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Whirlpool Galaxy - M51

Optics TEC 140 APO with Flattener at f/7.1
Mount AstroPhysics 900GoTo
Camera Moravian G3-16200
Moravian C3-61000
Filters Astrodon LRGB Gen II
Date May 2016 - May 2022
Location Antares Observatory
SQM-L 19.5-21.0
Exposure LHaRGB = 26-86.5-9-11-14.3 hours
total: 146.8h
Software CCDAutoPilot / Voyager, MaxIm DL, PixInsight, Photoshop CS6
Notes The LRGB images where all captured with the CCD camera while half of the Halpha images were taken with the CMOS camera.

M51 is located at a distance of around 28 Mio. light years (8.6 Mpc) in the constellation Canes Venatici. In 1845, William Parson discovered its spiral arms - the first nebula-like object where spiral arms have been detected. The interacting pair - NGC 5194 (M51a) and NGC 5195 (M51b) - have been extensively studied. Yet the system continues to yield surprises: In 2018, A. Watkins et al. discovered a large ionized gas cloud north of the galaxy system. In their study, they demonstrate the association of the ionized gas cloud with the M51 system. For the image shown here more than half the exposure time was used to detect this extremely faint cloud.s
A. Watkins et al. (2018) also presented a deep wide-field image of M51 with faint tidal features / plumes that were detected in their image with a limiting magnitude of μB∼30. A side by side comparison (without Halpha data) is given here.

The image presented here shows these features in a combined view: The deep LRGB image (60.3 hours) and a deep image (86.5 hours) taken for Hα + [NII].

The new CMOS camera (Moravian C3-61000) proved to be very good for these faint emissions: narrowband filtered images clearly showed a higher signal-to-noise ratio and the combined 32.5 hours was clearly worth more than 54 hours of narrowband data with the CCD sensor.

The diffuse nebula on the upper right in this image is galactic cirrus (clouds of interstallar dust).

M51 preview

click here for a 50% size image
click here for a 80% size image

The left image below shows the effect of adding the deep Halpha data: In addition to the structures in the outskirts of M51, prominent star forming regions as well as a red halo around the spiral arms can be seen, a common phenomena. On the right a contrast enhanced and inverted luminance.

M51 side by side M51 luminance inverted

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