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(IAAC) Blue spiral in Cetus (M77, NGC 1068)



Dear all,
I wonder if anyone has ever attempted to observe the galaxy M77 (NGC 1068) or more
exactly its nucleus through a nebular filter. The galaxy is a well known
representative of Seyfert galaxies with strong nuclear emission in the forbidden blue
green lines of ionized oxygen ([OIII]), otherwise typical of planetaries, so I was
quite surprised to read recently in the book 'Problem In Astrophysics' by Agnes M.
Clerke (1903):
'Another object of dubious relationships [the description appeared in the chapter
'Nondescript nebulae'] is Messier 77 (N.G.C. 1068), Lord Rosse's "blue spiral" in
Cetus. The description intimates an anomaly, since true spirals are "white," and give
a continuous spectrum. Now the colour of this object corresponds, as might have been
expected, to a gaseous constitution, whether of the normal kind or in certain ways
peculiar, remains to be proved.'
The Rosse's observing record (the famous 6-feet reflector was used) referred to by
Clerke appeared in Phil. Trans. 151:713 (and his drawing on Plate 25, fig. 6):
'Sketched 4. Dec. 22, 1848. A blue spiral. Jan. 14, 1849. Spiral. Oct. 29, 1851. The
central part is flatter on the f. [following, i.e. eastern] side. Nov. 24. 1851. The
central part is, I am nearly quite sure, spiral, sketched. Jan. 13, 1852. Spiral form
of the centre seen. Nov. 29, 1856. Details of drawing seen very well. Jan. 10. 1858.
I can see nothing more than is given in the sketch, which appears to me correct,
though perhaps it defines too well the edges of the B. [bright] central disc.'
As you can see, Lord Rosse commented on the galaxy's color only once, in the first
record, and later focused his attention on the morphology instead. It's tempting to
conclude that he saw the galaxy blue because of the [OIII] emission, but one must
keep in mind that while the lines are quite strong, most emission come from the
central region a few arcseconds across so the story is no doubt just a curiosity.
Anyway, it should be interesting to try nebular filter (especially combined with high
power and aperture) on the galaxy's nucleus. Spectrum or photoelectric scan published
by Shields and Oke in ApJ 197:5, 1975 (Fig.2) suggests the filters should work well. 
Clear skies,
Leos Ondra
******************************************************
Leos Ondra, Skretova 6, 621 00 Brno, Czech Republic
ondra@bm.cesnet.cz
http://www.bm.cesnet.cz/~ondra
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