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[gnuastro-commits] master 48edcd91 13/39: Book: tutorial of zero point;
From: |
Mohammad Akhlaghi |
Subject: |
[gnuastro-commits] master 48edcd91 13/39: Book: tutorial of zero point; preparing images for using the script |
Date: |
Wed, 19 Apr 2023 12:18:23 -0400 (EDT) |
branch: master
commit 48edcd91da53130724495a62b4520bdbf932e5ff
Author: Elham Saremi <saremi_elham@yahoo.com>
Commit: Mohammad Akhlaghi <mohammad@akhlaghi.org>
Book: tutorial of zero point; preparing images for using the script
Until now, I wrote an introduction for this tutorial.
With this commit, I started to write the first subsection named "Using the
image as a zero point reference". In this step, I selected two images of
SDSS as a reference and an image of J-PLUS to find its zero
point. Downloading and preparing of data in this step are written.
---
doc/gnuastro.texi | 56 +++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 50 insertions(+), 6 deletions(-)
diff --git a/doc/gnuastro.texi b/doc/gnuastro.texi
index a2715716..fe2d38e0 100644
--- a/doc/gnuastro.texi
+++ b/doc/gnuastro.texi
@@ -629,13 +629,17 @@ MakeCatalog
* Detection and catalog production:: Discussing why/how to treat these
separately
* Brightness flux magnitude:: More on Magnitudes, surface brightness, etc.
-* Photometric calibration zeropoint:: Calculating zeropoint of images
+* Photometric calibration zero point:: Calculating zeropoint of images
* Quantifying measurement limits:: For comparing different catalogs.
* Measuring elliptical parameters:: Estimating elliptical parameters.
* Adding new columns to MakeCatalog:: How to add new columns.
* MakeCatalog measurements:: List of all the measurements/columns by
MakeCatalog.
* Invoking astmkcatalog:: Options and arguments to MakeCatalog.
+Photometric calibration zero point
+* Using the image as a zero point reference
+* Using the catalog as a zero point reference
+
Quantifying measurement limits
* Magnitude measurement error of each detection:: Derivation of mag error
equation
@@ -24609,14 +24613,14 @@ If you need to warp or convolve the image, do it
@emph{before} the conversion.
-@node Photometric calibration of images with finding zeropoint, Quantifying
measurement limits, Measuring elliptical parameters, Brightness flux magnitude,
MakeCatalog
-@subsection Photometric calibration of images with finding zeropoint
+@node Photometric calibration of images with finding zero point, Quantifying
measurement limits, Measuring elliptical parameters, Brightness flux magnitude,
MakeCatalog
+@subsection Photometric calibration of images with finding zero point
As described in @ref{Brightness flux magnitude}, to convert astronomical data
pixel values from counts to energy/time (physical units such as Janskys), we
need to know the zero point of the image.
This conversion is necessary to can compare two images independent of
instruments that were observed with them.
Actually, the zero point is used to calibrate an astronomical image to the
standard state.
-To find zero point, it is common to use photometric systems with defined zero
point such as some images or catalogs.
+To find the zero point, it is common to use photometric systems with defined
zero points such as some images or catalogs.
For example, the SDSS data can be a good reference for finding zero point in
optical and 2MASS data for near infra-red images.
The general outline of the steps that we use to estimate zero point in an
image is given below:
@@ -24624,10 +24628,10 @@ The general outline of the steps that we use to
estimate zero point in an image
@item
Download of Gaia catalog using Gnuastro’s Query program (see @ref{Query}) to
determine correct coordinates of stars in the image.
@item
-Select of reference image or catalog and download of it.
+Select of reference image or catalog and download it.
@item
Aperture photometry with MakeProfiles (see @ref{MakeProfiles}) and MakeCatalog
(see @ref{MakeCatalog}); a complete tutorial is in @ref{Aperture photometry}.
-If an image is selected as a reference for finding zero point, aperture
photometry should be done in the same way for it.
+If an image is selected as a reference for finding the zero point, aperture
photometry should be done in the same way for it.
@item
Match catalogs (see @ref{Match} and also a tutorial in @ref{Matching
catalogs}) to obtain differences of magnitudes in two catalogs and estimate
zero point value.
