{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# What are TargetPixelFile objects?" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Target Pixel Files (TPFs) are a file common to Kepler/K2 and the TESS mission. They contain data that is usually centered around a single star.\n", "\n", "TPFs can be thought of as stacks of images, with one image for every timestamp the telescope took data. Each timestamp is referred to as a **cadence**. These images are cut out 'postage stamps' of the full observation to make them easier to work with. \n", "\n", "TPFs are given in FITS files, which you can read more about [here](https://fits.gsfc.nasa.gov/fits_primer.html). `lightkurve` includes tools for you to work directly with these files easily and intuitively.\n", "\n", "In this tutorial we'll cover the basics of working with TPFs. In lightcurve there are classes to work with each mission. For example `KeplerTargetPixelFile` is used to work with data from the Kepler (and K2) mission. `TessTargetPixelFile` is used to work with data from the TESS mission.\n", "\n", "We'll use a Kepler TPF as an example. First, let's open a file. We can do this easily with the `KeplerTargetPixelFile.from_archive` function. This will retrieve the data from the [MAST data archive](https://archive.stsci.edu/kepler/), which holds all of the Kepler and K2 data.\n", "In this case we are downloading the Target Pixel File with the Kepler ID 6922244 for Quarter 4 (Kepler's observations were split into quarters of a year).\n", "You can also download a file with `from_archive` using the name of the target, or using the astronomical coordinates (Right Ascension and Declination, often referred to as \"RA\" and \"Dec\")." ] }, { "cell_type": "code", "execution_count": 1, "metadata": {}, "outputs": [], "source": [ "from lightkurve import KeplerTargetPixelFile\n", "tpf = KeplerTargetPixelFile.from_archive(6922244, quarter=4)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "We can access lots of meta data using this object very simply with properties of the `KeplerTargetPixelFile` object. For example, we can find the mission name, and the quarter that the data was taken in by typing the following:" ] }, { "cell_type": "code", "execution_count": 2, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'Kepler'" ] }, "execution_count": 2, "metadata": {}, "output_type": "execute_result" } ], "source": [ "tpf.mission" ] }, { "cell_type": "code", "execution_count": 3, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "4" ] }, "execution_count": 3, "metadata": {}, "output_type": "execute_result" } ], "source": [ "tpf.quarter" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "You can find the full list of properties in the [API documentation](http://lightkurve.keplerscience.org/api/targetpixelfile.html)." ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "The most interesting data in a `KeplerTargetPixelFile` object are the `flux` and `time` values which give access to the brightness of the observed target over time. You can access the timestamps of the observations using the `time` property:" ] }, { "cell_type": "code", "execution_count": 4, "metadata": { "scrolled": true }, "outputs": [ { "data": { "text/plain": [ "array([ 352.37632485, 352.39675805, 352.43762445, ..., 442.16263546,\n", " 442.18306983, 442.2035041 ])" ] }, "execution_count": 4, "metadata": {}, "output_type": "execute_result" } ], "source": [ "tpf.time" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "By default, `time` is in the Kepler-specific *Barycentric Kepler Julian Day* format (BKJD). You can easily convert this into [AstroPy Time objects](http://docs.astropy.org/en/stable/time/) using the `astropy_time` property:" ] }, { "cell_type": "code", "execution_count": 5, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "