Astrophysics (Index)About

carbon monoxide

(CO)
(compound of carbon and oxygen, one atom each)

Carbon monoxide (CO) is a compound with molecules each consisting of one oxygen and one carbon atom. In astronomy, CO emission lines are used to detect molecular clouds. Though the clouds are primarily molecular hydrogen, the hydrogen lines are weak and only detectable in nearby clouds. One series of useful CO lines is due to the steps in possible rotational energy, i.e.,

       J(J+1)h²
Erot = ————————
          2I

where I is the moment of inertial, h is Planck constant, and J is 0, 1, 2, etc. The lines' frequencies are generally multiples of ~115GHz. Interesting lines include:

CO(7-6)806.7 GHz0.37 mm
CO(6-5)691.473 GHz0.43 mm
CO(5-4)576.3 GHz0.52 mm
CO(4-3)461.0 GHz0.65 mm
CO(3-2)345.8 GHz0.87 mm
CO(2-1)230.5 GHz1.3 mm
CO(1-0)115.3 GHz2.6 mm
13CO(1-0)110.2 GHz2.72 mm

These can be detected in distant galaxies (e.g., z=1) in the millimeter/submillimeter range (e.g., submillimeter galaxy designator). and suggest gas clouds, i.e., indicating starburst galaxies and possibly mergers. CO lines, such CO(1-0) are useful for determining redshifts. CO(6-5) is used for observing protoplanetary disks and very distant (z>6) molecular clouds. This series is known as the CO ladder (CO rotational ladder or CO J ladder) and when observed together (yielding their spectral line energy distribution (SLED)), can yield qualities of the gas, in particular, its temperature.

From CO line widths, using the virial theorem, if virial stability is assumed, the mass of the cloud can be calculated. Assuming a particular CO to H2 factor, the mass of a distant molecular cloud can be calculated.

CO incorporating rarer isotopes, such as C17O, C18O, or 13CO, are sometimes preserved better or otherwise easier to observe, thus are sometimes measured, using normal ratios of isotopes to extrapolate the mass of CO, and from that, the mass of H2. Large clouds have sufficient CO to saturate the lines of the most abundant isotope combination, 12C16O, so the observer may determine from it no more than a minimum amount of CO present. Inclusion of another isotope affects the wavelength of the CO lines sufficiently that they can be independently measured, thus the value in detecting isotopes in analyzing molecular clouds above a certain size.


(compound,hydrogen,star formation,clouds,oxygen,carbon,chemistry)
Further reading:
http://en.wikipedia.org/wiki/Carbon_monoxide
https://astronomy.swin.edu.au/cosmos/M/Molecular+Cloud

Referenced by pages:
AIM-CO
alpha CO (αCO)
Atacama Pathfinder Experiment (APEX)
carbon (C)
carbon star (C)
CARMA EDGE
cold gas
COLD GASS
COMAP
Carbon Monoxide Mapping Array (COMA)
comet
COMPLETE Survey
COPSS
dendrogram
EMPIRE Survey
HITEMP
hydrogen (H)
intensity mapping
Large Millimeter Telescope (LMT)
luminosity function (LF)
molecular cloud turbulence
Millimeter-wave Intensity Mapping Experiment (mmIME)
molecular cloud
Molecular Deep Field
PAWS
PHIBSS
star formation rate (SFR)
sublimation
Tomographic Ionized-carbon Mapping Experiment (TIME)
tracer
CO to H2 factor (Xco)

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