Unstable non-radial modes in radial pulsators: theory and an example     

T. Van Hoolst  W. A. Dziembowski  & S. D. Kawaler 《Monthly notices of the Royal Astronomical Society》1998,297(2):536-544

We study the possibility of the excitation of non-radial oscillations in classical pulsating stars. The stability of an RR Lyrae model is examined through non-adiabatic non-radial calculations. We also explore stability in the presence of non-linear coupling between radial and non-radial modes of nearly identical frequency.   In our model, a large number of unstable low-degree (ℓ = 1,2) modes have frequencies in the vicinity of unstable radial mode frequencies. The growth rates of such modes, however, are considerably smaller than those of the radial modes. We also recover an earlier result that at higher degrees (ℓ = 6–12) there are modes trapped in the envelope with growth rates similar to those of radial modes.   Subsequently, monomode radial pulsation of this model is considered. The destabilizing effect of the 1:1 resonance between the radial mode and nearby non-radial modes of low degrees is studied, with the assumption that the excited radial mode saturates the linear instability of all other modes. The instability depends on the radial mode amplitude, the frequency difference, the damping rate of the non-radial mode, and the strength of the non-linear coupling between the modes considered. At the pulsation amplitudes typical for RR Lyrae stars, the instability of the monomode radial pulsation and the concomitant resonant excitation of some non-radial oscillation modes is found to be very likely.  相似文献   

Solar constant secular changes     

Kenneth H. Schatten  Jerome A. Orosz 《Solar physics》1990,125(1):179-184

Our recent model for solar constant secular changes suggests that over extended time intervals, a positive correlation of the solar constant with solar activity results. The positive correlation in this model is not associated with the direct result of active region, which may be in a close energy balance over their lifetimes, but rather is associated with global features - bright global faculae. These exist as both polar and network features on the solar disk. The high latitude faculae enable the solar constant to peak prior to sunspot maximum. Recent solar constant observations support the model's general trend. Using this model, we now calculate a proxy solar constant for: (1) the past four centuries, based upon the sunspot record, (2) the past nine centuries, based upon ¹⁴C observations and their relation to solar activity, and (3) the next decade, based upon a dynamo theory model for the solar cycle. The proxy solar constant data is tabulated as it may be useful for climate modelers studying global climate changes. This could be helpful in disentangling possible solar influences from any anthropogenic changes associated with trace gas increases in the terrestrial atmosphere. An important point for climate modelers to consider in fixing climate model parameters, is that the Sun has been relatively active and thus bright in the latter half of the 20th century, compared with the past few centuries.This paper was presented at the third meeting of the Solar Cycle Workshop, held in Sydney, Australia, January 9–13, 1989.Physics Dept., Univ. of Northern Colorado, U.S.A.  相似文献   

Fourteen years of multifrequency-coordinated observations of the X-ray/Be system A 0535+26/HDE 245770     

F. Giovannelli  C. Bartolini  A. Guarnieri  A. Piccioni  M. Burger  E. L. Van Dessel  V. G. Kurt  E. K. Sheffer  D. De Martino  R. Waters  I. Gonzalez Martinez-Pais  Yu. N. Gnedin  V. M. Larionov  N. I. Shakovskaya 《Astrophysics and Space Science》1990,169(1-2):139-145

Within the framework of a very long multifrequency campaign of coordinated, and very often simultaneous, observations of the transient X-ray/Be system A 0535+26/HDE 245770, we present a summary of this large collection of data taken with IUE and ASTRON satellites as well as with many ground-based telescopes in optical and IR regions.In this paper we emphasize the study of the physics and dynamics of the mass transfer at periastron and subsequent X-ray flaring, which is a typical problem of the X-ray/Be binary system class.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

The magnesium and calcium contents of sediments,especially pelites,as a function of age and degree of metamorphism     

J.C. Van Moort 《Chemical Geology》1973,12(1):1-37

The silicate and carbonate fraction of 98 non-metamorphic shale samples from the Australian platform and of different geological age were analysed for calcium, magnesium, ferrous iron and carbonate. Cainozoic and Mesozoic shales prove to be essentially calcitic, Cambrian and Proterozoic shales are essentially dolomitic and sideritic. A similar trend of high MgO values can be demonstrated for the silicate fraction of the old shales. Extensive literature study confirms these trends for shales and carbonate rocks from all over the world. Slates, hornfelses and schists are Mg rich and Ca poor, whether young or old.Ronov's model of the evolution of the earth's crust ocean and atmosphere, explaining these trends, is critically reviewed but rejected because of impossible storage problems of calcium in the Proterozoic. The increased magnesium content of the old sediments is explained by calcium carbonate sweating out of the sedimentary column, magnesium introduction from altering volcanic rocks within the sedimentary pile and magnesium introduction from connate brines in sandstones. The increasing calcium content of all kinds of sediments with decreasing age is claimed to be related to preferential weathering of extrusive volcanic rocks and sweating out of calcium carbonate from the sedimentary column.  相似文献   

A field method of analysis of bauxite samples for total aluminium and silicon and for aluminium present in gibbsite     

