Files can easily be read and written, and once in memory can be easily modified. Figure 6 shows a simple example of how to open an existing FITS file, access and modify the header and data, and write a new file back to disk. 4) which includes more interoperability of sub-packages, as well as new functionality. Thomas P. Robitaille1, Erik J. Tollerud2, 3, Perry Greenfield4, Michael Droettboom4, Erik Bray4, Tom Aldcroft5, Matt Davis4, Adam Ginsburg6, Adrian M. Price-Whelan7, Wolfgang E. Kerzendorf8, Alexander Conley6, Neil Crighton1, Kyle Barbary9, Demitri Muna10, Henry Ferguson4, Frdric Grollier12, Madhura M. Parikh11, Prasanth H. Nair12, Hans M. Gnther5, Christoph Deil13, Julien Woillez14, Simon Conseil15, Roban Kramer16, James E. H. Turner17, Leo Singer18, Ryan Fox12, Benjamin A. Weaver19, Victor Zabalza13, Zachary I. Edwards20, K. Azalee Bostroem4, D. J. Burke5, Andrew R. Casey21, Steven M. Crawford22, Nadia Dencheva4, Justin Ely4, Tim Jenness23,24, Kathleen Labrie25, Pey Lian Lim4, Francesco Pierfederici4, Andrew Pontzen26,27, Andy Ptak28, Brian Refsdal5, Mathieu Servillat29,5 and Ole Streicher30, 1 Max-Planck-Institut fr Astronomie, Knigstuhl 17, 69117 Heidelberg, Germany Frequency: 12 volumes per year The sub-package provides several pre-defined cosmology instances corresponding to commonly used cosmological parameter sets. This ensures the interface is designed with the workflow of working astronomers in mind. 28 NASA Goddard Space Flight Center, X-ray Astrophysics Lab Code 662, Greenbelt, MD 20771, USA From GNU/Linux, you can try to obtain this packages using the package installer of your distribution (apt-get in Ubuntu/Debian, yum in Fedora or YAST in SUSE). While only in early planning stages, such a package would aim to not be tied to the FITS representation used for the current astropy.wcs. They allow users to represent astronomical data in the form of tables or n-dimensional gridded datasets, including all metadata. interpolation, integration, clustering). It also supports implementation of new or custom coordinate systems that work consistently with the built-in systems. Not all contributions are necessarily accepted community consensus is needed for incorporating major new functionality in astropy, and any new feature has to be justified to avoid implementing features that are only useful to a minority of users, but may cause issues in the future.
3. Since all of the FITS header parsing is done using wcslib, it is assured the same behavior as the many other tools that use wcslib. 2005). It is also possible to decompose units into their base units, or alternatively search for higher-level units that are identical. 3 Hubble Fellow A future design goal is to seamlessly support arbitrarily large data sets. 2.4), common astronomical file formats (Sect. 2.5), world coordinate system (WCS) transformations (Sect. Chevallier & Polarski 2001; Linder 2003, here a is the scale factor). Furthermore, the data often includes a set of keyword-value pairs and comments (such as FITS headers). The actual data is stored in an ndarray, which allows for easy compatibility with other scientific packages. We have also implemented a feature that means that anyone reading the documentation at http://docs.astropy.org can suggest improvements to the documentation with just a few clicks in a web browser without any prior knowledge of the git version control system. A validation tool (volint) is also provided that outputs recommendations to improve the standard compliance of a given file, as well as validate it against the official VOTable schema. An example of a user-defined system is provided in the documentation6, illustrating the definition of a coordinate system useful for a specific scientific task. Figure 2 includes a simple example that shows how the gravitational force between two bodies can be calculated in Newtons using physical constants and user-specified quantities.
Users can also define their own units, either as standalone base units or by composing other units together. This includes support for deprecated formats such as GROUPS HDUs as well as more obscure non-standard HDU types such as FITS HDUs which allow encapsulating multiple FITS files within FITS files. This development workflow has worked very well so far, allowing contributions by many developers, and blurring the line between developers and users. 2.4) which is much more flexible and powerful than PyFITS current table interface. A primary guiding philosophy of Astropy is that it is developed for and (at least in part) by the astronomy user community.
The input time(s) can either be a single scalar such as "2010-01-01 00:00:00" or 2455348.5 or a sequence of such values; the format or representation specifies how to interpret the input values, such as ISO, JD, or Unix time; and the scale specifies the time standard used for the values, such as coordinated universal time (UTC), terrestial time (TT), or international atomic time (TAI). 2.5.3), which allow ASCII and VO tables to be seamlessly read or written respectively. These transformations map the pixel locations in an image to their real-world units, such as their position on the celestial sphere.
