COTM: Vela
Albert Brakel
Vela the Sails (possessive: Velorum) is part of the old mega-constellation of the ship Argo
Navis. We looked at the other parts, eastern and western Carina (the Keel) in April 2000 and April
2002, and Puppis (the Stern or Poop Deck) last month. Lying in the Milky Way, there are some rich
star fields, adorned with planetary nebulae, a reflection nebula, a supernova remnant, open
clusters, and a globular cluster.
With the CAS Bobroff 14" reflector now just a memory, I observed with my f/10 20 cm
Schmidt-Cassegrain from Downer, but to see the nebulae to best advantage (or at all), I had to go
to a dark sky site.
Open Clusters
NGC 2547 (RA08h 10.7m, Dec -49d 16') is a cluster about half a Moon diameter across, in
which the brighter stars stand out against a backdrop of fainter ones. A prominent arc of brighter
stars lies across the group, and includes a skew miniature of the Southern Cross in which "Beta
Crucis" is relatively fainter compared to the other stars than in the real Crux.
IC 2391 (8h 40.2m, -53d 04') is the mag. 2.5 patch of light just to the right of Delta
Velorum in the crossbar of the False Cross, and easily visible to the unaided eye. Much of its
brightness comes from the mag 3.6 star Omicron Vel. The large and very widely-spaced grouping of
bright and dimmer stars is strewn across an area of sky that is too large for any telescopic field.
Use binoculars or a finderscope, which will disclose that there are two main loose concentrations,
one of them faint.
IC2395 (08h 41.1m, -48d 12'), with an integrated magnitude of 4.6, can be seen with the
unaided eye. Its outliers give it a diameter of about 20', but there is an eastern concentration
about 10' across. It shows as a collection of some 30+ stars floating in Vela's stellar Milky Way
background.
Trumpler 10 (08h 47.8m, -42d 29') lies just east of the star d Velorum, and is easily
visible in binoculars or finderscope. It contains widely-spaced stars of magnitude 7 or fainter,
and is about 30'-40' across, but as it is set in a busy star field, it's hard to tell where the
cluster boundaries are.
IC 2488 (09h 27.6m, -56d 59'), a degree west of N Velorum on the southern Vela border, is
not one to rush out and show the neighbours. It features about 3 dozen widely-spaced stars (mag. 10
or fainter) in an unresolved misty background. The cluster has a rough wedge shape, with longest
dimension about 20'. It filled the field of view at 154x, but looked best at 118x.
NGC 3228 (10h 21.8m, -51d 43') is a sparse group of 25+ stars some 20' in diameter in the
surrounding starfield. The brightest member is mag. 7.9, the rest are mag. 10-11. For binocular
observers, the mag. 6.0 object looks like a small milky patch.
Nebulae
Only one of the nebulous objects (NGC 3132) was detectable from light-blighted Downer, so I
observed them from a site where the limiting unaided-eye magnitude was about 6.
NGC 2626 (08h 36m, -40d 40'), a reflection nebula about 2' across, is present around a
mag. 10 star. It appeared as a dim, ill-defined haze that was a bit more extended on the south side
of the star. If you're not careful you can miss it, by dismissing it as the dispersion that's often
present around stars in less than ideal conditions. It responded somewhat to the higher contrast
that higher magnifications provided.
NGC 2792 (09h 12.4m, -42d 26') is a tiny planetary nebula that looked like just another
star to the casual eye until examined closely, when a fuzziness became apparent. It could be seen
without an OIII filter, but needed the filter for definite identification.
NGC 2899 (09h 27.0m, -56d 07'), located midway between Kappa and N Vel at the top of the
False Cross, is another planetary that needed a bit of patience to find, with the OIII filter and
averted vision being essential. Although it has a similar integrated magnitude (11.8) to NGC 2792,
its larger diameter of 1.5' means that its surface brightness is less. The very dim disk had a hint
of a dimmer centre.
NGC 3132, the Eight-Burst Nebula (10h 07.7m, -40d 26') is a bright planetary nebula in
northern Vela about the size of Jupiter (40"). In the suburban sky at 77x it appeared as a hazy
patch around a mag. 10 star, but needed higher powers, or an OIII filter, to show it well. In the
dark sky no filter was necessary, although it did further enhance it. NGC 3132 has been compared to
the Ring Nebula in Lyra, but unlike the Ring it shows a solid grey disk, with some brightening
around the periphery. The brightening is most prominent on the eastern and western sides. Deep
images show a complex multilayered ring structure at different tilt angles, from which the nebula
gets its name. Oddly enough, the mag. 10 star is not the true central star - a mag. 16 white dwarf
is actually exciting the cast-off gas.
