A Swedish heterodyne facility instrument for the APEX telescope

Vassilev, Vessen; Meledin, Denis; Lapkin, Igor; Belitsky, Victor; Nyström, Olle; Henke, Doug; Pavolotsky, Alexey; Monje, Raquel; Risacher, C.; Olberg, M.; Strandberg, Magnus; Sundin, Erik; Fredrixon, Mathias; Ferm, Sven-Erik; Desmaris, Vincent; Dochev, D; Pantaleev, Miroslav; Bergman, P.; Olofsson, H.

doi:10.1051/0004-6361:200810459

Cited by 152 publications

(140 citation statements)

References 18 publications

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“…Since these are double-sideband receivers, three settings with slightly different band center frequencies (spaced by 80 MHz) were taken to identify blending from the other sideband. In 2008, we observed lines from different isotopologues of HCN, HCO + , and CO with the APEX-1, APEX-2 (Vassilev et al 2008), and CHAMP + receivers Güsten et al 2008), all of which are single-sideband receivers. CHAMP + allows simultaneous observations in the 690 GHz and the 850 GHz bands.…”

Section: Observations and Data Reductionmentioning

confidence: 94%

Structure of evolved cluster-forming regions

Rolffs

Schilke

Wyrowski

et al. 2011

A&A

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Context. An approach towards understanding the formation of massive stars and star clusters is to study the structure of their hot core phase, an evolutionary stage where dust has been heated, but molecules have not yet been destroyed by ultraviolet radiation. These hot molecular cores are very line-rich, but the interpretation of line surveys is also hampered by poor knowledge of the physical and chemical structure. Aims. To constrain the radial structure of high-mass star-forming regions containing hot cores, we attempt to reproduce by radiative transfer modeling both the intensity and shape of a variety of molecular lines. Methods. We observed 12 hot cores with the Atacama Pathfinder EXperiment (APEX) in lines of HCN, HCO + , CO, and their isotopologues, including high-J lines and vibrationally excited HCN. We investigate how well the sources can be modeled as centrally heated spheres with a power-law density gradient, making use of the radiative transfer code RATRAN and the radial profile of the submm continuum emission, taken from the APEX Telescope Large Area Survey of the GALaxy (ATLASGAL). Results. Most of the observed lines have complicated shapes that incorporate self-absorption, asymmetries, and line wings. Vibrationally excited HCN is detected in all sources, and vibrationally excited H 13 CN in half of the sources. We are able to successfully model most features seen in the APEX data, such as the ratio of the isotopologue lines (very high optical depths), self-absorption (temperature gradient), blue asymmetries (moderate infall), vibrationally excited HCN (high inner temperatures), and H 13 CN (high HCN abundance under dense and hot conditions). Other features could not be reproduced, such as an occasional lack of self-absorption, the emission from high-J lines in the outer pixels of the CHAMP+ receiver (15 −20 from the center), the outflow wings, and the red asymmetric profiles. Conclusions. The amount of molecular gas, in particular of HCN, at very high temperatures is larger than previously thought. A complex interplay between infall and outflow motions is present. Our basic model assumptions of pure central heating and a power-law radial density distribution can serve as approximations for most sources, but are too simple to explain all observed lines. In particular, taking into account clumpiness, multiplicity of heating sources and a more complex velocity field seems to be necessary to more closely match model calculations to observations. This would require three-dimensional radiative transfer modeling of high-resolution interferometric data.

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Section: Observations and Data Reductionmentioning

confidence: 94%

Structure of evolved cluster-forming regions

Rolffs

Schilke

Wyrowski

et al. 2011

A&A

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“…The pointing accuracy of the telescope has been determined at 2 (rms). We used the Swedish heterodyne facility instrument APEX-2 (Vassilev et al 2008) for the raster-mapping observations of ρ Oph A in the J = 3−2 rotational transition of the N 2 H + molecule. The central rest frequency is at 279 515.06711 MHz and the average zenith optical depth was 0.04.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Gas and dust in the star-forming regionρ Oph A

Liseau

Larsson

Lunttila

et al. 2015

A&A

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Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods. Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N 2 H + , which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N 2 H + (J = 3−2) and (J = 6−5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H 2 ), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, =88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions. Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C 18 O, also N 2 H + is frozen onto the grains.

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“…The Swedish heterodyne facility instrument APEX-3 (Vassilev et al 2008), a double sideband receiver, was used together with the facility FFT spectrometer covering about 4 GHz. The observations were made in April and June 2014 under programme O-093.F-9306.…”

Section: Observationsmentioning

confidence: 99%

Detection of CI line emission from the detached CO shell of the AGB star R Sculptoris

Olofsson

Bergman

Lindqvist

2015

A&A

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Context. Stars on the asymptotic giant branch (AGB) lose substantial amounts of matter, to the extent that they are important for the chemical evolution of, and dust production in, the Universe. The mass loss is believed to increase gradually with age on the AGB, but it may also occur in the form of bursts, possibly related to the thermal pulsing phenomenon. Detached, geometrically thin, CO shells around carbon stars are good signposts of brief and intense mass ejection. Aims. We aim to put further constraints on the physical properties of detached CO shells around AGB stars. Methods. The photodissociation of CO and other carbon-bearing species in the shells leads to the possibility of detecting lines from neutral carbon. We have therefore searched for the CI( 3 P 1 − 3 P 0 ) line at 492 GHz towards two carbon stars, S Sct and R Scl, with detached CO shells of different ages, ≈8000 and 2300 years, respectively. Results. The CI( 3 P 1 − 3 P 0 ) line was detected towards R Scl. The line intensity is dominated by emission from the detached shell. The detection is at a level consistent with the neutral carbon coming from the full photodissociation of all species except CO, and with only limited photoionisation of carbon. The best fit to the observed 12 CO and 13 CO line intensities, assuming a homogeneous shell, is obtained for a shell mass of ≈0.002 M , a temperature of ≈100 K, and a CO abundance with respect to H 2 of 10 −3 . The estimated CI/CO abundance ratio is ≈0.3 for the best-fit model. However, a number of arguments point in the direction of a clumpy medium, and a viable interpretation of the data within such a context is provided.

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A Swedish heterodyne facility instrument for the APEX telescope

Cited by 152 publications

References 18 publications

Structure of evolved cluster-forming regions

Structure of evolved cluster-forming regions

Gas and dust in the star-forming regionρ Oph A

Detection of CI line emission from the detached CO shell of the AGB star R Sculptoris

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