This study assesses the performance of the Weather Research and Forecasting (WRF) model to represent the near-surface weather conditions and the precipitable water vapour (PWV) in the Chajnantor plateau, in the north of Chile, from 2007 April to December. The WRF model shows a very good performance forecasting the near-surface temperature and zonal wind component, although it overestimates the 2 m water vapour mixing ratio and underestimates the 10 m meridional wind component. The model represents very well the seasonal, intraseasonal and the diurnal variation of PWV. However, the PWV errors increase after the 12 h of simulation. Errors in the simulations are larger than 1.5 mm only during 10 per cent of the study period, they do not exceed 0.5 mm during 65 per cent of the time and they are below 0.25 mm more than 45 per cent of the time, which emphasizes the good performance of the model to forecast the PWV over the region. The misrepresentation of the near-surface humidity in the region by the WRF model may have a negative impact on the PWV forecasts. Thus, having accurate forecasts of humidity near the surface may result in more accurate PWV forecasts. Overall, results from this, as well as recent studies, supports the use of the WRF model to provide accurate weather forecasts for the region, particularly for the PWV, which can be of great benefit for astronomers in the planning of their scientific operations and observing time.

In a radio interferometer, the geometrical antenna positions are determined from measurements of the observed delay to each antenna from observations across the sky of many point sources whose positions are known to high accuracy. The determination of accurate antenna positions relies on accurate calibration of the dry and wet delay of the atmosphere above each antenna. For the Atacama Large Millimeter/Submillimeter Array (ALMA), with baseline lengths up to 15 kilometers, the geography of the site forces the height above mean sea level of the more distant antenna pads to be significantly lower than the central array. Thus, both the ground level meteorological values and the total water column can be quite different between antennas in the extended configurations. During 2015, a network of six additional weather stations was installed to monitor pressure, temperature, relative humidity and wind velocity, in order to test whether inclusion of these parameters could improve the repeatability of antenna position determinations in these configurations. We present an analysis of the data obtained during the ALMA Long Baseline Campaign of October through November 2015. The repeatability of antenna position measurements typically degrades as a function of antenna distance. Also, the scatter is more than three times worse in the vertical direction than in the local tangent plane, suggesting that a systematic effect is limiting the measurements. So far we have explored correcting the delay model for deviations from hydrostatic equilibrium in the measured air pressure and separating the partial pressure of water from the total pressure using water vapor radiometer (WVR) data. Correcting for these combined effects still does not provide a good match to the residual position errors in the vertical direction. One hypothesis is that the current model of water vapor may be too simple to fully remove the day-to-day variations in the wet delay. We describe possible new avenues of improvement, which include recalibrating the baseline measurement datasets using the contemporaneous measurements of the water vapor scale height and temperature lapse rate from the oxygen sounder, and applying more accurate measurements of the sky coupling of the WVRs.

The Atacama Large Millimeter/submillimeter Array finds itself in the transition into full operations. Previous construction activities are being wrapped up, and regular, repetitive maintenance and upkeep will dominate the daily life, which asks for a consolidation and streamlining of the activities at the observatory. Especially the shifting focus to the high site of the observatory deserves more attention, since assembly, integration and verification activities at the base camp have ceased by now. In parallel, adjustments in the host country's labor legislation for operations at high geographic altitudes demand a review of the way things are done. This talk outlines the underlying operational concepts, lists the limiting constraints, describes the implementation of our reactions to those, and outlines our future intentions, which will be one in a number of steps towards optimization of the productivity of the observatory. The latter is the top level goal, which the Joint ALMA Observatory (JAO) has signed up for.

The ALMA Test Interferometer appeared as an infrastructure solution to increase both ALMA time availability for science activities and time availability for Software testing and Engineering activities at a reduced cost (<30000K USD) and a low setup time of less than 1 hour. The Test Interferometer could include up to 16 Antennas when used with only AOS resources and a possible maximum of 4 Antennas when configured using Correlator resources at OSF. A joined effort between ADC and ADE-IG took the challenge of generate the Test Interferometer from an already defined design for operations which imposed a lot of complex restrictions on how to implement it. Through and intensive design and evaluation work it was determined that is possible to make an initial implementation using the ACA Correlator and now it is also being tested the feasibility to implement the Testing Interferometer connecting the Test Array at AOS with Correlator equipment installed at the OSF, separated by 30 km. app. Lastly, efforts will be done to get interferometry between AOS and OSF Antennas with a baseline of approximately 24 km.

