Up: High density molecular clumps
The observations were carried out in July 1994 using
the IRAM 30-m radiotelescope at Pico Veleta (Spain). Spectra
were obtained in position switching with a reference position
at 30
offset or using the wobbler (i.e. a nutating
secondary) with a beam-throw of 240
and a phase duration of 2 s.
The calibration was performed with the chopper wheel method with
both hot (sky and absorber) and cold (nitrogen) loads.
The calibration was verified on well-known molecular sources and by continuum
scans across Jupiter, Uranus, Mars, and Saturn: we found it to be accurate
to within 20% at all frequencies.
The absolute pointing was good to 4
.The conversion factor from main beam brightness
temperature (
) to flux density is 4.7 Jy K-1.
The backends were: 1) two filterbanks spanning 512 MHz
and providing a frequency resolution of 1 MHz; 2) a filterbank with 25.6 MHz
bandwidth and 100 kHz resolution; and 3) an autocorrelator used in various
high spectral resolution configurations, so that three bands could be
observed simultaneously.
Two
point raster maps centred on the H2O maser position
(see Table 1)
were made; one with 24
sampling,
the other with 12
. In some cases,
larger fields were covered to complete
the mapping of the cloud.
The integration time (ON + OFF) per point was 1 min and the
maps were repeated up to three times and then averaged.
The pointing and the focus were verified regularly (every hour)
on nearby continuum sources.
A total of 7 molecular species and 11 rotational transitions were mapped.
They are summarised in Table 4 together with the corresponding
half power beam width (HPBW) of the telescope.
The data were reduced with the CLASS and GRAPHIC programs of the Grenoble
Astrophysical Group (GAG) package. A polynomial baseline was removed from
each spectrum and then spectra taken towards the same position were
averaged; however, in cases where more than one map had been taken
in the same tracer towards a given source, the different maps were
compared before average, to ensure consistency between them.
Finally, channel maps and integrated maps in suitable velocity intervals
were created.
Table 4:
Frequencies of observed molecular transitions and telescope HPBWs
a Frequency of the 30-20 E transition.
b Frequency of the K=0 transition.
c Frequency of the 50-40 E1 transition.
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Up: High density molecular clumps
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