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Astron. Astrophys. 322, 962-974 (1997)

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2. Observations

2.1. [FORMULA] 18cm OH emission measurements

We observed the 1667.359 MHz transition of OH with the NRAO 43m antenna in Green Bank during 1995 May and September. The measured beam width of the telescope during the observations was [FORMULA] and the nominal beam efficiency was [FORMULA] %. Results from the 43m are reported in terms of the antenna temperature [FORMULA]. We observed in dual circular polarization mode with 0.625 MHz correlator bandwidths in each of two 512-channel backends so that the velocity resolution and channel separation were 0.219 km s-1 ; the system temperature was typically 24 K. The spectra were taken by frequency-switching and represent 9 hours on-source integration toward the star and 4.5 hours at outlying positions taken at [FORMULA] intervals North-South and East-West of the center position. The absolute flux scale was set by continuum observations of 3C 286.

The OH profiles are shown in Figs. 1-3 and the variation of the OH line profile integral across the face of the gas distribution is given in Table 1.

[FIGURE] Fig. 1. Right: Line profiles of 1667 MHz OH (left) and 3335 MHz CH emission around [FORMULA] Oph. The spectral resolution of the data is 0.22 km s-1. CH resembles CO, rather than OH, in the higher-velocity gas to the South.

[FIGURE] Fig. 2. Right: Line profiles of 1667 MHz OH (left) and 115.3 GHz CO emission around [FORMULA] Oph. The spectral resolution of the OH data is 0.22 km s-1. For 12 CO the spectral resolution is 0.13 km s-1 along the North-South strip, using newer data, and 0.26 km s-1 otherwise.

[FIGURE] Fig. 3. Declination-velocity diagrams of OH, 12 CO and CH emission around [FORMULA] Oph using the data in Figs. 1 and 2. The OH contours are in 0.012 K increments starting at 0.012 K; those of 12 CO are at levels 0.0625, 0.125, 0.25, 0.5, 1, 2, 3, 4, 5, and 6 K. The CH contours are at increments of 0.014 K starting at 0.014 K. The spectral resolution is 0.22 km s-1 for OH and CH and and 0.13 km s-1 for 12 CO. The position of [FORMULA] Oph is marked by a horizontal line.


Table 1. Line profile integrals (K km s-1) around [FORMULA] Oph

2.2. [FORMULA] 9cm CH emission measurements

We observed the 3335.481 MHz line of CH with the NRAO 43m antenna in Green Bank during 1995 September. The beamwidth of the telescope was [FORMULA]. The bandwidth employed was twice as wide as for OH, which, in combination with the two times higher CH frequency, leads to a nearly identical resolution in velocity (0.219 km s-1). System temperatures were 36-44K. The observing was done in quite the same way as for OH, discussed in the preceding paragraph. Integration times were 2-4 hours per position.

The CH profiles are shown in Figs. 1 and 3, and the data are summarized in Table 1.

2.3. [FORMULA] 3mm observations of HCO [FORMULA], HCN, [FORMULA] H, CS, and CN

These data were taken at the NRAO 12m telescope in October 1994 and January 1995 using the dual-polarization receiver feeding twin banks of 100 kHz filters and the hybrid spectrometer at 97.6 kHz resolution sampled at 48.8 kHz intervals. The lines observed here are generally deserving of higher resolution but this was not feasible given the amount of observing time available. Typical integration times were 3-7 hours per point; the system temperature was 250-300 K below 100 GHz and 450 K at 113.5 GHz (for CN), all of which are worse than average for this telescope.

All these data were taken by frequency-switching and were subject to the presence of long-period sinusoidal standing waves: these have been removed from the spectra shown here. Part of the weaker hyperfine structure of HCN was lost because of our choice of a frequency-switching interval; only the strongest component could be recovered in the folded spectrum. The channel separation is 0.254 km s-1 for 12 CO, 0.258 km s-1 for CN, 0.266 km s-1 for 13 CO, 0.299 km s-1 for CS J=2-1, 0.328 km s-1 for HCO [FORMULA], 0.330 km s-1 for HCN and 0.335 km s-1 for [FORMULA] H.

