Paul
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« on: September 04, 2008, 08:30:59 am » |
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I took a few widefields of the sky when I got in last night and was looking at them this morning. Here's a nice shot (single shot 50mm f1.7 15secs ISO3200) of some of Cassiopeia and the Double Cluster...... The blue star to the lower right of Gamma Cass (middle of the W) is supposed to be of mag 6.1 but looks to be much brighter. I only noticed it as Cassiopeia didn't look quite right. It could be processing I suppose but.... Any thoughts? Paul.
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brianb
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« Reply #1 on: September 04, 2008, 11:12:54 am » |
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The blue star to the lower right of Gamma Cass (middle of the W) is supposed to be of mag 6.1 but looks to be much brighter. I only noticed it as Cassiopeia didn't look quite right. It could be processing I suppose but....
I doubt very much it's a nova ... a mag 6 star which goes nova will get well into the negative magnitudes! I see the star you're referring to & it appears to be "much" fainter than the two Nu Cas's (to the right and slightly below Gamma Cas and the suspect in your image). Now it's by no means unusual for blue giant stars to show some variability, Gamma Cas itself is a classic example. But it's going to be a bit hard to prove from a single image. What I suggest you do is to image the field around Gamma Cas with a longer focal length, don't worry about trying to get faint stars as photometry is best done on images where the core of the star image hasn't actually saturated the sensor. A couple of dozen one or two second exposures should be about right. The longer focal length is simply to seperate out the suspect from faint stars close to its position. Stack them in DSS making sure you have the hot pixel detection enabled. See what comes out then. If you want to mail me a (zipped) 16-bit TIFF or FITS of the result I'll get reasonably accurate photometry done on it.
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martinastro
Martin Mc Kenna
Global Moderator
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Posts: 5182
Maghera, N. Ireland
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« Reply #2 on: September 04, 2008, 02:28:50 pm » |
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Interesting image!. I would take another image of that location again tonight combined with a naked eye mag estimate just to me sure. Will be watching it now myself.
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brianb
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« Reply #3 on: September 05, 2008, 10:59:06 am » |
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I checked this field last night & it looked "normal" to me. Also took some images which I haven't downloaded from the camera yet (up till 5:30 BST & only just starting to wake up!) but I will be able to do photometry on them. Actually I image Cassiopeia fairly regularly, photography is the best way to check on variable stars with slow changes and small ranges like Gamma and Rho Cas, as visual observations can easily be "biased" by what you're expecting to see, and position angle errors can result in spurious variability with a period of 365.25 days and a magnitude range of ~0.3.
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John9929
Global Moderator
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Posts: 1105
Maghaberry, N.Ireland.
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« Reply #4 on: September 05, 2008, 05:48:24 pm » |
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Brian, I got this image at 0215 BST 4/5, camera driven on clock mount for 123 sec at f5.0 ISO1600. Nothing abnormal here as far as I can see, What about your images?
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John9929.
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brianb
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« Reply #5 on: September 07, 2008, 12:31:51 pm » |
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The blue star to the lower right of Gamma Cass (middle of the W) is supposed to be of mag 6.1 but looks to be much brighter. My catalogue gives V=5.53. The photometry I did on my images taken Sep 4th/5th reduces to 5.70 (+/- 0.08) which is close enough given that I'm not using standard filters - just whatever sensitivity there is in a Canon 5D.
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davegrennan
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« Reply #6 on: September 09, 2008, 01:07:06 pm » |
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Paul,
If you want to send me one the original unprocessed frame, I'd be happy to do a photometric analysis.
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