Dear CygA gang,

I am currently drafting paper 3 based on the spectropolarimetry and the HST archival images. My starting point is our contribution to the KNAW proceedings to which I propose to make the following changes/additions. I welcome comments and, more especially, offers of contributions beyong what some of us have recently discussed. I propose to send the paper to A&A or MNRAS.

What am I missing?

Title:
The optical structure of Cygnus~A

Authors:
Whoever has done/will do substantial work on this

Abstract:
Replace original abstract with an extended one including some mention of the emission lines.

Introduction:

ref. to  2nd HST MgII observation by Antonucci (KNAW proceedings)
ref. to possibility of Raman scattered Ha, Lee \& Yun 1998.
ref. to Conway et al. - HI disk and evidence for BH

Discuss the previous work on the analysis of the line spectrum, in particular Tadhunter, Metz and Robinson (1994 - TMR). Strong evidence for enhanced nitrogen. Put this in the context of other literature on abundance anomalies in galaxies and quasars (nuclei and EELR) at both low and high z.

Observations:
Basically as KNAW but:

give details of the extraction apertures
describe binning for polarimetry and line analysis
add a note of the E-galaxy fraction for nuclear extraction

Discussion:

mention the parabolic shape of the cones, dust structure in Jackson et al. (1998) We could plot our extraction apertures on their reddening maps.

refer to the line-free and continuum-free images in Jackson et al. (1998)

revise the table giving the continuum fit parameters as necessary and add data for the nuclear component

handle the case of underestimated Hb due to stellar absorption (see Montse's note)

expand the discussion of the stellar population and relate
to the work of Jackson et al. 1998. This should include the discussion of the SE/NW line ratio plot and a model of the effect of balmer absorption. There should also be a discussion of the effects of spatially distinct zones with different reddening.

discussion of the nuclear extraction. mention the Raman
scattering possibility - although this does not obviously fit the observations we have...

Characteristics of Raman scattering:
Ref: Lee, H-W. \& Yun, J-H., 1998, MNRAS, 000, 000 (astro-ph/9808046)
1) Red asymmetry in scattered flux
2) Red bump in polarized flux
3) Dip in fractional polarization at Ha
4) Width dependent on N_HI

Indications from the data:
a) The broad Ha is seen from the E and W extractions as well as the nucleus - and has similar widths. Hard to reconcile with high HI column at large R?
b) Central dip in P is caused by NLR
c) need to check the symmetry in polarized flux - but it is not strongly asymmetric.

Small apparent width of MgII probably a result of low s/n

add plot of nuclear extraction

insert section on emission lines and their polarization. The justification for doing this is:

Spectra are very deep, the elliptical galaxy has been carefully subtracted => a uniquely comprehensive line list for an AGN. The three extractions give us a measure of the spatial variation.

Particular discussions of:
1) The Balmer decrement
2) The nitrogen spectrum
3) The iron spectrum, especially the higher ions. (nb. check for atmospheric absorption in [Fe XI])

There will be an annotated line list with fluxed for the 3 extractions corrected for Galactic but not internal extinction.

Summary of TMR's discussion of nitrogen (and sulphur) and the original study of RG in Robinson et at (1987)

In both the nuclear and extended spectra of NLRG (R87), the strength of [NII] is hard to reconcile with standard power-law photoionization models. For a solar N/O ratio, better agreement can be obtained by using a hot (>10^5K) BB-like ionizing spectrum. However, the high [NII]/Ha ratio is observed in a wide variety of galactic nuclei - although Cyg A represents an extreme case - and the possibility of an enhanced N abundance has been suggested by several authors. The [NII] strength is not restricted to the nuclear regions in the radio galaxies - including Cyg A - it can be traced in the extended spectra even in the presence of variations in the ionization level.

[Discuss also the NV/CIV issue in quasars etc.]

What can we say about N in Cyg A which has not been said before?

There are some more comments we can make, however, about the ionization mechanism and the effect and location of the dust. This has been discussed extensively in Montse's series of notes (accessible on my web site). 

Add new references: these for a start:

\bibitem[]{}Tadhunter, C.N., Metz, S. \& Robinson, A., 1994, MNRAS, 268, 989 (TMR)

\bibitem[]{}Lynds, R. et al., 1994, BAAS, 26, 941

\bibitem[]{}Fosbury, R.A.E., Vernet, J., Villar-Mart\'\i n, M., Cohen,
M.H., Ogle, P.M., Tran, H.D. \& Hook, R.N., 1998, Knaw proceedings ref.

\bibitem[]{}Tran, H.D., 1995a, ApJ, 440, 565

\bibitem[]{}Lee, H-W. \& Yun, J-H., 1998, MNRAS, 000, 000 (astro-ph/9808046)