LEMON is a CCD differential-photometry pipeline, written in Python, developed at the Institute of Astrophysics of Andalusia (CSIC) and originally designed for its use at the 1.23m CAHA telescope for automated variable stars detection and analysis. The aim of this tool is to make it possible to completely reduce thousands of images of time series in a matter of hours and with minimal user interaction, if not none at all, automatically detecting variable stars and presenting the results to the astronomer.

A first overview of LEMON, now slightly outdated, was presented some time ago at http://adsabs.harvard.edu/abs/2011hsa6.conf..755T.

The pipeline consists of nine commands, six of which are considered to be essential because they implement the data reduction and analysis steps and are usually run sequentially. However, depending on your needs only a specific subset of them may be used. In this sense, LEMON can be viewed as a set of tasks that may be used as a pipeline. The other three commands are auxiliary in the sense that they provide features that are convenient in some, but not all, scenarios.

usage: lemon [--help] [--version] [--update] COMMAND [ARGS]

The essential commands are:
   astrometry   Calibrate the images astrometrically
   mosaic       Assemble the images into a mosaic
   photometry   Perform aperture photometry
   diffphot     Generate light curves
   periods      Dworetsky's string-length method
   juicer       LEMONdB browser and variability analyzer

The auxiliary, not-always-necessary commands are:
   import       Group the images of an observing campaign
   seeing       Discard images with bad seeing or elongated
   annuli       Find optimal parameters for photometry

See 'lemon COMMAND' for more information on a specific command.

• Current version: 0.2
• View CHANGELOG

LEMON stands on the shoulders of many giants, using excellent, robust programs developed by people much more skilled than us to detect sources, do aperture photometry and compute astrometric solutions on the FITS images. The disadvantage, however, is that for many of them there are not (yet?) Debian packages available, so they have to be installed manually — the configuration of IRAF and PyRAF, although heavily simplified in recent versions, is particularly tedious and painful.

These are the steps to install LEMON on a clean Debian machine:

1. apt-get install git python-dev python-pip libfreetype6-dev libpng-dev csh libx11-dev libblas-dev liblapack-dev gfortran
2. apt-get install openmpi-dev # you may need this to compile Montage
3. git clone git://github.com/vterron/lemon.git ~/lemon
4. cd ~/lemon
5. pip install numpy>=1.7.1
6. pip install -r pre-requirements.txt
7. pip install -r requirements.txt
8. Install IRAF
9. Install SExtractor (version 2.19.5 or newer)
10. Install Astrometry.net
11. Install the MPI-enabled Montage binaries¹
12. python ./setup.py
13. echo 'PATH=$PATH:~/lemon' >> ~/.bashrc
14. echo "source ~/lemon/lemon-completion.sh" >> ~/.bashrc
15. ./run_tests.py — optional, although recommended!

Note that, starting from version 2.16, IRAF is now released under a free software license. There is, thus, reasonable hope that it may be packaged for drop-in installation in GNU/Linux systems in the near future, which would enormously simplify the process of installing LEMON. Until then, please bear with us.

# uncomment the next two lines to build MPI modules
# MPICC  =    mpicc
# BINS =  $(SBINS) $(MBINS)