Showing papers by "Smithsonian Astrophysical Observatory published in 1977"
TL;DR: In this paper, it was suggested that the explosion of a Type II supernova triggered the collapse of a nearby interstellar cloud and led to the formation of the solar system, and the abundances resulting from nuclear processing of the supernova ejecta were presented.
432 citations
15 Mar 1977
TL;DR: In this paper, a set of formulae were proposed to compute the exospheric temperature and the expected deviations from the static models as a result of all the recognized types of thermospheric variation.
Abstract: The models essentially consist of two parts: the basic static models, which give temperature and density profiles for the relevant atmospheric constituents for any specified exospheric temperature, and a set of formulae to compute the exospheric temperature and the expected deviations from the static models as a result of all the recognized types of thermospheric variation. For the basic static models, tables are given for heights from 90 to 2,500 km and for exospheric temperatures from 500 to 2600 K. In the formulae for the variations, an attempt has been made to represent the changes in composition observed by mass spectrometers on the OGO 6 and ESRO 4 satellites.
389 citations
TL;DR: In this paper, changes in the level of solar activity and in climate are found in historical records and in fossil radiocarbon in tree-rings, and they are compared with a record of world climate, showing that when longterm solar activity falls, mid-latitude glaciers advance and climate cools; at times of high solar activity glaciers recede and climate warms.
Abstract: Long-term changes in the level of solar activity are found in historical records and in fossil radiocarbon in tree-rings. Typical of these changes are the Maunder Minimum (A.D. 1645–1715), the Sporer Minimum (A.D. 1400–1510), and a Medieval Maximum (c. A.D. 1120–1280). Eighteen such features are identified in the tree-ring radiocarbon record of the past 7500 years and compared with a record of world climate. In every case when long-term solar activity falls, mid-latitude glaciers advance and climate cools; at times of high solar activity glaciers recede and climate warms. We propose that changes in the level of solar activity and in climate may have a common cause: slow changes in the solar constant, of about 1% amplitude.
306 citations
TL;DR: In this article, the morphology of limb flares is investigated and the observed spatial structure is related with the other physical parameters of the region (temperature, density, characteristic times, and energy density).
Abstract: The data used in the investigation were obtained by the American Science and Engineering S-054 experiment on board Skylab. The instrument employed was a grazing incidence X-ray telescope which records images of the sun on film. The morphology of limb flares is investigated and the observed spatial structure is related with the other physical parameters of the region (temperature, density, characteristic times, and energy density). It is concluded that two physically distinct classes of flares exist that differ both in their morphology and in the physical properties which characterize the emitting regions.
289 citations
TL;DR: In this paper, the relativistic random-phase approximation (RRPA) is applied to study radiative transitions from $n=2$ states along the He isoelectronic sequence.
Abstract: The relativistic random-phase approximation (RRPA) is applied to study radiative transitions from $n=2$ states along the He isoelectronic sequence. The strengths of various decay modes and the energy splittings of the $n=2$ multiplets are investigated. At low $Z$ the present results agree with earlier nonrelativistic studies, whereas, at high $Z$ our results provide new information about oscillator strengths, branching ratios, and multiplet structure for the $n=2$ states.
199 citations
TL;DR: Open magnetic field lines, those which extend from the solar photosphere to interplanetary space, are traced in the current-free approximation using measured photospheric fields as a boundary condition as discussed by the authors.
Abstract: Open magnetic field lines, those which extend from the solar photosphere to interplanetary space, are traced in the current-free (potential field) approximation using measured photospheric fields as a boundary condition. It is found that (1) only a relatively small fraction of the photospheric area connects via open field lines to the interplanetary magnetic field; (2) those photospheric areas which do contribute open field lines lie beneath coronal holes and within the boundaries of the holes as projected onto the photosphere or else between loop systems of an active region; (3) the interplanetary magnetic field in the plane of the sun's equator, essentially the field in the ecliptic plane, may connect to photospheric regions of high latitude; and (4) the fastest solar wind streams are correlated with those magnetic flux tubes which expand least in cross-sectional area over the distance between the photosphere and the coronal height where the solar wind begins.
191 citations
TL;DR: In this paper, the current-free magnetic field of the solar corona and the reliability of the spherical harmonic analysis of the photospheric magnetic field pattern are improved by data with much greater dynamic range and spatial resolution than previously available and a new algorithm which permits spherical harmonic expansion to a much higher value of the principal index.
Abstract: The mapping of the current-free magnetic field of the solar corona and the reliability of the spherical harmonic analysis of the photospheric magnetic field pattern are improved by data with much greater dynamic range and spatial resolution than previously available and a new algorithm which permits spherical harmonic expansion to a much higher value of the principal index. Coronal field maps can be drawn for local regions, for just the open field lines, and for various spatial resolutions on a global scale.
