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4. The catalogue

4.1. LMC catalogue

We summarize in Table 4 all our results for the 277 LMC PNe. The 4 candidates (Sa108, Sa119, Sa125 and Sa127) have been excluded (see Sect. 3.1). Excluded also are WS03 (not confirmed as a PN candidate, see SMP and Fehrenbach et al. 1978), and N016, N047 (extended), N099 (point like) VLE objects (Monk et al. 1988), but coordinates are available. The PNe are listed, first ordered by catalog names and then, within each catalogue, by increasing Right Ascension.
Column 1 indicates the selected name, with one cross-identification (first SMP, if available, then, in decreasing order of priority, Sanduleak, Jacoby, Henize, Westerlund, Lindsay, etc...). The complementary cross-identifications can then be found, if necessary, in the original papers. In Col. 2 Right Ascension and declination coordinates are given in equinox J2000 and B1950.
Column 3 is a number which gives a rough idea of the position error (1 for precision better than 0tex2html_wrap_inline19432, 2 between 0tex2html_wrap_inline19452 and 0tex2html_wrap_inline19473, 3 between 0tex2html_wrap_inline19493 and 0tex2html_wrap_inline19515, and finally 4 for coordinates less precise than 0tex2html_wrap_inline19535). In parentheses, respectively, the number of position determinations (a maximum of 4), and the number of positions kept for the final averaged coordinate. The derived B magnitude are listed in Col. 4 (the number of plates used is given in parentheses). Because of intense crowding, some measurements were impossible.

4.2. LMC finding charts

The second product of this work is the complete set of finding charts for the LMC PNe. As already mentioned, only a fraction of the known PNe had published finding charts, and these were not always of usable quality. We therefore produced a homogeneous set of charts for all the objects. Plates 1-25 give the 280 finding charts taken from the IIIa-J plates of the ESO/SERC Southern Sky Atlas.
Only a few exceptions (SMP098, Sa104, Mo01, Mo02, Mo49 and Mo54) are taken from Red plates. Field sizes are all tex2html_wrap_inline1969 and North is up and East to the left.

Note that, as a by-product, accurate positions are now also available for the standard stars.

Cross-identification with IR sources

As an example of possibilities opened by the knowledge of precise coordinates for PNe, we have looked for associations with IRAS sources, as given in the catalogue of Schwering & Israel (1990). While this is of obvious interest for the study of the PNe, it is however not illustrating the best possibilities of our catalogue, as the IRAS positions themselves are not known with an extreme accuracy. The uncertainty of the IRAS positions is given in Table 3 (click here) as the size of the error-ellipse from the Point Source Catalogue (PSC), when an association exists, as explained in the Catalogue of Schwering & Israel. The main criterion for an association of a PN with an IRAS source is the coincidence in position. We have, somewhat arbitrarily (but nevertheless based on the size of the average error-ellipse) separated sources in 3 categories: association closer than tex2html_wrap_inline1975 in distance, between tex2html_wrap_inline1977 and tex2html_wrap_inline1979, and between tex2html_wrap_inline1981 and tex2html_wrap_inline1983. With the density of sources in the LMC, at these larger distances however, many unrelated sources would enter the catalogue. A second criterion has thus been applied, based on the expected IR flux distribution for PNe. Following experience from galactic PNe (Pottasch et al. 1988), a very broad selection on flux densities can be used to select PNe: tex2html_wrap_inline198525tex2html_wrap_inline1987 / tex2html_wrap_inline198912tex2html_wrap_inline1991 > 2 (to eliminate stars) and tex2html_wrap_inline199525tex2html_wrap_inline1997 / tex2html_wrap_inline199960tex2html_wrap_inline2001 > 0.2 to eliminate galaxies. We have applied this criterion for those objects were the distance of the IRAS source to the optical PN was larger than tex2html_wrap_inline2005, to eliminate many spurious associations. For the closer associations, we have left all of them in Table 3 (click here), but will apply the criterion subsequently to assess the reality of the identification. When the tex2html_wrap_inline2007 flux was not well estimated due to confusion, the source was kept, pending further identification (a C is then printed instead of a flux value).

Table 3: Possible IRAS associations

The results are given in Table 3, where we list the serial number from Schwering's list, in Col. 1, the PN name (Col. 2), the IRAS PSC cross-identification when appropriate (Col. 3) and the associated error ellipse (Cols. 4-6). If no PSC identification could be done the typical errors are tex2html_wrap_inline2035 in both RA. and Dec. (Schwering & Israel 1990).
Columns 7 to 9 give respectively the optical and IR positions (in J2000 equinox) and the distance between the two determinations (in arcsec).
Columns 10 to 13 show the IR fluxes at 12, 25, 60 and tex2html_wrap_inline2037, while in column 14, a ``p'' indicates a point-source. More details about the IRAS data can be found in the original reference (Schwering & Israel 1990).

Zilstra et al. (1994) published a list of 12 IRAS sources associated with LMC PNe. Five of them do not show up here: SMP006, SMP061, SMP098, MG45 and Mo18, which indicates a distance between IRAS and optical position larger than 2'. As we used only the catalogue of Schwering & Israël (1990), based on a special observation in the Deep Sky Mapping mode, (while Zilstra et al. used indifferently this list or the Faint Source Catalogue (FSC)), this difference has probably to be ascribed to a discrepancy between the two catalogues, which needs further investigation.
Applying now the flux ratio criteria in addition to the association with separations smaller than tex2html_wrap_inline2041, we end with a ``quality criterion'' (Q) for the association, given in the last column of Table 3. Quality 1 is a secure association, both because of small distances and adequate flux ratios, while quality 2 is less secure (flux ratios at the limit, or unclear due to confusion, and larger separation between optical and IR sources). Quality 3 is a doubtful association, while 0 means rejection. In the latter category enter SMP013, SMP043, SMP064, SMP069 and MG58 because the IR flux distribution indicates a stellar source (for SMP064, the IRAS source is clearly associated to the cluster NGC1984), while for SMP092 and Mo19 the flux distribution would indicate a cold galaxy. If the two latter objects are indeed PNe, which is confirmed for SMP092 (Meatheringham & Dopita 1991b), then they have in fact an optically thick dust shell, with a cooler exciting source, which is known to mimic the flux distribution of a galaxy. Further spectroscopy will be necessary. The same remark applies to some of the quality 3 associations in the first part of Table 3, which could be the same type objects, or lower excitation HII regions (SMP024, SMP029, SMP036, SMP075). The known (high) excitation class for the first three PNe suggests an IR excess due to a dust shell. Note that some objects are already classified as Very Low Excitation objects. It should be noted also that, because of the metallicity which is different in the Clouds compared to our Galaxy, the color criteria for the PNe might also be slightly modified. We end with 15 associations of quality 2 or better, closer than tex2html_wrap_inline2043 (among them 7 in the list of Zijlstra et al. 1994). These objects are worth further study. In the case of associations with larger separation, a close inspection of the finding charts reveals in almost all cases a better identification for the IRAS source than the PN.


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