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Thread: Object of the Week,October 14, 2012 - Cassiopeia A SNR

  1. #1
    Member Howard B's Avatar
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    Object of the Week,October 14, 2012 - Cassiopeia A SNR

    Cassiopeia A

    Supernova Remnant

    RA 23 23 26
    Dec +58 48

    MAG: ? My guess is approximately 14th magnitude.

    An article about little known and seldom observed supernova remnants in issue 63 of Amateur Astronomy magazine (pages 17–19) caught my attention before the 2009 OSP. It’s the fourth article in a series on the subject written by William Gates. Bill is a terrific observer but what really caught my attention was his report that he was able to observe a shard of the Cassiopeia A SNR as an relatively easy object in his 9.25 inch SCT equipped with an OIII filter. Wow!

    Until then I'd always had the impression that Cas A was essentially invisible at optical wavelengths to all but the largest optical telescopes and that only radio and infrared telescopes could get a good image of it. Checking Wikipedia I found a quote to that effect:

    “Cassiopeia A (Cas A) is a supernova remnant in the constellation Cassiopeia and the brightest astronomical radio source in the sky… Despite its radio brilliance, however, it is extremely faint optically, and is only visible on long-exposure photographs.”
    http://en.wikipedia.org/wiki/Cassiopeia_A

    I’m happy to say that Bill was right and that Cas A is indeed visible in amateur sized telescopes from a dark sky site, and that at least some of its structure can be seen. Heck, it’s easier to see than some NGC objects. My best view to date is from the 2011 OSP under a 21.71 SQM sky when Cas A was near the meridian. My pencil sketch below and its inverted version show what I saw during an hour and a half of observing that night, which was a bit more than I saw in my first observation from 2009 when the skies weren't quite so dark and transparent.

    Cas A for Hawaii presentation_adjusted.jpgCas A for Hawaii presentation_adjusted_inverted.jpg

    I used 220x to 355x with the NPB filter on my 28 inch f/4 Newtonian for the best view, but Cas A was easily visible without a filter. My old Lumicon OIII filter dimmed the view too much for my liking but showed more than the non-filtered view.

    As far as I can tell Cas A isn't listed in Megastar or Sky Tools 3 Pro but is plotted in Uranometria. I've found that star hopping from M52 to the Bubble Nebula (NGC 7635) and then along a ragged line of faint stars to Cas A is a relatively easy way to get to the right spot.

    Cas A DSS.jpg

    My goal now is to detect a piece of the southern arc, which may be near the limit of my scope under ideal conditions. The DSS image here hints at its difficulty – should be a piece of cake for Jimi’s 48 though.

    So remember,

    "GIVE IT A GO AND LET US KNOW"

    GOOD LUCK AND GREAT VIEWING!
    Last edited by Howard B; October 14th, 2012 at 08:27 PM. Reason: deleted double title line
    Howard
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    Member FaintFuzzies's Avatar
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    Quick note - glad that you mentioned it as last night at Shot Rock (NELM 7.0), I decided to take a quick look at it while taking a break from a bunch of trios I was observing. It was pretty easy at 96x in my 22" without filters.
    Clear skies,
    Alvin #26
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  3. #3
    Co-Founder DSF.com Jimi Lowrey's Avatar
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    Great object Howard this is much brighter than you would think!

    I did a test on this SNR last Monday night to see which filter worked best for me. AT 375X the SNR was a easy fairly large unfiltered glow on a below average night of seeing and transparency here. First I bumped up the power to 488X and tried the NPB filter. I got a good response to the NPB filter and it improved on the unfiltered view. Next I tried a old Orion Ultra Block that I have had for many years. I must say that I thought it improved the view of the SNR over the NPB this was a surprise to me as I would have bet on the NPB. The improvement was slight but I thought it revealed more faint detail than the NPB. Next up was the OIII. I am not a big fan of this filter as it darkens the field too much for my taste on most objects but on this SNR the OIII really lit it up! I now was seeing faint lacy like strings of detail that was not visible with the other filters it was really something to see and was quiet exciting to see this kind of detail. So for me on this object the OIII is the winner by a large margin. I would like to hear what filter works best for others on the forum.

    I did not look at the south end for any of the faint SNR as I was concentrating on fine detail on the brighter North end with the filters I will look for its faint glow next time I am at the scope.
    Last edited by Jimi Lowrey; October 17th, 2012 at 05:27 PM.
    Clear Skies,

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  4. #4
    Member Marko's Avatar
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    This object proved to be not at all easy in 12" dob but seen coming and going in my 18" in NELM 6.9 skies at SQM 21.7 (mighty fine sky) at Bumpass Hell parking lot, Mt Lassen, CA. I am a bit in question of 'normal' persons eyes seeing this object in a 9.25" scope except perhaps in the finest of fine skies but William Gates is known for exceptional eyes so I bet it was 'easy' for him but not so for myself. I am now quite tempted to try for it in my 12" f/5 dob from a very dark site perhaps soon AND perhaps with my spanky new 6mm Delos I got for my 18" f/3.7 or 9mm Nagler (The 12" will yield 250x at 6mm but with a bit of a tiny exit pupil of 1.2mm, wish I had the 8mm still on pre-order!)

