SDSS filters missing atmospheric transmission factor?

[tloredo]

Hi specliters-

In trying to move to speclite from some quick-and-dirty synthetic photometry code of my own, using SDSS filters, I found that I could get my calculations to agree w/ speclite only by dropping the atmospheric transmission factor from the SDSS filter responses in my calculations.

The speclite documentation indicates that its SDSS filter responses are "calculated as the reference response multiplied by the reference APO atmospheric transmission": https://speclite.readthedocs.io/en/stable/filters.html.

The filter data tables have comments indicating the same. E.g., for the u band, a comment reads, "Values are the product of the u and atmospheric transmission columns from Table 4 of Doi...": https://github.com/desihub/speclite/blob/v0.13/speclite/data/filters/sdss2010-u.ecsv

Here are the first few entries in the speclite SDSS u band filter data file:

wavelength response
2930.0 0.0
2940.0 0.0001
2960.0 0.0003
2980.0 0.0005
3000.0 0.0009
3020.0 0.0014
3040.0 0.0029

Here is the content at the start of the Doi+ Table 4 (ASCII version here: https://iopscience.iop.org/1538-3881/139/4/1628/suppdata/aj330387t4_ascii.txt?doi=10.1088/0004-6256/139/4/1628):

lambda  u   g   r   i   z   T_1.3 air mass  
2940    0.0001   ...     ...     ...     ...    0.0162  
2960    0.0003   ...     ...     ...     ...    0.0242  
2980    0.0005   ...     ...     ...     ...    0.0351  
3000    0.0009   ...     ...     ...     ...    0.0459  
3020    0.0014   ...     ...     ...     ...    0.0644  
3040    0.0029   ...     ...     ...     ...    0.0828  

I checked a couple other SDSS data files, with similar findings. It appears the speclite SDSS filter responses do not include the atmospheric transmission factor.

Have I misunderstood something here?

[dkirkby]

Thanks for reporting this @tloredo. Looking back at my correspondence with Mamoru Doi, I see that I was confused about whether the atmosphere was already included in the Table 4 values (despite the fact that it is obvious from the curves).

At this point, I think the simplest fix is to update the metadata for the existing curves to reflect the fact that there is no atmospheric extinction included.

Would it then be useful to add new curves with the Table 4 reference atmosphere included?

[dkirkby]

I just updated the SDSS filter curve metadata to clarify that no atmosphere is included in these curves.

Closing this now, but feel free to add a new issue if you need a separate set of curves with the X=1.3 atmosphere included.

[tloredo]

Hi David. Just a quick follow-up. speclite came up today in a Rubin DP0 discussion, where we had a quick look at the docs in a Zoom breakout. I noticed that the docs at ReadTheDocs still indicate that the SDSS curves include atmospheric transmission. So it looks like the docs need a quick update.

[dkirkby]

Thanks @tloredo. The ECSV metadata is already updated (e.g. here) and I am re-opening this issue to update the sphinx docs as well.

[moustakas]

@dkirkby would it be possible to add a new set of SDSS filter curves (and arguably make those the default) which include the atmosphere. I'm doing some comparisons with K-correct and only just realized that the discrepancies I'm seeing with my code are likely due to this issue.

[moustakas]

Also note that this ticket is a duplicate of #39.

[andreufont]

Could this be related to the discrepancies in data flux vs mock flux that Alma and Hiram are seeing?

On Tue, 12 Jul 2022, 19:43 Moustakas, @.***> wrote:

Also note that this ticket is a duplicate of #39 https://github.com/desihub/speclite/issues/39.

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[moustakas]

Done in #76.