L.-Å. Nyman

A composite CO survey of the entire milky way

Large-scale CO surveys of the entire Galactic plane and specific nearby clouds have been combined to produce a panorama of the entire Milky Way in molecular clouds at an angular resolution of 1/2°. Covering 10°–20° in latitude at all longitudes and all large, nearby clouds at higher latitude, the composite survey is the only molecular line survey to date with sky coverage and resolution comparable to that of the early 21 cm surveys.

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.

ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns

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.

The Atacama Pathfinder EXperiment (APEX) - a new submillimeter facility for southern skies -

APEX, the Atacama Pathfinder EXperiment, has been successfully commissioned and is operational. 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 world’s outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of only 17–18 µm makes APEX suitable for observations up to 200 µm, through all atmospheric submm windows accessible from the ground. First scientific results will be presented in the accompanying papers of this special issue.

THE 2014 ALMA LONG BASELINE CAMPAIGN: FIRST RESULTS FROM HIGH ANGULAR RESOLUTION OBSERVATIONS TOWARD THE HL TAU REGION

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0. ′′ 075 (10 AU) to 0. ′′ 025 (3.5 AU), revealing an astonishing level of detail in the cir cumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72 ◦ ± 0.05 ◦ ) and position angle (+138.02 ◦ ± 0.07 ◦ ). We obtain a high-fidelity image of the 1.0 mm spectral index (�), which ranges from � � 2.0 in the optically-thick central peak and two brightest ring s, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation incl ude an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO + (1-0) which exhibits a pattern over LSR velocities from 2-12 km s -1 consistent with Keplerian motion around a �1.3M⊙ star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protost ars XZ Tau (A/B) and LkH�358 at 2.9 mm. Subject headings: stars: individual (HL Tau, XZ Tau, LkH�358) — protoplanetary disks — stars: formation — submillimeter: planetary systems — techniques: interferometric

SIMBA survey of southern high-mass star forming regions. I. Physical parameters of the 1.2-mm/IRAS sources

We report the results of a 1.2 mm continuum emission survey toward 146 IRAS sources thought to harbour high- mass star forming regions. The sources have FIR colors typical of UCHII regions and were detected in the CS(2 → 1) line survey of Bronfman et al. (1996). Regions of 15 � × 10 � , centered on each IRAS source, were mapped with an angular resolution of ∼24 �� , using the SIMBA array on the SEST telescope. 1.2 mm emission was detected toward all IRAS sources. We find that the dust cores associated with these sources have typical sizes of 0.4 pc and masses of 5 × 10 3 M� . Dust temperatures and luminosities, derived from the SED, are typically 32 K and 2.3 × 10 5 L� .

Unveiling the gas-and-dust disk structure in HD 163296 using ALMA observations

Aims. The aim of this work is to study the structure of the protoplan etary disk surrounding the Herbig Ae star HD 163296. Methods. We have used high-resolution and high-sensitivity ALMA observations of the CO(3‐2) emission line and the continuum at 850µm, as well as the 3- dimensional radiative transfer code MCFOST to model the data presented in this work. Results. The CO(3‐2) emission unveils for the first time at sub-millim eter frequencies the vertical structure details of a gaseou s disk in Keplerian rotation, showing the back- and the front-side of a flared disk. Continuum emission at 850 µm reveals a compact dust disk with a 240 AU outer radius and a surface brightness profil e that shows a very steep decline at radius larger than 125 AU. The gaseous disk is more than two times larger than the dust disk, with a similar critical radius but with a shallower radial pr ofile. Radiative transfer models of the continuum data confirms the need for a s harp outer edge to the dust disk. The models for the CO(3‐2) channel map require the disk to be slightly more geometrically thick than previous models suggested, and that the temperature at which CO gas becomes depleted (frozen-out) from the outer regions of the disk midplane is T < 20 K, in agreement with previous studies.

Unexpectedly large mass loss during the thermal pulse cycle of the red giant star R Sculptoris.

The asymptotic-giant-branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star underwent a brief period of increased mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse—parameters that determine the lifetime of the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3″. What was previously thought to be only a thin, spherical shell with a clumpy structure is revealed to also contain a spiral structure. Spiral structures associated with circumstellar envelopes have been previously seen, leading to the conclusion that the systems must be binaries. Combining the observational data with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse about 1,800 years ago, lasting approximately 200 years. About 3 × 10−3 solar masses of material were ejected at a velocity of 14.3 km s−1 and at a rate around 30 times higher than the pre-pulse mass-loss rate. This shows that about three times more mass was returned to the interstellar medium during and immediately after the pulse than previously thought.

Mass-loss from dusty, low outflow-velocity AGB stars: I. Wind structure and mass-loss rates

We present the first results of a CO(2-1), (1-0), and 86 GHz SiO maser survey of AGB stars, selected by their weak near-infrared excess. Among the 65 sources of the present sample we find 10 objects with low CO outflow velocities, vexp < 5k m s −1 . Typically, these sources show (much) wider SiO maser features. Additionally, we get 5 sources with composite CO line profiles, i.e. a narrow feature is superimposed on a broader one, where both components are centered at the same stellar velocity. The gas mass-loss rates, outflow velocities and velocity structures suggested by these line profiles are compared with the results of hydrodynamical model calculations for dust forming molecular winds of pulsating AGB stars. The observations presented here give support to our recent low outflow-velocity models, in which only small amounts of dust are formed. Therefore, the wind generation in these models is dominated by stellar pulsation. We interpret the composite line profiles in terms of successive winds with different characteristics. Our hydrodynamical models, which show that the wind properties may be extremely sensitive to the stellar parameters, support such a scenario.

Discovery of four new massive and dense cold cores

We report the identification, from a 1.2 mm dust continuum emission survey toward massive star-forming regions, of four strong 1.2 mm sources without counterparts at mid-infrared (Midcourse Space Experiment [MSX]) and far-infrared (IRAS) wavelengths. They have radii in the range 0.2-0.3 pc, dust temperatures ≤17 K, masses in the range 4 × 102-2 × 103 M☉, and densities of ~2 × 105 cm-3. We suggest that these objects are massive and dense cold cores that will eventually collapse to form high-mass stars.