Erratum: Detailed observations of NGC 4151 with IUE – III. Variability of the strong emission lines from 1978 February to 1980 May

• Published in: Monthly notices of the Royal Astronomical Society 1984-08, Vol.209 (3), p.479-479
• Main Authors: Ulrich, M. H., Boksenberg, A., Bromage, G. E., Clavel, J., Elvius, A., Penston, M. V., Perola, G. C., Pettini, M., Snijders, M. A. J., Tanzi, E. G., Tarenghi, M.
• Format: Article
• Language: English
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/209.3.479

‘Detailed observations of NGC 4151 with IUE – III. Variability of the strong emission lines from 1978 February to 1980 May’ by M. H. Ulrich et al. was published in Mon. Not. R. astr. Soc., 206, 221–237 (1984). It has been drawn to our attention by Dr Y. N. Chen of Sulzer Brothers Limited, Winterthur, Switzerland that we made an arithmetical error of a factor 10 in our estimate of the mass of the central object. The mass entries in Table 4 should read 5 × 108, 6 × 108 and 109 respectively. This affects our argument given directly under Table 4 concerning the identification of short wavelength continuum excess as thermal emission from a Lynden-Bell (1969) accretion disc around a black hole. There is no longer such an interesting coincidence between the radius of the hypothetical blackbody which could emit the short wavelength continuum excess ($r \simeq 10^{14}\enspace \text {cm}$) and the radius of the last stable circular orbit associated with a $5 \times 10^8 M_\odot$ Schwarzschild black hole (~ 1015 cm). However, the accretion disc interpretation might be maintained if one or more of the following is true: (1) If the motion of the Broad Line clouds are parabolic rather than circular; this reduces the deduced masses by a factor of 2. It has been shown recently (Kwan & Carroll 1983, Astrophys. J., 261, 25; Bradley, Puetter & Hubbard 1984, preprint) that parabolic or highly elliptical orbits for Broad Line clouds fit naturally to the line profiles seen in active galaxies and quasars. (2) If the temperature of the accretion disc is lower than 30 000 K then the area is increased: for example by a factor ~ 2 if T ~ 25 000 K. (3) If the nuclear black hole is rotating and has Kerr geometry, the radius of the last stable orbit is reduced and the area of the disc near the maximum temperature can be smaller by a factor of ~ 5.