Astron. Astrophys. 364, 613-624 (2000)
2. Observations
2.1. Molecular observations
The observations were performed in 1996-1997 with the 15-m SEST
telescope on La Silla, Chile. The telescope and its instrumentation
are described by Booth et al. (1989). The most important parameters of
our measurements are summarized in Table 1. Further details are
given below.
![[TABLE]](img13.gif)
Table 1. Parameters of molecular line observations.
Notes:
*1) The system temperatures are given in the scale.
The observations were performed with SIS receivers in a
single-sideband mode. At 220 GHz, we used dual beam switching with a
beam throw of 12´ and 2
acousto-optical spectrometers in parallel: (1) a 2000 channel
high-resolution spectrometer with a 86 MHz bandwidth, 43 kHz
channel separation and 80 kHz resolution and (2) a 1440 channel
low-resolution spectrometer (LR1) with a 1000 MHz total
bandwidth, 0.7 MHz channel separation, and 1.4 MHz spectral
resolution. The LR1 band was centered on the
HNCO( - )
transition. However, it also covered C18O(2-1),
SO(65-54) and other lines (see Table 1).
The C34S(3-2) measurements at 145 GHz were made in a
dual beam switching mode, too, using a high-resolution spectrometer as
backend. The beam size is 23" (HPBW) at 230 GHz and 35" at
145 GHz.
Throughout the paper, we adopt the IRAS co-ordinates as the central
source position ( ,
. The area of
40" 40" around this position was
mapped with 10" spacing in SO(65-54),
C18O(2-1), and
HNCO( - )
and with 15" spacing in C34S(3-2). The peak position was
also observed in 34SO(65-54).
The CO(2-1) map for IRAS 12326-6245 was sampled with 2/3 beamwidth
intervals of 15 The observations were
made in the position-switch mode with an OFF position of 30´ to
the east and an integration time of 30 seconds per ON and per OFF
position. Based on the repeated measurements of smaller parts of the
map, the total integration time per ON position ranged between 1
minute and 3.5 minutes, resulting in a
(rms) between 0.18 and 0.46 K.
The pointing was checked every two to three hours with the source
W Hya and was found to be accurate to better than
6
We express the results in units of the main beam brightness
temperature ( ) assuming the main beam
efficiencies at 230 GHz and
0.52 at 220 GHz. The temperature scale was checked by
observations of Orion A.
2.2. Bolometer observations
The continuum observations were performed in March 1996 with the
one-channel He3-cooled SEST facility bolometer (Kreysa
1990). The bolometer has an equivalent bandwidth of
50 GHz and a central frequency
of = 236 GHz
( = 1.27 mm). The beam size at this
wavelength is 23" (HPBW).
The maps were obtained with the standard "double beam" technique
(Emerson et al. 1979), i.e. by scanning the telescope continuously in
azimuth over the source position while chopping with a frequency of
6 Hz and a beam throw of 67" in scan direction. The beam switching was
performed with a focal plane chopper. A scanning velocity of 8"/second
was used and the elevation spacing between adjacent scans was
8
Three individual maps with a size of
5´ 4´ were combined to
produce the final map of the source. The atmospheric transmission was
measured by sky dips and amounted to
during the whole observing run. Telescope pointing and focus were
checked frequently towards nearby quasars. The pointing was repeatable
within 5 Uranus served as calibration
standard, adopting a brightness temperature of 96 K (Griffin &
Orton 1993). The average 1 rms noise
in the final map (outside the source) is 48 mJy/beam. Data reduction
was performed with the MOPSI software package (R. Zylka).
2.3. Imaging in H, J, and H2
The near-infrared (NIR) broad- and narrow-band imaging was
performed using IRAC2b (Moorwood et al. 1992) at the ESO 2.2-m
telescope in June, 1998, during the time slot alloted to the
Max-Planck-Institut (MPI), Heidelberg. Dithered images were taken at
five positions yielding an overall field-of-view of about
160" 160
The resulting total integration times for the central region are as
follows: 800 s (J), 400 s (H), 200 s
( ), and 20 minutes for the narrow-band
filters BP4 (continuum, 2.105 µm) and H2
(2.122 µm). The limiting magnitudes (3
point source detection) of the J, H,
and images are 17, 18, and 18.5 mag,
respectively. In order to obtain a continuum-subtracted H2
image, the BP4 image was convolved to match the point spread function
(PSF) of the H2 image. After this step, the continuum
emission was subtracted from the H2 image. Nevertheless,
residuals of bright stars are still present in the subtracted image
(Fig. 2b).
The intrinsic image scale of lens C
( ) was resampled to
during the mosaicking of the final
image. The angular resolution as derived from stellar profiles is
1 The astrometry is based on stellar
positions extracted from the DSS2 image of the region and is accurate
to
1
2.4. N- and Q-band imaging
Diffraction limited thermal-infrared images were obtained in March,
1998 during Max Planck time using MANIAC (Böker et al. 1997) at
the ESO 2.2-m telescope. The observations were performed with the
common chopping/nodding technique at a pixel scale of
and a total on-source integration
time of 3.5 min. A chopper throw of 30" was applied. The individual
images were subject to a wavelet-filtering algorithm (Pantin &
Starck 1996) which preserves both flux and spatial resolution while
suppressing the noise considerably. These images were then resampled
to half the original pixel size and combined using a shift-and-add
algorithm to compensate for image motion. The coarse astrometry
derived using the telescope offsets from the reference star indicated
that two infrared sources are close to the unresolved ultracompact
H II regions found by Walsh et al. (1998). Thus, the
final astrometry was tied to the radio positions. The N and
Q band photometry of the detected sources (above 3
noise level) is based on the
12.13 µm and 21.34 µm MSX flux densities.
The 3 detections limits are 0.16 Jy
in N and 11 Jy in Q, respectively. The individual flux
contributions were derived using a multi-component PSF fitting
algorithm. The MIR source 4 is either a binary or is associated with
extended emission. For the derivation of the flux, it was treated as a
binary source. We should stress that MIR3 is present in the Q
band image at a 2 level.
We also added mid-infrared data from the MSX-SPIRIT III point
source catalog (Egan et al. 1999). The 1
error ellipse of the point sources
detected by MSX in the field is .
© European Southern Observatory (ESO) 2000
Online publication: January 29, 2001
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