The observations of the southern sources () were made
during two periods in October 1995 and in April 1996, with the
SEST
on La
Silla in Chile. We measured the (v=0,J=2-1) and (v=0,J=3-2) transitions
of SiO simultaneously, using the 80 - 116GHz and 135 - 165GHz SIS
receivers. The backend was a 2000 channel acousto-optical spectrometer with
a bandwidth of 86MHz. The AOS was split in two bands, each of 43 MHz. The
precise transition frequencies, the half-power beam widths (HPBW), and the
antenna (
) and beam efficiences (
) of the
telescope are listed in Table 1. Also the Jy/K conversion factors assuming a
point source, and the velocity resolutions corresponding to the channel
separation at the frequencies 87 and 130 GHz are listed there. Further
details of the equipment can be found in Booth et al. (1989) or in the
SEST manual (see http://www.ls.eso.org/lasilla/Telescopes/SEST).
Typical system temperatures at 87 and 130 GHz were 130 and 160K,
respectively. The observations were made in the dual beam switching mode,
with a beam throw of . The pointing was checked by
observing circumstellar SiO maser sources, and the accuracy was found to be
better than
.
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The northern sources () were observed in January 1995 and
in March 1996 with the 20-m radio telescope of Onsala Space Observatory in
Sweden. The SiO(v=0,J=2-1) line was measured using a 3mm SIS receiver.
As backends we used both the autocorrelator with a resolution of 50kHz,
and the 256 channel filterbank of resolution of 250kHz. The antenna
parameters and the velocity resolutions of the spectrometers are listed in
Table 1. For most of the sources the signal-to-noise ratio in the
autocorrelator spectra was not high enough to study the line profiles at low
intensity levels. On the other hand, the relatively low resolution of the
filter-bank (0.86kms-1 at the line frequency) is sufficient as the
lines are typically broad. Therefore the analysis is based on the
filter-bank spectra alone.
The first observing run was hampered by snow and rain, and consequently the
system temperature varied between about 240-1000K. During the second run,
the typical system temperatures were between 300-400K. The observing
mode was dual beam switching with a beam throw of . The
focus and pointing was checked by observing SiO masers in late-type stars.
The pointing accuracy was found to be better than 4
.
Because many of the spectra are asymmetric, gaussian fits are not
applicable. Linear baselines were first subtracted from the spectra. Due to
spectral noise it is difficult to determine the minimum and maximum
velocities (,
in Tables B.1 and B2) of the
low-intensity line wings. Therefore the spectra were first smoothed by
averaging adjacent channels in order to reduce the noise level.
The SEST spectra were smoothed by averaging 8 adjacent channels resulting in a velocity resolution of 1.2 and 0.79kms-1 for the J=2-1 and J=3-2 transitions, respectively. In the Onsala spectra two adjacent channels were averaged and the resulting velocity resolution is 1.73kms-1. The smoothing lowers noise but also reduces the accuracy of the determined velocities. However, compared with the typical full widths of the lines as defined below, the obtained spectral resolution is reasonable.
The peak antenna temperatures and the corresponding velocities ( and
in Tables B.1 and B.2) were determined
directly from the smoothed spectra. The full velocity range of detectable
emission, which hereafter will be called the full width (FW), was then
determined as the range where the channel values are greater than twice the
RMS noise of the smoothed spectra. Due to smoothing the selected intensity
threshold corresponds to
for the SEST observations and
for the Onsala observations, where
is the RMS noise of the original spectra indicated in Tables B.1 and
B.2. The area, mean velocity and width (the columns Area,
and
Width in Tables B.1 and B.2, respectively) of the emission within the range
were calculated using the original spectra. The
mean velocity and width are defined as the first and second moments of the
channel values.
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