Early work on H
emission-line stars and nebulae was published by
Henize in 1956.
This survey, based on objective-prism photographs taken with a 10-inch
camera, yielded 415 objects in the LMC, and among them 97 point-like
emission sources, with no visible continuum, which could thus be
considered as candidates PNe.
Finding charts were provided.
Lindsay & Mullan (1963) and Lindsay (1963), using the same
instrument, selected, out of a sample of about 1000 emission objects, 109 point-like
H
emission sources with no continuum.
65 of these were classified as candidate PN because emission lines other than
H
were also seen, while the remaining 44 objects showed only
H
.
This later group however potentially also contained PNe, because it
consisted of fainter objects where other emission lines needed more sensitive
material to be revealed.
Unfortunately, no finding charts were ever published for this sample, so that
recovery of all the PNe is necessary.
In 1964, Westerlund and Smith used a blue objective-prism with a 20/26 inch
Schmidt telescope to survey 100 square degrees of the LMC and produced a
catalogue of 42 LMC PNe with approximate coordinates and manually drawn
finding charts.
Only point sources were retained.
Sanduleak et al. (1978) obtained objective prism plates with the Curtis
Schmidt telescope at Cerro Tololo over a large fraction of the LMC.
They presented a list (SMP) of 102 PNe, with cross-references to previous
work.
Objects were selected with no evidence of a continuum, and simultaneously
with unresolved structure on direct plates (with the possible exception of
SMP007).
Unfortunately the coordinates are only approximate and no finding charts
are provided, which makes the identification difficult.
For further studies, these PNe have therefore to be ``re-discovered''.
This was the most complete list of confirmed PNe at that time and therefore
their designation is preferred to older ones.
Some objects, believed to be of to low excitation to represent classical PNe
(and denominated Very Low Excitation (VLE) objects) were presented in an
independent list (Sanduleak & Philipp 1977).
A few of the objects initially rejected by SMP, have been detected
again in later surveys.
Sanduleak (1984) added 26 PNe (denoted Sa in our table, from Sa104 to Sa126)
candidates to this list thanks to deeper plates obtained in the central
region of the LMC.
Nine of those had already been found by Jacoby (1980), but have been labeled
with the Sanduleak denomination in our table.
Five objects were later rejected.
The candidate Sa103 is a galaxy, with z=0.035, see Dennefeld (1986).
Four objects (108-119-125-127) could not be found again:
we took ON and OFF line CCD images in H
and couldn't detect any
emission object inside the 4 fields (from 
for Sa108
and Sa119, to 
for Sa125, and up to
for Sa127).
We note that almost all the objects observed with the smaller field (0.90 m
Dutch telescope + CCD camera, with a field of 
)
fall on the edges of the field.
As an example, Sa104 was hard to recovered because the position was
erroneous by about 
.
However for Sa125 and Sa127 the field is large enough to conclude that no
PNe are present in these 2 regions.
This has been independently confirmed by Morgan & Good (1992) who suggest
in addition that Sa108 and Sa119 are carbon stars.
Sa104a was first discovered by Savage et al. (1982) and is a true PNe
(with particularly low abundances, Leisy & Dennefeld 1995).
Later on, while this work was in progress, Meatheringham et al. (1991a,b) published, with their spectroscopic observations, better positions for 60 out of the 102 SMP PNe, while 10 others were measured by Vassiliadis et al. (1992). However the R.A. of these 70 PNe are rounded-up to the nearest second of time!
Jacoby (1980) used the Cerro Tololo 4 m telescope at the prime focus with a
direct imaging technique (on-line/off-line narrow filters photography
at [OIII] and H
) in 4 central regions of LMC (small area of the
Bar). This is a much deeper survey which produced 41 faint PNe, 5-6 mag
fainter than the brightest ones.
Later on, Boroson & Liebert (1989) rejected 14 objects: 9 were early type
stars, 3 M giant stars, 2 objects were not found at all.
Furthermore, 8 PNe candidates were already known and confirmed by previous
surveys.
The coordinates are good to 
but the finding charts are difficult
to use at the
telescope because they are taken in narrow-band emission line filters:
the object is then difficult to recognize in a typical telescope acquisition
camera or a broad band CCD image.
In 1990, Jacoby et al. published the [OIII] photometry and interference filter
images of the fields of the 102 PNe from the first Sanduleak list (1978).
These images suffer from the same shortcomings at the telescope as only the
brightest stars are visible.
Recently Morgan & Good (1992) and Morgan (1994) published
respectively 86 and 54, new PNe candidates from plates taken with the 1.2 m UKST and
objective prism, covering
the entire LMC system.
The errors on coordinates are ``typically 
arcsec''.
Finding charts are provided, but the first series is hardly usable, specially
in crowded areas, because of the small dynamics.
These objects have also been included here for completeness and
homogeneity.
The various lists discussed above provide the basic set of candidate PNe used here. No attempt has been made to be exhaustive. It should be further noted that these are only candidates, and only follow-up slit spectroscopy can confirm the nature of the object. When this was available (from our or published work), it is noted in Table 4. To date, 139 only out of the 277 candidates have been observed with slit spectroscopy.