opacity minimum region of λ 1.65 μ are described. This differential technique proved to be successful in rejecting undesirable low frequency noises due to the atmosphere and to the instrument. Analysis of observations made in 1977, 1978, and 1981 indicates the persistance of global fluctuations of the IR differential, center-to-limb intensity at the wellknown 160 min period with an average amplitude of about ± 2 × 10^-4 in units of the ‘average Sun’ intensity near 1.65 μm.     

An analysis of the solar-activity effects in the upper atmosphere

A study of the upper-atmosphere variations induced by solar activity was made by using 29,574 densities derived from the drag of 10 satellites in the interval 1958–1971. In a comparison of the respective merits of the Ca II-plage index and the 10.7 cm solar flux to represent the erratic (‘27 day’) component of the variation, the latter is shown to give invariably better results. The ratio $\text{ΔT}\text{δF}$ of the temperature variations to the variations of the decimetric flux is shown to vary considerably with solar activity, but little with height or with local solar time. The time lag of the atmospheric variations behind those of the decimetric flux varies from a minimum of 0.9 day at noon to 1.6 days at midnight.     

New Measurements of the Solar Disk-Center Spectral Intensity in the Near IR from 645 Nm to 1070 Nm

At the high-altitude station on Terskol Peak (central Caucasus, 3100 m) by the Main Astronomical Observatory of the National Academy of Sciences of the Ukraine in 1992, spectral measurements of the solar disk-center intensity for the near IR region were performed. These measurements are a continuation of the solar absolute spectral energy distribution investigation programme. Data published earlier (Burlov-Vasiljev, Gurtovenko, and Matvejev, 1995a) are expanded now in the long-wave spectral region up to 1070 nm. The measurements were made with the specialized solar telescope SEF-1. The method of comparison of the solar disk-center brightness with the brightness of the calibrated region of a standard ribbon tungsten lamp was used. The atmospheric extinction was taken into account with Bouger's long method accompanied by the parallel-independent control of atmospheric stability. The uncertainty of the absolute solar disk-center intensity values is estimated to be 2% in regions free from the strong telluric absorption of atmosphere oxygen and water vapour. In these regions an additional reduction was carried out, which was derived from the synthetic atmospheric absorption spectra computed on the basis of the molecular parameter data and the standard model of the Earth's atmosphere. The 1-nm integrals of the disk-center radiance in the wavelength range 650–1070 nm, which are established on 5-day measurements in March–October 1992, are given. With the help of the solar disk-darkening coefficients, the solar flux values at 1 AU are available. The measured 1-nm integrals were used for the high-resolution solar spectral atlas calibration in order to locate the solar continuum in absolute units. A comparison is made of the data obtained with the data by Neckel and Labs (1984) and data of some other authors.     

Noble gas space exposure ages of individual interplanetary dust particles

Abstract— The He, Ne, and Ar compositions of 32 individual interplanetary dust particles (IDPs) were measured using low‐blank laser probe gas extraction. These measurements reveal definitive evidence of space exposure. The Ne and Ar isotopic compositions in the IDPs are primarily a mixture between solar wind (SW) and an isotopically heavier component dubbed “fractionated solar” (FS), which could be implantation‐fractionated solar wind or a distinct component of the solar corpuscular radiation previously identified as solar energetic particles (SEP). Space exposure ages based on the Ar content of individual IDPs are estimated for a subset of the grains that appear to have escaped significant volatile losses during atmosphere entry. Although model‐dependent, most of the particles in this subset have ages that are roughly consistent with origin in the asteroid belt. A short (<1000 years) space exposure age is inferred for one particle, which is suggestive of cometary origin. Among the subset of grains that show some evidence for relatively high atmospheric entry heating, two possess elevated ²¹Ne/²²Ne ratios generated by extended exposure to solar and galactic cosmic rays. The inferred cosmic ray exposure ages of these particles exceeds 10⁷ years, which tends to rule out origin in the asteroid belt. A favorable possibility is that these ²¹Ne‐rich IDPs previously resided on a relatively stable regolith of an Edgeworth‐Kuiper belt or Oort cloud body and were introduced into the inner solar system by cometary activity. These results demonstrate the utility of noble gas measurements in constraining models for the origins of interplanetary dust particles.     