The data that is stored in arrays and tables often contains vital metadata: the data is associated with units, and might also contain additional arrays that either mask or provide additional attributes to each cell. 2.4), where it can be edited and then written back to a VOTable file without any loss of data. 4 makes use of the SIMBAD database, operated at CDS, Strasbourg, France. This flexibility is achieved in astropy.coordinates through the internal use of a transformation graph, which keeps track of a network of coordinate systems and the transformations between them. Furthermore, tables can be easily read from and written to common file formats using the Table.read and Table.write methods. This has led to duplication and a lack of homogeneity across packages, making it difficult for users to install all the required packages needed in an astronomers toolkit. A standard astronomical example is the relationships between the frequency, wavelength and energy of a photon it is common practice to treat such units as equivalent even though they are not strictly comparable. The file is read using streaming to avoid reading in the entire file at once and greatly reducing the memory footprint. By combining the best aspects of these other packages, as well as testing against them, astropy.coordinates seeks to provide a high-quality, flexible Python coordinates library. The Table class provides a high-level wrapper to NumPy structured arrays, which are essentially arrays that have fields (or columns) with heterogeneous data types, and any number of rows. These objects support arithmetic with other numbers and Quantity objects while preserving their units. We present the first public version (v0.2) of the open-source and community-developed Python package, Astropy. Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform. If you don't know anything about Python, just begin with official tutorial, its brief and clear. fitsdiff can be used to compare two FITS files on a number of criteria, and also includes a powerful API for programmatically comparing FITS files. Header-data units (HDUs) are represented by Python classes, with the data itself stored using NumPy arrays, and with the headers stored using a Header class. 2004; Shupe et al. 2011); implementing a generalized model-fitting framework; implementing statistical functions commonly used in Astronomy. Since Quantity objects can operate with NumPy arrays, it is very simple and efficient to convert the units on large datasets. The final object can then be converted to a specified set of units or decomposed, effectively canceling and combining any equivalent units and returning a Quantity object in some set of base units. The project has grown rapidly, and to date, over 200 individuals are signed up to the development mailing list for the Astropy project2. This sub-package includes the concept of equivalencies in units, which is intended to be used where there exists an equation that provides a relationship between two different physical quantities. Specific emphasis is placed on supporting time scales (e.g. It is also dedicated to remaining open source to enable wide adoption and render input from all users easier, and is thus released with a 3-clause BSD-style license (a license of this sort is permissive in that it allows usage of the code for any purposes as long as notice of the Astropy copyright and disclaimers of warranty are given). This sub-package is a wrapper around the wcslib library11. 2), our development workflow (Sect. We would like to thank the NumPy, SciPy (Jones et al. Key words: methods: data analysis / methods: miscellaneous / virtual observatory tools. Figure 7 gives examples showing how to use the pre-defined cosmologies, and how to define a new cosmology with a time-varying dark energy w(a). Figure 4 shows some typical usage examples for astropy.coordinates. 2.1), and also allows the Table object to contain arbitrary metadata (stored in Table.meta). 2011), a Python package that makes it easy to use C code in Python. This package provides core astronomy-related functionality to the community, including support for domain-specific file formats such as flexible image transport system (FITS) files, Virtual Observatory (VO) tables, and common ASCII table formats, unit and physical quantity conversions, physical constants specific to astronomy, celestial coordinate and time transformations, world coordinate system (WCS) support, generalized containers for representing gridded as well as tabular data, and a framework for cosmological transformations and conversions. We also are grateful to Read the Docs (https://readthedocs.org/), Shining Panda (https://www.shiningpanda-ci.com/), and Travis (https://www.travis-ci.org/) for providing free documentation hosting and testing respectively. While the term celestial coordinates can be taken to refer to only on-sky angles, in astropy.coordinates a coordinate object is conceptually treated as a point in three dimensional space. We provide an overview of the current capabilities (Sect. 2.2), celestial coordinates (Sect. On top of the basic FITS WCS support, it adds support for the simple imaging polynomial (SIP) convention and table lookup distortions (Calabretta et al. This workflow aids in increasing the quality, documentation and testing of the code to be included in astropy. 2004, 2009). Leveraging the robust and well-tested SOFA routines ensures that the fundamental time scale conversions are being computed correctly. This functionality is built around the Angle object, which can be instantiated and used on its own.
