How do we go about computing the object counts from an emission nebula in H alpha? Do need to search the object in Vizier, get the reported FLux for the object in a catalog?.. Do I use synphot-astropy somehow?

The general formula I use for computing the counts from an extended object in typical BVRI filters from a known BVRI magnitude, is:

Targetelectrons = (Flux/PhotonEnergy) * QE * FilterBandwidth * EffectiveTelescopeAperture * imagescale^2

I suppose a similar formula will work for narrowband too, but there is no narrowband magnitude so that I can compute the Flux, hence my lack of understanding how this is done.

Update: Could this be a valid approach for Flux?

# Retrieve Object H-alpha Flux from VizieR in erg/s/cm²/Å else do a conversion for the whatever flux units you find
h_alpha_flux = your_h_alpha_flux * units.erg / (u.s * u.cm**2 * u.Angstrom)

# Define H-alpha Wavelength
h_alpha_wavelength = 656.3 * u.nm

# Create filter for H-alpha
Hydrogen_filter = SpectralElement(Box1D, amplitude=1, x_0=6563, width=30)

# Create Source Spectrum for H-alpha
spectrum = SourceSpectrum(ConstFlux1D, wave=h_alpha_wavelength, flux=h_alpha_flux)

# Convolve Source Spectrum with Hydrogen_filter
observed_spectrum = Observation(spectrum, Hydrogen_filter)

# Integrate Over Wavelength to Calculate Photon Count Rate
integrated_flux = observed_spectrum.integrate(flux_unit=units.FLAM)


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