Christophe Risacher

ATLASGAL - The APEX telescope large area survey of the galaxy at 870 μm

Context. Thanks to its excellent 5100 m high site in Chajnantor, the Atacama Pathfinder Experiment (APEX) systematically explore s the southern sky at submillimeter wavelengths, both in continuum and in spectral line emission. Studying continuum emission from interstellar dust is essential to locate the highest densit y regions in the interstellar medium, and to derive their masses, column densities, density structures, and larger scale morpholog ies. In particular, the early stages of (massive) star forma tion are still quite mysterious: only small samples of high-mass proto-stellar or young stellar objects have been studied in detail so far. Aims. Our goal is to produce a large scale, systematic database of massive pre- and proto-stellar clumps in the Galaxy, in order to better understand how and under what conditions star formation takes place. Only a systematic survey of the Galactic Plane can provide the statistical basis for unbiased studies. A well characteriz ed sample of Galactic star-forming sites will deliver an evolutionary sequence and a mass function of high-mass star-forming clumps. Such a systematic survey at submillimeter wavelengths also represents a pioneering work in preparation for Herschel and ALMA. Methods. The APEX telescope is ideally located to observe the inner Milky Way. The recently commissioned Large APEX Bolometer Camera (LABOCA) is a 295-element bolometer array observing at 870 µm, with a beam of 19. ′′ 2. Taking advantage of its large field of view (11. ′ 4) and excellent sensitivity, we have started an unbiased survey of the whole Galactic Plane accessible to APEX, with a typical noise level of 50‐70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). Results. As a first step, we have covered ∼95 deg 2 of the Galactic Plane. These data reveal∼6000 compact sources brighter than 0.25 Jy, or 63 sources per square degree, as well as extended structures, many of them filamentary. About two thirds of the c ompact sources have no bright infrared counterpart, and some of them are likely to correspond to the precursors of (high-mass) proto-stars or proto-clusters. Other compact sources harbor hot cores, compact Hii regions or young embedded clusters, thus tracing more evolved stages after star formation has occurred. Assuming a typical distance of 5 kpc, most sources are clumps smaller than 1 pc with masses from a few 10 to a few 100 M⊙. In this first introductory paper, we show preliminary resul ts from these ongoing observations, and discuss the mid- and long-term perspectives of the survey.

A Swedish heterodyne facility instrument for the APEX telescope

Aims. In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. Methods. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K. Results. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.

Waveguide-to-microstrip transition with integrated bias-T

A novel device, a waveguide-to-microstrip transition with an integrated bias-T, is presented. The substrate-based planar structure comprises a waveguide E-probe, shaped as a radial line. The probe couples the RF field of a full-height waveguide to a microstrip line or directly to an active component, e.g., a transistor or diode in a mixer or direct detector. The radial probe is connected on its wide side to another port via a specially shaped high impedance line that provides RF/DC isolation. This port can then be used to inject DC and/or extract IF signals. The design of the presented structure was done using CAD (3-D EM simulation) and an X-band device was produced and fully characterized. The measured performance is in excellent agreement with the simulations; the device has return loss better than -20 dB, insertion loss less or equal to -0.15 dB and isolation for the bias-T line better than -20 dB. RF bandwidth for the transition is 30% of the central frequency.

A 1.3-THz Balanced Waveguide HEB Mixer for the APEX Telescope

In this paper, we report about the development, fabrication, and characterization of a balanced waveguide hot electron bolometer (HEB) receiver for the Atacama Pathfinder EXperiment telescope covering the frequency band of 1.25-1.39 THz. The receiver uses a quadrature balanced scheme and two HEB mixers, fabricated from 4- to 5-nm-thick NbN film deposited on crystalline quartz substrate with an MgO buffer layer in between. We employed a novel micromachining method to produce all-metal waveguide parts at submicrometer accuracy (the main-mode waveguide dimensions are 90 times 180 mum ). We present details on the mixer design and measurement results, including receiver noise performance, stability and ldquofirst-lightrdquo at the telescope site. The receiver yields a double-sideband noise temperature averaged over the RF band below 1200 K, and outstanding stability with a spectroscopic Allan time more than 200 s.

APEX: the Atacama Pathfinder EXperiment

APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the worlds outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.

