THE 654-1046 NM LINE SPECTRUM OF THE PLANETARY-NEBULA NGC-7027

Deep CCD spectra of the planetary nebula NGC 7027, taken over the rang e 654-1046 nm at a spectral resolution of order 0.1 nm, are presented. About 465 different lines are detected and intensities are provided f or 405 features. A total of 680 emission lines is considered. In the b est conditions, namely shortward of 900 nm and outside the telluric ab sorption bands, emission lines can be detected and measured down to a de-reddened intensity of (1.5-2.5) x 10(-5) relative to H beta. The ra te of line detection and identification achieved is a one-order-of-mag nitude improvement over previous far-red spectroscopic surveys of nebu lae, now superseding available optical surveys. Many of these lines ha ve not been seen before. Altogether, the permitted and forbidden lines encompass 47 ions from 22 elements in this spectral range. Forbidden lines are produced by 31 ions from 18 elements. Iron-peak elements, no tably chromium, manganese, iron, nickel, copper, and possibly vanadium , as well as heavy elements, notably krypton, xenon, selenium, bromine and strontium are detected. Identification of many permitted lines fr om high- and low-ionization stages of carbon, nitrogen, and oxygen is reported. Extrapolation of known energy levels is required in some cas es. C II, C III, and C IV series discovered in the far red can be foll owed up to large principal quantum numbers, providing a clue to explai n optical lines, left unidentified for tens of years. Available compil ations of high-nl atomic energy levels may not be sufficiently compreh ensive to fully exploit the nebular spectroscopic data now accessible to common astrophysical devices. The quadrupolar line [S III]882.98 nm is identified. The natural broadening of the upper autoionizing level of C II 879.4 is disclosed by the peculiar profile of the line. The i mportance of dielectronic recombination of C II through quartet terms is confirmed by the presence of the strong multiplet C II(14). The int ensity and decrement of the Paschen lines suggest a markedly uneven di stribution of dust absorption across the nebula. A diffuse interstella r band and K I lines are detected in absorption. About 13 % of all lin es are not identified, a majority of them being weak and affected by l arge errors. Only 4 of them exceed a de-reddened intensity of 3 x 10(- 4) I-beta. Some 15 lines are left unidentified, which either exceed a de-reddened intensity of 10(-4) I-beta or are measured with an uncerta inty smaller than 20%. Half these unidentified lines are affected by t elluric absorption and only 6 fulfill both criteria.