Sky & Telescope - August 2019 - 32

Wolf-Rayet Nebulae

My 80-mm ﬁnder 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 ﬁlament shoots 10′ east from the north side of the
bubble. My 24-inch f/3.7 reﬂector reveals a ﬁlamentary, multishell 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 [sickle-shaped] nebula,

and remarked it was
brighter to the south following [east] 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 ﬁnder as a nebulous bar. In a
13.1-inch reﬂector, 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 deﬁned. 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 CRESCENT If 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 observed, including by the European
Southern Observatory's 2.6-meter
Very Large Survey Telescope,
which captured this image.

Wind-Blown Bubbles
WR No.

Spectral Type

Mag(v)

Size

Dec.

NGC 6888

136

192163

WN6

7.5

17′

20h

12.1m

WR 134 Nebula

134

191765

WN6

8.1

20′

20h 10.2m

+38° 21′
+36° 11′

54.2m

-23° 56′

Sh 2-308

50896

WN4

6.7-6.9

40′

06h

NGC 2359

56925

WN4

11.6

27′

07h 18.5m

-13° 13′

22′

10h

17.0m

-57° 55′

41.6m

-58° 46′
-67° 43′

NGC 3199

89358

WN4

10.8

WR 23 Nebula

92809

WC6

9.0

30′

10h

NGC 2020

269748

WN4

13.2

3′

05h 33.2m

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 magnification of the
viewing instrument. Right ascension and declination are for equinox 2000.0.

AUGU S T 2 019 * SK Y & TELESCOPE

ESO

Object

Sky & Telescope - August 2019

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