4 Results

In Table 2 all narrow-line OH sources found are listed. In total there are 286 sources, 125 of which have been identified with known OH-1612-MHz masers. Ten sources have only one spectral peak. A reliable (see Sect. 5.5 for definition) IRAS identification is found for 207 sources. The median "residual" rms-noise level is 25 mJy (Fig. 3, Sect. 5.1.1).

Figure 4: a) and b) The longitude-latitude diagram and longitude-velocity diagram for the 286 sources of Table 2. The central velocities (Col. 10) are plotted

Figure 5: a) and b) The histograms of the central velocities and outflow velocities for the 286 sources of Table 2

For each source the table gives an entry number (Col. 1), the OH$\ell{-}b$ name (Col. 2), observing date (Col. 3, see Table 1), position in J2000 coordinates (Cols. 4, 5), the formal positional error (Col. 6) - much smaller than the actual error (Sect. 5.2) -, the distance from the source to the pointing centre (Col. 7), the peak, stellar and outflow velocities (Cols. 8 to 11), the peak fluxes (Cols. 12, 13), calibration flag (see Sect. 5.3) and error in the peak flux density (Col. 14; see Sect. 5.3), the empirical residual noise in the field where the source was detected (Col. 15), presence of previous OH detection and the name of the nearest IRAS point source (Col. 16) and the distance to this nearest IRAS point source expressed as a fraction of the corresponding IRAS error ellipse (Col. 17).

The spectra for all sources are shown in Fig. 10. They are displayed with 50kms^-1 on either side of the velocity range of each object. The spectra were extracted from cleaned (128² 1 $^{\prime \prime }$ pixels around the source position) and restored cubes, summing over $3 \times 3$ pixels around the peak pixel. Only spectra #237 and #280 were extracted from raw cubes, as cleaning was impossible due to the awkward beam shape. No "continuum fitting" other than the described RFI excision (Sect. 3.1) was applied (cf. spectra #097, 104, 253, 275, 280).

Figure 6: A source (solid black circle in right panel) in the field of pointing centre A will create sidelobes in that field, as well as that of B (42$^\prime$ away from A). The furthest strong (30%) sidelobe of a typical synthesized beam in the VLA survey is at $\sim$500 $^{\prime \prime }$ (small hatched circles). In the left panel, the response to a unity-flux-density source is given in the main lobe (solid curve) and in this furthest sidelobe, which we take to be on a spoke of the beam that runs through A and B, to calculate the extreme case. The dashed curves, from top to bottom at offset < 12$^\prime$) give the response in the lobe offset towards A (1), away from A (2) and the latter seen from B (3), all using the known VLA primary-beam attenuation. The vertical line indicates the largest possible offset of sources detected in fields that are not on the boundary of the survey region. Only for sources on the very edge of a field, the main lobe of the synthesized beam is no longer observed to be brightest point

Dots over peaks in the spectra give an indication of the velocity range of the detections; note eg. the sidelobe from spectrum #223 in spectrum #219. Sidelobes are still present in the spectra, as most confusing sources would be outside the cleaned area. Negative sidelobes are obvious in e.g. spectra #127 (from #132), #150 (from #149) and in an unfortunate way in #222 (from #223). Note the extreme velocity coincidence of #159 and #172, as well as #242 and #244.

In Fig. 4 the longitude-latitude diagram and longitude-velocity diagram are shown and in Fig. 5 the histograms of central- and outflow velocity.

Table 2 Compact OH-maser sources in the northern galactic Disk region (This table is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/366/481

The columns of Table 2 contain the following information:

• 1. Sequence number (coincident with spectra in Fig. 10).

• 2. Name in the OH$\ell{-}b$ convention.

• 3. Date of observation. Date "000000" means data were taken during more than one observing run (see Table 1 for parameters).

• 4. Right ascension of the brightest peak for epoch J2000 (typical error 2 $^{\prime \prime }$, Sect. 5.2).

• 5. Declination of the brightest peak for epoch J2000 (typical error 2 $^{\prime \prime }$, Sect. 5.2).

• 6. Formal measurement error in position from IMFIT (determined in the channel of the brightest peak) in arcsec (Sect. 5.2).

• 7. Radial offset of the source from pointing centre in arcmin.

• 8. Line-of-sight velocity with respect to the LSR of the blue-shifted (L) peak. For single-peaked spectra the velocity of the peak is always given as blue-shifted for reasons of tabulation (typical error 1kms^-1, Sect. 5.4).

• 9. Same for the red-shifted (H) peak (typical error 1kms^-1, Sect. 5.4).

• 10. Stellar velocity (typical error 1kms^-1/14kms^-1, Sect. 5.4).

  $v_{\rm c} =0.5\cdot \left(v_{\rm H}+v_{\rm L} \right).$

• 11. Outflow velocity; zero for single-peaked sources (typical error 1kms^-1, Sect. 5.4).

  $V_{\rm exp}=0.5\cdot \left( v_{\rm H}-v_{\rm L} \right).$

• 12. Flux density in image domain at peak pixel of cleaned, restored image (IMSPEC), corrected for primary-beam attenuation, but not for any "continuum" of the blue-shifted (L) peak (typical error 20%, Sect. 5.3).

• 13. Same for the red-shifted (H) peak (typical error 20%, Sect. 5.3).

• 14. Formal measurement error in flux density, determined in the channel of the brightest peak (IMFIT). An asterisk indicates that the corresponding field was not calibrated properly (Sect. 5.3).

• 15. Empirical noise in "empty" cube for the present field (Sect. 5.1.1, channel width 2.27 kms^-1).

• 16. A "+", "$\ast$" or "x" for a, or "-" for no, OH identification within 1$^\prime$ in the Simbad database (Sect. 5.6), and the IRAS PSC position with highest identification probability (i.e. smallest N, see Col. 17, Sect. 5.5).

• 17. Ratio between the size of the error ellipse of, and and the distance to, the IRAS PS of Col. 16, in the direction of the OH position (Sect. 5.5).