    Note that there are many other observations including my own in the Cas A thread in the 'Off the beaten Path' section a few weeks after this fine DSF was formed. One thing of note as a finder it can be said a bright eq triangle of stars lies 7.5' NE and 'points' to Cas A area with it's southern most star. Following that 7 or so min SW you will see a much dimmer EQ triangle with 2.5' sides and one side is EW. The southern most stellar object in this 2.5' eq triangular pattern is the center of the brightest part of Cas A where a few tiny stellar points reside. Cas A brightest segment runs EW through this stellar tiny star grouping.
    Last edited by Marko; October 17th, 2012 at 07:47 AM.
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  5. #5
    Member Howard B's Avatar
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    Bill Gates does a lot of his observing from high elevation sites in Arizona which often have superb conditions, so his sighting of Cas A with an 9.25 inch SCT was probably made in ideal conditions. On the other hand, I've seen it with a 16 inch f/4 Newtonian under 21 .2-ish sky fairly easily using an OIII filter. My guess is that sky transparency makes a huge difference for this object.

    I'm eager to give Cas A a shot with my 8 inch Dob some fine night, but I'd really like to see it through Jimi's 48!
    Howard
    30-inch f/2.7 alt-az Newtonian
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  6. #6
    Member Pawel_T's Avatar
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    I saw it few hours ago in my 18" f/4.4 under 6.2 mag skies. Easy to detect at 143x (Denkmeier 14mm) with an OIII filter - looked like a thick arc with even surface brightness.
    13" f/4.6; FS102; Miyauchi Bj100

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  7. #7
    Member RolandosCY's Avatar
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    Quote Originally Posted by Pawel_T View Post
    I saw it few hours ago in my 18" f/4.4 under 6.2 mag skies. Easy to detect at 143x (Denkmeier 14mm) with an OIII filter - looked like a thick arc with even surface brightness.
    Good to know Powel! Charts have been prepared, ready for attack tomorrow night if the weather cooperates!
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    Cool object Howard,

    better and easier than expected.

    10", 143x, UHC, NELM 6m5+
    nothing without filter; UHC brings out an round plob in just the place of the brighter arc; a friend and I could hold the glow easily with averted vision; [OIII] to dark

    16", 180x, [OIII], NELM 6m5+
    brighter arc already without filter; with [OIII] the brighter arc is visible as a curved glow with brighter and thicker E end; two stellar peaks; S arc not visible
    CasA.jpg

    27", 172x, [OIII], NELM 6m5+
    bright even without filter; brighter N arc totally mottled with five stellar peaks; only detail from the S arc is the brightest spot, which could be detected as a very faint stellar spot; no laminar detail
    Clear Skies, uwe
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  9. #9
    Member RolandosCY's Avatar
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    Quote Originally Posted by RolandosCY View Post
    Good to know Powel! Charts have been prepared, ready for attack tomorrow night if the weather cooperates!
    Weather 1 - RolandosCY 0!

    We started out with excellent conditions at our high altitude site (1300m), with SQM readings peaking at 21.37 overhead in Aries. I had my best ever views of M31, M32, M110, M33, NGC 891, and Taffy 1 galaxies (OOTW Sept 30). Even the Horsehead nebula was detectable without a filter although Orion was just clearing the mountains to the east. Unfortunately, by the time I arrived at this object, the sky grew noticeably brighter (down to 20.90 in Cassiopeia). What's more, even with 18", a lot of objects (especially diffused ones) simply disappeared from the sky. I was totally unable to spot Cas I, and although I made a new, detailed sketch of the Taffy 1 galaxies (with the "hook" plainly visible), after checking them out again they just were not there! Later on during the day I found out from the local Met Office that a thick layer of high-level humidity moved in around 01.00 local time ahaead of a major low pressure system, thus reducing contrast considerably and rendering lsb and faint targets practically invisible. Oh well... We'll give it a go in two weeks!
    Last edited by RolandosCY; October 20th, 2012 at 06:55 PM.
    The Darker the Better!
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  10. #10
    Member ScottH's Avatar
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    I can confirm that it's visible in my 10-inch SCT with a filter and as Uwe attested, in (my) 16-inch without a filter at 300x (just tried it a few days ago). This is one bright SNR considering it's only the fifth one out of eleven that I've seen without a filter!

    Scott
    Contributing Editor for Sky & Telescope
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