We took two additional HCO [FORMULA] emission profiles to establish the degree to which they follow the characteristic CO emission patterns. The HCO [FORMULA] data are shown in Fig. 5 and are summarized in Table 2 which gives the integrated intensities of HCO [FORMULA] and the two lower lines of 12 CO. The multi-species observations taken at the HCO [FORMULA] emission peak are summarized in Table 3, where we give the single-channel rms at 100 kHz resolution, the integrated intensity taken over the range defined by the relatively strong HCO [FORMULA] emission, and the fraction of the intensity of the transition which is expected to be contained in the strongest hyperfine component. The data are shown in Fig. 6 where they are compared with observations in the core of L134 ([FORMULA], [FORMULA] B1950).

[FIGURE] Fig. 4. Comparison of line profile integrals for CO, CH, and OH. Filled symbols are used for the integral taken at v [FORMULA] 0 km s-1, open symbols are used for v [FORMULA] 0 km s-1. Upward-pointing symbols denote positions toward or North of [FORMULA] Oph, downward-pointing symbols represent positions to the South. Symbols corresponding to the weaker of the CO emission branches are drawn less heavily in the two rightmost panels to distinguish their behaviour.
[FIGURE] Fig. 5. Line profiles of HCO [FORMULA], 12 CO J=1-0, and J=2-1 around [FORMULA] Oph. The resolution and channel spacing are 0.33 km s-1 for HCO [FORMULA] and 0.13 km s-1 for either CO line.
[FIGURE] Fig. 6. Right: Line profiles observed at the CO and HCO [FORMULA] emission peak [FORMULA] S of [FORMULA] Oph in 100 kHz channels. Left; Observations of the same species toward L134 are shown for comparison but at 48 kHz resolution. The lines toward [FORMULA] Oph are substantially broader.


Table 2. [FORMULA] (K km s-1) for HCO [FORMULA] and CO


Table 3. [FORMULA] (K km s-1) [FORMULA] South of [FORMULA] Oph

2.4. New 12 CO, 13 CO, and C18 O J=1-0 profiles

Using the NRAO 12m telescope in 1995 May and July and 1996 April, new CO J=1-0 emission profiles were taken at [FORMULA] intervals in declination about the star, supplanting the earlier profiles reported in Liszt (1992). The new data were taken in a frequency-switching mode with the hybrid spectrometer. The spectra shown here have 48.8 kHz resolution and channel spacing for the stronger two isotopes (0.127 km s-1 for 12 CO, 0.132 km s-1 for 13 CO) and 97.6 kHz (0.267 km s-1) for C18 O.

We integrated for periods of 1-3 hours on the 12 CO line, leading to noise levels [FORMULA] K. For 13 CO, we took (four) profiles at declinations displaced [FORMULA], [FORMULA], [FORMULA], and [FORMULA] from the star, integrating for periods of 3-5 hours with resulting noise levels of 0.02-0.03K. For C18 O, we integrated for a total of 11 hours at the position [FORMULA] South of the star, resulting in a single-channel rms of 0.005 K.

The newer CO results are reported in Tables 1 and 2. The 13 CO lines have integrated intensities identical to those reported earlier, well within the expected noise levels. Some of the 12 CO lines are brighter in the newer data by 20%-30% which is outside the expected noise but not inconsistent with the 10% overall calibration errors of mm-wave emission work and with the substantial upgrading of the telescope that has taken place since the first of the earlier data was taken in 1987. The newer data have slightly larger 12 CO/13 CO intensity ratios but the main result, that this ratio is relatively large for such strong 12 CO lines as are seen around [FORMULA] Oph, (up to 6.6 K), is of course preserved.

The 12 CO emission around [FORMULA] Oph is quite extended (de Geus, Bronfman, and Thaddeus 1990; de Geus and Burton 1991) and heavily structured (Liszt 1992, 1993; Kopp et al. 1996). We will usually assume that the forward response is filled. The nominal beam efficiency of the 12m telescope in the [FORMULA] 3mm band is 0.7.

2.5. Conventions

The central position was taken as [FORMULA], [FORMULA] (B1950). At the usually-adopted distance to the star, 140 pc, [FORMULA] corresponds to 0.041 pc, or 1 pc to [FORMULA]. All velocities reported here are with respect to the Local Standard of Rest (for conversion to heliocentric, subtract 13.7 km s-1 from the LSR values). The antenna temperature scale at the 12m is [FORMULA], supposedly corrected for all losses and for all beam coupling factors other than that which describes the filling of the forward response by the actual emission. For the 43m, all results are reported in terms of the antenna temperature [FORMULA]. At cm-wavelengths, atmospheric attenuation is negligible and all line strengths were calibrated by observing the continuum emission from 3C 286.

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998