@end enumerate
@@ -24638,6 +24642,46 @@ Here we have a tutorial on how to use
@command{astscript-zeropoint}.
This tutorial is divided into two parts to cover both of using image or
catalog as reference data.
+@node Using the image as a zero point reference, Using catalog as a zero point
reference
+@subsubsection Using the image as a zero point reference
+
+First, let's find the zero point for a single exposure image from the
@url{https://www.j-plus.es,J-PLUS survey} based on an SDSS reference image
@url{http://www.sdss.org/, Sloan Digital Sky Survey} with a zero point of 22.5
mag.
+With the commands below, you can download an image such as one used in
@ref{Moire pattern and its correction} from J-PLUS dataset in the r (SDSS) band
and then crop the center part of the image to speed up the analysis in this
tutorial.
+
+@example
+## Download a single exposure image from J-PLUS dataset.
+$ jplusdr2=http://archive.cefca.es/catalogues/vo/siap/jplus-dr2/reduced
+$ wget $jplusdr2/get_fits?id=771463 -Ojplus.fits.fz
+
+## crop the center part of image with the sky coordinates.
+$ astcrop jplus.fits.fz --center=107.7263056,40.17544223 \
+ --width=0.6 --output=jplus-crop.fits
+@end example
+
+Although we cropped the J-PLUS image, it is still very large in comparison
with SDSS image.
+So let's download two SDSS images in the region of J-PLUS cropped image for
having a more accurate result.
+
+@example
+## Download two SDSS images in r filter and decompress it.
+## (Bzip2 is not a standard FITS compression algorithm).
+$ sdssbase=https://dr12.sdss.org/sas/dr12/boss/photoObj/frames
+$ wget $sdssbase/301/6509/5/frame-r-006509-5-0115.fits.bz2 \
+ -O sdss1.fits.bz2
+$ wget $sdssbase/301/6509/5/frame-r-006573-5-0174.fits.bz2 \
+ -O sdss2.fits.bz2
+@end example
+
+
+
+
+
+
+@node Using the catalog as a zero point reference
+@subsubsection Using the catalog as a zero point reference
+
+
+
+
- [gnuastro-commits] master 1a987e04 19/39: Book: tutorial of zero point; using keepzpap and completion of results, (continued)
- [gnuastro-commits] master 1a987e04 19/39: Book: tutorial of zero point; using keepzpap and completion of results, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master a3c0f0e2 31/39: Zeropoint: optimize the script for overlaping check, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 156da6c7 28/39: Book: Increase readability and correction, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master d8402f1a 32/39: Book: some command and some tips is added to better recognition, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 6ff43d00 05/39: Zeropoint: script for estimating the zeropoint of an image, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 76c8a482 03/39: Zeropoint: add a script for bing it on Gnuastro, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master dddb483f 01/39: zeropoint: First make file for obtainaing the zeropoint photometry, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master a841d3f2 02/39: zeropoint: catalogs can be used as reference, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 2c027224 08/39: Zeropoint: change the output file, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master ea79c2ba 14/39: Book: tutorial of zero point; removing the sky and running the script, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 48edcd91 13/39: Book: tutorial of zero point; preparing images for using the script,
Mohammad Akhlaghi <=
- [gnuastro-commits] master 88b4c298 23/39: Book: tutorial of zero point; subsection catalog reference, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master aeb507b8 22/39: Book: correct the info format menus, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 069e12f4 24/39: Zeropoint: a bug about the matching of reference and main catalog, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master c4af3dfc 25/39: Book: tutorial of zero point; completing the catalog reference, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 536052fb 35/39: astscript-zeropoint: writting all receipes as in one shell, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 96137885 09/39: Zeropoint: keep Mag-vs-Zeropoint for best aperture in output, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 151e8bfc 20/39: Book: editing zero point estimation section, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 85a5ad67 21/39: zeropoint: using single equal instead of the double for checking, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master ea82d80a 29/39: Book: Use suggestive instead of imperative word, Mohammad Akhlaghi, 2023/04/19
- [gnuastro-commits] master 4bf867d3 26/39: Book: open imge by 'zscale' scale and options are written as code format, Mohammad Akhlaghi, 2023/04/19