NGC 346 & NGC 371 in the SMC

Object Details:

Designation:  NGC 346   Constellation:  Tucana     Visual magnitude:   +10.3
Apparent size: 14′ x 11′  Diameter: 1149 light years.  Distance: 200,000 light years

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A large bright nebula, which is a long way away!

NGC 346 is located in another galaxy, the Small Magellanic Cloud (SMC). Many of the stars in this image are also in the SMC galaxy and one of the brightest of them all, HD 5980, is actually visible in the centre of this nebula.

Here is a blow up (in future: literally) of NGC 346 showing HD 5980:

Image cropped to NGC 346 & interesting multiple star system HD5980. On the right, IC1611 & IC1612 are both open clusters in the Small Magellanic Cloud. (Image: R.Powell. Identifiers: Astrometry.net)

HD 5980 is a multiple star system. To quote Wikipedia:

HD 5980 has at least three components amongst the most luminous stars known: the unusual primary has a Wolf–Rayet spectrum and has produced a luminous blue variable (LBV) outburst; the secondary, also a Wolf–Rayet star, forms an eclipsing spectroscopic binary with the primary star; and a more distant O-type supergiant is also likely to be a binary.

Gosh, a stellar system with two eclipsing Wolf-Rayet stars – plus an O-type supergiant which orbits the two WR stars. What a fascinating system that would be for a physicist to study!

Wolf-Rayets are extremely hot stars, up to about 210,000° K  (our Sun is about 6000°K), depleted of hydrogen, and with very strong stellar winds. O type stars are also very hot. So all three stars have a short life-expectancy and each will ultimately go supernova. Not a good star system to reside in.

The SMC itself is one of our closest galaxies, gravitationally bound to the Milky Way. With a declination of -72°, it is only fully visible in the Southern Hemisphere, although theoretically visible as far north as +18°. It’s seen as a misty patch, about 5° wide (six Moon widths).

Here in SW Sydney the SMC is circumpolar (never sets) and looks like a piece of Milky Way that has broken away.

Also in image:
NGC 371, a hexagonal looking open cluster, with a diameter of 434 light years.

NGC 371 is listed as an open star cluster but the nebula is obvious, always reminding me of a hexagonal nut. (Image: R.Powell. Identifiers: Astrometry.net)

NGC 299, NGC 300, NGC 361, NGC 376, NGC 395, NGC 416.

IC 1611, IC1612.

See my above image with Astrometry.net annotated overlay.

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Technical stuff:

Image & Processing:

Date:  2019-11-07 Exposure:  32 x 89 sec  =  47 min. Gain:   68	Location:  outer suburban. Conditions:  clear sky, bright Moon Sky brightness:   0.78 e/pixel/sec .
Image acquisition:  SharpCap. Method: Live stacked. Darks:  6x	Image post-processing:  GIMP. Cropping: no

Gear:

Telescope:	SkyWatcher Esprit	Type:	120 triplet refractor
Focal:	840 mm F/7	Mount:	SkyWatcher EQ6-R Pro
Camera:	ZWO ASI 071 MC Pro	Type:	CMOS 28.4mm 16 Mpx
Optical aids:	Flattener: Y; filter: LP	Guiding:	Yes/No
Polar aligning:	QHYCCD PoleMaster	Polar Error:	2’ 25”

Geek Log:

[ZWO ASI071MC Pro] Debayer Preview=On Pan=0 Tilt=0 Output Format=FITS files (*.fits) Binning=1 Capture Area=4944×3284 Colour Space=RAW16 Hardware Binning=Off Turbo USB=40 Flip=None Frame Rate Limit=4 fps Gain=68 Exposure=88.871802 Timestamp Frames=Off White Bal (B)=50 White Bal (R)=53 Brightness=8 Temperature=-10.5 Cooler Power=92 Target Temperature=-10 Cooler=On Auto Exp Max Gain=300 Auto Exp Max Exp M S=30000

Auto Exp Target Brightness=100 Mono Bin=Off Anti Dew Heater=On Banding Threshold=35 Banding Suppression=0 Apply Flat=None Subtract Dark=C:\Users\Roger\Desktop\SharpCap Captures\darks\ZWO ASI071MC Pro\RAW16@4944×3284\88.9s\gain_68\dark_6_frames_-10.0C_2019-11-07T10_56_03.fits #Black Point Display Black Point=0.0238095238095238 #MidTone Point Display MidTone Point=0.547619047619048 #White Point Display White Point=1 TimeStamp=2019-11-07T11:51:48.8458556Z SharpCapVersion=3.2.6086.0 TotalExposure(s)=2843.897664 StackedFrames=32

Images © Roger Powell

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