An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) The relative amount of a given → chemical element with respect to other elements.
2) The amount of an → isotope relative to other isotopes of the same element in a given sample. → overabundance; → underabundance.

M.E., from O.Fr. abundance, from L. abundantia "fullness," from abundare "to overflow," from L. → ab- "away" + undare "to surge," from unda "water, wave."

Farâvâni "abundance," from farâvân "abundant," from feré "much, more; increase; priority;" Mid.Pers. frêh "more, much;" O.Pers. fra- "before, forth;" Av. frā, fərrā "forth, forward;" PIE base *pro-; cf. L. pro "on behalf of, in place of, before, for;" Gk. pro- "before, in front of."

The relative amount of a given → chemical element or → chemical compound with respect to another element or compound in a given sample.

→ chemical; → abundance.

The number of → deuterium (D) atoms with respect to → hydrogen (H) in an astrophysical object. Deuterium is a primordial product of → Big Bang nucleosynthesis. According to theoretical models, the primordial D/H ratio is estimated to be (2.61 ± 0.15) x 10^-5 (Steigman et al. 2007, MNRAS 378, 576). Nuclear reactions in stars convert D into He tending to a lower D/H ratio in the → interstellar medium over time (→ deuterium burning). However, chemical and physical → fractionation processes can produce local → enhancements in the D/H ratio. For example, low-temperature ion-molecule reactions in → molecular cloud cores can enhance the D/H ratio in icy grains by as much as two orders of magnitude above that observed in the interstellar medium.
The D/H ratio in the → solar nebula, estimated from observations of CH₄ in → Jupiter and → Saturn, is 2.1 ± 0.4 x 10^-5, assuming that these gaseous planets obtained most of their hydrogen directly from solar nebula gas. This estimate is consistent with → protosolar D/H value inferred from the → solar wind implanted into lunar soils. Moreover, the D/H ratio derived from the interstellar Dα line (which is displaced from the → Lyman alpha line of ¹H at 1216 Å by -0.33 Å) is 1.6 x 10^-5 (Linsky et al. 1995, ApJ 451, 335).
High D/H ratios (relative to Earth's water) are measured spectroscopically from water in three comets (all from the → Oort cloud): → Halley (3.2 ± 0.1 x 10^-4), → Hyakutake (2.9 ± 1.0 x 10^-4), and → Hale-Bopp (3.3 ± 0.8 x 10^-4). These are all about twice the D/H ratio for terrestrial water (1.49 x 10^-4) and about 15 times the value for the above-mentioned solar nebula gas. Note that → carbonaceous chondrites have the highest water abundance of all → meteorites. Their D/H ratios range from 1.20 x 10^-4 to 3.2 x10^-4 with a case at (7.3 ± 1.2) x10^-4.
Different authors interpret the high comet ratios in very different ways. Some consider the high D/H ratio as evidence against a cometary origin of most of the terrestrial water. Others, on the contrary, argue that comets are the main reservoir of deuterium-rich water that raised the terrestrial D/H a factor of six above the protosolar value.
For more details see "Sources of Terrestrial and Martian Water" by Campins, H. and Drake, M. (2010) in "Water & life: the unique properties of H20" Eds. R. Lynden-Bell et al. CRC Press, pp. 221- 234.

→ deuterium; → abundance.

Emission nebulae: The relative amount of a given → chemical element in an ionized nebula with respect to another element, usually → hydrogen. Elemental abundance ratios of → emission nebulae are obtained either by adding the observed → ionic abundances of the element or by using → ionization correction factors. Same as → total abundance.

Elemental, from M.L. elementalis, → element + -al; abundance, from O.Fr. abundance, from L. abundantia "fullness," from abundare "to overflow," from L. ab- "away" + undare "to surge," from unda "water, wave;" → abundance.

The relative amount of helium with respect to another → chemical species, usually → hydrogen, in an astronomical object.

→ helium; → abundance.

A quantity, pertaining to an ion of a chemical element, expressing the relative number of the ion with respect to that of hydrogen.

→ ionic; → abundance.

The abundance of a chemical element as derived from meteorites. Meteoritic abundances measured from carbonaceous → CI chondrites are believed to represent → protosolar abundances.

→ meteoritic; → abundance.

The abundance of a chemical element exceeding a reference value, in particular compared to that of the Sun.

→ over-; → abundance.

The relative amount of a light element (e.g. deuterium, lithium, helium) synthesized in the early Universe.

→ primordial; → abundance.

The abundance of a chemical element pertaining to the proto-→ solar nebula from which the → solar system was formed. → CI chondrite; → CAI meteorite.

→ protosolar; → abundance.

→ solar photospheric abundance, → solar system abundance.

→ solar; → abundance.

The abundance of a → chemical element as determined from the observation of solar → spectral lines. The solar chemical composition is an important ingredient in our understanding of the formation, structure and evolution of both the Sun and our solar system. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared (Asplund et al. 2009, arXiv:0909.0948). The photospheric abundances relative to hydrogen are not representative of the → protosun, or global → solar system abundances. This is because heavy-element fractionation in the Sun has altered photospheric abundances (Lodders 2003, ApJ 591, 1220).

→ solar; → photospheric; → abundance.

Same as → protosolar abundance.

→ solar system; → abundance.

Same as → elemental abundance.

→ total; → abundance.

The abundance of a chemical element being lower than a reference value, in particular compared to that of the Sun.

→ under-; → abundance.