An Etymological Dictionary of Astronomy and Astrophysics
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Nonmetallic chemical element; symbol C. → Atomic number 6; → atomic weight 12.011; → melting point about 3,550°C; → boiling point 4,827°C. The most abundant isotope of carbon is ¹²C. Carbon is one of the most important elements for life. The burning of carbon in the form of coal and oils has been essential in the development of industrial societies. It is the element that hardens → steel and the sole element in → diamonds. The carbon in nature is produced inside massive stars. → triple-alpha process; → Hoyle state.

Carbon, from Fr. carbone, coined by Antoine Lavoisier (1743-1794) to distinguish it from charbon (Fr.) "charcoal," from L. carbo (genitive carbonis) "a coal, charcoal."

The stage in the evolution of a star after → helium burning when the core of the star consists mainly of carbon and oxygen. In stars of mass greater than about 8 solar masses, whose cores reach a temperature above 5 × 10⁸ K and density above 3 × 10⁹ kg m^-3, carbon burning can begin via reactions such as the following:
¹²C + ¹²C → ²⁰Ne + ⁴He
¹²C + ¹²C → ²³Na + p
¹²C + ¹²C → ²³Mg + n.
The time-scale for this phase of → nucleosynthesis is of order of five hundred years.

→ carbon; → burning.

A problem raised in the past by observations suggesting that the amount of carbon necessary for standard → dust models was larger than what actually observed for the → interstellar medium (ISM) (Snow & Witt 1995). The problem was especially acute for the → 2175 A bump in the ultraviolet part of the → extinction curve. The so-called "crisis" was finally solved by, on the one hand, revising downward the → solar abundances, thought to represent the ISM abundances (Asplund et al. 2009, arXiv:0909.0948, and references therein), and, on the other hand, revising upward the ISM carbon abundances (Sofia et al., 2011, AJ 141, 22S).

→ carbon; → crisis.

1) A complex series of processes through which all the carbon atoms on Earth is cycled through the air, ground, plants, animals, and fossil fuels. During the cycle, plants absorb → carbon dioxide (CO₂) from the atmosphere and through → photosynthesis incorporate the associated carbon atoms into sugars and other molecules necessary for growth. Plants return carbon atoms back to the atmosphere in the form of CO₂. However, much of the carbon absorbed remains "locked up" in the living organisms until decomposition or fire releases it back to the atmosphere.
2) For nuclear fusion in stars → CNO cycle.

→ carbon; → cycle.

CO₂, also called carbonic acid gas. A colorless gas which occurs in the atmosphere playing an essential part in animal respiration and the growth of green plants. → photosynthesis, → carbon cycle. It is formed by the → oxidation of carbon and carbon compounds. Carbon dioxide is the most important → greenhouse gas produced by human activities, primarily through the combustion of fossil fuels. Its concentration in the Earth's atmosphere has risen by more than 30% since the Industrial Revolution. CO₂ forms a solid at -78.5 °C at atmospheric pressure, and is used as a refrigerant in this form as a dry ice for the preservation of frozen foods. As carbon dioxide gas is heavier than air and does not support combustion, it is used in fire extinguishers.
CO₂ is present in the → interstellar medium and is one of the main → molecules in → comets.

→ carbon; → dioxide.

A colorless, odorless, very poisonous gas which burns in air with a bright blue flame to form → carbon dioxide. CO gives rise to a violent explosion when ignited in air in certain proportions. It occurs in coal gas and in the exhaust fumes of motor engines. Melting point -207 °C; boiling point -191.1 °C.
Carbon monoxide is the most important → molecule found in the → interstellar medium, and is produced through several chemical reactions, → CO formation. It was discovered in 1970 by R. Wilson and A. Penzias of Bell Laboratories, using the 11-m telescope of the National Radio Astronomy Observatory (NRAO) in the direction of the → Orion nebula. Because the CO line is so intense and widely distributed in space, this molecule is a most useful tool for tracing the ISM. In addition, measurement of its rare isotopes have shown that the main line ¹²C¹⁶O (wavelength 2.6 mm, 115 GHz) is → optically thick, that is the → column density of the molecule is so high that the material becomes opaque at the transition frequency. Moreover, the upper-energy levels of the CO molecule are easily excited by collision with → molecular hydrogen. The combination of high → optical depth and the ease of → excitation imply that CO emission brightness will accurately reflect the local gas temperature. CO is also one of the principal molecules detected in → comet nuclei.

→ carbon; → mono-; → oxide.

A class of → red giant stars whose spectra show strong → molecular bands of → carbon compounds.

→ carbon; → star.

A radioactive isotope of carbon, whose nucleus contains 6 protons and 8 neutrons; also called → radiocarbon. ¹⁴C is naturally produced in the atmosphere when a neutron created by a cosmic ray hits the nucleus of an atom of nitrogen-14. The nucleus absorbs the neutron and ejects a proton, thereby transforming itself into ¹⁴C. It decays back to nitrogen, with a half-life is 5730 years, after emitting an electron (¹⁴₆C → ¹⁴₇N + e^- + ν_e). See also → radiocarbon dating.