A submillimetre search for cold extended debris disks in the β Pictoris moving group

Context: Previous observations with the Infrared Astronomical Satellite and the Infrared Space Observatory, and ongoing observations with Spitzer and AKARI, have led to the discovery of over 200 debris disks, based on detected mid- and far infrared excess emission, indicating warm circumstellar dust. To constrain the properties of these systems, e.g., to more accurately determine the dust mass, temperature and radial extent, follow-up observations in the submillimetre wavelength region are needed. Aims: The β Pictoris moving group is a nearby stellar association of young ( 12 Myr) co-moving stars including the classical debris disk star β Pictoris. Due to their proximity and youth, they are excellent targets when searching for submillimetre emission from cold, extended, dust components produced by collisions in Kuiper-Belt-like disks. They also allow an age independent study of debris disk properties as a function of other stellar parameters. Methods: We observed 7 infrared-excess stars in the β Pictoris moving group with the LABOCA bolometer array, operating at a central wavelength of 870 μm at the 12-m submillimetre telescope APEX. The main emission at these wavelengths comes from large, cold dust grains, which constitute the main part of the total dust mass, and hence, for an optically thin case, make better estimates on the total dust mass than earlier infrared observations. Fitting the spectral energy distribution with combined optical and infrared photometry gives information on the temperature and radial extent of the disk. Results: From our sample, β Pic, HD 181327, and HD 172555 were detected with at least 3σ certainty, while all others are below 2σ and considered non-detections. The image of β Pic shows an offset flux density peak located near the south-west extension of the disk, similar to the one previously found by SCUBA at the JCMT. We present SED fits for detected sources and give an upper limit on the dust mass for undetected ones. Conclusions: We find a mean fractional dust luminosity bar{f}_dust = 1.1 × 10-3 at t ≈ 12 Myr, which together with recent data at 100 Myr suggests an f_dust ∝ t-α decline of the emitting dust, with α > 0.8. Based on observations with APEX, Llano Chajnantor, Chile (ESO programmes 079.F-9307(A) and 079.F-9308(A)).

Micromachining Approach in Fabricating of THz Waveguide Components

In this paper, we describe our progress in micromachining of submillimeter waveguide structures such as a quadrature waveguide coupler which is a part of a THz balanced heterodyne receiver. We have set up and developed pilot testing of the micromachining process with required high quality of structure.

q1 Eridani : a solar-type star with a planet and a dust belt

Context. Far-infrared excess emission from main-sequence stars is due to dust produced by orbiting minor bodies. In these disks, larger bodies, such as planets, may also be present and the understa ...

Facility heterodyne receiver for the Atacama Pathfinder Experiment Telescope

APEX, the Atacama PAthflnder Experiment (APEX) Telescope, is a partnership between Max Planck Institut fur Radioastronomie (in collaboration with Astronomisches Institut Ruhr Universitat Bochum (AIRUB)), Onsala Space Observatory and the European Southern Observatory. The telescope antenna, supplied by VERTEX Antennentechnik, is a 12 m antenna with a 17 mum rms surface accuracy operating at the Atacama Desert in the Chilean Andes at a 5100 m altitude. The APEX heterodyne facility receiver is placed in the telescope Nasmyth Cabin A. The receivers are coupled to the antenna via relay optics allowing the operation of two different Pi-type instruments and a 6-channel facility heterodyne receiver to cover approximately 210 - 1500 GHz frequency range while providing frequency independent illumination of the secondary. In this report, we present details on the optics for the APEX facility heterodyne receiver and details of its design. The report includes a very brief review of the APEX Band 1, 211 - 270 GHz, Band 2, 270 - 370 GHz, Band 3, 385 - 500 GHz, all based on sideband separation SIS mixer technology and Band T2, 1250 - 1390 GHz, a balanced waveguide HEB mixer, all developed by GARD.

A sideband separating mixer for 85-115 GHz

This paper presents the results of development and tests of a sideband separating heterodyne receiver for the 85-115 GHz band with superconducting tunnel junctions (SIS) as frequency down converters. Sideband separation is achieved by using a quadrature scheme where two identical mixer junctions are pumped by a local oscillator (LO) with 90/spl deg/ phase difference. We used an innovative mixer layout where the quadrature scheme is implemented using waveguide-based and integrated on-chip components. We employed an additional pair of SIS junctions as terminations for LO-injection directional couplers.