(IAAC) NGC 246 - 17.5" F/4.5

Observer: Yann POTHIER (France)
Your skill: advanced (many years)
Object: NGC 246 (PK 118-74.1; PN G118.8-74.7; ARO 43)
Category: planetary nebula
Constellation: CET
Object data: Vmag=10.9; Bmag=8.0; 240"x210"; type IIIb; central star of
Vmag=11.95; discovered by W. Herschel in 1785; ELCAT: [OIII, 496+501nm] = 5
x [Hbeta, 486nm].
RA/DE: 00h47.00m, -1153.' (2000.0)
Date and UT of observation: 02 August 1995, 02h20UT
Location & latitude: La Clapiere Obs. (France, latN44 40 00, longE06 27 36)
Site classification: rural, alt.1650m (5500ft)
Limiting magnitude (visual in UMi): 6.31 with averted vision 10% of the time
Transparency (1 to 5 - best to worst): 1
Seeing (1 to 5 - best to worst): 2
Moon up (phase?): no
Instrument: Coulter 445mm/17.5" F/4.5
Magnification: 312x
Filters used: OIII, UHC
Description: at 312x and OIII filter, large and bright PN, round about 4.1'
(246") in diameter, or, more accurately, slightly oval (246x222") along a
NW-SE axis, the edges are very sharp; the PN is clearly annular from the E
(PA90) to the SSE (PA165) going through N and W sides (3/4 of the entire
circle); a small and very faint crescent of nebulosity seems to miss from
the E and S sides (from PA90 to PA165); the thickness of the ring is
varying between 40 and 60"; the central star of mag11 is in the center,
another 2 of mag11 are 1.0'WSW (PA240) on the disc and 2.3'NW (PA325)
just against the border; one last star of mag14 stands in the "faint
crescent" region, 1.6'ESE (PA115); a kind of dark globule (diam.50")
stands against the central star to the NE; another dark globule more
elongated (50"x40" in PA150/330) stands to the W of the SW (from central
star) mag11 star, but farther from its star-companion compared to the first
one; UHC and OIII both provides good contrast gain on this object; I
suspected the central star's companion as a mag15 star appearing as an
elongation from the central's glare towards SSW (PA210).
Note: the low OIII/Hbeta ratio, typical of low excitation PNs (as for NGC
40, but less extreme case).
I can provide a scanned drawing of NGC 40 to anyone who can read the binhex
encoding of Eudora (for Mac); just mail me to try (yann.pothier@fnac.net),
it works quite often with other configurations...
Yann Pothier
11 impasse Canart, 75012 PARIS, FRANCE
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