Table input/output and manipulation using the astropy.table sub-package. The astropy.coordinates sub-package was designed such that it should be easy for a user to add new coordinate systems. Managing Editor: D. Elbaz, ISSN: 0004-6361 ; e-ISSN: 1432-0746 The core development team is actively making additions and enhancements to the current code base, and we encourage anyone interested to participate in the development of future Astropy versions. An instance of this class has attributes giving all the parameters required to specify the cosmology uniquely, such as the Hubble parameter, CMB temperature and the baryonic, cold dark matter, and dark energy densities at z=0. This functionality is provided in Astropy by the astropy.coordinates sub-package. The flexible image transport system (FITS) standard (Pence et al. One can then use methods of this class to perform calculations using these parameters.
e-mail: robitaille@mpia.de Although PyFITS will continue to be released as a separate package in the near term, the long term plan is to discontinue PyFITS releases in favor of Astropy. 29 Laboratoire AIM, CEA Saclay, Bt. A design goal of the input parser is to be able to determine the angle value and unit from the input alone if a person can unambiguously determine them. 2011); support for the Table Access Protocol (TAP; Louys et al. Finally, the data comes in a plethora of astronomy specific formats (FITS, specially formatted ASCII tables, etc. First and perhaps foremost is integration with Astropys Table interface (Sect. We will also be able to integrate Astropys unit support (Sect. 3), and planned functionality (Sect. Others, such as the frames of palpy (Jenness & Berry 2013) and pyast (Berry & Jenness 2012) or the ephemeris system of pyephem (Rhodes 2011), are still under design for astropy. The astropy.wcs sub-package contains utilities for managing WCS transformations in FITS files. For some classes, they also contain added functionality specific to a subset of systems, such as code to precess a coordinate to a new equinox. 16 ETH Zrich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, Building HIT, Floor J, 8093 Zurich, Switzerland https://groups.google.com/forum/?fromgroups#!forum/astropy-dev, http://docs.astropy.org/en/v0.2.4/coordinates/sgr-example.html, http://www.stsci.edu/institute/software_hardware/, http://vizier.u-strasbg.fr/doc/catstd.htx, http://irsa.ipac.caltech.edu/applications/DDGEN/, http://www.atnf.csiro.au/people/mcalabre/WCS/. Sect. In this guide you will find which are the most common packages and documentation for astronomy and where to obtain them. In addition, the International Virtual Observatory Alliance (IVOA) has a forthcoming VOUnit standard (Derriere et al. NDData is not meant for direct user interaction but more for providing a framework for higher-level subclasses that can represent for example spectra or astronomical images.
Support is also included for common but non-standard header conventions such as CONTINUE cards and ESO HIERARCH cards. Two command-line utilities for working with FITS files are packaged with Astropy: fitscheck can be used to validate FITS files against the standard. This paper is not intended to provide a detailed documentation for the package (which is available online3), but is rather intended to give an overview of the functionality and design. Future versions of Astropy will include additional common systems, including ecliptic systems, supergalactic coordinates, and all necessary intermediate coordinate systems for the IAU 2000/2006 equatorial-to-horizontal mapping (e.g., Soffel et al. 8 Department of Astronomy and Astrophysics, University of Toronto, 50 Saint George Street, Toronto, ON M5S3H4, Canada 3), which has enabled an international collaboration of scientists and software developers to create and contribute to the package. The name resolution functionality shown in Fig. 2010) defines a unit standard, as well as both the Centre de Donnes astronomiques de Strasbourg (CDS; Ochsenbein 2000) and NASA/Goddards Office of Guest Investigator Programs (OGIP; George & Angelini 1995). Some aspects, such as coordinate transformation approaches from kapteyn (Terlouw & Vogelaar 2012) and class structures resembling astropysics (Tollerud 2012), have already been implemented. The coordinate classes represent different coordinate systems, and provide most of the user-facing functionality for astropy.coordinates. 26 Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK We outlined our plans for the future (Sect. 2.3), tabular and gridded data (Sect. Differing from monolithic-packages as IDL or Matlab, where you have one plotting library, one GUI library, a standard IDE (integrated Development Environment) and so on, all with a common documentation, in Python, as with any general use programming language, you have to choose the modules you need and install them, refering to the documentation of each module separately. 2013), but has been significantly enhanced in behavior and implementation (with the intent that pynbody will eventually become interoperable with astropy.units). 24 Department of Astronomy, Cornell University, Ithaca, NY 14853, USA If you are using GNU/Linux or a Mac, its already installed by default on this systems. Such a package would also include closer connection to other parts of Astropy, for example astropy.coordinates (Sect. All of the code in the sub-package is tested against the web-based cosmology calculator by Wright (2006) and two other widely-used calculators12,13. Examples of using this sub-package are provided in Fig. We thank the referee, Igor Chiligarian, for suggestions that helped improve this paper. We have presented the first public release of the Astropy package (v0.2), a core Python package for astronomers. In addition, the NDData class intends to provide methods to arithmetically combine the data in a meaningful way. It also contains a framework for working with less frequently employed cosmologies that may not be flat, or have a time-varying pressure to density ratio, w, for dark energy. 