Current large observatories, both in operation and projects in development or construction, face the challenge to find skilled personnel for integration and operation. Typical locations of these observatories are found to be remote, mainly due to electromagnetic pollution prevention, which in many if not all cases reduces the attractiveness of the work posts. Additional budgetary limitations restrict the recruitment radius for certain positions to the local labor market. This paper outlines these staffing constraints in more detail and elaborates on the need for training programs on various levels, which can be costly. This, in turn, drives the need for creative retention efforts. Therefore, financial modeling, contingency, risk and quality management, and the reliability, availability, and maintainability of an observatory are directly coupled to the local embedding in the labor market of the host country.

Aims. We aim at deriving the excitation conditions of the interstellar gas as well as the local FUV intensities in the molecular cloud surrounding NGC 3603 to get a coherent picture of how the gas is energized by the central stars. Methods. The NANTEN2-4 m submillimeter antenna is used to map the [CI] 1-0, 2-1 and CO 4-3, 7-6 lines in a 2' x 2' region around the young OB cluster NGC 3603 YC. These data are combined with C(18)O 2-1 data, HIRES-processed IRAS 60 mu m and 100 mu m maps of the FIR continuum, and Spitzer/IRAC maps. Results. The NANTEN2 observations show the presence of two molecular clumps located south-east and south-west of the cluster and confirm the overall structure already found by previous CS and C(18)O observations. We find a slight position offset of the peak intensity of CO and [CI], and the atomic carbon appears to be further extended compared to the molecular material. We used the HIRES far-infrared dust data to derive a map of the FUV field heating the dust. We constrain the FUV field to values of chi = 3-6 x 10(3) in units of the Draine field across the clouds. Approximately 0.2 to 0.3% of the total FUV energy is re-emitted in the [CII] 158 mu m cooling line observed by ISO. Applying LTE and escape probability calculations, we derive temperatures (T(MM1) = 43 K, T(MM2) = 47 K), column densities (N(MM1) = 0.9 x 10(22) cm(-2), N(MM2) = 2.5 x 10(22) cm(-2)) and densities (n(MM1) = 3 x 10(3) cm(-3), n(MM2) = 10(3) - 10(4) cm(-3)) for the two observed molecular clumps MM1 and MM2. Conclusions. The cluster is strongly interacting with the ambient molecular cloud, governing its structure and physical conditions. A stability analysis shows the existence of gravitationally collapsing gas clumps which should lead to star formation. Embedded IR sources have already been observed in the outskirts of the molecular cloud and seem to support our conclusions.

The content of precipitable water vapor (PWV) in the atmosphere is very important for astronomy in the infrared and radio (sub-millimeter) spectral regions. Therefore, the astrometeorology group has developed different methods to derive this value from measurements and making forecasts using a meteorological model. The goal is use that model to predict the atmospheric conditions and support the scheduling of astronomical observations. At ESO, several means to determine PWV over the observatories have been used, such as IR-radiometers (IRMA), optical and infrared spectrographs as well as estimates using data from GOES-12 satellite. Using all of these remote sensing methods a study undertaken to compare the accuracy of these PWV measurements to the simultaneous in-situ measurements provided by radiosondes. Four dedicated campaigns were conducted during the months of May, July, August and November of 2009 at the La Silla, APEX and Paranal observatory sites. In addition, the astrometeorological group employs the WRF meteorological model with the goal of simulating the state of the atmosphere (every 6 hours) and forecasting the PWV. With these simulations, plus satellite images, radiosonde campaign data can be classified synoptically and at the same time the model can be validated with respect to PWV.

APEX, the Atacama Pathfinder EXperiment, is being operated successfully, now for five years, on Llano de Chajnantor at 5107m altitude in the Chilean High Andes. This location is considered one of the worlds outstanding sites for submillimeter astronomy, which the results described in this contribution are underlining. The primary reflector with 12 m diameter is cautiously being maintained at about 15 mu m by means of holography. This allows to access all atmospheric submillimeter windows accessible from the ground, up to 200 mu m. Telescope and instrument performance, operational experiences and a selection of scientific results are given in this publication.

