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 Vels 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 299.9°

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 Aurigae.

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 difference.

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 pairs 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.

NGC 2792 Fig. 6

Fig 6. Closeup of ESO 261-6. CDS Aladin Colour Image Combined AAO Red (red), J plates (blue), average (green). Image about 2½′×2½′

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

Southern Astronomical Delights © (2012)

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