# Difference between \`objects\_ext.r\_psfFluxNdata\` and \`objects.nrSources\`

**URL:** <https://www.rubin.community/t/difference-between-objects-ext-r-psffluxndata-and-objects-nrsources/11880>\
**Category:** Lasair\
**Created:** [April 16, 2026, 9:41am UTC](https://www.rubin.community/t/difference-between-objects-ext-r-psffluxndata-and-objects-nrsources/11880 "2026-04-16T09:41:26Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![ChrisFro](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/chrisfro/32/4082_2.png) [@ChrisFro](https://www.rubin.community/u/ChrisFro)\
**Post date:** [April 16, 2026, 9:41am UTC](https://www.rubin.community/t/difference-between-objects-ext-r-psffluxndata-and-objects-nrsources/11880/1 "2026-04-16T09:41:27Z")

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Hi Lasair team,  
What is the difference between `objects_ext.r_psfFluxNdata` and `objects.nrSources`?  
When I include these in a simple supernova query, I find:

- Most of the objects have nrSources \> 0
- Some objects have nrSource == r\_psfFluxNdata
- Most objects have r\_psfFluxNdata == 0

The schema browser says:  
nrSources : ‘Number of r sources’  
r\_psfFluxNdata : ‘The number of r-band data points.’

So I guess a more fundamental question is, what is the difference between a source and a data point?

Thanks!  
Chris

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**Author:** ![roy](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/roy/32/1254_2.png) [@roy](https://www.rubin.community/u/roy)\
**Post date:** [April 16, 2026, 12:21pm UTC](https://www.rubin.community/t/difference-between-objects-ext-r-psffluxndata-and-objects-nrsources/11880/2 "2026-04-16T12:21:40Z")

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The `nrSources` is made by Lasair, and pre-dates the Rubin attribute `r_psfFluxNdata`. I have no idea why the latter is often zero even when the number of r-band `diaSources` is not zero.

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**Author:** ![galaxyumi331](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/galaxyumi331/32/2677_2.png) [@galaxyumi331](https://www.rubin.community/u/galaxyumi331)\
**Post date:** [April 20, 2026, 10:11pm UTC](https://www.rubin.community/t/difference-between-objects-ext-r-psffluxndata-and-objects-nrsources/11880/3 "2026-04-20T22:11:21Z")

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Hi @ChrisFro,

The column description for `r_psfFluxNdata` in the `DiaObject` table is “The number of data points used to compute r\_psfFluxChi2”, which seems different from `objects.nrSources`. In case this isn’t the answer you were looking for, feel free to unmark the solution and we can keep looking into it.