Three-component dust models for interstellar extinction

Interstellar extinction curves obtained from the ‘extinction without standard’ method were used to constrain the dust characteristics in the mean ISM (R _V = 3.1), along the lines of sight through a high latitude diffuse molecular cloud towards HD 210121 (R _V = 2.1) and in a dense interstellar environment towards the cluster NGC 1977 (R _V = 6.42). We have used three-component dust models comprising silicate, graphite and very small carbonaceous grains (polycyclic aromatic hydrocarbons) following the grain size distributions introduced by Li & Draine in 2001. It is shown that oxygen, carbon and silicon abundances derived from our models are closer with the available elemental abundances for the dust grains in the ISM if F & G type stars atmospheric abundances are taken for the ISM than the solar. The importance of very small grains in modelling the variation of interstellar extinction curves has been investigated. Grain size distributions and elemental abundances locked up in dust are studied and compared at different interstellar environments using these three extinction curves. We present the albedo and the scattering asymmetry parameter evaluated from optical to extreme-UV wavelengths for the proposed dust models.     

The frequency composition of the Madden-Julian oscillation. An indication of the solar activity contribution to the global atmospheric circulation and the Earth's rotation

In the series of the solar activity indices, the zonal component of the atmospheric momentum (AAM), and the Earth rotation variations (UT1-TAI), power spectra concentrations at 40, 50, and 60–80 day period are detected. This result indicates the solar origin of the Madden-Julian oscillation in atmospheric circulation and the 50-day oscillation of the Earth's rotation.     

A New Analysis of the Spectra Obtained by the <Emphasis Type="Italic">Venera</Emphasis> Missions in the Venusian Atmosphere. I. The Analysis of the Data Received from the <Emphasis Type="Italic">Venera-11</Emphasis> Probe at Altitudes Below 37 km in the 0.44–0.66 µm Wavelength Range

The processes of the solar radiation extinction in deep layers of the Venus atmosphere in a wavelength range from 0.44 to 0.66 µm have been considered. The spectra of the solar radiation scattered in the atmosphere of Venus at various altitudes above the planetary surface measured by the Venera-11 entry probe in December 1978 are used as observational data. The problem of the data analysis is solved by selecting an atmospheric model; the discrete-ordinate method is applied in calculations. For the altitude interval from 2–10 km to 36 km, the altitude and spectral dependencies of the volume coefficient of true absorption have been obtained. At altitudes of 3–19 km, the spectral dependence is close to the wavelength dependence of the absorption cross section of S₃ molecules, whence it follows that the mixing ratio of this sulfur allotrope increases with altitude from 0.03 to 0.1 ppbv.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 4, 2005, pp. 304–320.Original Russian Text Copyright © 2005 by Maiorov, Ignat’ev, Moroz, Zasova, Moshkin, Khatuntsev, Ekonomov.     

Atmospheric transparency over Mount Shatdzhatmaz in the optical and near-infrared ranges

We present the results of a three-year-long monitoring of atmospheric extinction over Mount Shatdzhatmaz (2112 m) in Northern Caucasus in a photometric band with λ _eff = 480 nm and the results of measurements of precipitable water vapor (PWV), which characterizes the atmospheric transparency in the near infrared. The yearly mean fraction of photometric weather is estimated to be 50% of the clear night time. The yearly median extinction is 0ṃ21; themedian PWV on clear nights is 7.7 mm.     

Applicability of Broad-Band Photometry for Determining the Properties of Stars and Interstellar Extinction

The feasibility of the determination of the physical conditions in star’s atmosphere and the parameters of interstellar extinction from broad-band photometric observations in the 300–3000 nm wavelength interval is studied using SDSS and 2MASS data. The photometric accuracy of these surveys is shown to be insufficient for achieving in practice the theoretical possibility of estimating the atmospheric parameters of stars based on ugriz and JHK_s photometry exclusively because such determinations result in correlations between the temperature and extinction estimates. The uncertainty of interstellar extinction estimates can be reduced if prior data about the temperature are available. The surveys considered can nevertheless be potentially valuable sources of information about both stellar atmospheric parameters and the interstellar medium.