150 citations
TL;DR: In this paper, the properties of X-ray bright points (XBP) and ephemeral active regions (ER) are compared using high-resolution Kitt Peak National Observatory magnetograms and sequences of simultaneous S-054 soft Xray solar images.
Abstract: Using high-resolution Kitt Peak National Observatory magnetograms and sequences of simultaneous S-054 soft X-ray solar images, the properties of X-ray bright points (XBP) and ephemeral active regions (ER) are compared. All XBP appear on the magnetograms as bipolar features, except for very recently emerged or old and decayed XBP. The separation of the magnetic bipoles is found to increase with the age of the XBP, with an average emergence growth rate of 2.2 plus or minus 0.4 km per sec. The total magnetic flux in a typical XBP living about 8 hr is found to be about two times ten to the nineteenth power Mx. A proportionality is found between XBP lifetime and total magnetic flux, equivalent to about ten to the twentieth power Mx per day of lifetime.
147 citations
TL;DR: In this article, the authors used high-resolution harmonic analysis of the solar magnetic field to calculate the geometry of open magnetic field lines in the solar corona and found that a significant part of the area of coronal holes must contain closed magnetic fields.
Abstract: High-resolution harmonic analysis of the solar magnetic field has been used succesfully to calculate the geometry of open magnetic field lines in the solar corona. Comparison of the loci of open-field-line footpoints with solar X-ray photographs shows that all the coronal holes during two solar rotations are successfully represented, including details of their evolution. Some open magnetic configurations derived in the calculations precede by up to one solar rotation the manifestation of coincident dark areas on the X-ray photographs. The only other areas that contribute open field lines to the corona are separations between active-region loop systems. By varying the radius at which field lines are forced to be open in the calculation, it is possible to reproduce more closely the surface configuration of particular coronal holes. Comparison of the size of X-ray holes with the fraction of the solar surface covered by open field lines leads to the conclusion that a significant part of the area of coronal holes must contain closed magnetic fields. Comparison of open field lines which lie in the equatorial plane of the sun with solar-wind data indicates that eventual high-speed solar-wind streams are associated with those parts of open magnetic structures that diverge the least.
97 citations
TL;DR: The Harvard College Observatory instrument on the Skylab was a seven-channel spectrometer-spectroheliometer operating in the 280-1340-A wavelength range and capable of a variety of observing modes encompassing both spatial and spectral scans of a wide range of solar features.
Abstract: The extreme UV spectroheliometer flown on ATM observed within the 280-1340 A spectral range at seven wavelengths simultaneously, with a spatial resolution element 5 x 5 sq arcsec field of view in 5.5 min. The instrument could also obtain spectral scans over the same wavelength range with a spectral resolution of 1.6 A in 3.8 min. The instrument is described in detail with attention given to the telescope, the spectrometer, and the detection system.
96 citations
01 Jan 1977
TL;DR: The early intense bombardment of the moon has not necessarily gardened most of the crust to more than a few kilometers depth Deep crustal material sampled by the largest impacts is most likely to be preserved as melt-rock deposits on or near the rims of mare basins.
Abstract: The early intense bombardment of the moon has not necessarily gardened most of the crust to more than a few kilometers depth Deep crustal material sampled by the largest impacts is most likely to be preserved as melt-rock deposits on or near the rims of mare basins The Apollo 17 melt-rock boulders and the matrices of the Apollo 15 'black-and-white' rocks (15445, 15455) are considered the most likely of all lunar samples to represent deep crustal material These samples have the composition of low-K Fra Mauro (LKFM) basalt A two- or three-layer crustal model is proposed, in which a layer of anorthositic gabbro, which forms most of the exposed surface of the lunar highlands, is underlain by a layer of LKFM basalt If the Apollo 15 and 17 heat-flow measurements are representative of the mean lunar heat flow, they constrain the LKFM layer to be no more than 20 km thick
TL;DR: In this article, three polar plumes were studied using Skylab Mg x and O vi data and the mean temperature of the plumes is about 1.1 × 106 K and they have a small vertical temperature gradient.
Abstract: Three polar plumes were studied using Skylab Mg x and O vi data. The plumes lie within the boundaries of a polar coronal hole. We find that the mean temperature of the plumes is about 1.1 × 106 K and that they have a small vertical temperature gradient. Densities are determined and found consistent with white light analyses. The variation of density with height in the plumes is compared with that expected for hydrostatic equilibrium. As is the case for other coronal features, polar plumes will be a source of solar wind if the magnetic field lines are open. On the basis of the derived plume model and estimates of the numbers of plumes in polar coronal holes, it appears that polar plumes contain about 15% of the mass in a typical polar hole and occupy about 10% of the volume.
