Bringing high spatial resolution to the far-infrared: A giant leap for astrophysics.

The far-infrared (FIR) regime is one of the wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist. None of the medium-term satellite projects like SPICA, Millimetron, or the Origins Space Telescope will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO), light hydrides, and especially from water lines would open the door for transformative science. A main theme will be to trace the role of water in proto-planetary discs, to observationally advance our understanding of the planet formation process and, intimately related to that, the pathways to habitable planets and the emergence of life. Furthermore, key observations will zoom into the physics and chemistry of the star-formation process in our own Galaxy, as well as in external galaxies. The FIR provides unique tools to investigate in particular the energetics of heating, cooling, and shocks. The velocity-resolved data in these tracers will reveal the detailed dynamics engrained in these processes in a spatially resolved fashion, and will deliver the perfect synergy with ground-based molecular line data for the colder dense gas.

Ground-based measurements of the 1.3 to 0.3 millimeter spectrum of Jupiter and Saturn, and their detailed calibration.

One of the legacies of the now retired Caltech Submillimeter Observatory (CSO) is presented in this paper. We measured for the first time the emission of the giant planets Jupiter and Saturn across the 0.3 to 1.3 mm wavelength range using a Fourier Transform Spectrometer mounted on the 10.4-meter dish of the CSO at Mauna Kea, Hawaii, 4100 meters above sea level. A careful calibration, including the evaluation of the antenna performance over such a wide wavelength range and the removal of the Earth's atmosphere effects, has allowed the detection of broad absorption lines on those planets' atmospheres. The calibrated data allowed us to verify the predictions of standard models for both planets in this spectral region, and to confirm the absolute radiometry in the case of Jupiter. Besides their physical interest, the results are also important as both planets are calibration references in the current era of operating ground-based and space-borne submillimeter instruments.

High-resolution rotational spectroscopy in a cold ion trap: H2D+ and D2H+.

The lowest-lying 1(01) <-- 0(00) transition of para-H(2)D(+) and 1(11) <-- 0(00) of ortho-D(2)H(+) has been detected by the enhancement of the D/H isotope exchange reaction in collisions with p-H2 upon rotational excitation. These are the first pure rotational spectra of molecular ions by action spectroscopy. For this purpose, a cryogenic multipole ion trap has been combined with narrow-band tunable radiation sources operating in the 1.25 to 1.53 THz range. The low temperature of the ions allows us to determine the astronomically important transitions with a relative precision of Delta nu/nu=10(-8). While the 1 476 605.708(15) MHz line center frequency for the o-D(2)H(+) transition agrees very well with previous unpublished work, the 1 370 084.880(20) MHz line center frequency for the p-H(2)D(+) transition deviates by 61 MHz. Potential future applications of this new approach to rotational spectroscopy are discussed.