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Astron. Astrophys. 347, 194-202 (1999)

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2. Observations

We observed the 12CO(J=[FORMULA] and 2[FORMULA]1), 13CO(J=[FORMULA] and 2[FORMULA]1), SiO(v=0, J=[FORMULA]), and HCN(J=[FORMULA]) lines towards HD101587 in August 1997 with the Swedish-ESO Submillimetre Telescope (SEST) 1, La Silla, Chile. The telescope was equipped with SIS-receivers operating in SSB-mode, and broadband acusto-optical spectrometers with a channel separation of 0.7 MHz. The data are calibrated using the standard chopper-wheel method, and the intensity scale is given in main beam brightness temperature. The velocity scale is given with respect to the Local Standard of Rest (LSR). For HD101584 the difference between heliocentric and LSR velocity is 9.3[FORMULA]. Relevant telescope and receiver data are given in Table 1. We used the coordinates [FORMULA](1950) = 11h38m33[FORMULA]0, [FORMULA](1950) = -55o17´45" for HD101584.


Table 1. Telescope and receiver data.
a) The receiver noise temperature
b) The telescope beam full width at half power
c) The main beam efficiency

The 12CO(J=[FORMULA] and 2[FORMULA]1) emissions were mapped simultaneously over an area of about 45"[FORMULA]40" with a spacing of 7[FORMULA]5, i.e., about 1/3 of the CO(2[FORMULA]1) full half-power beam width (HPBW). The pointing was regularly checked on the SiO(v=1, J=[FORMULA]) masers of R Car and IRSV1540, but despite this it turned out to be quite variable in the direction of HD101584. We therefore divided the data into 18 subsets (covering different parts of the map, but always including the central area), in which all data were obtained within about a 2-hour interval. For each subset we determined the position of maximum intensity (integrated over the velocity range -20 to 100[FORMULA]). Finally, all subsets were shifted [a maximum shift of 8" was used, the average shift is 6" and the average maximum intensity position is (-1[FORMULA]5,-2[FORMULA]5)], and a regridded map for each line was produced. We estimate that the centra of our final maps coincide with the position of the star to within 5". The CO emission is essentially unresolved even at [FORMULA]20" resolution, but we will show below that it is possible to determine relative differences in the spatial location of emission at different velocities on a scale much smaller than this.

The results obtained towards the map centre position are given in Table 2, where I=[FORMULA][FORMULA]dv, and the spectra are presented in Fig. 1. The upper limits to the HCN and SiO integrated intensities are obtained as the peak-to-peak noise temperature, in spectra reduced to a resolution of 100[FORMULA], multiplied with 100 (i.e., we expect any possible HCN and SiO emission to come from the velocity range that dominates the CO emission).

[FIGURE] Fig. 1. 12CO(J=[FORMULA] and 2[FORMULA]1) and 13CO(J=[FORMULA] and 2[FORMULA]1) spectra obtained towards HD101584 (the map centre position spectra are shown). The intensity and velocity scales are given in main beam brightness temperature and with respect to the local standard of rest, respectively


Table 2. Observational results towards HD101584.
a) The intensity-weighted centre velocity

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© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999