Frank Schäfer

Probing the Early Stages of Low-Mass Star Formation in LDN 1689N: Dust and Water in IRAS 16293–2422A, B, and E

We present deep images of dust continuum emission at 450, 800, and 850 mum of the dark cloud LDN 1689N, which harbors the low-mass young stellar objects (YSOs) IRAS 16293-2422 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+, (HCO+)-C-13, DCO+, H2O, HDO, and H2D+). Toward I16293A we report the detection of the HDO 1(01)-0(00) and H2O 1(10-)1(01) ground-state transitions as broad self-reversed emission profiles with narrow absorption and a tentative detection of H2D+ 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 0: 7 kms(-1), an age of t = (0.6-2.5) x 10(4) yr, and amass of 6.1 M.. The density in the envelope of I16293E is fitted by a radial power law with index -1.0 +/- 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 = 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 = 6-5 and 7-6 emission lines originate in this flow, while the HDO and H2O 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 H2O abundance is 3 x 10(-9) in the cold regions of the envelope of I16293A (T-kin 14 K), and 10(-8) in the outflow. The HDO abundance is constant at a few times 10(-10) throughout the envelopes of I16293A and I16293E. Because the derived H2O 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]/[H2O] abundance ratio in the warm inner envelope of I16293A of a few times 10(-4) is comparable to that measured in comets. This supports the idea that the [HDO]/[ H2O] ratio is determined in the cold prestellar core phase and conserved throughout the formation process of low-mass stars and planets.

GREAT: the first-generation German heterodyne receiver for SOFIA

A consortium of German research laboratories has been established for the development of a modular dual-channel heterodyne instrument (GREAT: German Receiver for Astronomy at Terahertz Frequencies) for high-resolution spectroscopy aboard SOFIA. The receiver is scheduled to be available in time for SOFIAs very first astronomical mission in late 2002. The first-flight version will offer opportunities for parallel observations in two frequency bands. We will have a choice of backends, including an acousto-optic array (4 X 1 GHz) and a high-resolution chirp transform spectrometer.

Excitatory action of the bird antidiuretic hormone vasotocin on neurons in the subfornical organ.

The responsiveness of spontaneously active neurons in the subfornical organ (SFO) of adult ducks to angiotensin II (ANGII) and the bird specific anti-diuretic hormone, arginine vasotocin (AVT), the analog of the mammalian arginine vasopressin (AVP), were investigated in brain slices with extracellular recording technique. 65% (n = 66) of the neurons increased their activity after superfusion with ANGII, the rest were unresponsive. Application of AVT activated 52% (n = 68) of the investigated neurons and like ANGII never caused an inhibition of the spontaneously active SFO neurons. A close correlation exists between the ANGII and AVT sensitivity of duck SFO neurons, because 29 out of 33 neurons were excited by AVT as well as ANGII. The relatively weak antagonistic effect of the V1-type receptor antagonist Pmp-Tyr (Me)-Arg8-vasopressin on the AVT induced excitation suggests a different pharmacology of the bird AVT receptor as compared to the mammalian AVP receptor. The excitatory response of ANGII and AVT on the very same neurons suggest a similar function of both peptides on SFO mediated effects in vivo, such as an increase in water intake. However, peripheral AVT concentrations, unlike ANGII concentrations in the blood are not high enough to activate SFO neurons from the blood side of the blood brain barrier. Therefore AVT is presumably released from synapses of neurons originating within or projecting to the SFO. The identity of the ANGII and AVT reactive neurons suggests that synaptically released AVT should facilitate SFO mediated drinking.

Cryogenic Low-Noise mHEMT-Based MMIC Amplifiers for 4–12 GHz Band

Two broadband very low-noise amplifiers operating in the frequency range from 4 to 12 GHz at cryogenic temperature are presented. The amplifier circuits have been developed using a 100 nm gate length InAlAs/InGaAs metamorphic high electron mobility transistor (mHEMT) technology. The three-stage amplifiers are monolithic microwave integrated circuit (MMIC) chips manufactured in coplanar technology. At cryogenic temperature the first MMIC amplifier achieved a linear gain of 22 dB and an average noise temperature of 11.6 K with a power dissipation of 41 mW. The second MMIC amplifier, with external input matching network, exhibited a gain of 26 dB, and an excellent average noise temperature of 8.1 K with a power dissipation of 12 mW. Both LNA units demonstrate broad bandwidth, high gain, low noise temperature, and compact chip size. The results obtained prove that mHEMT technology is suitable for applications in large instantaneous bandwidth cryogenic receivers for radio astronomy applications.

