Using CN λ 3883 spectroheliograms to map weak photospheric magnetic fields

By photographically averaging time sequences of high-resolution CN 3883 spectroheliograms, the noise level due to the rapidly fluctuating intensity of the solar background has been reduced significantly. Very faint faculae that are lost in the noise on a single frame are easily visible on such an enhanced picture. A comparison between these enhanced spectroheliograms and a photoelectric magnetogram suggests that the brightness-magnetic field correlation extends to much weaker field strengths and fainter faculae than can be detected on a single, high quality CN 3883 spectroheliogram.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

On the solar oblateness: The combined effect of a pole-equator difference in effective temperature and mechanical heating

With the help of a model atmosphere of the Sun we evaluate the pole-equator difference in flux (as measured by Dicke and Goldenberg) assuming the following type of pole-equator temperature difference (T=T _e –T _p ): (a) T 2K for > ₀ (₀ 0.05); (b) T 10K for < ₀.The small T at all optical depths given by (a) could, for example, be due to a pole-equator difference in effective temperatures. At small optical depths a difference in mechanical heating could give rise to the larger temperature difference given by (b). We compare the results of our calculations with Dicke and Goldenberg's observations.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Results of spectral observations of CH Cygni for 1967–1969

Conclusions Our observations permit certain conclusions concerning the changes that occurred in the spectrum of CH Cyg during the observation period. It was found that, in conformity with the results of [14], the relative monochromatic brightness and continuous radiation in the violet vary in general as a function of the variation of emission in H (Figs. 6 and 5; the graph of the variation of emission in H is given only in Fig. 6). But continuous radiation in the violet decreases slowly with fluctuations and does not disappear with the end of the outburst. The curves of the relative monochromatic brightness in different light change differently (Fig. 6).As regards the excesses of continuous radiation in red, green, and blue (Figs. 3–5), we attributed their presence in the spectrum partially to the effect of the red component of CH Cyg. This follows from the fact that these excesses were observed before the outburst, and during the outburst the green and blue excesses decreased in general. In addition, the red excess does not duplicate exactly the variations of hydrogen emission. This is also noted in [16], where it is shown that the variation in V is greater than in r, whereas the contribution of the Balmer and Paschen hydrogen emission to V is less than to r. Therefore, part of the red and violet excesses should be attributed to the effect of the red component.Abastumani Astrophysical Observatory. Translated from Astrofizika, Vol. 7, No. 3, pp. 363–375, July–September, 1971.     

Measurements of the oscillatory and slowly-varying components of the solar velocity field

Spectroheliograms with high spatial resolution are presented to illustrate the decomposition of the solar velocity field into its oscillatory and slowly-varying components. An analysis of data obtained in the lines Fei λ 5434 and Feii λ 4924 yield essentially the same principal results:

1. Spectroheliograms of the oscillatory component have a mottled appearance of rising and falling elements ranging from 2000 km to 3000 km in size. These elements oscillate vertically with a period in the range 275–300 s and an amplitude of 0.5 km/s. Although most oscillations last two cycles some have been observed for as many as four cycles.
2. Spectroheliograms of the slowly-varying component show a velocity granulation pattern whose spatial properties correspond closely to those of the photospheric granulation visible on direct photographs of the Sun. The velocity granules are approximately 1000 km in diameter and rise relative to their intergranular spaces with speeds that are typically 0.6 km/s, but which may occasionally be as large as 0.9 km/s. Most velocity granules seem to live for at least 10 min with many lasting 10–30 min, and a few of the biggest and fastest moving lasting 30 min to 1 hr.

It is concluded that Spectroheliograms of the slowly-varying component represent the velocity field of the photospheric granulation.     

Quantitative reconstruction of Early Pleistocene climate in southeastern Australia and implications for atmospheric circulation

Today, southeastern Australia experiences a winter-dominated rainfall regime, governed by the seasonal migration of the highly zonal Southern Hemisphere subtropical anticyclone. The late Cenozoic history of this rainfall regime is poorly understood, but it has been widely accepted that its onset was a product of the intensification and northward migration of the subtropical anticyclone, driven by steepening of hemispheric temperature gradients associated with the initiation of extensive Northern Hemisphere glaciation, ～2.6 million years ago (Ma). Here, we use fossil beetle remains from Stony Creek Basin, a small palaeolake record in upland southeastern Australia deposited over ～280,000 years between ～1.84 and 1.56 Ma, to quantitatively reconstruct regional climate during the Early Pleistocene. Climate reconstructions based on coexistence of extant beetle taxa indicate that temperatures were consistently 1–3 °C warmer than present, and rainfall as high as or substantially higher than today, throughout the record. In particular, beetle data indicate that rainfall was similar to today during winter, but 2–2.4 times higher than today during summer. This is consistent with the presence of diverse rainforest pollen also present in the record, and indicates that the modern, winter-dominated rainfall regime was not yet in place by ～1.5 Ma, at least one million years later than previously thought. We suggest that the Southern Hemisphere anticyclonic circulation must have been much less intense during the Early Pleistocene than today, rather than shifted meridionally as previously argued.     

