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.     

On the influence of seeing on photospheric velocity measurements

It is shown that the short-period fluctuations of photospheric velocity records can be explained by the scanning effect of atmospheric seeing (image motion) and the velocity gradients present on the solar surface. Some observations supporting this explanation are presented.Mitteilungen aus dem Fraunhofer Institut Nr. 76.     

On the use of mosaic direct-vision prism for radial velocity measurements

Mosaic direct-vision objective prisms satisfy the three conditions necessary for a whole-sky survey of spectroscopic binaries and short-period variables. We point out that the use of rectangular component prisms instead of square ones may cut by half the light loss caused by frame obstruction. The portion of the aperture not covered by the prism can be used to produce a direct image which can serve as a reference point in the spectral line measurement, thus dispensing with any rotating mechanism.     

Energy fluxes of the (1,1,1) atmospheric oscillation

The global mean vertical energy flux of the (1,1,1) mode of atmospheric oscillation is evaluated at 80 km altitude by classical tidal theory for mean January, April, July and October conditions using revised profiles of water vapour and ozone heating. Fluxes calculated for January and July are lower than those for April and October due to seasonal changes in water vapour, solar declination and Sun-Earth distance. Flux values obtained are compared with a previously stated requirement for maintaining the residual thermosphere and are adequate unless damping, which is ignored in the present calculations, introduces a factor of more than an order of 10 in magnitude. The relative changes of flux between the above four months are noted to be similar in form to the semi-annual variation of thermospheric air densities.     

Measurements of the light flash produced by high velocity particle impact

The impact light flash produced by electrostatically accelerated iron particles with diameters meters ranging from 5 to 0.05 μm and velocities lying between 1 km/sec and 30 km/sec has been investigated by means of photomultipliers. As target materials mainly gold and tungsten were used. The pulse of the multiplier was registered directly and after electronic integration. The pulse height of the multiplier signal, the amplitude of the integrated signal as well as its rise time were found to be unique functions of the mass and velocity of the impacting particle. For the pulse height of the differential signal the relation I = c₁ × m^1.25 × v⁵ was obtained, and for the integrated signal the relation I = c₂ × m^1.25 × v^3.8, with only c₁ and C₂ depending on the target material. The rise time of the integrated signal follows the relation T = 2.2 × 10² × v^?0.4 using gold as target, and in the case of tungsten material follows the relation T = 9.8 × 10² × v^?1.2, where v is expressed in km/sec and T in μsec. Using the spectral distribution of the light intensity, measured by means of calibrated photomultipliers, the total amount of light energy emitted in the visible range could be calculated. As a result we obtained that for v = 4 km/sec and m = 10^?11 g about 3 × 10^?4 of the kinetic energy of the particle was converted into light energy. The variation of the impact flash intensity with the target material and the measured spectral distribution allowed the temperature of the crater after the impact to be estimated as between 2000 and 3000 K.     

On the accuracy of line-of-sight velocity measurements using telluric lines as reference lines

It is demonstrated that telluric lines H₂O and O₂ are displaced as much as 0.2 mÅ as the solar disk is being scanned. The temporal variations of such displacements have a quasi-periodic character.     

Emission line shapes produced by dissociative excitation of atmospheric gases

Special line shapes are derived fro the λ 1356 Å (${}^5\text{S}{}^0\text{-}{}^3\text{P}$) transition of atomic oxygen from metastable (${}^5\text{S}{}^0\text{-}{}^3\text{P}$) time-of-flight spectra produced by electron impact dissociative excitation of O₂, CO₂, CO, and NO, and they are compared with the broadened λ 1304 A resonance line shapes deduced by Poland and Lawrence (1973) from atomic oxygen absorption studies. The non-thermal line shapes for both airglow emission features are shown to have an effective width comparable to a 60,000 K thermal doppler line shape for an electron impact energy of 100eV. The variation of the effective line width with electron-impact energy from threshold to 300 eV is given. Since the effective line width of the resonance radiation produced by dissociative excitation is very large compared with the doppler absorption widths of the ambient O atoms at normal exospheric temperatures, the anomalously broadened resonance lines will propagate through a planetary atmosphere as though they were optically thin. Thus, electron-impact dissociation of CO and CO₂ will contribute to the observed optically thin component of the λ 1304 Å emission in the upper atmospheres of Venus and Mars. However, the process cannot account for more than 10% of the observed optically thin emission because of the small magnitude of the excitation cross-section and the comparatively high-energy threshold for the process. The possibility that the source of the kinetically energetic $\text{O}\text{(}{}^3\text{S}$) atoms is the dissociative recombination of vibrationally excited CO₂⁺ ions is discussed.     

