Methods and constraints for the correction of the error
 beam pick-up in single dish radio observations

Bensch, F.; Stutzki, J.; Heithausen, A.

doi:10.1051/0004-6361:20000485

Cited by 11 publications

(11 citation statements)

References 13 publications

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“…We find that the IRAM 30m data (when convolved to the same resolution as CSO) agrees to within 20%. The IRAM data shows stronger emission, which could be attributed to a 10-20% contribution from the error beam of the larger IRAM telescope (see Bensch et al 2001). Given these differences, we have assigned a calibration uncertainty of 20% to all 230 and 345 GHz data.…”

Section: Observations and Resultsmentioning

confidence: 99%

The Thermal Structure of Gas in Prestellar Cores: A Case Study of Barnard 68

Bergin¹,

Maret²,

Tak³

et al. 2006

ApJ

121

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International audienceWe present a direct comparison of a chemical/physical model to multitransitional observations of C18O and 13CO toward the Barnard 68 prestellar core. These observations provide a sensitive test for models of low UV field photodissociation regions and offer the best constraint on the gas temperature of a prestellar core. We find that the gas temperature of this object is surprisingly low (~7-8 K), and significantly below the dust temperature, in the outer layers (AV<5 mag) that are traced by C18O and 13CO emission. As shown previously, the inner layers (AV>5 mag) exhibit significant freezeout of CO onto grain surfaces. Because the dust and gas are not fully coupled, depletion of key coolants in the densest layers raises the core (gas) temperature, but only by ~1 K. The gas temperature in layers not traced by C18O and 13CO emission can be probed by NH3 emission, with a previously estimated temperature of ~10-11 K. To reach these temperatures in the inner core requires an order of magnitude reduction in the gas to dust coupling rate. This potentially argues for a lack of small grains in the densest gas, presumably due to grain coagulation

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Section: Observations and Resultsmentioning

confidence: 99%

The Thermal Structure of Gas in Prestellar Cores: A Case Study of Barnard 68

Bergin¹,

Maret²,

Tak³

et al. 2006

ApJ

121

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“…To accurately scale the FCRAO data, it is essential to remove the error beam component before scaling the intensities to the main beam scale. Methods for correcting millimeter-wave data for error beam pickup have been discussed by Bensch et al (2001), who introduce the "corrected main beam temperature scale" (T mb,c ) with which optimum calibration accuracy is achieved by scaling the data by 1/η mb after removal of radiation detected by the error beam.…”

Section: Error Beam Correctionmentioning

confidence: 99%

The Relation Between Gas and Dust in the Taurus Molecular Cloud

Pineda

Goldsmith

Chapman

et al. 2010

ApJ

252

336

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We report a study of the relation between dust and gas over a 100 deg 2 area in the Taurus molecular cloud. We compare the H 2 column density derived from dust extinction with the CO column density derived from the 12 CO and 13 CO J = 1 → 0 lines. We derive the visual extinction from reddening determined from 2MASS data. The comparison is done at an angular size of 200 ′′ , corresponding to 0.14 pc at a distance of 140 pc. We find that the relation between visual extinction A V and N (CO) is linear between A V ≃ 3 and 10 mag in the region associated with the B213-L1495 filament. In other regions the linear relation is flattened for A V 4 mag. We find that the presence of temperature gradients in the molecular gas affects the determination of N (CO) by ∼30-70% with the largest difference occurring at large column densities. Adding a correction for this effect and accounting for the observed relation between the column density of CO and CO 2 ices and A V , we find a linear relationship between the column of carbon monoxide and dust for observed visual extinctions up to the maximum value in our data ≃ 23 mag. We have used these data to study a sample of dense cores in Taurus. Fitting an analytical column density profile to these cores we derive an average volume density of about 1.4 × 10 4 cm −3 and a CO depletion age of about 4.2 × 10 5 years. At visual extinctions smaller than ∼3 mag, we find that the CO fractional abundance is reduced by up to two orders of magnitude. The data show a large scatter suggesting a range of physical conditions of the gas. We estimate the H 2 mass of Taurus to be about 1.5 × 10 4 M ⊙ , independently derived from the A V and N (CO) maps. We derive a CO integrated intensity to H 2 conversion factor of about 2.1×10 20 cm −2 (K km s −1 ) −1 , which applies even in the region where the [CO]/[H 2 ] ratio is reduced by up to two orders of magnitude. The distribution of column densities in our Taurus maps resembles a log-normal function but shows tails at large and low column densities. The length scale at which the high-column density tail starts to be noticeable is about 0.4 pc.

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“…Line profiles may be slightly distorted (cf. Bensch et al 2001). However, as the error beams are not yet completely characterized and may moreover be somewhat time variable, we ignore their influence in the following.…”

Section: Nanten2 Observationsmentioning

confidence: 99%

Clumpy photon-dominated regions in Carina

Krämer¹,

Cubick²,

Röllig³

et al. 2007

A&A

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Context. 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. Aims. 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.Methods. The NANTEN2-4 m submillimeter telescope was used to map the [C i] 3 P 1 − 3 P 0 , 3 P 2 − 3 P 1 and CO 4-3, 7-6 lines in two 4 × 4 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 Tr 14, and the second region is in the molecular cloud south of η Car and Tr 16. These data were combined with 13 CO SEST spectra, HIRES/IRAS 60 µm and 100 µm maps of the FIR continuum, and maps of 8 µm IRAC/Spitzer and MSX emission. Results. 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 10 3 in Draine units while the field of the southern region is about a factor 10 weaker. While the IRAC 8 µm emission lights up at the edges of the molecular clouds, CO and also [C i] appear to trace the H 2 gas column density. The northern region shows a complex velocity and spatial structure, while the southern region shows an edge-on PDR with a single Gaussian velocity component. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the 38 beam (0.43 pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 2 × 10 5 cm −3 is needed to reproduce the observed line emission at two selected interface positions. Conclusions. Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.

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Methods and constraints for the correction of the error beam pick-up in single dish radio observations

Cited by 11 publications

References 13 publications

The Thermal Structure of Gas in Prestellar Cores: A Case Study of Barnard 68

The Thermal Structure of Gas in Prestellar Cores: A Case Study of Barnard 68

The Relation Between Gas and Dust in the Taurus Molecular Cloud

Clumpy photon-dominated regions in Carina

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