Astron. Astrophys. 331, 669-696 (1998)

3. Summary of the observations

The (J=1-0) and J=2-1 maps extend over 6' 8' in Polaris, 5' 10' in L1512 and 3' 16' in L134A. The (J=1-0), (J=1-0) and (J=2-1) maps (completed simultaneously) are smaller (5' 7' in Polaris, 5' 7' in L1512 and 3' 7' in L134A). The three selected fields lie within 150 pc from the Sun so that the angular resolution reached by fully sampled 230GHz maps at the IRAM-30m telescope is AU. The ¹² CO maps consist of more than 3000 positions for each source. With a spacing of , the low frequency maps are more than fully sampled. The frequency resolution of the autocorrelator was 20kHz for the high and low frequency lines, providing a velocity resolution of 0.026 km s^-1 and 0.052 km s^-1 respectively.

The description of the observing procedure and strategy is given in a companion paper (Panis et al. 1998). This paper also presents a quantitative description of the gain stability of the system, over the entire duration of the observations (runs scattered over 18 months). The line intensity calibration was monitored by repeated observations at the (0,0) positions of each map. This paper also describes the different steps of the data reduction process and discusses the various contributions to the final noise level in the maps. The (J=2-1) and (J=2-1) KOSMA observations which have been carried out to perform the subtraction of the power collected in the IRAM error beams at these frequencies and the details of the error beam subtraction will be presented in Bensch et al. (1998). This correction is important because the fields mapped lie in the vicinity of bright regions (see Fig. 1). At 230 GHz, the error beam pick-up accounts on average for 30% to 50% of the detected intensity. We have also subtracted the emission collected by the IRAM-30m error beam at low frequency by using the high frequency KOSMA maps scaled down by an appropriate factor. This is discussed in Panis et al. (1998). As a result, all the line brightnesses given in this paper are corrected for the pickup from the error beam at both frequencies. We denote this temperature scale, , for main beam temperature corrected for error beam pick-up, as it is the closest estimate of the true main beam brightness temperature i.e. it is the convolution of the brightness temperature of the source with a Gaussian of width equal to the half-power width of the main beam.

© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998
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