Messier 46 is a rich cluster of young stars with a beautiful ring shaped planetary nebula with three stars within the ring – giving it the appearance of a human face.
It is seemingly embedded within the M46 cluster. However, the planetary nebula (NGC 2438) is not a part of M46 because it is:
(a) travelling at a different speed to the cluster;
(b) an old dying star, whilst the stars in the cluster were “recently” born; and
(c) believed to be much closer than the cluster’s distance of about 5,400 light years.
NGC 2438, PK 231+04.2, W43.
Location: in open cluster M46 (NGC 2437).
Visual magnitude: 11.5
Apparent size: 1.2′
Distance: 2,900 or 3,300 light years according to different reference sources.
Altitude: 41° above East horizon.
Exposure: 46.7 minutes. Live stacked.
Date: 2018-12-26 commencing approx 11.05 pm
Location: Leumeah, NSW.
Sky: outer suburban.
Moon: rose towards end of session.
Image acquisition software: SharpCap.
Image post-processing: GIMP.
[ZWO ASI071MC Pro]
Output Format=PNG files (*.png)
Frame Rate Limit=Maximum
White Bal (B)=55(Auto)
White Bal (R)=29(Auto)
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Anti Dew Heater=Off
Display Black Point=0
Display MidTone Point=0.5
Display White Point=1
Imaging telescope: Skywatcher Esprit 120ED Super APO triplet refractor.
Focal length: 840 mm, focal ratio: f/7.
Imaging camera: ZWO ASI 071 MC Pro
Telescope mount: SkyWatcher EQ6-R Pro.
Polar aligning method: QHYCCD PoleMaster.
Polar alignment error: <10′.
Field flattener: yes; filter: no.
Imaged with SharpCap Live Stack from 11.05pm to 12.12 am (67 min) obtaining 115 x 24.169 sec frames.
Recorded 2803 seconds of exposure (46.7 min), so 20 mins were ignored by Live Stack, before I increased the FWHM from about 4 to 6.1.
Moon rose behind the trees at 11.19 pm but I did not notice it until about 11.45 when it was still a subdued colour. By midnight it was getting brighter, so I terminated imaging at 12.12 am.
See next post for details of additional planetary nebulae in Messier 46.
Image © R.Powell