TL;DR: In this article, the authors investigated the structure of active region loops and made estimates of the energy necessary to form and maintain the loops, and of the relative importance of radiation and thermal conduction as energy loss mechanisms.
Abstract: The structure of the active region loops is investigated by the study of a loop complex which undergoes a dramatic evacuation of most of the mass it contains. The need for continual energy deposition in loops is emphasized by the apparent cessation of energy input to the loops studied and their subsequent behavior. Estimates are made of the energy necessary to form and to maintain the loops, and of the relative importance of radiation and thermal conduction as energy loss mechanisms. Models based on the observed EUV emission are used to place limits on the size of loops seen in various lines and on the density and temperature structure. It is found that the cool cores of active region loops are likely to be no more than a few hundred kilometers in radius and that several such cool threads may be imbedded in a common hot outer sheath. The primary energy loss on a large scale is radiation with thermal conduction contributing to local disturbances. There is a tendency for the development of apparently unstable condensations or knots along the length of a loop.
TL;DR: The overall objective of this experiment is exploratory reconnaissance of Jupiter, Saturn, their satellites, and Saturn's rings as discussed by the authors, at resolutions and phase angles unobtainable from Earth, can be expected to provide much new data relevant to the atmospheric and/or surface properties of these bodies.
Abstract: The overall objective of this experiment is exploratory reconnaissance of Jupiter, Saturn, their satellites, and Saturn's rings. Such reconnaissance, at resolutions and phase angles unobtainable from Earth, can be expected to provide much new data relevant to the atmospheric and/or surface properties of these bodies. The experiment also has the following specific objectives:
TL;DR: In this article, the rotational spectrum of CH3CH2CN has been measured at frequencies above 41 GHz to derive precise radial velocities from the astronomical data, and a laboratory measurement of the rotation spectrum of ethyl cyanide has been made.
Abstract: Twenty-four millimeter-wave emission lines of ethyl cyanide (CH3CH2CN) have been detected in the Orion Nebula (OMC-1) and seven in Sgr B2. To derive precise radial velocities from the astronomical data, a laboratory measurement of the rotational spectrum of ethyl cyanide has been made at frequencies above 41 GHz. In OMC-1, the rotational temperature of ethyl cyanide is 90 K (in good agreement with other molecules), the local-standard-of-rest radial velocity is 4.5 + or - 1.0 km/s (versus 8.5 km/s for most molecules), and the column density is 1.8 by 10 to the 14th power per sq cm (a surprisingly high figure for a complicated molecule). The high abundance of ethyl cyanide in the Orion Nebula suggests that ethane and perhaps larger saturated hydrocarbons may be common constituents of molecular clouds and have escaped detection only because they are nonpolar or only weakly polar.
TL;DR: The derivation of the preflight photometric calibration of the uv spectrometer on Skylab is described, and an uncertainty of +/-35% is assigned over most of the 296-1340-A wavelength range.
Abstract: This paper describes the derivation of the preflight photometric calibration of the UV spectrometer on Skylab. The calibration of the orbiting instrument through cross-comparison with two rocket instruments is discussed in assessing the observed changes in response to quiet solar regions during the mission. Formulas are presented for the determination of the instrument sensitivity, and an uncertainty of plus or minus 35% is assigned over most of the 296-1340-A wavelength range.
TL;DR: In this article, the relativistic random-phase approximation is used to calculate the excitation energies and absorption oscillator strengths for the 3s/sup 2/ /sup 1/S/sub 0/-3s3p /sup1/P/sub 1/, -3s4p 1/P 1/sub 2/P 2/S 1/1/sub 3/s 3p/sub
Abstract: The relativistic random-phase approximation is used to calculate the excitation energies and absorption oscillator strengths for the 3s/sup 2/ /sup 1/S/sub 0/-3s3p /sup 1/P/sub 1/, -3s4p /sup 1/P/sub 1/, -3s5p /sup 1/P/sub 1/, and -3s3p /sup 3/P/sub 1/ transitions of selected elements of the magnesium isoelectronic sequence through nuclear charge Z = 92. The results are compared with previous theoretical and experimental values. The data, plotted as a function of Z/sup -1/ enable us to study deviations from the predictions of the nonrelativistic Z-expansion theory.
TL;DR: In this paper, the frequencies of 46 CW laser lines with wavelengths between 0.1 and 0.7 mm have been measured by heterodyne methods, with threshold pump powers of 3 W or less.
