No Transient Source

[MickaelRigault]

Hello,

I was wondering if it would be possible to implement a simple ConstantSource that is a Source but with no phase. That could for instance be a Star. It would only need a spectra.

Worse case scenario I could create a Source and then give phase=0 all the time, but that is a not so elegant.

Cheers

[MickaelRigault]

something like that I think work but is not nice

class ConstantSource(  sncosmo.TimeSeriesSource ):
    
    def __init__(self, wave, flux, name=None, version=None):
        # 
        nphase_bins = 2
        phase = np.linspace(-1., 1., nphase_bins)
        # w
        return super().__init__(phase, wave, np.repeat(flux[None,:], nphase_bins, axis=0), 
                                name=name, version=version, time_spline_degree=1)
    
    def bandmag(self, band, magsys):
        return super().bandmag(band, magsys, 0)
    
    def bandflux(self, band, zp=None, zpsys=None):
        """ """
        return super().bandflux( band, phase=0, zp=None, zpsys=None)
    
    def flux(self, wave):
        """ """
        return super().flux(0, wave) 

[benjaminrose]

Initially, I like the idea, but what is the story behind this feature? What would people want to accomplish with a constant source?

[MickaelRigault]

I am writting a simulation tool. I am using sncosmo to simulate the transients, and I would like to be able to simulate stars too.

[benjaminrose]

I wonder if it would be easier to flip the hierarchy, have sncosmo.TimeSeriesSource inherit from a new sncosmo. ConstantSource. Thoughts?

[MickaelRigault]

That is exactly what needs to be done, but it changes the fundamental spirit of some core functions of sncosmo that expect phase_or_time.

But indeed the hierarchy should be something like

Source # very very generic

ConstantSource( Source ) # flux depend on band no time

VariableSource(Source ) # flux depend on band and time or Period

PeriodicSource( VariableSource) # like Cepheids !

Star( ConstantSource ) # here we could imaging having the calspec as default template

VariableSource would then be what is currently called Source

so TimeSeriesSource( VariableSource )

[benjaminrose]

I have been thinking that SNCosmo could transition to a broader transient package. A change like this would need to be a new major release. We would also need to figure out how SNCosmo differs from other simulation tools like galsim. I wonder if it is best to let galsim focus on static sources, and we focus on transients.

[MickaelRigault]

Then a periodic variable source would be enough. I may already have a Source class that may do the job. Need some time to check all aspects

[benjaminrose]

Does https://sncosmo.readthedocs.io/en/stable/api/sncosmo.Spectrum.html work?