What is the error on a counting variable?

Question

I don't know if a variable that acts as a counter has an associated error. I don't see it as a measured quantity so I think that it has no error.

The problem is this: you have an image of a star and you want to measure its flux (along with the error in your measurement)

My question: do k and i (see below) have an error?

This is some pseudocode describing my solution:

flux, e_flux = 0
sky, e_sky = 0
k,i = 0

Draw circle around star
for pixel in circle:
    flux = flux + pixel.counts
    e_flux = e_flux + sqrt(pixel.counts)
    k = k + 1

for pixel around star:
    sky = sky + pixel.counts
    e_sky = e_sky + sqrt(pixel.counts)
    i = i + 1

sky = sky/i
flux = flux - (sky * k)

I think of k and i as known quantities of pixels. Of course, the measurement of a number of pixels representing the star has a certain error, but since we are approximating the star with a circle at the beginning, is that error encompassed within the approximation of the star? (so k and i are known without uncertainty)

Answer 1

If the count is not always the same, there is an associated error (in the sense of uncertainty, not of mistake).