We present deep images of dust continuum emission at 450, 800, and 850 m of the dark cloud LDN 1689N, which harbors the low-mass young stellar objects (YSOs) IRAS 16293À2422 A and B (I16293A and I16293B) and the cold prestellar object I16293E. Toward the positions of I16293A and I16293E we also obtained spectra of CO-isotopomers and deep submillimeter observations of chemically related molecules with high critical densities (HCO + , H 13 CO + , DCO + , H 2 O, HDO, and H 2 D + ). Toward I16293A we report the detection of the HDO 1 01 -0 00 and H 2 O 1 10 -1 01 ground-state transitions as broad self-reversed emission profiles with narrow absorption and a tentative detection of H 2 D + 1 10 -1 11 . Toward I16293E we detect weak emission of subthermally excited HDO 1 01 -0 00 . Based on this set of submillimeter continuum and line data, we model the envelopes around I16293A and I16293E. The density and velocity structure of I16293A is fitted by an inside-out collapse model, yielding a sound speed of a ¼ 0:7 km s À1 , an age of t ¼ (0:6 2:5) Â 10 4 yr, and a mass of 6.1 M . The density in the envelope of I16293E is fitted by a radial power law with index À1:0 AE 0:2, a mass of 4.4 M , and a constant temperature of 16 K. These respective models are used to study the chemistry of the envelopes of these pre-and protostellar objects. We made a large, fully sampled CO J ¼ 2 1 map of LDN 1689N, which clearly shows the two outflows from I16293A and I16293B and the interaction of one of the flows with I16293E. An outflow from I16293E reported elsewhere is not confirmed. Instead, we find that the motions around I16293E identified from small maps are part of a larger scale fossil flow from I16293B. Modeling of the I16293A outflow shows that the broad HDO, water ground state, and CO J ¼ 6 5 and 7-6 emission lines originate in this flow, while the HDO and H 2 O line cores originate in the envelope. The narrow absorption feature in the ground-state water lines is due to cold gas in the outer envelope. The derived H 2 O abundance is 3 Â 10 À9 in the cold regions of the envelope of I16293A (T kin < 14 K), 2 Â 10 À7 in warmer regions of the envelope (>14 K), and 10 À8 in the outflow. The HDO abundance is constant at a few times 10 À10 throughout the envelopes of I16293A and I16293E. Because the derived H 2 O and HDO abundances in the two objects can be understood through shock chemistry in the outflow and ion-molecule chemistry in the envelopes, we argue that both objects are related in chemical evolution. The [HDO]/[H 2 O] abundance ratio in the warm inner envelope of I16293A of a few times 10 À4 is comparable to that measured in comets. This supports the idea that the [HDO]/[H 2 O] ratio is determined in the cold prestellar core phase and conserved throughout the formation process of low-mass stars and planets.

We present observations of the ν 2 =0 and vibrationally excited ν 2 =1 J=9-8 rotational lines of HCN at 797 GHz toward the deeply embedded massive young stellar object GL 2591, which provide the missing link between the extended envelope traced by lower-J line emission and the small region of hot (T ex ≥ 300 K), abundant HCN seen in 14 µm absorption with the Infrared Space Observatory (ISO). The line ratio yields T ex = 720 +135 −100 K and the line profiles reveal that the hot gas seen with ISO is at the velocity of the protostar, arguing against a location in the outflow or in shocks. Radiative transfer calculations using a depth-dependent density and temperature structure show that the data rule out a constant abundance throughout the envelope, but that a model with a jump of the abundance in the inner part by two orders of magnitude matches the observations. Such a jump is consistent with the sharp increase in HCN abundance at temperatures > ∼ 230 K predicted by recent chemical models in which atomic oxygen is driven into water at these temperatures. Together with the evidence for ice evaporation in this source, this result suggests that we may be witnessing the birth of a hot core. Thus, GL 2591 may represent a rare class of objects at an evolutionary stage just preceding the 'hot core' stage of massive star formation.

Different noise sources in HEMTs are discussed, and state-of-the-art low-noise amplifiers based on the Fraunhofer IAF 100 nm and 50 nm gate length metamorphic HEMT (mHEMT) process are presented. These mHEMT technology feature an extrinsic fT of 220 / 375 GHz and an extrinsic transconduction gm, max of 1300 / 1800 mS/mm. By using the 50 nm technology several low-noise amplifier MMICs were realized. A small signal gain of 21 dB and a noise figure of 1.9 dB was measured in the frequency range between 80 and 100 GHz at ambient temperature. To investigate the low temperature behaviour of the 100 nm technology, single 4 * 40 ?m mHEMTs were integrated in hybrid 4 - 8 GHz (Chalmers) and 16 - 26 GHz (Yebes) amplifiers. At cryogenic temperatures noise temperatures of 3 K at 5 GHz and 12 K at 22 GHz were achieved

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This paper reports on the monolithic integration of layout-optimized Schottky diodes realized in an established 50-nm gate-length metamorphic high-electron-mobility transistor technology for use in multifunctional nonlinear circuits. The suitability of the realized Schottky diodes is demonstrated by a broadband millimeter-wave I/Q-mixer (In-phase/Quadrature) and local oscillator (LO) chain comprising two power amplifiers and a frequency tripler, fabricated on monolithic microwave integrated circuits (MMICs). Both circuits are based on an anti-parallel Schottky diode topology. The subharmonically-pumped I/Q-mixer covers an RF (radio frequency) and IF (intermediate frequency) range of at least 75 GHz to 110 GHz and 0.5 GHz to 15 GHz, respectively. The single-sideband conversion loss is between 14 dB and 16 dB across most of the entire RF and IF bands. The core of the LO chain consists of a frequency tripler (multiplier by three) and features a bias-adjustable output power with almost constant conversion efficiency and a control range of more than 8 dB. The fully-integrated LO chain MMIC matches the needs of the presented I/Q-mixer and exhibits an average output power of 16.3 dBm with a covered frequency range of 38 GHz to 60 GHz. The unwanted harmonics are suppressed by at least =25.9 dBc below the third harmonic for the entire frequency range and better than =32.1 dBc for most part of the band. Thus, the mixer and tripler MMICs demonstrate state-of-the-art performance with regards to, e.g., covered bandwidth, output power, harmonic suppression, or 1 dB compression point.