Radio emission of fast cosmic ions

It is usually assumed that the ions of cosmic rays contribute nothing to the observable electromagnetic radiation. However, this is true only when these ions are moving in a vacuum or a quiet (nonturbulent) plasma. In the case of fast ions in a turbulent plasma, there is an effective nonlinear mechanism of radiation which is discussed in this paper. The fast ion (relativistic or nonrelativistic) moving in the plasma creates a polarization cloud around itself which also moves with the particles. The turbulent plasma waves may scatter on the moving electric field of this polarization cloud. In the process of this scattering an electromagnetic wave with frequency (2.7) is generated. Let ₁ and k₁ be the frequency and wave vector of turbulent plasma waves,V is the velocity of the ion, and is the angle between the wave vector of electromagnetic radiation and the direction of the ion velocity. The method of calculating the probability of the conversion of plasma waves (k₁) into electromagnetic waves (k) by scattering on an ion with velocityV is described in detal in Section 2 (Equation (2.14)).The spectral coefficients of spontaneous radiation in the case of scattering of plasma waves on polarization clouds created by fast nonrelativistic ions are given in (3.6) for an ion energy distribution function (3.4) and in (3.8) for more general evaluations. The Equations (3.9)–(3.13) describe the spectral coefficients of spontaneous emission for different modes of plasma turbulence (Langmuir (3.9), electron cyclotron in a weak (3.10) or strong (3.11) magnetic field and ion acoustic (3.12)–(3.13) waves). The coefficients of reabsorption or induced emission are given by Equations (3.14) and (3.16)–(3.19). There is a maser effect in the case of scattering of plasma waves on a stream of ions. The effective temperature of the spontaneous emission is given by Equation (3.15). The spectral coefficients of radiation due to scattering of plasma waves on relativistic ions are calculated in the same manner (Equations (4.14)–(4.15)). The total energy loss due to this radiation is given in Equations (4.23)–(4.25). The coefficients of induced emission are given in (4.26)–(4.28).The results are discussed in Section 5. It is shown that the loss of energy by nonlinear plasma radiation is much smaller than the ionization loss. However, the coefficients of synchrotron radiation of electrons and nonlinear radiation of ions under cosmic conditions may be comparable in the case of a weak magnetic field and fairly low frequencies (5.5)–(5.6). Usually the spectrum of nonlinear plasma radiation is steeper than in the case of synchroton radiation. Equation (5.10) gives the condition for nonlinear radiation to prevail over thermal radiation.Translated by D. F. Smith.     

VLA observations of extreme hydrogen deficient stars

VLA observations at 2 and 6 cm have been obtained for six hydrogen-deficient stars R CrB, HD 160641, BD — 9°4395, V348 Sgr, MV Sgr and Sgrv Upper limits to the massloss rates have been estimated for some of these using the upper limits to the radio flux density. National Radio Astronomy Observatory’s Very Large Array is operated by Associated Universities Inc. under contract with National Science Foundation, USA     

Friedmann cosmology with a cosmological constant in the modified Brans-Dicke theory

Homogenous isotropic cosmologies in the presence of a cosmological constant A are studied in the modified Brans-Dicke theory. A class of exact solutions are obtained in Dicke's revised units for empty space as well as for the models filled with dust or radiation. Behaviour of these models near the singularity are discussed.     

The solar causes of geomagnetic disturbances

Geomagnetic disturbances have been identified with respect to their sources for 1977–1983. The disturbance level was found using the daily planetary index A _p. High-amplitude ( 50), mean-amplitude (24) and low-amplitude ( 12) disturbances are caused by solar flares of importance 1, coronal holes, and filament cavities, respectively. The ranges of probable amplitudes of disturbances of different nature and their relative number are found from Poisson random distributions of amplitudes.     

An UV survey of the galactic plane

The present paper is the introduction to a systematic analysis of 123 6-degree fields near the galactic plane, recorded in the medium ultraviolet (2000 Å) by the ballon-borne experiment SCAP 2000 of the Laboratoire d'Astronomie Spatiale, Marseille, and Geneva Observatory. The available data are presented and the general properties of the images are briefly discussed.It is shown that the high selectivity of the UV passband regarding spectral type, together with the strong interstellar extinction at that wavelength, provide the necessary conditions for an efficient application of Wolf's method to study the distribution of interstellar matter in the solar neighbourhood. The results of a fast analysis of the available data are presented here.