Butterfly Cluster, M6

This beautiful cluster was riding high in the clear night sky, almost at the zenith. It was the first image of five objects which I obtained during an evening out in the field with my friends from Macarthur Astronomical Society.

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The M6 cluster is about 94 million years old. It needs some considerable imagination to see a butterfly shape but if you begin with the two almost symmetrically curved rows of small stars arranged in a v-shape – the antennae – then perhaps you might be off to a good start.

Most of the stars in the cluster are hot B-type stars but the bright orange star is BM Scorpii, an orange supergiant (mag.6) which has exhausted its hydrogen and swollen in size as it converts helium into heavier elements. It lies in front of the cluster at about 790 light years distance – about half the distance to the cluster. Despite being a supergiant, it is a K2 star which is cooler than our  G2 Sun.

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There was great excitement amongst our hardy group of astronomers at the news that a bright comet P/2008 Y12 (SOHO) had arrived in the sky.

However, I had other targets in mind – and I’m glad I did, because my friends spent much of the evening searching for it, to no avail. It clearly was much dimmer than the predicted 10th magnitude, which is not uncommon.

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After seventeen minutes of this first image, my mount stopped tracking, so here it is – a seventeen minute image of the Butterfly Cluster.

Unfortunately, I had hardware/software/gearware problems which resulted in imaging for shorter durations than I intended but taking a couple more objects (five instead of three) – with a resultant reduction in quality.

The other images will no doubt follow.

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Object Details:

Designation: Messier 6, M6, Butterfly Cluster.
Constellation: Scorpius
Visual magnitude:  +4.2
Apparent size:  20′ x 20′
Diameter:  9.2 light years.
Distance:  1,600 light years.
Altitude during exposure:  82° above W. horizon.

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My previous image of M6.

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Technical stuff:

Image: Exposure:  12 x  86.2 sec = 17.25 min. Gain: 230 Date:  2019-08-24 Location:  semi-dark rural. Conditions:  clear Moon: no.

Processing: Image acquisition:  SharpCap. Method: Live stacked. Darks: no. Image post-processing:  GIMP. Cropping:   no. Sky:  0.22 e/pixel/s .

Gear:

Telescope:	SkyWatcher Esprit	Type:	120ED 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: N	Guiding:	No
Polar aligning:	QHYCCD PoleMaster	Polar Error:	00’ 19”

Geek Log:

[ZWO ASI071MC Pro] Debayer Preview=On 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=1 every 4 seconds Gain=230 Exposure=86.233669 Timestamp Frames=Off White Bal (B)=50 White Bal (R)=53 Brightness=36 Temperature=-15.4 Cooler Power=37 Target Temperature=-15 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=Off Banding Threshold=35 Banding Suppression=0 Apply Flat=None Subtract Dark=None #Black Point Display Black Point=0.0523809523809524 #MidTone Point Display MidTone Point=0.604761904761905 #White Point Display White Point=1 TimeStamp=2019-08-24T10:04:05.0749418Z SharpCapVersion=3.2.6086.0 TotalExposure(s)=1034.804028 StackedFrames=12

Image © Roger Powell

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