Quick Start

This tutorial is designed to let you quickly see ArtPop in action. For a deeper dive into each of the components of the code, we recommend stepping through the list of tutorials on the home page.

Note: To generate MIST synthetic photometry using ArtPop, MIST isochrone grids are required. The first time you use a MIST grid, ArtPop will download it and save it to your MIST_PATH. If this environment variable is not set, the grid(s) will be saved in ~/.artpop/mist.

# Third-party imports
import numpy as np
import matplotlib.pyplot as plt
from astropy import units as u
from astropy.visualization import make_lupton_rgb

# Project import
import artpop

# artpop's matplotlib style
plt.style.use(artpop.mpl_style)

# use this random state for reproducibility
rng = np.random.RandomState(100)

To create an artificial image, there are three main steps:

• Create a Source object, which requires stellar magnitudes and positions.

• Initialize an Imager object, which can be an IdealImager or ArtImager.

• Mock observe the source using the observe method.

Step 1: Create a Source

Here we create an SSP with a Sersic distribution using the helper MISTSersicSSP class:

# create young, metal poor SSP source at 5 Mpc
src = artpop.MISTSersicSSP(
    log_age = 8.5,        # log of age in years
    feh = -1.5,           # metallicity [Fe/H]
    r_eff = 250 * u.pc,   # effective radius
    n = 0.8,              # Sersic index
    theta = 135 * u.deg,  # position angle
    ellip = 0.3,          # ellipticity
    num_stars = 1e6,      # number of stars
    phot_system = 'LSST', # photometric system
    distance = 5 * u.Mpc, # distance to system
    xy_dim = 701,         # image dimension
    pixel_scale = 0.2,    # pixel scale in arcsec / pixel
    random_state = rng,   # random state for reproducibility
)

Step 2: Create an Imager

Let’s use the ArtImager, which creates fully artificial images taking the instrument and sky properties into account to calculate the noise.

# instantiate an imager object
imager = artpop.ArtImager(
    phot_system = 'LSST', # photometric system
    diameter = 6.4 * u.m, # effective aperture diameter
    read_noise = 4,       # read noise in electrons
    random_state = rng    # random state for reproducibility
)

Step 3: Observe

Finally, we mock observe the source using ArtImager’s observe method. We’ll use astropy’s make_lupton_rgb function to make a pretty color image, which we will display using ArtPop’s show_image function:

# PSF with 0.6'' seeing
psf = artpop.moffat_psf(fwhm=0.6*u.arcsec)

# observe in gri (assuming the same seeing in all bands)
obs_g = imager.observe(
    source = src,         # source object
    bandpass = 'LSST_g',  # bandpass of observation
    exptime = 15 * u.min, # exposure time
    sky_sb = 22,          # sky surface brightness
    psf = psf             # point spread function
)
obs_r = imager.observe(src, 'LSST_r', 15 * u.min, sky_sb=21, psf=psf)
obs_i = imager.observe(src, 'LSST_i', 30 * u.min, sky_sb=20, psf=psf)

rgb = make_lupton_rgb(obs_i.image, obs_r.image, obs_g.image, stretch=0.4)

artpop.show_image(rgb);