Issue |
A&A
Volume 365, Number 2, January 2001
|
|
---|---|---|
Page(s) | 275 - 284 | |
Section | Numerical methods and codes | |
DOI | https://doi.org/10.1051/0004-6361:20000475 | |
Published online | 15 January 2001 |
The IRAM key-project: Small-scale structure of pre-star forming regions*
III. Influence of and correction for the error beam pick-up
1
I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
2
ASIAA, Academica Sinica, PO Box 1-87, Nankang, Taipei 115, Taiwan, PR China
3
Radioastronomie, CNRS URA 336, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
4
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Corresponding author: F. Bensch, bensch@ph1.uni-koeln.de
Received:
27
January
2000
Accepted:
1
August
2000
The goal of the IRAM key-project "Small-scale structure of pre-star
forming regions"is to map three nearby (), 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
12CO
1 maps, 10% to 35% for the
13CO
1 maps, and 16.5% in the
12CO
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 13CO
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.
Key words: methods: data analysis -techniques: miscellaneous -radio lines: ISM -line: profiles -interstellar medium (ISM): clouds -ISM: structure
© ESO, 2001
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