we propose to search for far-infrared emissions from shock-heated water in extremely high states of rotational excitation. the water transitions considered in this proposal possess upper state energies (e/k) between 2300 and 4700 kelvin and thereby provide a unique probe of the very hottest molecular regions that are present within the interstellar medium. the study of such highly-excited transitions is complementary to - but does not form part of - the guaranteed time programme. because of the low luminosities that are expected for the water lines to be studied in this project, we will search for them in cepheus a (west), a source of luminous shock-excited h2 line emission which shows a relatively small infrared continuum flux in the spectral region where the target water transitions lie. our choice of transitions is motivated by a theoretical model for the excitation of water emission in molecular shock waves, constructed by kaufman and neufeld. that model, in common with previous studies, predicts that water will be copiously produced in the warm region behind the shock front and that far-infrared water rotational emissions will dominate the cooling of dense, non-dissociative molecular shocks. the high-lying transitions that we propose to study will provide a more sensitive diagnostic of the physical conditions in the water-emitting region region than will the lower-lying rotational lines to be studied in the guaranteed time programme. the high atmospheric opacity at the far-infrared wavelengths of these transitions, and the expected weakness of the emission lines, necessitate the use of iso for the project proposed here.
Instrument
SWS02
Temporal Coverage
1996-06-24T01:21:53Z/1996-06-24T02:25:09Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the world's first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, 1999, Search For Ultra-High-Excitation Rotational Lines Of Water: A Probe Of The Hottest Molecular Gas In The Ism, 1.0, European Space Agency, https://doi.org/10.5270/esa-n6t76kz
