{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Flux and magnitude conversion"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In this tutorial we will use the [F115W filter](http://svo2.cab.inta-csic.es/svo/theory/fps3/index.php?id=JWST/NIRCam.F115W&&mode=browse&gname=JWST&gname2=NIRCam#filter) of [JWST/NIRCam](https://www.jwst.nasa.gov/content/observatory/instruments/nircam.html) to convert a magnitude into a flux and vice versa. The magnitudes are defined in the Vega System with the magnitude of Vega set to 0.03 for each filter."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Getting started"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We start by importing `species` and initiating the database."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "==============\n",
      "species v0.6.0\n",
      "==============\n",
      "Working folder: /Users/tomasstolker/applications/species/docs/tutorials\n",
      "Creating species_config.ini... [DONE]\n",
      "Configuration settings:\n",
      "   - Database: /Users/tomasstolker/applications/species/docs/tutorials/species_database.hdf5\n",
      "   - Data folder: /Users/tomasstolker/applications/species/docs/tutorials/data\n",
      "   - Interpolation method: linear\n",
      "   - Magnitude of Vega: 0.03\n",
      "Creating species_database.hdf5... [DONE]\n",
      "Creating data folder... [DONE]\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "<species.core.init.SpeciesInit at 0x14e533810>"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import species\n",
    "species.SpeciesInit()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Magnitude to flux"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We now create an instance of [SyntheticPhotometry](https://species.readthedocs.io/en/latest/species.analysis.html#species.analysis.photometry.SyntheticPhotometry) with the filter name as listed by the [SVO Filter Profile Service](http://svo2.cab.inta-csic.es/svo/theory/fps3/index.php?mode=browse&gname=JWST&gname2=NIRCam)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Adding filter: JWST/NIRCam.F115W..."
     ]
    },
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "Downloading data from 'https://archive.stsci.edu/hlsps/reference-atlases/cdbs/current_calspec/alpha_lyr_stis_011.fits' to file '/Users/tomasstolker/applications/species/docs/tutorials/data/alpha_lyr_stis_011.fits'.\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " [DONE]\n"
     ]
    },
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "100%|████████████████████████████████████████| 288k/288k [00:00<00:00, 130MB/s]"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Adding Vega spectrum... [DONE]\n",
      "Reference: Bohlin et al. 2014, PASP, 126\n",
      "URL: https://ui.adsabs.harvard.edu/abs/2014PASP..126..711B/abstract\n"
     ]
    },
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "\n"
     ]
    }
   ],
   "source": [
    "synphot = species.SyntheticPhotometry('JWST/NIRCam.F115W')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "To covert from apparent magnitude to flux, we use the [magnitude_to_flux](https://species.readthedocs.io/en/latest/species.analysis.html#species.analysis.photometry.SyntheticPhotometry.magnitude_to_flux) method. The zero-point flux can be provided but is otherwise calculated from a flux-calibration Vega spectrum. Both the filter profile and the Vega spectrum will be downloaded and stored into the database. Let's calculate the flux for a magnitude of 15 +/- 0.2."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Flux (W m-2 um-1) = 4.04e-15 +/- 7.48e-16\n"
     ]
    }
   ],
   "source": [
    "flux, error = synphot.magnitude_to_flux(15., error=0.2)\n",
    "print(f'Flux (W m-2 um-1) = {flux:.2e} +/- {error:.2e}')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Flux to magnitude"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "To convert backwards from flux to magnitude, we use the [flux_to_magnitude](https://species.readthedocs.io/en/latest/species.analysis.html#species.analysis.photometry.SyntheticPhotometry.flux_to_magnitude) method. When the `parallax` (in mas) or `distance` (in pc) is provide, both the apparent and absolute magnitude are calculated. The uncertainty on the parallax/distance is propagated into the uncertainty of the absolute magnitude."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Apparent magnitude = 15.00 +/- 0.20\n",
      "Absolute magnitude = 10.00 +/- 0.30\n"
     ]
    }
   ],
   "source": [
    "app_mag, abs_mag = synphot.flux_to_magnitude(flux, error=error, parallax=(10., 1.))\n",
    "print(f'Apparent magnitude = {app_mag[0]:.2f} +/- {app_mag[1]:.2f}')\n",
    "print(f'Absolute magnitude = {abs_mag[0]:.2f} +/- {abs_mag[1]:.2f}')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "As expected, we obtain again the magnitude that we started out with."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Zero point flux"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Finally, let's see what the zero-point flux (i.e. the flux of Vega) is for the `JWST/NIRCam.F115W` filter. The value is stored by the `zero_point` attribute of the `SyntheticPhotometry` object."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Zero point flux (W m-2 um-1) = 3.92908e-09\n"
     ]
    }
   ],
   "source": [
    "print(f'Zero point flux (W m-2 um-1) = {synphot.zero_point:.5e}')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This flux is indeed very similar to the zero point that is provided on the website of the [SVO Filter Profile Service](http://svo2.cab.inta-csic.es/svo/theory/fps3/index.php?id=JWST/NIRCam.F115W&&mode=browse&gname=JWST&gname2=NIRCam#filter): 3.92904e-10 erg cm$^{-2}$ s$^{-1}$ A$^{-1}$."
   ]
  }
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