Sky & Telescope - USA (2019-08)

32 AUGUST 2019 • SKY & TELESCOPE

Wind-Blown Bubbles

Object WR No. HD Spectral Type Mag(v) Size RA Dec.

NGC 6888 136 192163 WN6 7.5 17 ′ 20 h 12.1m +38° 21′

W R 134 Nebula 134 191765 W N6 8.1 20 ′ 20 h 10.2m +36° 11′

Sh 2-308 6 50896 WN4 6.7–6.9 40 ′ 06 h 54.2m –23° 56′

NGC 2359 7 56925 WN4 11.6 27 ′ 07 h 18.5m –13° 13′

NGC 3199 18 89358 WN4 10.8 22 ′ 10 h 17.0m –57° 55′

WR 23 Nebula 23 92809 WC6 9.0 30 ′ 10 h 41.6m –58° 46′

NGC 2020 — 269748 WN4 13.2 3 ′ 05 h 33.2m –67° 43′

Angular sizes are from recent catalogs. Visually, an object’s size is often smaller than the cataloged value and varies according to the aperture and magnifi cation of the

viewing instrument. Right ascension and declination are for equinox 2000.0.

Wolf-Rayet Nebulae

My 80-mm fi nder shows a 5′ roundish glow at 13×, and

higher power adds a portion of the wings. Through my

18-inch at 108×, the wispy central bubble has a brighter rim

along the west side, forming a thick semicircular C. Near the

north edge, three 12th-magnitude stars are aligned, and an

11th-magnitude star is attached at the south end. WR 7 is

offset northwest of center, near the bubble’s inner edge.

The helmet’s southern wing angles west-southwest as a

bright 4′ bar, then narrows and stretches west an additional

5 ′. The northern wing sprouts to the northwest and is slightly

broader and more uniform in surface brightness. A third,

dimmer fi lament shoots 10′ east from the north side of the

bubble. My 24-inch f/3.7 refl ector reveals a fi lamentary, mul-

tishell structure with knots and lacy arcs of nebulosity.

NGC 3199, dubbed the Southern Crescent, is one of

several showpieces in the constellation Carina. This nebula

lies too far south for most U.S. observers, but place it on your

bucket list for a trip near or south of the equator. From the

Cape of Good Hope, John Herschel described it as,

the great falcated [sic k le -sh ap e d] nebula,

and remarked it was

brighter to the south following [ea s t] part, and dies off to the

north preceding [west], having a curved form and forked tail.

In deep optical images, NGC 3199 is the brightest part of

a complete wreath spanning 22′ in diameter. As we’ve seen

with other nebulae, the 11th-magnitude WR star HD 89358

is displaced 4.5′ west of the geometric center, and it’s nestled

within a small triangle of fainter stars. Distance estimates

range from 7,500 to 12,000 light-years, implying a physical

diameter of at least 50 light-years.

At a Costa Rica star party (latitude 10° north), NGC 3199

was faintly visible in my 9×50 fi nder as a nebulous bar. In a

13.1-inch refl ector, I saw an impressive kidney-shaped nebula,

extending 12′× 7 ′ north to south and opening to the east. The

southern half was brighter than the northern, and the inner

(eastern) edge was more sharply defi ned. Several 11th- and

12th-magnitude stars glittered on the southeast end. Despite

a careful look, I found no sign of the bubble’s eastern half.

SOUTHERN CRESCENTIf you’re

a Northern Hemisphere observer,

you’ll have to travel south to see

NGC 3199, which lies in Carina.

This object has been much ob-

served, including by the European

Southern Observatory’s 2.6-meter

Very Large Survey Telescope,

which captured this image.

ES

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