Supernova Remnant
NGC 2736, The Pencil (09h 00m, -45° 54') is the brightest part of the Vela Supernova
Remnant, an extensive structure some 8 degrees across that has its centre about 4 deg. to the west.
It is a long narrow streak over 20' long, oriented 020 in PA, and is sharpest along its eastern
side. Though not visible from the suburbs, in a dark sky of high transparency the faint nebulosity,
just 30" wide, is said to be detectable with a 20 cm aperture. The transparency evidently was not
good enough on the night I looked, as despite searching in a dark sky and using an OIII filter I
still could not glimpse it.
Globular Cluster
NGC 3201 (10h 17.6m, -46° 25'). This loose, irregularly round cluster, presenting as
a nebulous haze with embedded very faint pinpricks of light at 77x magnification, is set in a field
of foreground stars. Higher powers increased the resolution, but unresolved nebulosity remained in
the background. Its lack of a defined central condensation makes it appear more like a distant open
cluster than a typical globular.
Double Stars
Of the dozens (hundreds?) of double stars available in Vela, the following is a selection of the
most notable for moderately-sized telescopes. Only one shows any real color; all the rest are white
or pale bluish-white.
Gamma Velorum (08h 09.5m, -47d 20') is the brightest star in Vela. In recent times it has
come to be known as Regor, which is "Roger" spelled backwards, in honor of Roger Chaffee, one of
the astronauts who died in the Apollo 1 fire. Bluish-white Gamma Vel is a very rare type of star
called a Wolf-Rayet (spectral type W), with a surface temperature of 60,000 deg.K and the only one
visible to the unaided eye. The primary actually consists of an unresolvable pair of stars orbiting
1 AU apart, the other being a heavier O-type giant. The Wolf-Rayet component is in the last stages
of preparing to explode as a supernova - we can only wait. There is a third component a wide 41" to
the southwest, a white mag. 4.3 star of spectral type B. In the same field there is also a small
white unequal pair 1' to the SE, the four stars forming a pretty Y or Greek lambda pattern,
depending on your perspective.
h4104 (08h 29.1m, -47d 56') was discovered by John Herschel from the Cape of Good Hope in
the first half of the 19th Century. It is an unequal pair (mags. 5.5 and 7.3) 3.4" apart. There are
a number of other stars in the same field, including one 19" to the NE.
Dunlop 70 (08h 29.5m, -44d 44') is one of the discoveries of J. Dunlop, who observed from
the old Parramatta Observatory in the 1820s. It's another unequal pair (mags. 5.2, 7.1), separated
by 4.6". A filament of the Vela Supernova Remnant arcs through the field, but is only (just)
visible with large scopes and an OIII filter - given my lack of success with the brightest part of
the remnant (NGC 2736), I didn't try for it.
Delta Vel (08h 44.7m, -54d 43') in the False Cross consists of very unequal (mags. 2.1
and 5.0) white stars 2.2" apart. This is quite a difficult binary because of the large magnitude
difference and the relative closeness, so use plenty of magnification to give yourself a chance.
The seeing is critical too - I failed to resolve it despite using 235x and 380x, even when thin
cloud came over to dim the glare of the primary.
Russell 87 (08h 56.3m, -52d 43') was found by H.C. Russell at Sydney Observatory in the
late 19th Century. The mags. 4.9 and 7.7 twosome is spaced at 2.6", and was split with 154x
power.
h4188 (09h 12.5m, -43d 37') in a starry field has a mag. 6.0 primary 2.8" from the mag.
6.8 secondary. This is another John Herschel discovery.
h4220 (09h 33.7m, -49d 00') is a fine mag. 5.6 and 6.3 whitish-very pale yellowish pair,
with a separation of 2.0". The closest double on this list, it was just resolved with 154x.
h4245 (09h 46.1m, -45d 55') - at last a binary with significant color, at least as far as
the yellow mag. 6.8 primary is concerned. The wide (9.4") companion is too faint (mag. 9.4) to show
color in moderate apertures, and looked greyish, though it has been reported as slightly bluish as
a contrast effect.
Dunlop 81 (09h 54.3m, -45d 17') is an unequal (m.5.8, 8.3) double at 5.3", set against a
stellar backdrop.
Galaxy
Despite Vela's location smack in the Milky Way, it harbours a number of faint galaxies in its
northeast. The brightest is NGC 3256 (10h 27.8m, -43° 54'), which eluded me even from my dark
sky site, probably because by now the first indications of condensation on my scope's corrector
plate had started to appear. Larger mirrors or better conditions should be able to show a 1.5' x 1'
diffuse oval rising to a brighter centre. The object is actually a galaxy merger with streamers of
stars being thrown out, like the Antennae Galaxies in Corvus.
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