photometry

The photometry package is a simple synthetic photometry package.

The emphasis has been put on speed (as much as I could) rather than on economy of memory. For example, all the data necessary to interpolate passbands or spectra are computed once (or rather each time the internal representation changes) and stored in memory.

There was a slight emphasis on (sub)mm wave astronomy as this package as been written during my participation to the commissioning of NIKA2, the new 1mm and 2mm camera at the IRAM 30m telescope, but I am using now to with my work on the Euclid (visible and near-infrared) where it is used extensively for the Science Perfomance Verification. Yet, it can be used in any wavelength domain (except the high energy, as I work with frequencies or wavelengths, not energies).

Dependencies

• python 3
• numpy
• scipy
• astropy
• BeautifulSoup

Installation

git clone https://github.com/haussel/photometry.git

and make sure the photometry/ directory is in your PYTHONPATH.

All the passband data are provided with the distribution, but some spectral libraries are not, as they are a bit on the heavy side. If you need these, you will have to download them yourselves and let photometry know where they are located on your computer. This is done in the config.py file that you have to edit:

STELLAR_LIBRARY_DIR = '/path/to/the/top/directory/of/stellar/libraries'
GALAXY_LIBRARY_DIR = '/path/to/the/top/directory/of/galaxy/libraries'

Documentation

the notebooks/ directory contains a few notebooks to get you started.

Provides

photometry contains the following files, all imported by default:

• config: define global environment variables

• phottools: some useful functions and constants used accross various submodules, plus the PhotometryHeader and PhotometryInterpolator classes.

• photcurve: the PhotCurve class that is used to represent passbands and spectra.

• passband: the Passband class and the tophat() function.

• spectrum: the BasicSpectrum, GalaxySpectrum and StellarLibrary classes.

• standards: some convenience function to obtain classical spectra, including various Vega spectra and the BaSeL 2.2 and Pickles (1998) stellar libraries.

• extinction: Milky Way extinction in the UV-IR range. Provide the ExtinctionLaw, CCMExtinction and ODonnellExtinction classes.

• euclidtu: Euclid specific functions and classes to use the stellar and galaxy libraries used in OU-SIM True Universe.

• atmosphere: defines the IramAtmosphere class to handle GILDAS atmosphere models, and the Atmosphere class for atmospheric transmission.

• irampassband: defines the IramPassband class, to handle varying opacity and emission of the sky in the sub-mm.

• planets: define the GiantPlanet class to compute the flux of Uranus and Neptune and the Mars class for... Mars.

Usage

A typical session would go as this: Read a passband from a file *.pb. See in the photometry/data/passbands directory for some examples. They are grouped per instruments in subdirectories.

import photometry as pt
w1 = pt.Passband(file='W1.WISE.pb')

Read a spectrum. Alternatively, the data directory contains a few classical standard spectra as well as some libraries. For example, to get the Vega spectrum used by Jarrett et al. (2011) for the calibration of the WISE data:

vega = pt.vega_cohen_1992()

To get the AB magnitude of Vega in the W1 passband:

w1.mag_ab(Vega)

The notebook directory provides more examples of usage.

• nika2_primary_calibrator: run this notebook to provide the primary calibrator fluxes for a NIKA2 run.
• passband_creation: how to add a passband to the photometry package.
• planet_fluxes: how to use the GiantPlanet and Mars class to derive the flux of a planet at (sub-)mm wavelengths
• submm-atmosphere: how to work with the IramAtmosphere and IramPassband classes.