Anomalous absorption in cosmic molecules

Prof. Dr. S. Chandra

(School of Physical Sciences, S.R.T.M. University, Nanded 431 606, India)

Donnerstag/Thursday, 2006-5-18 10:15, PN 114

Eugene-Paul-Wigner Gebäude (Physik-Neubau), Hardenbergstr. 36, 10623 Berlin

Abstract:

Besides the normal features (emission and absorption), some molecules in cosmic objects show anomalous behaviour: (i) Maser action, and (ii) absorption against the cosmic microwave background (CMB). Molecules OH, H2O, SiO, etc. show maser action where a brightness temperature is found up to 1014K or even higher, while the kinetic temperature in the objects is a few hundred Kelvin. The second anomalous phenomenon, also known as the anomalous absorption, is generally found in cool cosmic objects where the kinetic temperature is 10-20K. Two molecules, H2CO through its transitions 111-110 at 4.831 GHz and 211-212 at 14.488 GHz and C3H2 through its transition 220-211 at 21.587 GHz have been found in
anomalous absorption in a number of cosmic objects. For anomalous absorption the brightness temperature TB and the excitation temperature Tex of the line must satisfy the criterion that 0<Tex<TB<Tbg, where Tbg=2.73 K is the temperature of the CMB. Finding the brightness temperature of a line less than that of the CMB is indeed an interesting situation. I shall discuss about the anomalous absorption, its requirements and limitations of our calculations.

The anomalous absorption may play a significant role in identification of asymmetric top molecules in cool cosmic objects where kinetic temperatures may not help in the emission process. In these objects, the absorption may however be feasible as lower energy levels of a molecule are always populated. Identification of a large number of molecules in a cosmic object helps in better understanding the chemical reaction going on in the object and provides valuable information about the physical conditions prevailing in the object.