M. De Bruin  P.J.M. Korthoven  R.J.C. Van Straalen 《Chemical Geology》1976,18(2):85-92

A method is described for a fast and accurate determination of the water content of bauxite samples by measuring thermal neutron scattering.Combination of this technique with an activation analysis for Al and Si with isotopic neutron sources leads to a method for determining the amount of gibbsite in bauxite samples.The results of the activation analysis for Al appeared to depend on the amount of water present in the sample; knowledge of the water concentration allows for the appropriate correction.  相似文献   

Some geochemical controls on Ni and Co concentrations in marine ferromanganese deposits     

C.H. Van Der Weijden 《Chemical Geology》1976,18(1):65-80

The uptake of Ni and Co in the hydrous Mn oxide or the amorphous Fe-oxide phases of ferromanganese deposits in the oceans was studied by electron-microprobe analyses of 17 natural manganese nodules and by experiments on desorption-dissolution of these metals from synthetic Fe oxide or Mn oxides and natural nodule material. Ni was found to occur nearly always in the Mn-oxide phases of natural nodules, while Co occurs both in the Mn-oxide and Fe-oxide phases, with a slight preference for the latter. The solubility of Ni and Co (from coprecipitates of these metals with Fe hydroxides after aging) in seawater was found to depend strongly on the crystallinity of the host phase. The adsorption of Co by the synthetic Mn oxides from seawater was higher than that of Ni. The experimentally determined solubility of Ni and Co in seawater from natural nodule material is extremely low and matches the concentration range of these metals in ocean water.  相似文献   

Shear in the tethys and the Permian paleomagnetism in the Southern Alps, including new results     

J. D. A. Zijderveld  G. J. A. Hazeu  M. Nardin  R. Van Der Voo 《Tectonophysics》1970,10(5-6):639-661

To verify paleomagnetic proof for megatectonic translation in the Tethys a large collection of samples from a key area, the Bolzano Quartz Porphyry Plateau in the Southern Alps, was examined. Their natural remanent magnetization was analyzed with thermal, and mainly alternating field demagnetization. The result is a well-established paleomagnetic direction of D: 150° and I: −19.5° (₉₅ = 4.9), obtained from 152 samples from 39 sites distributed over 12 volcanic units. It is argued that the inclination of this result is not significantly different from that which can be extrapolated for the Southern Alps from Early Permian paleomagnetic directions of the stable European shield. Consequently it is concluded that a paleomagnetic indication for megatectonic translation of the Southern Alps is virtually absent. But a large counterclockwise deviation of the declination is evident, and is easily explained by a counterclockwise rotation of 50° of the Southern Alps with respect to stable Europe. Since the paleomagnetic direction of the Early Permian volcanics of the Southern Alps fits in reasonably well with the (poorly known) Early Permian paleomagnetic pattern of Africa, a coherence between both regions is presumed.  相似文献   

Short term evolution of coronal hole boundaries     

Jerome T. Nolte  Allen S. Krieger  Craig V. Solodyna 《Solar physics》1978,57(1):129-139

In an examination of the evolution of coronal hole boundaries on a time scale of 1 day, we find that 38% of all the boundaries of coronal holes observed near central meridan passage during the Skylab period shifted in location by >1° heliocentric in 1 day. Of these boundary changes, 70% were on a scale 3 times the average supergranulation cell size. However, large-scale shifts in the boundary locations also occurred, which involved changes in the X-ray emission from these areas of the Sun. X-ray emitting structures on the borders of isolated and evolving holes were less clearly defined than those on the boundaries of well-established, elongated holes. There were generally more changes in the boundaries of the most rapidly evolving holes, but no simple relationship between the amount of change and the rate of hole growth or decay.Skylab Solar Workshop post-doctoral appointee 1975–1976. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmosoheric Research.  相似文献   

Infrared photometry,extinctions andR values for some Northern Milky Way stars     

I. G. Van Breda  D. C. B. Whittet 《Astrophysics and Space Science》1977,48(2):297-304

Infrared wideband photometry for 21 early-type stars in the Northern Milky Way is used to determine extinction values by the colour-difference method. The mean extinction curve is similar to the van de Hulst theoretical curve No. 15, and there is no significant difference in the results for stars lying towards and away from nebulosity. None of the stars exhibit infrared excesses at 3.5 . A mean value ofR=3.15±0.15 is deduced for the ratio of total to selective extinction.R is found to be normal towards the open cluster IC 1805 for which high values have been suggested; a distance of 2.0±0.2 kpc is deduced for this cluster.Visiting astronomer, Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

Inferred phase relations in part of the system Au–Ag–Te: an integrated analytical study of gold ore from the Golden Mile, Kalgoorlie, Australia     

L. Bindi  M. D. Rossell  G. Van Tendeloo  P. G. Spry  C. Cipriani 《Mineralogy and Petrology》2005,83(3-4):283-293

Summary Integrated X-ray powder diffraction, scanning electron microscopy, electron probe, and transmission electron microscopy studies have identified the rare contact assemblage calaverite–sylvanite–hessite in a sample of gold ore from the Golden Mile deposit, Kalgoorlie, Australia. The presence of coexisting calaverite–hessite at Kalgoorlie is a non-equilibrium assemblage whereby the stable hessite-bearing assemblage is hessite–sylvanite, which formed from the breakdown of the -phase or -phase below 120°C, stützite+-phase, or sylvanite+stützite+-phase, as predicted by Cabri (1965).  相似文献