---------------- --------------------------------------------------------
  [C]{}            1334.530,1335.660,1335.708
  [C]{}            1174.930,1175.260,1175.590,1175.710,1175.987,1176.370
  [N]{}            1199.550,1200.220,1200.710
  [O]{}            1152.150,1302.170,1304.860,1306.030
  [Mg]{}           1239.925,1240.395,1367.257,1367.708,1369.423,
                   4482.383,4482.407,4482.583
  [Al]{}           1670.787,1719.442,1724.922,1724.982,1760.106,1761.977,
                   1763.869,1763.952,1765.816
  [Al]{}           1379.670,1384.132,1605.766,1611.873
  [Si]{}           1190.416,1193.292,1194.500,1197.394,1246.740,1248.426,
                   1250.091,1250.436,1251.164,1260.422,1264.738,1265.002,
                   1304.370,1305.592,1309.276,1309.453,1311.256,1346.884,
                   1348.543,1350.072,1350.516,1350.656,1352.635,1353.721,
                   1526.707,1533.431,3854.758,3857.112,3863.690,4129.219,
                   4132.059,5042.430,5057.394,6348.864,6373.132
  [Si]{}           1140.546,1141.579,1142.285,1144.309,1144.959,1154.998,
                   1155.959,1156.782,1158.101,1160.252,1161.579,1206.500,
                   1206.555,1294.545,1296.726,1298.892,1301.149,1303.323,
                   1312.591,1341.458,1342.389,1365.253,1417.237
  [Si]{}           1393.775,1402.770
  [P]{}            1149.958,1152.818,1153.995,1155.014,1156.970,1159.086,
                   1249.830,1452.900,1532.533,1535.923,1536.416,1542.304,
                   1543.133,1543.631
  [P]{}            1334.813,1344.326
  [S]{}            1250.584,1253.811,1259.519
  [S]{}            1194.041,1194.433
  [Ca]{}           1169.029, 1169.198,1341.890,3737.965,3934.777
  [Sc]{}           1418.773,1418.793
  [Ti]{}           1298.633,1298.697,1298.996,1327.603
  [V]{}            1148.465,1149.945,1149.945
  [Cr]{}           1136.669,1146.342,1247.846,1252.616,1259.018,1261.865,
                   1263.611
  [Mn]{}           1162.015,1188.505,1192.316,1192.330,1197.184,1199.391,
                   1201.118,1233.956,1254.410
  [Mn]{}           1174.809,1177.478,1179.851,1183.308,1183.863,1183.880
  [Fe[/iii]{}]{}   many weak lines, individually recognisable 1140-1152
  [Ni]{}           1317.217,1335.201,1370.123,1381.286,1393.324,1411.065

  : \[t-idlines\] List of major line features used for the abundance determinations and upper limits. Because of the different wavelength ranges of the available spectra not all lines could be used for all four stars.

\[s-abundances\] Metal abundances
---------------------------------

The COS spectra of the four white dwarfs contain a multitude of absorption lines from a range of elements. GALEX1931+0117 has the richest absorption spectrum, in which we securely identified transitions of nine elements (C, O, Al, Si, P, S, Cr, Fe, Ni), and we included those metals in the abundance analysis of all four targets. We also include in the analysis N, Na, Ti, V, Mn, which have moderately strong transitions in the wavelength range covered by the COS observations, but that were not detected. All metals were fully included in the 