Are local and 1 kpc distant Cosmic Background Radiation Temperatures the same?

 

Sydney Leach

Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique, CNRS-UMR 8112, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 - Meudon, France

 

The most accurate determination of the Cosmic Background Radiation (CBR) temperature Tg has been carried out by the orbiting observatory Cosmic Radiation Explorer (COBE), which therefore measures its local value at about 1 AU from the Sun. Measurement of the CBR temperature Tg(CN) from interstellar CN absorption provides  values of Tg in several clouds within 1 kpc. Published data on interstellar CN absorption shows that Tg(CN) is slightly greater than the standard cosmological CBR temperature, Tg(COBE) = 2.725 ± 0.001 K, determined by the COBE satellite, even when the effects of local excitation of CN, mainly by electron collisions, are taken into account. One way of dealing with this discrepancy is to consider whether the local and distant values of Tg could be different.  If one discounts this possibility then other factors must be considered. A source of possible error, not previously considered, in the determination of  Tg(CN) from interstellar CN absorption is proposed. This concerns the intrinsic assumption of the validity of using Hönl-London rotational line intensity factors to determine the rotational components of the oscillator strengths of the CN B2S+ - X2S+ (0,0) band  R(0), R(1) and P(1) lines. The difference between the Tg(COBE) and Tg(CN) values  are used to estimate the maximum corrections, a few percent, to the ratio of the line strengths and to the ratio of the Hönl-London factors. Fluorescence lifetime data are shown to give similar values for the corrections as well as providing evidence for intramolecular coupling between the relevant B2S+ state rotational levels and close-lying levels of the A2P state, this being responsible for rendering the standard Hönl-London factors invalid [1].

 

[1] S.Leach, Can.J.Chem., in press (2004, special memorial issue for Gerhard Herzberg).