Hydrogen solar abundance

SNII events alone explain the observed solar abundance distribution between oxygen and chromium. This can be taken as a major theoretical achievement. Complementary sources of hydrogen, helium, lithium, beryllium, boron, carbon and nitrogen are required, and these have been identified. They are the Big Bang, cosmic rays and intermediate-mass stars. Around iron and a little beyond, we must invoke a contribution from type la supernovas (Pig. 8.5). These must be included to reproduce the evolution of iron abundances, a fact which suggests... 

Finally, we mention the central star of NGC 246. This star is known to display CIV as the strongest absorptions in the blue spectrum and broad shallow lines of Hell hydrogen can not be detected (Heap, 1975 Husfeld, 1986). Analysis by Husfeld (1986) revealed that this CSPN is extremely hydrogen-deficient solar abundance of this element cannot be excluded. 

The solar abundances of all of the chemical elements are shown in Figure 12.2. These abundances are derived primarily from knowledge of the elemental abundances in Cl carbonaceous chrondritic meteorites and stellar spectra. Note that 99% of the mass is in the form of hydrogen and helium. Notice that there is a general logarithmic decline in the elemental abundance with atomic number with... 

Natural isotopes of hydrogen and their solar abundances... 

The four giant planets have hydrogen- and helium-rich compositions reminiscent of the Sun, but all of them clearly depart from strict solar composition in that their densities are too high and the few heavier elements whose tropospheric abundances can be measured all show clear evidence of enrichment. For all four giant planets we have spectroscopic compositional data on the few compounds that remain uncondensed in the visible portion of their atmospheres, above their main cloud layers. These include ammonia, methane, phosphine, and germane. For Jupiter, these volatile elements (C, N, S, P and Ge) are enriched relative to their solar abundances by about a factor of five. For Saturn, with no detection of germane, the enhancement of C, N, and P is about a factor of 10. For Uranus and Neptune the methane enrichment factor is at least 60, consonant with their much higher uncompressed densities. 

The key processes for the formation of the simplest carbon-, oxygen- and nitrogenbearing molecules have been discussed extensively before (Dalg2imo iuid Bktck 1976 Watson 1978 Crutcher itnd Watson 1985 vein Dishoeck 1988), emd will be only briefly reiterated here. Since H and are so much more abundemt in interstellar clouds than any other species, the dominant reactions usually involve hydrogen, whenever possible. Table 2 lists the current best estimates of the solar abundances of the veirious elements relative to hydrogen. Some of the heavier elements are depleted from the gas phase in interstellar clouds. In diffuse clouds, this depletion is very mild and tends to exceed a feictor of four only for heavier metals like Ca, Ti, Mn, emd Fe. The freiction of the solar abundemce of element X in the gas phase is denoted by the depletion foctor Sx, with Sx < 1-... 

The atmospheres of the Jovian planets have some of the characteristics of dense Interstellar clouds in consisting almost entirely of molecular hydrogen with an envelope of atomic hydrogen produced by photodissociation. Helium is present probably at near the solar abundance ratio, but because it is more massive than H and H2 its concentration falls rapidly with increasing altitude and it plays bjit a minor role in the chemistry. The Jovian planets are distant from the Sun and ultraviolet photons are less Important and cosmic rays are more Important in driving the chemistry than for the terrestrial planets. 

Figure 10 Gas-phase abundances measured towards the star z Oph of various elements relative to atomic hydrogen (X/H) and normalized with respect to solar abundances (X/H)o plotted versus condensation temperature of these elements. The condensation temperature is the temperature at which 50% of that element is depleted from the gas phase into the solid phase. The error bars on the squares indicate measurement errors only. Representative uncertainties in the solar abundances, oscillator strength and condensation temperature are indicated in the lower left hand corner.

As can be seen in Fig. 2-1 (abundance of elements), hydrogen and oxygen (along with carbon, magnesium, silicon, sulfur, and iron) are particularly abundant in the solar system, probably because the common isotopic forms of the latter six elements have nuclear masses that are multiples of the helium (He) nucleus. Oxygen is present in the Earth s crust in an abundance that exceeds the amount required to form oxides of silicon, sulfur, and iron in the crust the excess oxygen occurs mostly as the volatiles CO2 and H2O. The CO2 now resides primarily in carbonate rocks whereas the H2O is almost all in the oceans. 

Fig. 2. The deuterium abundance (by number relative to hydrogen), yi> = 105(D/H), derived from high redshift, low metallicity QSOALS [3] (filled circles). The metallicity is on a log scale relative to solar depending on the line-of-sight, X may be oxygen or silicon. Also shown is the solar system abundance (filled triangle) and that from observations of the local ISM (filled square).

Fig. 3. The 3He abundances (by number relative to hydrogen), j/3 = 10B(3He/H), derived from Galactic H n regions [4], as a function of galactocentric distance (filled circles). Also shown for comparison is the solar system abundance (solar symbol). The open circles are the oxygen abundances for the same H n regions (and for the Sun).

Fig. 1. Evolution of 3He/H in the solar neighborhood, computed without extra-mixing (upper curve) and with extra-mixing in 90% or 100% of stars M < 2.5 M (lower curves). The two arrows indicate the present epoch (assuming a Galactic age of 13.7 Gyr) and the time of formation of the solar system 4.55 Gyr ago. Symbols and errorbars show the 3He/H value measured in meteorites (empty squares) Jupiter s atmosphere (errorbar) the local ionized ISM (filled triangle) the local neutral ISM (filled circle) the sample of simple Hll regions (empty circles). Data points have been slightly displaced for clarity. The He isotopic ratios has been converted into abundances relative to hydrogen assuming a universal ratio He/H= 0.1. See text for references.

The Sun formed some 4.5 Gyr ago (Gyr is a Gigayear or 109 years) from its own gas cloud called the solar nebula, which consisted of mainly hydrogen but also all of the heavier elements that are observed in the spectrum of the Sun. Similarly, the elemental abundance on the Earth and all of the planets was defined by the composition of the solar nebula and so was ultimately responsible for the molecular inventory necessary for life. The solar system formed from a slowly rotating nebula that contracted around the proto-sun, forming the system of planets called the solar system. Astronomers have recently discovered solar systems around... 

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