Nebulae - Glittering Lights - Marco Lorenzi
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Henize2-111 and Alpha Centauri

Henize2-111 and Alpha Centauri

Blazing brightly in the southern sky, the supergiant binary Alpha Centauri is the host of an expansive starscape sprinkled with numerous deep sky objects in this telescopic view. The most visually striking of its retinue of glittering jewels is the exotic and unique planetary nebula Hen 2-111, which is one of 468 planetary nebulae that were catalogued by Karl Henize in 1967. The main central part of Hen 2-111 is a bright peanut shaped core that measures only 29 x 15 arcseconds. However, its most visually striking aspect is a faint giant ionized halo that spans 10 x 5 arcminutes! This extreme structure was discovered by B. Louise Webster in 1978 in deep photographic plates taken with the (at the time) Anglo-Australian Observatory. At an estimated distance of 7800 light years, the entire nebula spans approximately 23 light years! The halo is actually a rare bipolar outflow and the other notable planetary nebula known to exhibit this unique feature is the northern hemisphere nebula KjPn 8 in Cassiopeia. Hen 2-111 exhibits some of the highest radial velocities detected in a planetary nebula to date! The radial velocities of the outer lobes are 370 kms, which is indicative of the high speed of the material ejected. Bipolar outflows with even greater velocities have been observed in a few other planetary nebulae. Almost perfectly symmetrical, the geometric regularity of the outflow is due to the ionized gas flowing outwards along the walls of two bi-conical structures. The twisted appearance is caused by the axis of the structures being viewed at an angle of 45 degrees from our line of sight. The most likely explanation for the origin of the outer lobes is an eruptive event of the central star within a circumstellar disk. To the right of Hen 2-111 is the attractive pairing of the open clusters NGC 5617 and Pismis 19. NGC 5617 is the larger and younger of the two and despite its apparent youthful appearance, it is actually an intermediate age cluster with an estimated age of 80 million years. Contrastingly, the smaller rich condensed cluster Pismis 19 appears much older than NGC 5617 and indeed its golden ancient light betrays its great age of 800 million years! It is at a similar distance to Hen 2-111 of about 7800 light years whereas NGC 5617 is much nearer at 5000 light years. However, it is subject to severe reddening due to interstellar dust between us and the cluster and would shine more brightly if this dust was less prevalent. Pismis 19 is one of 24 open clusters that were discovered by Paris Pismis in 1959 by analysing photographic plates taken at the Tonantzintla Observatory. Also barely visible in the glare of Alpha Centauri is a round broken roughly circular shell, which can be seen to the north of the halfway point between Alpha Centauri and Hen 2-111. This is the supernova remnant G315.4-0.3, which was discovered by Anne Green in 1974 and identified as a supernova remnant in 1975. However, its extremely dim optical shell was discovered recently in 2011 in a search for new supernova remnants in SuperCOSMOS Ha Survey (SHS) images by Milorad Stupar and Quentin Parker.

Thanks to Sakib Rasool for suggesting me this little known object and for preparing the above object description.

Apo TEC140 (140/f7.2) - FLI Proline 16803 - Ha (720m) OIII (660m) R (160m) G (120m) B (180m) - Warrumbungle Observatory, Coonabarabran, NSW, Australia