mag_ab

skypy.utils.photometry.mag_ab(wavelength, spectrum, filters, *, redshift=None, coefficients=None, distmod=None, interpolate=1000)[source] [edit on github]

Compute AB magnitudes from spectra and filters.

This function takes emission spectra and observation filters and computes bandpass AB magnitudes [1].

The filter specification in the filters argument is passed unchanged to speclite.filters.load_filters. See there for the syntax, and the list of supported values.

The emission spectra can optionally be redshifted. If the redshift parameter is given, the output array will have corresponding axes. If the interpolate parameter is not False, at most that number of redshifted spectra are computed, and the remainder is interpolated from the results.

The spectra can optionally be combined. If the coefficients parameter is given, its shape must match spectra, and the corresponding axes are contracted using a product sum. If the spectra are redshifted, the coefficients array can contain axes for each redshift.

By default, absolute magnitudes are returned. To compute apparent magnitudes instead, provide the distmod argument with the distance modulus for each redshift. The distance modulus is applied after redshifts and coefficients and should match the shape of the redshift array.

Parameters
wavelength(nw,) Quantity or array_like

Wavelength array of the spectrum.

spectrum([ns,] nw,) Quantity or array_like

Emission spectrum. Can be multidimensional for computing with multiple spectra of the same wavelengths. The last axis is the wavelength axis.

filtersstr or list of str

Filter specification, loaded filters are array_like of shape (nf,).

redshift(nz,) array_like, optional

Optional array of redshifts. Can be multidimensional.

coefficients([nz,] [ns,]) array_like

Optional coefficients for combining spectra. Axes must be compatible with all redshift and spectrum dimensions.

distmod(nz,) array_like, optional

Optional distance modulus for each redshift. Shape must be compatible with redshift dimensions.

interpolateint or False, optional

Maximum number of redshifts to compute explicitly. Default is 1000.

Returns
mag_ab([nz,] [ns,] nf,) array_like

The AB magnitude of each redshift (if given), each spectrum (if not combined), and each filter.

Warning

The speclite package must be installed to use this function.

References

1
    1. Blanton et al., 2003, AJ, 125, 2348