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V3890 SGR looks redder than the B-V?

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lmk
lmk's picture
V3890 SGR looks redder than the B-V?

See attached DSLR image from tonite. It appears quite red in this unprocessed image, while recent B-V measurements seem quite ordinary around +0.6 or so. 

Image is 60 sec at ISO 1600 with a stock Canon 450D, no filters through an 8" f/3.7 Newtonian and Astrotech coma corrector. Any thoughts?

Mike

 

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HQA
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red nova

Hi Mike,

The DSLR is showing a red object because of the broad, large Halpha emission, common in novae.  This is seen in the recent spectrum submitted by BJFB to the AAVSO spectral database:

https://www.aavso.org/apps/specdb/obs/596

(B-V) avoids Halpha.  All broad-band colors will start highlighting emission lines rather than continuum later in the outburst, so most photometry will deviate from a simple fade.  Ulisse Munari came up with a neat filter combination (using Stromgren filters plus typicall narrow-band filters) to follow both the growth of the emission lines as well as the fading continuum.  So while the DSLR gives a beautiful image of novae, getting the best science is sometimes more difficult!

Arne

lmk
lmk's picture
Thanks for the reply, Arne.

Thanks for the reply, Arne. Yes, I kind of expected it might be an emission line issue, which affects visual observation too, with "deviant" estimates! Here, the color contrast between it and the 139 comp just to its left, is very apparent. That comp has about the same B-V as the recent nova measurements.

I could judge the object's magnitude by looking at the "size" of it on the image compared to the 139 & 130 comps, and doing so, I would guess it about 13.7, but what band? Should I even report it as "unfiltered with V zero point" in WebObs, or better avoid estimating off this image?

Mike

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