Investigations Of The Interstellar Medium By Observation Of Radio Recombination Lines At Decametric Wavelength - The Largest Bound Atoms In Space

Details Investigations Of The Interstellar Medium By Observation Of Radio Recombination Lines At Decametric Wavelength - The Largest Bound Atoms In Space Investigations Of The Interstellar Medium By Observation Of Radio Recombination Lines At Decametric Wavelength - The Largest Bound Atoms In Space

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..12e..34s&link_type=abstract

Long Wavelength Astrophysics, 26th meeting of the IAU, Joint Discussion 12, 21 August 2006, Prague, Czech Republic, JD12, #34

Astronomy and Astrophysics

Astrophysics

Scientific paper

Spectroscopy at extremely low frequencies with radio recombination lines (RRLs) provides effective ways for studying the cold interstellar medium. Using radio telescope UTR-2 we have detected a series of RRLs in absorption near 26 MHz, arising from bound carbon atoms undergoing delta transitions (quantum level n~ 1 009) in the cool tenuous medium located in the Perseus arm in front of the supernova remnant Cassiopeia A. They are by far the largest bound atoms, million times larger than the ground state atom, occurring in ionised plasma in space. We also report high signal to noise ratio detection of alpha (n~631), beta (n~795), and gamma (n~910) transitions arising in the same medium. The variation of line widths with quantum levels is well explained by the radiative (which dominates) and pressure mechanisms when we take into account the decrease in the strengths of the Galactic background and Cassiopeia A radio emissions at frequencies less than 30 MHz. This effect had not been included in the earlier models. Our data indicates that we have seen atoms very close to the theoretical upper limit of quantum levels (n ~ 1500) of a stable atom state. The ionosphere and interference influence strongly hamper such investigations. Nevertheless, the progress in instrumentation and methodology opens new opportunities for the low frequency spectroscopy. Particularly, it can be among important scientific tasks for the coming new generation of giant low frequency instruments such as LOFAR.

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