The Beam Shape of the NRAO 900-ft Telescope and its Influence on 21-cm Line Measurements

Heiles, Carl; Hoffman, W.

doi:10.1086/110644

Cited by 8 publications

(3 citation statements)

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“…This standard is best realized by injecting a correlated noise source into the two feed outputs or, alternatively, by radiating a noise source into the feed with a polarization that provides equal amplitudes in the feed outputs. Under some circumstances, it is desirable to inject noise separately into the two inputs to simulate uncorrelated noise; these matters are discussed in detail by Heiles & Fisher (1999).…”

Section: Introduction To Cross-correlation Spectropolarimetrymentioning

confidence: 99%

Cross‐Correlation Spectropolarimetry in Single‐Dish Radio Astronomy

Heiles

2001

PUBL ASTRON SOC PAC

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Section: Introduction To Cross-correlation Spectropolarimetrymentioning

confidence: 99%

Cross‐Correlation Spectropolarimetry in Single‐Dish Radio Astronomy

Heiles

2001

PUBL ASTRON SOC PAC

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“…Early studies of the influence of the stray radiation pick-up and methods for its correction have been done for HI observations (cf. Heiles & Hoffman 1968;Westerhout et al 1973;Hartmann et al 1996), based on accurate beam pattern measurements (cf. Baars & Mezger 1964;Hartsuijker et al 1972;Harten 1973).…”

Section: Introductionmentioning

confidence: 99%

The IRAM key-project: Small-scale structure of pre-star forming regions

Bensch

Panis

Stutzki

et al. 2001

A&A

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Abstract. The goal of the IRAM key-project "Small-scale structure of pre-star forming regions" is to map three nearby (d ∼ 150 pc), quiescent molecular clouds with a high angular and spectral resolution to study the molecular cloud structure down to the smallest linear scales currently accessible by single dish radio telescopes. Here, we give a detailed discussion of the influence and the correction of the error beam pick-up. A new set of corrected data is presented using the beam pattern parameters of the IRAM 30 m telescope recently published by Greve et al. (1998). For the correction we use observations made at lower angular resolution with the KOSMA 3 m telescope. Smeared to the resolution of the error beam, they provide an estimate of the pick-up therein. The error beam pick-up accounts for a significant fraction of the observed intensity in the key-project maps: on average 31% to 50% for the 12 CO J = 2 → 1 maps, 10% to 35% for the 13 CO J = 2 → 1 maps, and 16.5% in the 12 CO J = 1 → 0 map of MCLD 123.5+24.9. In addition, the line profiles are significantly modified by the error beam pick-up. The large data set available with the IRAM key-project allows us to investigate the accuracy of the correction method and its limitations in detail. For the corrected maps, we determine the overall accuracy of the temperature scale to be better than 15%, except for the 13 CO J = 2 → 1 map of MCLD123.5+24.9 and L1512 where we estimate an accuracy of 22% and 18%. The key-project maps presented here and the released maps published by Falgarone et al. (1998) (with the correction done using the previous beam pattern parameters determined by Garcia-Burillo et al. 1993) differ by no more than 10% and only in localized regions. Both data sets and the supplementary observations made with the KOSMA telescope are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html The "error beam problem" is not limited to observations obtained with the IRAM 30 m. Similar beam pattern are found for other large single dish (sub-)mm telescopes, although few quantitative studies exist. In particular, for observations of spatially extended sources, the error beam contribution has to be considered and corrected for if necessary.

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“…The error or stray pattern responsible for the additional pick-up mainly resulted from surface irregularities in the primary reflector (cf. Harten 1973;Heiles & Hoffman 1968). The improved reflector surface of present day cm wave telescopes greatly reduced the amplitude of these components and the residual error beam is often found to be dominated by spillover and scattering.…”

Section: Introductionmentioning

confidence: 99%

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

Bensch

Stutzki

Heithausen

2001

A&A

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Abstract. The beam pattern of a single dish radio telescope is given by the main beam and additional components at larger angles, usually called error beam or stray pattern. The latter have relatively small peak amplitudes (typ. below −25 dB), depending on the rms surface error of the primary reflector. However, because of their large angular extent, they are sensitive to extended sources, and a significant fraction of the observed intensity can result from error beam pick-up. For (sub-)mm observations suffering from error beam pick-up we introduce a new temperature scale for the corrected data, the corrected main beam brightness temperature T mb,c , which provides a better approximation to the intensity detected by the main beam than the commonly used antenna temperature and main beam brightness temperature. We consider two different correction methods. The first method uses complementary observations obtained with a smaller telescope. Smeared to the angular resolution of the error beam pattern they provide an estimate of the error beam pick-up in the observations of the large telescope. For the second method, the error beam pick-up is de-convolved from the observed map in Fourier space. The requirements for both correction methods and their advantages and limitations are discussed in detail. Both correction methods require additional observations, unless the full spatial extent of the emission is observed. We find that the deconvolution method is attractive for the correction of fully sampled maps with an angular extent much larger than the error beam pattern. For smaller maps and more sparsely sampled observations, the subtraction method is favorable, because the additional observations with a small telescope are less time consuming.

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The Beam Shape of the NRAO 900-ft Telescope and its Influence on 21-cm Line Measurements

Cited by 8 publications

References 0 publications

Cross‐Correlation Spectropolarimetry in Single‐Dish Radio Astronomy

Cross‐Correlation Spectropolarimetry in Single‐Dish Radio Astronomy

The IRAM key-project: Small-scale structure of pre-star forming regions

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

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