(IAAC) NGC 40 - 17.5" F/4.5

Observer: Yann POTHIER (France)
Your skill: advanced (many years)
Object: NGC 40 (PK 120+09.1; PN G120.0+09.8; ARO 1)
Category: planetary nebula
Constellation: CEP
Object data: Vmag=12.3; Bmag=10.7; 60"x38"; type IIIb+III; central star of
Vmag=11.61 (HD 826); discovered by W. Herschel; ELCAT: [OIII, 496+501nm] =
0.3 x [Hbeta, 486nm].
RA/DE: 00h13.01m, +7231.3' (2000.0)
Date and UT of observation: 21 August 1998, about 23h50UT
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
Transparency (1 to 5 - best to worst): 2
Seeing (1 to 5 - best to worst): 2 (stellar stars until 400x)
Moon up (phase?): no
Instrument: Coulter 445mm/17.5" F/4.5
Magnification: 400x
Filters used: OIII, UHC, Hbeta, Rainbow Optics spectroscope

Description: at 400x, large and bright PN, with two brighter lobes forming
a "Z" letter on the nebula; quite sharp edges, annular with partial ring
structure; about 52"x46" in a ENE-WSW axis; ring thickness of about 8",
partially visible ont the E and W sides; 2 brighter knots are on the ring
to the N and NNW from the central star (about mag11); a mag15 star is
visible on the SW border; very nice object and quite strange as no filter
enhances it, UHC, OIII and Hbeta are giving the same result: no contrast
gain (but no loss of detail too). The spectroscope explains this all: the
OIII and Hbeta images are of the same brightness merged together as a
nebulous, homogeneous and extended double-image; the central star's
spectrum is also very much interesting, showing a bright blue emission
region, two very faint green emission lines and one nearly red faint
emission line. Intriguing object indeed, full of surprise.

Note: the sub-zero OIII/Hbeta ratio rarely found in PNs, typical of low
excitation PNs.

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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