The 1.0m Survey

We have chosen PNe as the tracers because they are less affected by metallicity bias than most other tracers and, they are strong emitters in H - this make their velocities easy to measure.

The Low Dispersion Survey Spectrograph (LDSS) of the Anglo-Australian Observatory was attached to the 1.0m telescope of Siding Spring Observatory and was used as a focal reducer (without grism). This instrument, with 100 mm interference filters and a 1024 x 1024 CCD, gives a useful circular field of 30 arcmin at 2.35 arcsec per pixel. We conducted the survey in H (6562 Å , FWHM 19 Å ) and the nearby continuum (6450 Å , FWHM 42 Å ).

The 1.0m telescope optical imaging survey covers the region of the southern galactic bulge: l = and b = to , chosen because of its lower extinction relative to the northern bulge. By uniformly spacing our 30 arcmin fields of view over the area l = and b = to , we produced a grid of 488 fields. In two seasons of observation, we covered 94% of the grid (458 fields ). In addition, we obtained 40 fields in the equivalent area of the northern bulge. In figure 1, the filled circles represent the fields we have observed. Each circular field covers roughly half of the total area associated with each grid point. Added together, they represent about 1% of the far-IR flux from the bulge (section 3).

In studying the bulge of the Milky Way, we are challenged with the difficulty of finding H emitters in dense star fields. The most straightforward method to detect our H candidates was to combine the two H frames and then divide the H image by the continuum image for each field.

After a thorough and systematic visual examination of the quotient images for our 498 fields, we obtained a total of 148 H detections. We used the Acker et al. (1992) catalogue of planetary nebulæ  (which is the most up-to-date) in order to identify already known PNe. This cross-check yielded 97 new candidates.

© Copyright Astronomical Society of Australia 1997