NEAT SOUTHERN PLANETARIES : 03
NGC 3699 & He2-67 in Centaurus
This next part of the series includes two planetaries.
NGC 3699 is the most northern, followed by He2-67 Both planetaries
are separated by merely 11.1 arcmin, make an interesting pair.
Together, that I name these together as the “The Double Planetaries of
Centaurus.”
NGC 3699 / He2-65 / Sa2-74 / Wray 16-90 / PK 277+7.1 / PN
G292.6+01.2 (11279-5957) lies within the eastern portion of Centaurus
next to western Crux. Visible in 20cm., this bright 11.0p magnitude
planetary subtends the visual diameter of about 45.0 arcsec. This is
a strange looking object, and you would be forgiven to easily mistake
it for some small emission nebula. Using Sky Catalogue
2000.0 or Sky Atlas 2000.0, it is still remarkably printed
as an emission nebula. Interestingly, AOST1 also states NGC 3699 this
too.
From what I can ascertain, NGC 3699 was first recognised as a true
planetary around 1978. A photograph can be seen in Plate 10 in AOST1,
which was taken by Westerland and Henize, whose description (and
photograph) can be seen in AJ.Sup.Ser., 14, 154
(1969)
This PN is contained within a fairly starry field, extending in
the telescope to some 60 arcsec across. NGC 3699 is likely just
visible in 10.5cm, though 20cm vastly improves its appearance.
Dividing the image into two portions shows a dark rift, slightly
south of centre, at PA 80° to 200°. This can be seen in
20cm and O-III filter, and is visible in all telescopes above 25cm.
NGC 3699 does remind me of some smaller version of Centaurus’ irregular galaxy, NGC 5128 (Centaurus
A).
AOST2 says the appearance appear mottled, but this effect I could
be just begin to see using 30cm. At the edge of the PNe appears to me
as irregular and wavy. NGC 3699 is also considered among the
Peimbert Type 1 Bipolar (BPNe) exhibiting extreme filamentary
structures. Earlier, the structural details of these PNe types were
thought to be caused by extreme shocks and instabilities. Modern
theory says they are produced by high velocity dense shell(s),
catching up and overtaking the circumstellar envelope previously
ejected in the AGB phase. In turn, this produces the seemingly
chaotic and bizarre appearance of the nebula. All BPNe progenitors of
this type are suspected to weigh between 3M⊙ and 5M⊙. NGC
3699’s surface temperature is above
140,000K. All BPNe, are in essence, are among the hottest of all the
known PNNe.
Observational Descriptions
Technical Data
He2-67 / Sa2-76 / Wray 16-92 / ESO 129-22 / PK 292+1.2 / PN
G292.8+01.1 (11288-6007) lies towards the direction SE of NGC 3699.
Such planetaries in the sky, like this one are literally a dime a
dozen, but extraordinary other descriptions about NGC 3699 never
mention this particular nearby one! At 13.2 magnitude, it is just
visible in 20cm, and like most of these planetaries the O-III filter
is a godsend. Its 5 arcsec stellar-like appearance jumps out at you
while flickering the O-III filter over the visible field. To find it,
it is recommended using any wide-field eyepiece and with the field
diameter between 0.4° and 0.5° (c.80×). Place NGC 3699
at the very top south-western edge of the field, then this PNe
becomes obvious — very close to the centre of the field.
Appearance-wise, I saw what looked like a smallish grey disk, though
I suspect that one of the large Dobsonians could perhaps see some
colour. In 30cm, I could not see any apparent structure, except for
glimpsing an uneven edge.
He2-67 own PNN is of 15.8 magnitude and could be glimpsed in 40cm
telescopes, though I I have never seen it. Although not physically
related to NGC 3699, it has the same similar Type 1 structure as its
neighbour. Distance of this galactic planetary is likely to be many
kiloparsecs.
Observational Descriptions
Technical Data
Very little is known about this faint object, with
scant details in the literature. It is moving a the radial velocity
of +59.5 km.s-1
References.
- Stanghellini, L., Shaw, R.A., Villaver, E.,
“The Magellanic cloud calibration of
the Galactic planetary nebula distance scale.”, AJ.,
689, 1942 (2008)
Last Update : 04th November 2011
Southern Astronomical Delights ©
(2011)
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