No abstract

Models of the upper atmosphere for different levels of solar activity have been calculated by solving the heat conduction equation under quasi‐hydrostatic conditions by means of the procedure described in detail in a previous paper. In these calculations the fluxes of both heat sources (EUV and corpuscular heat source) are varied in proportion to the long term averages of the 10.7‐cm solar fluxes in order to account for different levels of solar activity during the solar cycle. The resulting temperatures of the exosphere can be represented by Tmin = 4.5 · S + 275 (°K) and Tmax = 7.1 · S + 372 (°K) where Tmin and Tmax are the diurnal minimum and maximum temperatures respectively, and S is the monthly average of the 10.7‐cm solar flux in units of 10−22 w/m2 cps. The slope for Tmin is in good agreement with that found by L. G. Jacchia from analysis of satellite drag. In this paper the physical properties (temperature, density, scale height, and mean molecular weight) are illustrated as functions of local time and of altitudes between 120 and 2050 km for five different values of S.

No abstract

It would be hard to find a cosmologist today who does not believe that the vast bulk of the Universe (95% or more) is hidden from our eyes. We review the evidence for this remarkable consensus, and for the latest proposal, that the mysterious dark matter consists of as many as four separate ingredients: baryons, massive neutrinos, new "exotic" dark matter particles, and vacuum energy, also known as the cosmological constant (lambda). Of these, only baryons fit within standard theoretical physics; the others, if their existence is confirmed, will mean rewriting textbooks. Fresh experimental evidence has recently appeared for and against all four components, so that the subject is in a state of turmoil and excitement. The past 3 years in particular have seen the fourth (vacuum) component come into new prominence, largely at the expense of the third (exotic dark matter). We conclude our review by exploring the possibility that the energy density of the vacuum is in fact so dominant as to leave little room for significant amounts of exotic dark matter.

The Lya forest absorption lines in the spectra of quasars are interpreted as caused by the crossings of the light beam with the walls of a bubble structure (expanding with the Hubble flow only). Then, the typical separation between the absorption lines is proportional to the mean size of the bubbles. The variable factor is the expansion rate H [ z ] . T h e Friedmann regression analysis of the observed line separations determines the density parameter 0 0 and the normalized cosmological term A0 = A c 2 / 3 H i of the appropriate cosmological model: 00 = 0.014 f 0.002, Xo = 1:OSO f 0.006.Depending on the Hubble parameter this method reveals the values of the present mean matter density p~, o = 2.6 h Z . kg m-' and of the cosmological constant A = 3.77 hZ m-' (with h = Ho/(100 km/sMpc)). According to our analysis all models with A = 0 must be excluded. The curvature of space is positive. The curvature radius Ro is 3.3 times the Hubble radius ( c / H o ) . The age t o is 2.8 t,imes the Hubble age (IT;'). A A A subject classification: 161Recently, Hoell and Priester (1991b) ([HP91] hereafter) showed that the Lycr forest in quasar spectra can be understood as the result of a homogeneous bubble structure at least up to a redshift of z = 4.4 if the universe is represented by a Friedmann-Lemaitre model with an actual expansion rate Ho = 90 km/(s.Mpc) and an age of about 30. lo9 years. In the present paper we include data from further spectra, partly new, partly omitted in the first paper because of a too cautious estimation of their sensitivity. The analysis is now based on published spectra of 21 quasars with a total of 1320 Lya absorption lines and supports our former result (Liebscher, Priester, Hoell (1992) ([LPH92] hereafter)). The apparent increase in scatter is balanced by the increase in number. Hence, the estimated variance of the parameters does not change appreciably. The Friedmann regression analysis yields the values of the density parameter Q , and of the normalized cosmological term A 0 = A c 2 / 3 H i . The generalized density parameter Of = Qo + A0 turns out to exceed 1, i.e. the space is closed and the curvature index is k = $1.The method is based on the assumption that the bubble structure in the large scale distribution of matter, which is observed in our galactic neighbourhood up to a redshift of 0.05 (deLapparent et al. 1986) was at rest in comoving coordinates at least since the emission of the quasar light, and that the L y a forest in the quasar spectra is due to the cuts of the light beam through hydrogen filaments within the walls of the bubble structure. For a homogeneous and comoving bubble structure the size parameter X of the voids is independent of time. The mean spacing 2 between the absorption lines is measured as a function of the redshift z itself, and we replace the time t by the corresponding value of the redshift z . If we denote the typical bubble size in comoving radial distance x by X = Ax and the corresponding spacing of the redshifts by 2 = Az, we obtain I8 Astron. Nachr. 313 ...