Detection of the CO (J = 7 = 6) rotational transition at lambda = 0.37 millimeters toward Orion

Ground-based terahertz CO spectroscopy towards Orion

“…First, the peak antenna temperature is fairly constant within this extended region, with T * A ≈ 50 K. Since the CO(J = 7 → 6) line towards Orion KL, which was observed with the same receiver, has almost exactly the same peak brightness temperature (Kawamura et al 1999a), the line center is most certainly optically thick. In their survey of giant molecular clouds, Boreiko & Betz (1991) determined that the line emission of 12 CO(J = 9 → 8) is optically thick in all cases, and we would expect Orion-KL to be similar to these, in contrast to earlier work by Goldsmith et al (1981) and Schultz et al (1985) who claimed that lower-J CO lines at line center were optically thin towards Orion-KL. Since the line is optically thick, the line brightness temperature can be used to compute the excitation temperature of the gas, T ex = 154 ± 35 K. This value is consistent with many other independent measurements of the gas temperature near the plateau/core region made using high-density molecular tracers (Boreiko et al 1989;Schloerb et al 1983;Blake et al 1987).…”

THz Instruments for Space

“…Breakthroughs both in cooled detector technology and spectroscopic techniques enabled a diverse suite of both ground based and high altitude balloon and aircraft measurements [20]. Very strong and omnipresent molecular spin transition lines of carbon monoxide, to to 7, at 115, 230, 345 GHz, etc., up to at least 690 GHz [21] became primary targets for these early observations. These and higher frequency transitions were also measured from high altitude aircraft such as the Kuiper Airborne Observatory [22] and stratospheric balloon platforms [23].…”