salt-finder-charts 0.1.0

Generate finder charts for the Southern African Large Telescope (SALT)

SALT Finder Charts

Generate finder charts for the Southern African Large Telescope (SALT).

This package will change...

This is a preliminary and rudimentary version, and you should expect major changes in future versions.

Installation

The package can be installed with pip.

pip install salt_finder_charts

Usage

You can generate a finder chart with the finder_chart function.

from salt_finder_charts import finder_chart, Mode, Survey, Target

# Replace with a file path of your choice.
# The file extension must be one of those supported by the Pillow package.
out = "/path/to/finder_chart.png"

target = Target(ra=189.99763271, dec=-11.62305428, name="Sombrero Galaxy")
fc = finder_chart(target=target, mode=Mode.IMAGING, pa=15, survey=Survey.POSS2UKSTU_RED)
fc.save(out)

The function takes a mode, target details, a position angle and (optionally) a survey as its arguments and returns an Image object. Refer to the documentation for the Pillow package for details on how to use this object.

The generated finder chart image contains RGBA data. Depending on your needs, you might have to convert it to RGB data. For example, you would have extend the above example for saving the finder chart as a pdf.

from PIL import Image
from salt_finder_charts import finder_chart, Mode, Survey, Target

# Replace with a file path of your choice.
# The file extension must be one of those supported by the Pillow package.
out = "/path/to/finder_chart.pdf"

target = Target(ra=189.99763271, dec=-11.62305428, name="Sombrero Galaxy")
fc = finder_chart(target=target, mode=Mode.IMAGING, pa=15, survey=Survey.POSS2UKSTU_RED)
rgb = Image.new('RGB', fc.size, (255, 255, 255))  # white background
rgb.paste(fc, mask=fc.split()[3])                 # paste using alpha channel as mask
rgb.save(out)

Input arguments

The finder_chart function expects target details, a mode, a position angle and (optionally) a survey as its input arguments.

Target

The target details should be supplied as an instance of the Target class. This is a named tuple with the following properties.

Property	Explanation	Example
dec	Declination, in degrees between -90 and 90	16.9235
name	Target name	"My Interesting Target"
ra	Right ascension, in degrees between 0 and 360	-57.36229

The target name is included in the finder chart's title.

Mode

The mode should be one of the enumeration members of the Mode enumeration, as listed in the following table.

Enumeration value	Explanation
Mode.IMAGING	An imaging observation.

Position angle

The position angle must be a valid angle in degrees.

Survey

The survey should be one of the enumeration members of the Survey enumeration. The following surveys are available.

Enumeration value	Survey
Survey.POSS1_BLUE	POSS1 Blue
Survey.POSS1_RED	POSS1 Red
Survey.POSS2UKSTU_BLUE	POSS2/UKSTU Blue
Survey.POSS2UKSTU_IR	POSS2/UKSTU IR
Survey.POSS2UKSTU_RED	POSS2/UKSTU Red
Survey.TWO_MASS_H	2MASS-H
Survey.TWO_MASS_J	2MASS-J
Survey.TWO_MASS_K	2MASS-K

The POSS2/UKSTU Red survey is used if no survey is supplied.

Not all of the surveys cover all of the declinations observable with SALT, and you may get cryptic errors if you try to use a survey with a target position not covered by it. As such it is advisable to use the default whenever possible.