<p>In plotting out the magnitude errors in SDSS photometry, I get the following pattern:</p>
<p><a href="https://i.sstatic.net/3s7w0.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3s7w0.png" alt="enter image description here" /></a></p>
<p>Why do the errors go up to about 0.5, then down? In other words, why does it look like a high-heeled shoe (or Italy)?</p>
<p>Secondary question: I'm trying to find the magnitude limit according to the <span class="math-container">$5\sigma$</span> method listed at <a href="https://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/megapipe/docs/photo.html" rel="nofollow noreferrer">this link</a>. Would the magnitude limit be the highest magnitude in the 'sole' of the pattern, or at the back of the 'heel'?</p>
<p>The data comes from <a href="https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=VII/289&amp;-out.max=50&amp;-out.form=HTML%20Table&amp;-out.add=_r&amp;-out.add=_RAJ,_DEJ&amp;-sort=_r&amp;-oc.form=sexa" rel="nofollow noreferrer">VizieR</a>.</p>

CC BY-SA 4.0
2024-03-24T18:24:29.693Z
Are these data from quasars?
James K
CC BY-SA 4.0
2024-03-24T18:31:34.790Z
Yes, from SDSS quasar catalog, sixteenth data release (DR16Q) (Lyke+, 2020).
Jim421616
<photometry><sky-survey><sdss>
Errors in SDSS photometry
Jim421616
# Errors in SDSS photometry

(Asked by: username_0 on 2024-03-24)

In plotting out the magnitude errors in SDSS photometry, I get the following pattern:

[![enter image description here](https://i.sstatic.net/3s7w0.png)](https://i.sstatic.net/3s7w0.png)

Why do the errors go up to about 0.5, then down? In other words, why does it look like a high-heeled shoe (or Italy)?

Secondary question: I'm trying to find the magnitude limit according to the $5\sigma$ method listed at [this link](https://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/megapipe/docs/photo.html). Would the magnitude limit be the highest magnitude in the 'sole' of the pattern, or at the back of the 'heel'?

The data comes from [VizieR](https://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=VII/289&-out.max=50&-out.form=HTML%20Table&-out.add=_r&-out.add=_RAJ,_DEJ&-sort=_r&-oc.form=sexa).

**Tags:** photometry, sky-survey, sdss
> **Comments:**
> **username_1**: Are these data from quasars?  
> **username_0**: Yes, from SDSS quasar catalog, sixteenth data release (DR16Q) (Lyke+, 2020).  

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## 0 answers

