61 Paper I, Manchado et al. (1989A&A...214..139M)
62 Kenyon et al. (1990AJ.....99..869K)
63 Hrivnak & Kwok (1991ApJ...368..564H)
64 Paper II, Garcma-Lario et al. (1990A&AS...82..497G)
65 Kwok et al. (1995ApJ...454..394K)
66 Blommaert et al. (1993A&A...267...39B)
67 Allen (1974MNRAS.168....1A)
68 Allen (1973MNRAS.161..145A)
69 Hu et al. (1993A&AS..100..413H)
70 Campbell et al. (1989AJ.....98..643C)
71 Zijlstra et al. (1991A&A...243L...9Z)
72 Fouque et al. (1992A&AS...93..151F, Cat. <II/177>)
73 Kastner et al.(1992ApJ...398..552K)
74 Lepine et al. (1995, Cat. <J/A+A/199/453>)
75 Miroshnichenko et al. (1996A&A...312..521M)
76 Gaylard & Whitelock (1988MNRAS.235..123G)
77 Persson & Campbell (1988AJ.....96.1019P)
78 Liseau et al. (1992A&A...265..577L)
79 Allen & Glass (1975MNRAS.170..579A)
80 Hrivnak et al. (1989ApJ...346..265H)
81 Hu et al. (1990A&A...227L..17H)
82 Hu et al. (1989A&A...208..213H)
83 Gaylard et al. (1989MNRAS.236..247G)
84 Elias (1978ApJ...224..857E)
85 Lloyd-Evans (1985MNRAS.217..493L)
86 van der Veen et al. (1989A&A...226..108V)
87 Persi et al. (1987, in "Planetary and proto-planetary nebulae: from IRAS to
87 ISO", Preite-Martinez A. (ed.). Reidel-Dordrecht, p. 221)
88 Le Bertre (1993, Cat. <J/A+AS/97/729>)
89 Epchtein et al. (1987A&AS...71...39E)
90 Nyman et al. (1993A&A...280..551N)
91 Epchtein & Nguyen-Q-Rieu (1982A&A...107..229E)
92 Hu et al. (1993A&A...273..185H)
93 Persi et al. (1990AJ.....99..303P)
94 Jones et al. (1982ApJ...253..208J)
95 Lawrence et al. (1990AJ.....99.1232L)
96 Hrivnak et al. (1988ApJ...331..832H)
97 Kastner & Weintraub (1995ApJ...452..833K)
98 Cohen (1974MNRAS.169..257C)
99 Whitelock et al. (1995MNRAS.276..219W)
 1 te Lintel Hekkert et al. (1991, Cat. <J/A+AS/90/327>)
 2 David et al. (1993, Cat. <J/A+A/277/453>)
 3 Ratag (1991, priv. comm.)
 4 te Lintel Hekkert (1991A&A...248..209T)
 5 Omont et al. (1993, Cat. <J/A+A/267/515>)
 6 Wouterloot & Brand (1989, Cat. <J/A+AS/80/149>)
 7 Likkel et al. (1991A&A...246..153L)
 8 Wouterloot et al. (1993, Cat. <J/A+AS/98/589>)
 9 Lewis (1992ApJ...396..251L)
10 Lewis et al. (1990ApJ...362..634L)
11 Woodsworth et al. (1990A&A...228..503W)
12 Casoli et al. (1986A&A...169..281C)
13 Nyman et al. (1992, Cat. <J/A+AS/93/121>)
14 Likkel (1989ApJ...344..350L)
15 Wouterloot et al. (1989A&A...215..131W)
16 Clemens & Barvainis (1988ApJS...68..257C)
17 Yun & Clemens (1994ApJS...92..145Y)
18 Hu et al. (1994A&AS..103..301H)
19 Davis et al. (1979ApJ...230..434D)
20 Garcia-Lario et al. (1993A&A...267L..11G)
21 Loup et al. (1990A&A...227L..29L)
22 Zijlstra et al. (1991A&A...243L...9Z)
23 Zuckerman et al. (1986ApJ...304..401Z)
24 Bujarrabal et al. (1992A&A...257..701B)
25 van der Veen et al. (1993A&A...269..231V)
26 de Vries et al. (1984A&AS...56..333D)
27 Knapp & Morris (1985ApJ...292..640K)
28 Knapp (1986ApJ...311..731K)
29 Morris et al. (1987ApJ...321..888M)
30 te Lintel Hekkert et al. (1989A&AS...78..399T) and references therein
31 te Lintel Hekkert et al. (1988A&A...202L..19T)
32 Hu et al. (1993A&AS..100..413H)
33 Silva et al. (1993A&A...275..510S)
34 Brand et al. (1987A&AS...68....1B)
35 Bujarrabal & Bachiller (1991A&A...242..247B)
36 Chapman (1988MNRAS.230..415C)
37 Gaylard et al. (1989MNRAS.236..247G)
38 Zijlstra et al. (1989A&A...217..157Z)
39 Sevenster et al. (1997b, submitted)
40 Likkel & Morris (1988ApJ...329..914L)
41 Zuckerman & Dyck (1986ApJ...311..345Z)
42 Sevenster et al. (1997, Cat. <J/A+AS/122/79>)
43 van Langevelde et al. (1992ApJ...396..686V)
44 Frail & Beasley (1994A&A...290..796F)
45 Slysh et al. (1994A&AS..106...87S)
46 Mauersberger et al. (1988A&A...206L..34M)
47 Knapp et al. (1995ApJ...455..293K)
48 Likkel et al. (1987A&A...173L..11L)
49 Zuckerman & Dyck (1989A&A...209..119Z)
50 Lewis et al. (1987AJ.....94.1025L)
51 Eder et al. (1988ApJS...66..183E)
52 Volk et al. (1993ApJ...402..292V)
53 Arquilla et al. (1986MNRAS.220..125A)
54 Knapp et al. (1989ApJ...336..822K)
55 Galt et al. (1989AJ.....98.2182G)
56 Zuckerman et al. (1977ApJ...211L..97Z)
57 Jenness et al. (1995MNRAS.276.1024J)
58 Lindqvist et al. (1988A&A...205L..15L)
59 Garcia-Lario et al. (1991A&A...249..223G)