We present a model of the longwave atmospheric spectrum that improves in many respects widely used older models such as the microwave propagation model (MPM) [1],[2], since it is based on recent broadband measurements and calculations. According to our data, the model is fully applicable from 0 to 2 THz while including lines up to 10 THz. Its primary goal is to simulate the millimeter/submillimeter region accessible from the ground (frequencies up to 2 THz at most, with a few windows between 1 and 2 THz accessible only under exceptional conditions at very dry sites). Line-by-line calculations of the absorption are performed using a line database generated from the latest available spectroscopic constants for all relevant atmospheric species. The collisional line widths are obtained from published laboratory data. The excess of absorption in the longwave range that cannot be explained by the line spectrum is modeled by introducing two different continuum-like terms based on our own recent FTS measurements between 170 and 1100 GHz: collision-induced absorption of the dry atmosphere due to transient dipoles in symmetric molecules (N 2 and O 2 ) and continuum-like water vapor opacity. All H 2 O lines up to 10 THz are included in order to correctly account for the entire H 2 O far-wing opacity below 2 THz for a given line-shape. Hence, this contribution does not need to be part of a pseudocontinuum term below that frequency cutoff (still necessary, as shown in this paper) in contrast to other models used to date. Phase delays near H 2 O and O 2 resonances are also important for ground-based astronomy since they affect interferometric phase. The frequency-dependent dispersive phase delay function is formally related to the absorption line shape via the Kramers-Krönig dispersion theory, and this relation has been used for modeling those delays. Precise calculations of phase delays are essential for the future Atacama large millimeter array (ALMA) project. A software package called atmospheric transmission at microwaves (ATM) has been developed to provide the radioastronomy and aeronomy communities with an updated tool to compute the atmospheric spectrum in clear-sky conditions for various scientific applications. In this paper, we use this model to provide detailed simulations of atmospheric transmission and phase dispersion for several sites suitable for submillimeter astronomy.

We perform a sensitive (line confusion limited), single-side band spectral survey towards Orion KL with the IRAM 30 m telescope, covering the following frequency ranges: 80−115.5 GHz, 130−178 GHz, and 197−281 GHz. We detect more than 14 400 spectral features of which 10 040 have been identified up to date and attributed to 43 different molecules, including 148 isotopologues and lines from vibrationally excited states. In this paper, we focus on the study of OCS, HCS + , H 2 CS, CS, CCS, C 3 S, and their isotopologues. In addition, we map the OCS J = 18−17 line and complete complementary observations of several OCS lines at selected positions around Orion IRc2 (the position selected for the survey). We report the first detection of OCS ν 2 = 1 and ν 3 = 1 vibrationally excited states in space and the first detection of C 3 S in warm clouds. Most of CCS, and almost all C 3 S, line emission arises from the hot core indicating an enhancement of their abundances in warm and dense gas. Column densities and isotopic ratios have been calculated using a large velocity gradient (LVG) excitation and radiative transfer code (for the low density gas components) and a local thermal equilibrium (LTE) code (appropriate for the warm and dense hot core component), which takes into account the different cloud components known to exist towards Orion KL, the extended ridge, compact ridge, plateau, and hot core. The vibrational temperature derived from OCS ν 2 = 1 and ν 3 = 1 levels is 210 K, similar to the gas kinetic temperature in the hot core. These OCS high energy levels are probably pumped by absorption of IR dust photons. We derive an upper limit to the OC 3 S, H 2 CCS, HNCS, HOCS + , and NCS column densities. Finally, we discuss the D/H abundance ratio and infer the following isotopic abundances: 12 C/ 13 C = 45 ± 20, 32 S/ 34 S = 20 ± 6, 32 S/ 33 S = 75 ± 29, and 16 O/ 18 O = 250 ± 135.

The unprecedented sensitivity of Herschel coupled with the high resolution of the HIFI spectrometer permits studies of the intensity-velocity relationship I(v) in molecular outflows, over a higher excitation range than possible up to now. In the course of the CHESS Key Program, we have observed toward the bright bowshock region L1157-B1 the CO rotational transitions between J=5-4 and J=16-15 with HIFI, and the J=1-0, 2-1 and 3-2 with the IRAM-30m and the CSO telescopes. We find that all the line profiles I CO (v) are well fit by a linear combination of three exponential laws ∝ exp(−|v/v 0 |) with v 0 = 12.5, 4.4 and 2.5 km s −1 . The first component dominates the CO emission at J ≥ 13, as well as the high-excitation lines of SiO and H 2 O. The second component dominates for 3 ≤ J up ≤ 10 and the third one for J up ≤ 2. We show that these exponentials are the signature of quasi-isothermal shocked gas components : the impact of the jet against the L1157-B1 bowshock (T k ≃ 210 K), the walls of the outflow cavity associated with B1 (T k ≃ 64 K) and the older cavity L1157-B2

We report on the detection with the Infrared Space Observatory of strong infrared absorption from NH 3 and C 2 H 4 in CRL 618. The observed NH 3 and C 2 H 4 bands arise from a region with kinetic temperatures Ӎ200 K, i.e., the dense gas in the photodissociation region associated to the dense torus surrounding the central star, as was the case for the polyynes and cyanopolyynes (see the companion Letter). Several absorption bands, probably arising from small gas-phase hydrocarbons, are observed between 5.5 and 11 mm. Two of these species have been identified with the 30 m IRAM telescope as the methylpolyynes CH 3 C 2 H and CH 3 C 4 H. However, the absorption around 6.2 mm is particularly broad and could arise from the combination of these small hydrocarbons and from the aromatic CuC stretching of polycyclic aromatic hydrocarbons of moderate size. These bands and those associated to the polyynes, cyanopolyynes, methylpolyynes, and benzene are not present in the infrared spectrum of the asymptotic giant branch star IRC ϩ10216.