Two contrasting views of M1, the crab nebula

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timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Two contrasting views of M1, the crab nebula

#1

Post by timh »

First view is a Hubble palette image accumulated over a few clear nights in January. Being only a thousand years old and about 10 light years across the elemental composition of this supernova remnant is thought to mainly reflect materials made by the supernova and progenitor star itself - rather than interstellar space. OIII and SII light largely coincide - both perhaps arising from collisional excitation occurring in the same regions as the shock waves continue to move out. The intensities of SII, OIII and HA light are quite nearly even - unlike in HII star-forming regions where HA tends to dominate. It is interesting to see that red SII seems particularly localised at about 7 oclock and HA at 12 o 'clock.

However, although much of the light coming from M1 is narrowband - with the NB filters embracing at least most of it in the form of HA, NII, OIII and SII - perhaps the most interesting feature of M1 is the pulsar at the core. Only 10 km or so across and yet so hot and bright that it is clearly visible even at some 5000 light years - rotating at relativistic speeds which separates out charges even within a neutron star and generating rotating magnetic fields which trap charged particles and generate a continuous spectrum of synchrotron electromagnetic radiation. Within the visible spectrum this can be detected as bluish light from the UV up to about 500nm.

Thus the second view is a kind of hybrid narrow-band/ broad band image designed to try and capture a more complete - and colour faithful - image. Here I mapped both SII and HA together to RED (using the max function), OIII to GREEN and then both OIII and a broadband blue filter (< 500nm) image to BLUE (again using the max function). This seemed to work quite well and personally I prefer it as a way of imaging M1 since the blue smear of synchrotron light is clearly visible as well as the contributions from OIII and the combined light from SII and HA in a more naturalistic way.

(An interesting sidelight on this story is that the synchrotron light is clearly fading quite quickly. The status of M1 as M1 may reflect the fact that it was significantly brighter in the 18'th century.? ). This paper is a good read on the topic where the rate of fade is measured as the apparent increase in OIII linewidth as the baseline (synchrotron radiation) continues to fade. https://academic.oup.com/mnras/article/346/3/885/982620.

Also interesting a paper describing an optical telescope measurement of the 33ms pulse time of the core neutron star - probably a bit beyond my equipment though! ... https://www.messier.seds.org/more/m001_pulsar.html)

https://www.astrobin.com/full/cibcxy/0/


Tim
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SW200PDS Newtonian (f = 1000mm, F5.0) Baader MkIII coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm.

ZWO AS1294 MC camera for RGB (UHC) captures or ZWO ASI294MM mono camera for BLUE, HA, SII and OIII , both 4.63 uM pixels cooled to -10C

ZWO IR/UV cut filter, Astronomik UHC filter, Astronomik 6.0 nm OIII filter, Optolong 7 nm HA filter, Optolong 6.5nm SII filter, ZWO blue filter

80 min of RGB (some UHC) frames (20-110s) at gain 124 , 93 x 3min gain 151 OIII under moonless Bortle 6 skies. 70 x 3 min HA frames, 71 x 90s BLUE frames at gain 124 and 93 x 3 min SII frames captured with the moon risen but more than 90 degrees away.

All frames (0.95 AS/ pixel) pre-selected for quality using the FWHM and brightness filter within Sharpcap, darks and grayscale master flats (no bias) prepared using Sharpcap. Preprocessing in PixInsight.

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Following standard processing of the 5 aligned images - Crop, DBE background removal, Photometric colour calibration etc. the images were stretched. Then Starnet was used to create starless images of the three NB images as well as a star mask of the stars from the RGB image. The three NB and blue filter l images were then stretched to a similar level before being combined using PixMath into RGB images as described and further adjusted with curves, sharpening and noise reduction. Then the RGB stars from the starnet starmask were re-added.
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Last edited by timh on Mon Jan 24, 2022 11:33 pm, edited 2 times in total.
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Menno555
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Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
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Re: Two contrasting views of M1, the crab nebula

#2

Post by Menno555 »

Like usual a great post Tim! Love your explanations and examples :D
Fun fact: the neutron star is only around 30km big. Imagine: such a tiny object emitting these amounts of energy? Just mind blowing :o

Menno
ChrisMobley
Posts: 2
Joined: Sun Jan 23, 2022 11:16 pm

Re: Two contrasting views of M1, the crab nebula

#3

Post by ChrisMobley »

Outstanding!
Thanks for sharing.
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: Two contrasting views of M1, the crab nebula

#4

Post by timh »

Thanks indeed for your kind comments Menno and Chris!
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