Interferometric phase velocity measurements in the auroral electrojet

A double-probe electric field detector and two spatially separated fixed-bias Langmuir probes were flown on a Taurus-Tomahawk sounding rocket launched from Poker Flat Research Range in March 1982. Interesting wave data have been obtained from about 10s of the downleg portion of the flight during which the rocket passed through the auroral electrojet. Here the electric field receiver and both density fluctuation (δn/n) receivers responded to a broad band of turbulence centered at 105 km altitude and at frequencies generally below 4 kHz. Closer examination of the two (δn/n) turbulent waveforms reveals that they are correlated, and from the phase difference between the two signals, the phase velocity of the waves in the rocket reference frame is inferred. The magnitude and direction of the observed phase velocity are consistent either with waves which travel at the ion sound speed (C_s) or with waves which travel at the electron drift velocity. The observed phase velocity varies by about 50% over a 5 km altitude range—an effect which probably results from shear in the zonal neutral wind, although unfortunately no simultaneous neutral wind measurements exist to confirm this.     

On atmospheric wave generation by the terminator

The dominant response of the terminator is found to be due to the change in thermospheric absorption of solar radiation, and leads to two types of atmospheric waves: (i) a ducted acoustic wave at altitudes below 100 km and (ii) a boundary wave concentrated along the mesopause.     

Global oscillation measurements at Kumbel station in frame of the IRIS programme

The second of the IRIS network instruments was commissioned in August 1988 at Kumbel mountain, located 75 km from Tashkent (U.S.S.R.). Atmospheric and operating conditions on Kumbel are discussed, as well as preliminary results derived from this station's global solar oscillation measurements.     

On the supernova remnants produced by pulsars

We conclude that pulsar-driven supernova remnants (SNRs) are extremely rare objects. Indeed an analysis of the known sample of plerions suggests a very low birthrate ∼ 1 in 240 years. Long-lived and bright plerions like the Crab nebula are likely to be produced only when the pulsar has an initial period ∼ 10–20 milliseconds and a field ∼ 10¹² G. Such pulsars inside rapidly expanding shell remnants should also produce detectable plerions. The extreme rarity of SNRs with such hybrid morphology leads us to conclude that these pulsars must have been born with an initial period larger than ∼ 35–70 milliseconds. Joint Astronomy Program, Department of Physics, Indian Institute of Science, Bangalore 560012.     

A 3-dimensional calculation of the atmospheric neutrino fluxes

An extensive 3-dimensional Monte Carlo calculation of the atmospheric neutrino flux is in progress with the FLUKA Monte Carlo code. The results are compared to those obtained under the 1-dimensional approximation, where secondary particles and decay products are assumed to be collinear to the primary cosmic ray, as usually done in most of the already existing flux calculations. It is shown that the collinear approximation gives rise to a wrong angular distribution of neutrinos, essentially in the Sub-GeV region. However, the angular smearing introduced by the experimental inability of detecting recoils in neutrino interactions with nuclei is large enough to wash out, in practice, most of the differences between 3-dimensional and 1-dimensional flux calculations. Therefore, the use of the collinear approximation should not have introduced a significant bias in the determination of the flavor oscillation parameters in current experiments.     