Submillimeter heterodyne arrays for APEX

We report on developments of submillimeter heterodyne arrays for high resolution spectroscopy with APEX. Shortly, we will operate state-of-the-art instruments in all major atmospheric windows accessible from Llano de Chajnantor. CHAMP+, a dual-color 2×7 element heterodyne array for operation in the 450 μm and 350 μm atmospheric windows is in operation since late 2007. With its state-of-the-art SIS detectors and wide tunable local oscillators, its cold optics with single sideband filters and with 3 GHz of processed IF bandwidth per pixel, CHAMP+ does provide outstanding observing capabilities. The Large APEX sub-Millimeter Array (LAsMA) is in the final design phase, with an installation goal in 2009. The receiver will operate 7 and 19 pixels in the lower submillimeter windows, 285-375 GHz and 385-520 GHz, respectively. The front-ends are served by an array of digital wideband Fast Fourier Transform spectrometers currently processing up to 32×1.5 (optionally 1.8) GHz of bandwidth. For CHAMP+, we process 2.8 GHz of instantaneous bandwidth (in 16.4 k channels) for each of the 14 pixels.

Opposite effects of angiotensin II and nitric oxide on neurons in the duck subfornical organ

Angiotensin II (ANGII) is known to activate neurons in the subfornical organ (SFO) of mammals and birds and this activation is regarded as the basis for the ANGII induced increase in water intake. Application of the nitric oxide (NO) donor sodium nitroprusside inhibited the activity in 10 out of 12 duck SFO neurons, 8 of which were in addition excited by ANGII. These data, in combination with the histochemical detection of NO synthase in the duck SFO, demonstrate the involvement of NO in SFO mediated responses and might represent the cellular basis for the observed opposite effects of ANGII and NO on water intake.

A versatile and cryogenic mHEMT-model including noise

A versatile scalable small signal model for high electron mobility transistors (HEMTs) of gate length 50 nm and 100 nm has been developed. The model covers a large bias range and includes the temperature dependence from 300 K to 15 K. Especially, it is capable to predict the noise behaviour of the transistor in dependence of ambient temperature and frequency.

A single chip broadband noise source for noise measurements at cryogenic temperatures

This paper presents the design and performance of a single chip broadband noise source dedicated for on-chip measurements in a cryogenic environment. The noise source is used to generate the two input noise powers Pc and Ph which are required by the commonly used Y-factor method. High accuracy in temperature control and impedance presented to the device under test is achieved over a wide temperature range from 7 K to 100 K. Noise temperature measurements of a cryogenic low noise amplifier were performed on-chip and show a typical accuracy of ±1 K.

Photonic (sub)millimeterwave local oscillators

Optical heterodyne millimeter-wave (mm-wave) generation using traveling-wave photodetectors (TW-PDs) is examined both experimentally and theoretically. Ultrahigh-frequency (110 GHz, 160 GHz and 460 GHz) InP-based 1.55 /spl mu/m TW-PDs were fabricated and employed in experimental set-ups for optical heterodyning. For the first time a 1.55 /spl mu/m photonic sub millimetre-wave (460 GHz) local oscillator (LO) module has been developed and demonstrated.

Excitatory and inhibitory responses caused by norepinephrine in duck subfornical organ neurons are mediated by β- and α2-adrenoceptor activation

The responsiveness of spontaneously active neurons in the subfornical organ (SFO) of adult ducks to angiotensin II (ANGII), norepinephrine (NE), isoproterenol (Iso, β-agonist), phenylephrine (Phe, α1-agonist) and clonidine (Clo, α2-agonist) was investigated in brain slices with extracellular recording technique. 64% (n=90) of the neurons increased their activity after superfusion with ANGII, the rest were unresponsive. Application of NE activated 10 and inhibited 8 neurons (n=22); the excitation being correlated with an excitatory ANGII responsiveness of the same neurons and the inhibition with the absence of an ANGII responsiveness. Iso activated 74% (n=58) and Clo inhibited 88% (n=16) of the investigated neurons. Phe did not have an effect on the majority (60%) of the neurons and produced both excitatory and inhibitory actions on the remaining cells. These results offer a plausible explanation for the dose dependent dipsogenic effect of Iso and the failure of NE to elicit dose dependent drinking, which can be explained by its dual, excitatory and inhibitory effect on SFO neurons. It is further concluded, that peripherally applied Iso exerts its dipsogenic action in high concentration by a direct excitatory effect on SFO neurons via the open blood brain barrier. Under physiological conditions, afferent neuronal input of still unknown origin might specifically modulate the activity of SFO neurons, because plasma concentrations of NE are probably not high enough to activate SFO neurons from the blood side of the blood brain barrier.