LMC-N70 = LHa 120-N 70 = DEM L 301

05 43 25 -67 50 48; Dor
Size 7′

18″ (4/6/16 – Coonabarabran, 139x): Using a 17mm Nagler unfiltered, N70 appeared as a large, irregular hazy glow surrounding the stellar association LH 114 = S-L 673. S-L 673 resolved into nearly a dozen stars. Most of these were faint but included a mag 12.5 star on the south side.

The NPB filter provided an excellent contrast gain. A very large circular glow was easily visible, extending 5′ to 6′ in diameter. This isolated Superbubble (round ring) appeared brighter on the western half and in general slightly brighter along the rim, giving a weak annular appearance. Some of the interior glow was certainly due to the many stars in the association.

A 5′ string, including two wide pairs, extends to the NW of N70. A mag 12.5 star is a near the N end of the nebula. A mag 11/12.5 pair at 30″ is 2.5′ further NW and a mag 13 pair at 35″ is another 2.5′ NW.

Notes: Robert Innes discovered N70 on plates taken with the 10-inch Franklin-Adams camera around 1918 at the Union Observatory in Johannesburg, South Africa (Union Observatory Circular, No. 61, p.260, 1918). He described it as a “Large but faint spiral with stars; a small cluster [S-L 673] forms the nucleus.” From a second plate, he noted: “Fine circular spiral with stars” and a third plate, “Very fine circular spiral with stellar nucleus.” In 1926, he observed the field visually with the observatory’s 26.5-inch refractor and reported, “the stars in this spiral nebula are shown as a letter “S” but the nebulosity is virtually invisible.”

Jenka Mohr (Harvard Bulletin, No. 902, 26) independently discovered this object in 1936 on long exposure Harvard plates taken with the 24-inch Bruce, 10-inch Metcalf and 3-inch Ross-Fecker telescopes. Her announcement was titled “A Planetary Nebula Superposed on the Large Magellanic Cloud”. She described N70 as a circular nebulous envelope of great clearness with diameter of 420″. Mohr noted it appeared to be a large planetary nebula with a mag 12.6 star as probably its central star. If it was a member of the LMC, then its diameter would be 50 parsecs (at the accepted distance of the LMC), so she concluded it was a planetary superimposed on the LMC at a distance of 1200-2000 parsecs with a linear diameter of 4 parsecs.

Probably due this misclassification, Anton Becvar plotted N70 (without a designation) as a planetary nebula in the Skalnate Pleso “Atlas of the Heavens”. Similarly, it is plotted as an unlabeled “planetary” in first edition of Tirion’s Sky Atlas 2000.0, but listed under “Bright Nebulae” in the Sky Catalogue 2000.0.

In 1950, Evans and Andrew David Thackeray (MNRAS, 110, 429) photographed this object with the 72-inch Radcliffe reflector at Pretoria and described a very faint nebulosity brighter on the preceding side and a diameter of 420″; with a wispy structure suggesting a spiral or helical form; the central occupied by two distinct and compact groups of stars, some of which appear to be directly mingled with nebulous wisps. They noted evidence favored it was member of the LMC and “probably not a planetary”, but suggested that based on appearance it resembled the final star of a supernova outburst.