How can I approach computing the object counts (photons/sec) from a H-alpha emission planetary nebula or a diffuse h-alpha emitting object in general? I need it for an exposure time calculator mini project
I did find an example here: wfc3_ihb.book (stsci.edu)
Section 9.93 Example 3: Imaging an HII region in M83 in Hα
What is the exposure time needed to obtain a signal-to-noise of 10 for an HII
region in M83 in Hα which has a diameter of 2" and a flux Fλ in Hα of 5×10–16
Although specific for HST … it is what I need to understand.
How do they get the Fλ value? Can I get it for an object of interest from a vizier catalog? I did search ESO Catalogue of Galactic Planetary Nebulae (Acker+, 1992) on Vizier and found Flux in H-alpha.
If getting the Flux from Vizier is not correct, should I use synphot to make a model spectrum?
Would something like this work?
# 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)