Abstract: The frequencies of 46 CW laser lines commonly used for submillimeter spectroscopy, with wavelengths between 0.1 and 0.7 mm, have been measured by heterodyne methods. All the fines are optically pumped by a CO 2 laser, with threshold pump powers of 3 W or less. The precision of measurement, limited by the laser linewidth, is typically ± 1 part per million.
TL;DR: In this article, a coronal hole made with the EUV spectroheliometer of the Harvard College aboard Skylab and with high resolution (2-4′) radio telescopes at Culgoora and Fleurs Australia and Bonn, West Germany is presented.
Abstract: We present observations of a coronal hole made with the EUV spectroheliometer of the Harvard College aboard Skylab and with ‘high resolution’ (2–4′) radio telescopes at Culgoora and Fleurs Australia and Bonn, West Germany. We attempt to derive the density and temperature distributions in the transition region and inner corona from the combined observations. No one ‘standard’ model can explain both sets of observations; characteristically, models based on EUV data yield higher radio brightnesses than are observed, while models based on radio data yield lower EUV line intensities than are observed. The discrepancy is essentially that the electron density inferred from the EUV data is about three times that inferred from the radio data.
TL;DR: In this article, the relativistic random phase approximation of the inner shells of the beryllium isoelectronic sequence was used to calculate the oscillator strength for high-Z elements.
Abstract: Oscillator strengths for the outer shells of the beryllium isoelectronic sequence are obtained using the relativistic random phase approximation in which the relativistic effects are included nonperturbatively. The results agree well with other accurate calculations that have been carried out for low-Z elements. For high-Z elements, our results should be very reliable. Both length and velocity formulas are used to calculate the oscillator strengths. The velocity formula is very sensitive to the weak inner-shell coupling, whereas the length formula is not. Inner-shell excitation energies and oscillator strengths are examined and compared with the helium isoelectronic sequence to show the effect of outer-shell screening.
TL;DR: In this article, a model potential method is used to calculate the potential curves of a large number of states of the lithium molecule and comparisons are made with other theoretical and experimental data.
TL;DR: In this paper, the relative motion of two fragments of a split comet is interpreted in terms of a slight difference between their effective solar attraction rather than the impulse imparted to them at separation.
TL;DR: An analysis of density measurements of Ar, N2, O, and He made at 280 km with the gas analyzer aboard the polar-orbiting satellite Esro 4 has yielded a global model of the variations in temperature, density, and composition that occur in the disturbed thermosphere.
Abstract: An analysis of density measurements of Ar, N2, O, and He made at 280 km with the gas analyzer aboard the polar-orbiting satellite Esro 4 has yielded a global model of the variations in temperature, density, and composition that occur in the disturbed thermosphere. In the model the increase of temperature over quiet conditions is a nonlinear function of the planetary geomagnetic index, its latitude profile being approximated by a fourth-power sin phi law, where phi is the 'invariant' magnetic latitude. A density wave proceeding from high latitudes is approximated by a fourth power cos phi law. A strong nonlinearity in the relation between the temperature variations and the variations in the height of the homopause explains a previously found behavioral difference in the variation of atomic oxygen during magnetic storms and during periods of sustained geomagnetic activity.
TL;DR: In this article, the available measurements of the solar constant made at ground sites and from recent space observations to determine whether sunspots or faculae produce a detectable modulation of either the solar flux or the earth's atmospheric transmission were studied.
Abstract: We study the available measurements of the solar constant made at ground sites and from recent space observations to determine whether sunspots or faculae produce a detectable modulation of either the solar flux or the earth's atmospheric transmission. The data from radiometers on Mariners 6 and 7 rule out any relative change of the solar constant in space due directly to faculae or spots exceeding 0.03%. This limit is two orders of magnitude smaller than previous values obtained from ground measurements. The measurements made at mountain stations of the Smithsonian Astrophysical Observatory between 1923 and 1952 show a marginally significant increase of solar constant at the level of 0.1%, related specifically to high projected facular area. Since this increase is not seen in the space measurements, we suggest that it may reflect a change in the earth's atmospheric transmission, possibly due to a change in ozone concentration induced by variation of facular ultraviolet radiation.
TL;DR: In this article, high-resolution harmonic analysis of the measured photospheric magnetic field of the sun is used to construct models of open magnetic structures over a period of 11 solar rotations.
