NEAT SOUTHERN PLANETARIES : 26b
Surrounding Objects of NGC
2792 / Pb 5
λ Vel / See 109 / Lambda
Velorum / HIP 44816 / PPM 313999 / SAO 220878 / HD 78647 (09080-4326)
is an orange star of 2.14v magnitude that is commonly named Al Suhail
or just Suhail. It is mentioned here as it can be used to star-hop to
our planetary in the NSP Series, NGC 2792. It lives in the
north-western part of Vela and is the 55th brightest star in the sky.
Al Suhail is also the double star See 109 (old listing as
λ109), however, it is a very
difficult object to resolve as the huge magnitude difference is
12.6v. Since discovered in 1897, no change has been observed in the
PA or separation, which is given as 18.2 arcsec in PA 137°.
Suhail : Technical Data
At 2.226V or 3.943B magnitude, λ
Vel’s appears to the eye as bright orange-reddish coloured star
with the B−V of 1.665±0.013 (HIP) or 1.685±0.006
(Tycho). Hipparcos (1991) originally found the parallax as
5.69±0.53mas. giving the distance of 176±16.5pc. or
573±54ly. (9.4%) Proper motions are
-23.30±10.50 mas.yr-1 and
+14.28±0.41 mas.yr-1 — very similar to both
the PPM and Tycho data.
Yet the more recent update of the HIP2 Catalogue (2007), states
the new parallax of 5.99±0.11mas. This is a remarkable
improvement in accuracy, whose distance (and formal distance) is now
167±3pc. or 544±10 ly. (1.8%). Individual proper
motions of -24.01±0.01 mas.yr-1 and
+13.25±0.09 mas.yr-1. Calculated cpm. is
27.42±0.10 mas.yr-1, while the radial velocity of
+18.4±0.4 km.s-1. Traverse velocity
(Vμ) is 21.7 km.s-1, makes
the true star velocity (V☆) +28.45 km.s-1 in PA
Physical properties for Suhail finds the effective surface
temperature is 4235K corrected from the [Fe/H] ratio of 0.23 or 23%
of the solar iron to hydrogen ratio. Total luminosity of about 10,500
times that of the Sun. Stellar mass is 10.5±1.5M whose
radii is about 200R⊙ or 130 million kilometres across. Age is
estimated as between 22.5±7.5 million years, though some
sources give the more precise 27 million years.
Suhail : Variable Star
This is an example of one of the rarely known Lc-type irregular
variable stars, being among only forty-five so far established. It
shares fellow kinship with first magnitude star,
α Tau / Aldebaran, the
bloodied tip of the horn of Taurus, which holds the honour of being
the second brightest example of its class. Brightness fluctuations
have been observed to diverge by some 0.08 magnitudes. All Lc
variables are significant because they sometimes show complete
absence of periodicity in their light-curves where, as others do show
changes. A few examples show the brightness changes that are slow and
continuous, but several similar like have changed quite abruptly.
Most display spectral types between K and S and are exactly the same
of the more common Lb-type irregular variables.
λ Vel spectral class is K4Ib-II,
upgraded from the earlier K5 in 2008.
The earlier mentioned Aldebaran is an Lb-type that varies roughly
by only about 0.2 magnitudes. Yet, although Aldebaran is of similar
spectral type, I.e. K5, it is instead a giant star of luminosity
class III. Other known bright Lc variables includes;
β Gru / Beta Gruis,
ο1 CMa / Omicron
(1) Canis Majoris, ψ Aur / Psi
Aurigae and η Aur/ Eta
I 11 (09152-4533) is a wonderful close and near equal
brightness R.T.A. Innes pair some 10.7′WSW (PA 244°) from
the planetary known as Pb5 or He2-24, and hence, is useful for
finding this PNe. I saw this pretty bluish-white / white pair
resolved with some difficulty using the 20cm. (C8) at 234×.
AOST2 describes I 11 as having “…no perceivable colour
My estimate for the Δm was 0.6,
and this is quite comparable with the WDS 2001 that gives 0.8 from
the 6.7v and 7.5v listed magnitudes. AOST2 claims it can be split in
15cm., though at present time, it would have to be the best observing
conditions to do so, as the pair’s distance is slowly
diminishing. I would consider 20cm. is closer to the mark, but using
telescopes greater than 30cm. will become much easier.
I 11 was first discovered by Innes in 1895 and was first measured
by R.P. Sellors in early 1896. Since this time, PA has increased
(direct motion) from 271° to 292°
(Δ=21°), while separation has
decreased by about -0.15 arcsec (2002). Spectral class of the duo is
B8V. This system is without doubt a binary system with moderately
long orbital period. It will be worth watching in the coming decades.
A nice double star.
ESO 261-6 / PGC 26605 / Leda 26605 (09236-4246) is the
brightest of the motley collection of galaxies in the area. It lies
about 2′W of NGC 2792. This is a hard object in 25cm., and
easier in 30cm., because of the faint 14.7B magnitude and the tiny
visual round smudge is just some 6 to 8 arcsec across.
Photographically, the spiral arms are revealed, which subtends about
56″×56″. (Fig.6.) The STScI image confirms its
general barred spiral structure and matches the classed tentative
Sb:. What is odd about this image is the central bar is offset
from the spiral. It almost looks like to me the ring wider structure
might not be part of the galaxy but another superimposed over
another. Little is presently known about this galaxy.
Fig 6. Closeup of ESO 261-6. CDS Aladin Colour
Image Combined AAO Red (red), J plates (blue), average (green). Image
ESO 315-7 / PGC 26653 (09244-4124) and ESO 315-10 / PGC
26754 (09261-4150). Another two other galaxies (not imaged here) are
near ESO 261-6, neither of which I have searched for, and are only
one or two fields away. I mention them only to keep the “big
boys” with apertures greater than 30cm. interested. ESO 315-7
is 15.4p, whose 0.8′×0.3′ visual size
(1.0′×0.4′ photographically) being oriented along PA
102°. It is classed as “L+*/”.
ESO 315-10 is suspected to be an even fainter 16.0 magnitude
spiral whose 0.7′×0.5′ photographic size is aligned
along PA 22°. Even less is known of these two galaxies.
Last Update : 24th February 2012
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