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absolute magnitude absorb absorption lines abundance appear astrophysical background Balmer band behavior calcium changes Chapter classification columns constant contains continuous cooler corresponding depth derived determined direct discussed Draper dwarf effect electron elements emission energy estimates evidence excitation fact Fo-Ma Fowler fraction giant give given hydrogen important increase indicate intensity ionization potential ionized atoms known laboratory lower marginal material maximum mean measured method Milne multiplets neutral neutral atoms normal observed obtained occur orbits origin photosphere Phys physical possible predicted present pressure probably problem Proc produced quantity question relations relative represented reversing layer rise Russell scale seen sequence silicon solar spectrum spectral class stars stellar atmosphere stellar spectra strength strong strontium suggested surface temperature theory thermal tion ultimate lines wave-length
Page 190 - In the stellar atmosphere and the meteorite the agreement is good for all the atoms that are common to the two, but several important elements are not recorded in the meteorite. The outstanding discrepancies between the astrophysical and terrestrial abundances are displayed for hydrogen and helium. The enormous abundance derived for these elements in the stellar atmosphere is almost certainly not real.
Page 47 - At the top is a deep layer, the chromosphere, in which the gases are held up by radiation pressure, acting on individual atoms. The pressure and density in this layer increase slowly downward (as gravity somewhat overbalances radiation pressure), and the pressure at its base may be of the order of io~7 atmospheres, or o.oooi mm of mercury. Below this level, gravity is predominant in the equilibrium, and the pressure increases rapidly with depth — the temperature remaining nearly constant, and not...
Page 206 - ... units, the energies of the initial and final states. Combinations between these terms occur according to definite laws, which enable us to classify them into systems, each containing a number of series of terms, which are usually multiple. . . . " Any term y may be expressed in the form y = R/(m + x)*, where R is the Rydberg constant and m an integer. For homologous components of successive terms of the same series, m changes by unity, while the "residual...
Page 33 - Me 3.93 3720 IONIZATION TEMPERATURE SCALE 33 The difference in temperature between giant and dwarf stars of the same spectral class is clearly shown in the foregoing tables. The relation of absolute magnitude to effective temperature within a given class must be regarded as definitely established by observation. The temperatures for the cooler giant stars in both these lists are somewhat lower than those given for the corresponding classes in Table V. The temperature of...
Page 108 - ... stationary states for hydrogen. On this view, b(T) = i for all atoms excepting those of H and He+, for which it is equal to 2. The convergence of the series for b(T) was not established by Fowler and Milne, but the authors regard the subsequent investigation by Urey 7 as justifying their assumption that " for physical reasons one must suppose the series effectively cut off after a certain number of terms. Usually the series then reduces (as regards its numerical value) practically to its first...
Page 186 - STELLAR ATMOSPHERE AND EARTH'S CRUST The preponderance of the lighter elements in stellar atmospheres is a striking aspect of the results, and recalls the similar feature that is conspicuous in analyses of the crust of the earth.6 A distinct parallelism in the relative frequencies of the atoms of the more abundant elements in both sources has already been suggested by Russell,7 and discussed by HH Plaskett,8 and the * Clarke and Washington, Proc.
Page 192 - ... groups. A classification devised from one point of view will not necessarily appear natural from another, and the best that can generally be done is to select the standpoint that seems to be the most important. From all other standpoints the classification is empirical, and must be treated as such The descriptions that are contained in the preface to the Henry Draper Catalogue, and which have long been classical, were designed to describe the salient features of the groups that had been formed....
Page 97 - At high temperatures, when the conditions of maximum entropy demands an appreciable amount of ionic dissociation, the requisite energy is drawn from the environment. . . . The work required to ionize a single molecule, when expressed as the number of volts through which an electron must fall to acquire this energy, is the ionization potential; it may be regarded as the latent heat of evaporation of the electron from the molecule " (Milne).12 10 See Chapter V, p. 69. A. Fowler, Bakerian Lecture, 1924,...
Page 58 - ... ultra-violet, and cannot be traced in the stars. The helium lines vary much in width and definition and are often winged. Their intensity does not certainly appear to vary with absolute magnitude within a given spectral class, and they cannot therefore be used in the estimation of spectroscopic parallaxes.30 The question of absolute magnitude effects cannot be usefully pursued in the absence of more reliable parallaxes, for the B stars, than are at present available.