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spectral mystery !

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#1 nytecam


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Posted 07 September 2013 - 04:46 AM

Last night after doing Nova Del spectrum I trawled some hot WR and gammaCas emission lines star and some cool carbon and M-type stars in Cygnus. I came across an oddity in V1511 Cyg LB-type; spect M10III; m[K]~3.0.

Whilst the real star image itself [A] is strongly recorded [below], its spectrum is virtually non-existant, even as expect, in the near-IR. Another red star in the field [B] shows a hint of spectrum in red-near IR whilst a third star [C] is a probably a 'normal' A-type will full visible spectrum. All three star record about the same [except for their spectra!]

Any ideas why this star records bright whilst its specrum is virtually non-existant?

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#2 groz


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Posted 11 September 2013 - 10:36 AM

My first guess.

It's the spectral response of your sensor. At the first order point, there is enough light over entire spectrum to tickle the adu count up, but, where the main components are farther down the streak, the bulk of the light is in the frequency areas where your sensor has very low sensativity, so it doesn't show up.

The way your image is displayed, the first order is seriously clipped. What is the maximum ADU count in the first order spot for each of the stars ? I'm going to guess right now, you will find the first order of star A is SUBSTANTIALLY lower than that of the others, and your image processing is hilighting it as a strong point, when indeed it's not really a strong point. The spectrum line itself is equally weaker, and when combined with sensor spectral response, bordering on non-existant.

#3 old_frankland



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Posted 18 September 2013 - 01:18 AM

Good stuff.

I believe that V1511 is an infrared star, and due to the near IR sensitivity of the CCD camera, there is spectrum visible on the far red end as you point out. Pretty much what qroz was suggesting.

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