The ArTeMiS submillimetric camera will observe simultaneously the sky at 450, 350 and 200 μm using 3 different focal planes made of 2304, 2304 and 1152 bolometric pixels respectively. This camera will be mounted in the Cassegrain cabin of APEX, a 12 m antenna located on the Chajnantor plateau, Chile. To realize the bolometric arrays, we have adapted the Silicon processing technology used for the Herschel-PACS photometer to account for higher incident fluxes and longer wavelengths from the ground. In addition, an autonomous cryogenic system has been designed to cool the 3 focal planes down to 300 mK. Preliminary performances obtained in laboratory with the first of 3 focal planes are presented. Latest results obtained in 2009 with the P-ArTeMiS prototype camera are also discussed, including massive protostellar cores and several star forming regions that have been clearly identified and mapped.

We demonstrate for the first time the closure of an electronic phase lock loop for a continuous-wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark-shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K.

ArTeMiS is a bolometer camera that will be installed at the APEX submillimeter telescope in Chile in 2010. This instrument will be a powerful tool for scientists with its three focal planes that will operate simultaneously in background limited conditions at 200, 350 and 450 microns (5760 pixels in total). A prototype called p-ArTeMiS has been tested at APEX in 2007 and thanks to its good performances, the team has been able to conduct scientific projects in star formation and on debris disks. This paper summarises the details of the ArTeMiS project, with a description of the detectors, the optics, the cryogenics and the electronics. We will also present the undergoing studies at CEA on detectors for the future submillimeter space missions.

NGC 2024, a sites of massive star formation, have complex internal structures caused by cal heating by young stars, outflows, and stellar winds. These complex cloud structures lead to intricate emission line shapes. The goal of this paper is to show that the complex line shapes of 12 CO lines in NGC 2024 can be explained consistently with a model, whose temperature and velocity structure are based on the well-established scenario of a PDR and the Blister model. We present velocity-resolved spectra of seven CO lines ranging from J=3 to J=13, and we combined these data with CO high-frequency data from the ISO satellite. We find that the bulk of the molecular cloud associated with NGC 2024 consists of warm (75 K) and dense (9e5 cm-3) gas. An additional hot (~ 300 K) component, located at the interface of the HII region and the molecular cloud, is needed to explain the emission of the high-J CO lines. Deep absorption notches indicate that very cold material (20 K) exists in front of the warm material, too. A temperature and column density structure consistent with those predicted by PDR models, combined with the velocity structure of a Blister model, appropriately describes the observed emission line profiles of this massive star forming region. This case study of NGC 2024 shows that, with physical insights into these complex regions and careful modeling, multi-line observations of CO can be used to derive detailed physical conditions in massive star forming regions.

We demonstrate for the first time the closure of an electronic phase lock loop for a continuous-wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark-shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K.

Context. Star formation at earlier cosmological times takes place in an interstellar medium with low metallicity. The Large Magellanic Cloud (LMC) is ideally suited to study star formation in such an environment. Aims. The physical and chemical state of the ISM in a star forming environment can be constrained by observations of submm and FIR spectral lines of the main carbon carrying species, CO, Ci and Cii, which originate in the surface layers of molecular clouds i lluminated by the UV radiation of the newly formed, young stars. Methods. We present high-angular resolution sub-millimeter observations in the N159W region in the LMC obtained with the NANTEN2 telescope of the 12 CO J = 4→ 3, J = 7→ 6, and 13 CO J = 4→ 3 rotational and [Ci] 3 P1− 3 P0 and 3 P2− 3 P1 fine-structure transitions. The 13 CO J = 4→ 3 and [Ci] 3 P 2− 3 P 1 transitions are detected for the first time in the LMC. We deri ve the physical and chemical properties of the low-metallicity molecular gas using an escape probability code and a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. Results. The separate excitation analysis of the submm CO lines and the carbon fine structure lines shows that the emitting gas in th e N159W region has temperatures of about 80 K and densities of about 10 4 cm −3 . The estimated C to CO abundance ratio close to unity is substantially higher than in dense massive star-forming regions in the Milky Way. The analysis of all observed lines together, including the [Cii] line intensity reported in the literature, in the context of a clu mpy cloud PDR model constrains the UV intensity to about �≈ 220 and an average density of the clump ensemble of about 10 5 cm −3 , thus confirming the presence of high density material in the LMC N159W region.