On the extinction law in the Carina nebula

Using the results of observations of the Carina nebula made with the space telescope Glazar, it is shown that the extinction law for the nebula is abnormal and that there is a single OB star complex within the nebula at a distance of about 2200 pc. It is suggested that the observed distribution of OB stars in the nebula and also the appearance of the nebula itself is due to a specific structure of the absorbing clouds within the nebula, and that the absorbing clouds may have such structure as a result of an explosion in the center of the nebula.     

Relation between the mode of oscillation and the velocity amplitude of chromospheric waves

The distribution of oscillation-amplitude for Doppler shifts in chromospheric lines is computed as a function of position on the disk and time frequency. High amplitude regions are restricted to a small part of the solar surface. Propagation modes are investigated with respect to the oscillation amplitude in the K line. Waves seem to be standing or evanescent for most of the points (small amplitude in K) and progressive for some other ones, with perhaps upward and downward motions (partial reflections). Mechanical energy could only escape into corona from narrow chromospheric structures.     

Test of a differential photometer for extinction gradient correction in full-disk helioseismology

The ground based full disk velocity Doppler measurements used in helioseismology suffer from an atmospheric noise component when the sky transparency is not perfect. It is due to the non uniform integration of the line of sight component of the solar rotation produced by the differential atmospheric extinction across the direction of the solar equator. A simple two-channel differential photometer is proposed for measuring this differential extinction. The first laboratory tests of this instrument show that it has the capability of performing the required correction without adding a significant level of new instrumental noise contribution.

     

New indications of the 4-month oscillation in solar activity,atmospheric circulation and Earth's rotation

The 4-month oscillation, detected earlier by the same authors in geophysical and solar data series, is now confirmed by the analysis of other observations. In the present results the 4-month oscillation is better emphasized than in previous results, and the analysis of the new series confirms that the solar activity contribution to the global atmospheric circulation and consequently to the Earth's rotation is not negligeable. It is shown that in the effective atmospheric angular momentum and Earth's rotation, its amplitude is slightly above the amplitude of the oscillation known as the Madden-Julian cycle.     

On the dipolar f mode of stellar oscillation

The classification of adiabatic modes of non-radial stellar oscillation was established by Cowling in 1941. In addition to acoustic and gravity modes he identified an intermediate mode, which he labelled the f mode, and which in simple stellar models has no radial node. The motion of a dipolar f mode (of spherical-harmonic degree l =1) shifts the centre of mass, and must have zero frequency. On the other hand, if the perturbation to the gravitational potential is neglected (the case considered by Cowling) the f mode has a frequency intermediate between those of the gravity and acoustic modes; this is true of modes of any degree ( l ≥1) . Here we consider the properties of the dipolar f mode, elucidating the origin of these differences through continuous transformations between the various relevant cases; in addition, we discuss the broader issues of the classification of modes of non-radial oscillation.     

Radial velocity measurements of the chromospherically-active stars (II)

From two sets of the spectroscopic observations covering a ten year period we have obtained 59 radial velocities of the chromospherically-active star HD 28591 = V492 Per. It is a G9III single-lined spectroscopic binary with a period of 21.2910 days and a circular orbit. Thev sini of 24.6 km s^–1, results in a minimum radius 10.3R . We estimate a distance of 165 ± 40 pc and an orbital inclination of 65 ± 25 degrees. The secondary is probably a mid to late-type K dwarf. The star is brighter than the limiting magnitude of theBright Star Catalogue. The mean photometric and the orbital periods are identical within their uncertainties. Since the star fills a significant fraction of its Roche lobe, about 62%, the photometric light curve may be the result of starspots and a modest ellipticity effect.Visiting astronomer, Kitt Peak National Observatory, NOAO, operated by AURA, Inc., under contract with the NSF     

Net circular polarization in magnetic spectral lines produced by velocity gradients: Some analytical results

The net circular polarization in a spectral line due to the combined effect of magnetic fields and velocity gradients is analyzed for a few schematic situations. In some particular cases, its dependence on the magnetic field, velocity field and line parameters can be expressed analytically.On leave from Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italia