→ carbon; → four + -teen, an inflected form of the root of → ten.

A star that presents very low → iron  → abundances [Fe/H] < -4 but an → anomalous richness in carbon. CEMP stars have been defined as a subset of → metal-poor stars that exhibit elevated [C/Fe] ≥ +1.0. It has been recognized that ~15-20% of stars with [Fe/H] < -2.0 are carbon enhanced. This fraction rises to 30% for [Fe/H] < -3.0, to 40% for [Fe/H] < -3.5, and ~75% for [Fe/H] < -4.0. This increasing trend of CEMP-star frequency with declining [Fe/H] is confirmed by the observation of many thousands of CEMP stars (Daniela Carollo + ApJ 2014, 788, 180). See also → extremely metal-poor star (EMPS)

→ carbon; → enhance; → metal; → metal; → poor; → star.

Containing or composed of carbon.

From → carbon + -aceous, from L. -aceus "-ous."

Karboni, adj. from karbon, → carbon; karbondâr "having carbon," with -dâr "having, possessor," from dâštan "to have, to possess;" O.Pers./Av. root dar- "to hold, keep back, maintain, keep in mind;" cf. Skt. dhr-, dharma- "law;" Gk. thronos "elevated seat, throne;" L. firmus "firm, stable;" Lith. daryti "to make;" PIE base *dher- "to hold, support."

A rare type of → stony meteorite having a higher → carbon content than other classes of meteorite. They represent only ~5% of the known meteorites. Their bulk composition is mainly → silicates, → oxides and sulfides, whilst the minerals → olivine and serpentine are characteristic. The six classes of carbonaceous chondrites are: → CI chondrites, CM chondrites, CV chondrites, CO chondrites, CK chondrites, CR chondrites, CH chondrites, and CB chondrites.

→ carbonaceous; → chondrite.

The radical -C=O, which occurs in several compounds, such as → aldehydes and ketones.

From → carbon + -yl a suffix used in the names of some radicals; → group.

Any of a class of compounds containing only → hydrogen and → carbon. Hydrocarbons are organic compounds found in coal, petroleum, natural gas, and plant life. They are used as fuels, solvents, and as raw materials for numerous products such as dyes, pesticides, and plastics. Petroleum is a mixture of several hydrocarbons.

→ hydro- + → carbon.

1) Chemistry: A family of → organic molecules composed of carbon and hydrogen atoms (→ hydrocarbons) in which → carbon atoms appear in multiple loops (polycyclic) with strong chemical → bonds that exist between them (aromatic). PAHs are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances like tobacco or charbroiled meat. As a pollutant, they are of concern because some compounds (benzo(a)pyrene) have been identified as tending to cause cancer.
2) Astro.: Strong → infrared emission features at 3.3, 6.2, 7.7, 8.6, and 11.2 microns, which are attributed to PAH molecules in the form of → dust grains with radii smaller than 10 Å. PAHs are common toward various sources characterized by a strong → ultraviolet radiation field (such as → active galaxies, → reflexion nebulae, → planetary nebulae, → H II regions). In particular, they trace the presence of → massive stars. The PAH features are thought to result from the fluorescent emission process of PAH molecules and ions excited by ultraviolet radiation of nearby stars. PAHs are likely produced by → photoevaporation of → very small grains.

→ poly-; → cyclic; → aromatic; → hydrocarbon.

A → radioactive → isotope of → carbon, especially → carbon-14.

→ radio; → carbon

A radioactive dating technique, applied to organic materials, which measures the content of the radioactive isotope of carbon ¹⁴C. The radioactive carbon isotopes created by the impact of cosmic rays with the nitrogen atoms of the atmosphere find their way, via carbon dioxide and photosynthesis, into living material. When an organic material dies it ceases to acquire further ¹⁴C atoms, and its ¹⁴C fraction declines at a fixed exponential rate due to the radioactive decay of ¹⁴C. Comparing the remaining ¹⁴C fraction of a sample to that expected from atmospheric ¹⁴C allows the age of the sample to be estimated.

→ radiocarbon; → dating.

A carbon atom → singly ionized by a photon of energy 11.3 eV. The ion C⁺ emits a → fine-structure line (²P_3/2→ ²P_1/2) at 157.7 μm when excitation conditions are satisfied (critical density ~ 3 x 10³ cm^-3). In → photodissociation regions, [C II] 157.7 μm is a major cooling line for regions exposed to significant → far ultraviolet (FUV) photon fluxes. In Galactic → H II regions, as well as in the central regions of external galaxies, the luminosity of the [C II] line is typically ~ 0.05-0.5% of the FUV luminosity and correlates well with → carbon monoxide (CO) line intensities.

→ single; → ionized; → carbon.