The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born, very massive stars within their natal giant molecular clouds (GMCs) at only 2.35 kpc distance. We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas. The NANTEN2-4m submillimeter telescope was used to map the [CI] 3P1-3P0, 3P2-3P1 and CO 4-3, 7-6 lines in two 4'x4' regions of Carina where molecular material interfaces with radiation from the massive star clusters. One region is the northern molecular cloud near the compact OB cluster Tr14, and the second region is in the molecular cloud south of etaCar and Tr16. These data were combined with 13CO SEST spectra, HIRES/IRAS 60um and 100um maps of the FIR continuum, and maps of 8um IRAC/Spitzer and MSX emission. We used the HIRES far-infrared dust data to create a map of the FUV field heating the gas. The northern region shows an FUV field of a few 1000 in Draine units while the field of the southern region is about a factor 10 weaker. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the 38" beam (0.43pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 2x10**5 cm-3 is needed to reproduce the observed line emission at two selected interface positions. Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.

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 2x7 element heterodyne array for operation in the 450 pm and 350 pm 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 32x1.5 (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.

ArTeMiS is a camera designed to operate on large ground based submillimetric telescopes in the 3 atmospheric windows 200, 350 and 450 mu m. The focal plane of this camera will be equipped with 5760 bolometric pixels cooled down at 300 mK with an autonomous cryogenic system. The pixels have been manufactured, based on the same technology processes as used for the Herschel-PACS space photometer. We review in this paper the present status and the future plans of this project.A prototype camera, named P-ArTeMiS, has been developed and successfully tested on the KOSMA telescope in 2006 at Gornergrat 3100m, Switzerland. Preliminary results were presented at the previous SPIE conference in Orlando (Talvard et al, 2006). Since then, the prototype camera has been proposed and successfully installed on APEX, a 12 m antenna operated by the Max Planck Institute fur Radioastronomie, the European Southern Observatory and the Onsala Space Observatory on the Chajnantor site at 5 100 m altitude in Chile. Two runs have been achieved in 2007, first in March and the latter in November. We present in the second part of this paper the first processed images obtained on star forming regions and on circumstellar and debris disks, Calculated sensitivities are compared with expectations. These illustrate the improvements achieved on P-ArTeMiS during the 3 experimental campaigns.

Studying molecular gas in the central regions of the star burst galaxies NGC4945 and Circinus enables us to characterize the physical conditions and compare them to previous local and high-z studies. We estimate temperature, molecular density and column densities of CO and atomic carbon. Using model predictions we give a range of estimated CO/C abundance ratios. Using the new NANTEN2 4m sub-millimeter telescope in Pampa La Bola, Chile, we observed for the first time CO 4-3 and [CI] 3P1-3 P0 at the centers of both galaxies at linear scale of 682 pc and 732 pc respectively. We compute the cooling curves of 12CO and 13CO using radiative transfer models and estimate the physical conditions of CO and [CI]. The centers of NGC4945 and Circinus are very [CI] bright objects, exhibiting [CI] 3P1 - 3 P0 luminosities of 91 and 67Kkms-1kpc2, respectively. The [CI] 3P1-3 P0/CO 4-3 ratio of integrated intensities are large at 1.2 in NGC4945 and 2.8 in Circinus. Combining previous CO J= 1-0, 2-1 and 3-2 and 13CO J= 1-0, 2-1 studies with our new observations, the radiative transfer calculations give a range of densities, n(H2) = 10^3-3*104^cm-3, and a wide range of kinetic temperatures, Tkin = 20 - 100K, depending on the density. Future CO J= 7-6 and [CI] 2-1 observations will be important to resolve the ambiguity in the physical conditions and confirm the model predictions.

The CO N Deuterium Observations Receiver, CONDOR, is one of the very few existing THz heterodyne receivers in the world. It covers a frequency range between 1.25 and 1.53 THz (240μm 196μm). CONDOR was built with a focus on observing star forming regions, using high-J CO lines H2D + and N In November 2005 we tested CONDOR on the APEX telescope, and successfully observed CO 13-12 in several regions in Orion. In FIR4 we find a surprisingly narrow CO 13-12 line width (5.4 km/s), from which we conclude that the hot gas is probably radiatively heated rather than shock excited. The observations of NGC2024 reviled additional hot gas. In order to model the CO lines between J= 3-2 and J=13-12 consistently a model with molecular gas in 4 different layers is required. High spectral resolution observations in the THz regime allow us not only to probe gas otherwise difficult to observe, but also to obtain information about the structure and kinematics of the source.