Why is T Cep so bright in this image? August 2022

[pipnina]

I was wondering why in this older image I took on a full-spectrum Nikon D3200, that T-Cep was so bright.

It is supposed to be at least 2 magnitudes darker than Alfirk even when it's at the peak of its variable phase, but despite how big and bright it looks in the image it has no halo like Alfirk.

Could it be something to do with the camera's full-spectrum mod?

[Nik271]

T Cep is a red giant of colour index B-V = 1.5 so most of its light is in the red part of the spectum. My guess is that its magnitude in R band is way higher than the visual (V) and your astromodified camera is very sensitive in the red. 

Edited May 12 by Nik271

[Nik271]

PS: just looked it up at AAVSO, in I (near infrared) in August 2022 T Cep has observed magnitude of less than 3.  

Edited May 12 by Nik271

[pipnina]

1 hour ago, Nik271 said:

T Cep is a red giant of colour index B-V = 1.5 so most of its light is in the red part of the spectum. My guess is that its magnitude in R band is way higher than the visual (V) and your astromodified camera is very sensitive in the red. 

1 hour ago, Nik271 said:

PS: just looked it up at AAVSO, in I (near infrared) in August 2022 T Cep has observed magnitude of less than 3.  

I suppose that would make sense then, it still seems a bit odd that it has no halo vs Alfirk's prominent one but the percieved brightness in blue vs R-NIR would explain the core size similarity.

Thanks!

 

 

[Norris Adams]

Thanks both,

I had exactly the same question!

A couple of nights ago I took the attached shot of T Cep. 

On later inspection, I couldn't understand why T Cep was so bright when the star to the right (HD201731) was nominally a very similar magnitude. I discovered that it was a variable star, but even at its brightest, it couldn't account for the apparent difference I was seeing. As you can see, the comparison is striking - so much so that I estimated it to be 3 or 4 magnitudes brighter than it should be!

I knew that had read somewhere about CCD cameras having a 'red sensitivity' (maybe on the CBAT site for supernova reporting), but I wasn't sure if the same was true of CMOS. 

I certainly looks like it is!

Equipment: 6 inch Skywatcher GoTo coupled to an ASI 183MC camera.