Abstract: High-resolution harmonic analysis of the measured photospheric magnetic field of the sun is used to construct models of open magnetic structures over a period of 11 solar rotations. The models successfully reproduce the surface location and topology of all coronal holes during the Skylab period. In addition, there is persistent evidence in the models that open field lines are associated with active regions in a systematic way. These associations are listed for the period studied; they suggest that open field lines are a basic feature of solar magnetism. Specific examples of the evolution of coronal holes and of calculated open structures are presented. Quantitative study of the measured field strength within and neighboring a hole confirms the fact that coronal hole regions are indistinguishable by local magnetic properties. However, the calculated field strengths at the footpoints of open field lines within coronal holes show distinct evolutionary patterns and may indicate that, at least in young coronal holes, a significant amount of magnetic flux is closed. Problems of studying magnetic field divergence by using these models are discussed.
01 Jul 1977
TL;DR: In this paper, a third-order solution for the motions of artificial satellites moving in the gravitational field of the Earth, whose potential includes the second-, third-, and fourth-order zonal harmonics, was developed.
Abstract: A third-order solution is developed for the motions of artificial satellites moving in the gravitational field of the Earth, whose potential includes the second-, third-, and fourth-order zonal harmonics. Third-order periodic perturbations with fourth-order secular perturbations are derived by Hori’s perturbations method. All quantities are expanded into power series of the eccentricity, but the solution is obtained so as to be closed with respect to the inclination. A comparison with the results of numerical integration of the equations of motion indicates that the solution can predict the position of a close-earth satellite with a small eccentricity with an accuracy of better than 1 cm over 1 month.
TL;DR: In this article, the relativistic random-phase approximation of the resonance transitions of elements of the zinc isoelectronic sequence was used to estimate the oscillator strength as a function of the inverse nuclear charge.
Abstract: Excitation energies, oscillator strengths, and transition probabilities for the $4{s}^{2}^{1}S_{0}\ensuremath{-}4s4p^{1}P_{1}$, $4{s}^{2}^{1}S_{0}\ensuremath{-}4s5p^{1}P_{1}$, and $4{s}^{2}^{1}S_{0}\ensuremath{-}4s6p^{1}P_{1}$ resonance transitions of elements of the zinc isoelectronic sequence are calculated using the relativistic random-phase approximation. The elements considered range from Gaii to Ulxiii and include many of interest in current fusion research. A graphical analysis of the systematic trends of the oscillator strength as a function of the inverse nuclear charge provides a means of estimating the oscillator strengths for those elements whose values are not explicitly calculated.
TL;DR: In this paper, the chemical abundance of boron in the photosphere is derived from photoelectric measurements of the solar spectrum near 2500 A obtained with a rocketborne high-resolution spectrometer.
Abstract: Positive evidence for the presence of boron in the sun is reported, and the chemical abundance of boron in the photosphere is derived from photoelectric measurements of the solar spectrum near 2500 A obtained with a rocketborne high-resolution spectrometer. Short sections of the spectrum in the vicinities of the B I lines at 2496.772 and 2497.723 A are plotted. The photospheric boron abundance is determined primarily by analyzing the solar-center spectrum near the first of the two lines in the framework of several single-component photospheric models. The logarithmic boron abundance obtained is 2.6, with an estimated uncertainty of plus or minus 0.3 dex, on the scale where that of hydrogen is 12.0. This value is shown to be in excellent agreement with that predicted for a nucleosynthesis model in which Li, Be, and B are produced by cosmic-ray spallation.
TL;DR: In this article, the green line emission from atomic oxygen was measured by a satellite-borne photometer and showed consistently larger volume emission rates in the evening than at comparable solar zenith angles in the morning.
Abstract: Measurements of the green line emission from atomic oxygen by a satellite-borne photometer show consistently larger volume emission rates in the evening than at comparable solar zenith angles in the morning between altitudes of 150 and 200 km. The temporal variation in the airglow is consistent with diurnal model calculations if we assume that the reaction N + O2+ → NO+ + O(¹S) provides a significant source for the green line, O(¹D−1S).
TL;DR: In this article, the authors separated the inner corona features into two sharply different components, including the strongly reduced emission areas or coronal holes (CH) and the extended regions of looplike emission features or large-scale structures (LSS).
Abstract: In connection with high-quality solar soft X-ray images the 'quiet' features of the inner corona have been separated into two sharply different components, including the strongly reduced emission areas or coronal holes (CH) and the extended regions of looplike emission features or large-scale structures (LSS). Particular central meridian passage observations of the prominent CH1 on August 21, 1973, are selected for a quantitative study. Histogram photographic density distributions for full-disk images at other central meridian passages of CH 1 are also presented, and the techniques of converting low photographic density data to deposited energy are discussed, with particular emphasis on the problems associated with the CH data.