The optical constants at low T have been determined analogous to the procedure described for the high temperatures in Zeidler et al., A&A 553, A81 (2013). The FPSQ-model oscillator parameters used for computing the n nad k values are the following ones (after S. Zeidler, Ph.D. thesis, FSU Jena, 2013): T=100 K: w_TO g_TO w_LO g_LO 231.790000 15.600000 232.120000 14.900000 308.290000 10.580000 311.590000 11.270000 429.750000 140.930000 445.870000 114.810000 482.060000 30.080000 611.050000 35.660000 533.970000 61.900000 560.360000 61.920000 581.920000 77.100000 544.650000 137.800000 674.920000 38.040000 864.140000 29.210000 801.410000 125.530000 789.030000 95.540000 eps_inf=2.87 T=10 K w_TO g_TO w_LO g_LO 231.800000 21.440000 232.410000 20.900000 307.620000 11.600000 310.950000 12.120000 429.030000 137.320000 443.050000 111.550000 480.470000 32.290000 609.560000 38.460000 532.050000 60.750000 557.190000 67.340000 579.010000 84.330000 543.140000 124.050000 670.030000 38.600000 862.870000 31.940000 800.230000 107.090000 788.410000 88.470000 eps_inf=2.80