On the absence of broad MgII emission-line variability in NGC3516 during 1996.

Session 78 - Seyfert Galaxies.
Display session, Friday, January 09
Exhibit Hall,

[78.10] On the absence of broad MgII emission-line variability in NGC3516 during 1996.

M. R. Goad, A. P. Koratkar (STScI), P. T. O'Brien (U. Leicester, UK), K. T. Korista (W. Michigan U.), D. J. Axon (U. Manchester, UK)

We report the first results of an 11 month HST/FOS monitoring campaign of the broad emission-line region in the Seyfert 1 nucleus NGC 3516. During the campaign the UV continuum showed a factor of 5 variation; correspondingly the strongest broad UV emission-lines (e.g. Ly\alpha, CIV) displayed a somewhat weaker, though still significant variation (a factor of 2). In contrast, no variation was detected in either the strong broad MgII emission-line or in the many strong blended lines of FeII from \lambda\lambda 2200--3400ÅP>While historically the flux in the broad MgII emission-line has varied (a factor of 2 within a few years), the profile shape has remained unchanged for at least a decade. In contrast, the high ionization lines (HILs, e.g. Ly\alpha, CIV) show both emission-line flux and profile changes on relatively short timescales, which appear to be correlated with changes in the continuum level. Differences between the rms and steady-state profiles of the HILs suggests that the variable component originates in a distinct (both spatially and kinematically) region of the BLR. Significantly, on Feb 21st 1996, the profile shapes of the HILs and MgII were identical. This suggests that the non-variable component of these lines either (a) arises from the same cloud population, or (b) is formed in self-similar structures (e.g. a terminal wind).

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