2.1), absolute dates and times (Sect. 2003; Kaplan 2005). Suggested resources for more tips on language editing in the sciences, Including author names using non-Roman alphabets, Astronomical objects: linking to databases, https://doi.org/10.1051/0004-6361/201322068, Vaex: big data exploration in the era of Gaia, Cygrid: A fast Cython-powered convolution-based gridding module for Python, GammaLib and ctools A software framework for the analysis of astronomical gamma-ray data, Nuclear data processing capabilities in OpenMC, Long-term lightcurves from combined unified very high energy -ray data. To enable this collaboration, we have made use of the GitHub14 open source code hosting and development platform. Please note that all the SIEpedia's articles address specific issues or questions raised by IAC users, so they do not attempt to be rigorous or exhaustive, and may or may not be useful or applicable in different or more general contexts. Since the code in this sub-package has been developed over more than a decade, it has been made to work with an extensive variety of FITS files, including ones that deviate from the FITS standard. NumPy structured arrays are however difficult to modify, so the Table class makes it easy for users to create a table from columns, add and remove columns or rows, and mask values from the table. Unit definitions are included in both the International System of Units (SI) and the Centimeter-Gram-Second (CGS) systems, as well as a number of astronomy- and astrophysics-specific units. 2012) are included (the WMAP5, WMAP7, and WMAP9 classes). Examples of usage of astropy.table are shown in Fig. The units must either be dimensionally equivalent, or users should pass equivalencies through the equivalencies argument (cf. 13 Max-Planck-Institut fr Kernphysik, PO Box 103980, 69029 Heidelberg, Germany Here are documentation of the main scientific packages: Page last modified on October 13, 2019, at 06:49 PM, CVN(2): Generar CVA (CV Abreviado) con formato MINECO, CVN(3): Importar por categoras (con ejemplo de importacin desde ADS), CVN(4): Importar a CVN un CV en formato CICYT/MICINN, CVN(5): Importar a CVN de tablas en formato CICYT/MICINN, HTCondor(3): Submit files (description and examples), Install Astronomical Software on a laptop, Installation of IRAF on macOS with Multipass, README files for Astronomical Software on laptop, PEP - Python and C library for source extraction and photometry, Using Python for interactive data analysis in astronomy, Practical Python for Astronomers Tutorial, A Demonstration of the 'IPython' Interactive Shell by Jeff Rush. Achieving these aims requires code collaboration between over 30 geographically-distributed developers, and here we describe our development workflow with the hope that it may be replicated by other astronomy software projects that are likely to have similar needs. Support for common astronomical file formats (Sect. One of the primary aims of the Astropy project is to develop a core astropy package that covers much of the astronomy-specific functionality needed by researchers, complementing more general scientific packages such as NumPy (Oliphant 2006; Van Der Walt et al. 1). 2.3). The Python community has various solutions for tables, such as NumPy structured arrays or DataFrame objects in Pandas (McKinney 2012) to name only a couple. Beeing Python so extensive, its easy to get lost with all the possible modules and its documentation, because there are many options to do the same. 2 Department of Astronomy, Yale University, PO Box 208101, New Haven, CT 06510, USA Becoming integrated with Astropy as the astropy.io. 2011) and 9-year results (Hinshaw et al. 5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA In this paper, we present the first public release (v0.2) of the astropy package. Celestial coordinate representation and conversion. Equivalencies are also included for monochromatic flux densities, which allows users to convert between F and F, and users can easily implement their own equivalencies. While there have been a number of efforts to develop Python packages for astronomy-specific functionality, these efforts have been fragmented, and several dozens of packages have been developed across the community with little or no coordination. Sect. Coordinate objects can easily be transformed from one coordinate system to another: Fig. 2009), 7-year (Komatsu et al. 2.3). 1). 2006) and is distinct from a planned Astropy package that will handle WCS transformations in general, regardless of their representation. Similarly, the NDData class provides a way to store n-dimensional array data easily and builds upon the NumPy ndarray class. In addition to generic formats such as space-delimited, tab-delimited or comma-separated values, astropy.io.ascii provides classes for specialized table formats such as CDS9, IPAC10, IRAF DAOphot (Stetson 1987), and LaTeX. The fundamental model for this sub-package is that any given cosmology is represented by a class. Significant functionality is under activedevelopment, such as a model fitting framework, VO client and server tools, and aperture and point spread function (PSF) photometry tools. 27 Department of Physics and Astronomy, University College London, London WC1E 6BT, UK Sect. The astropy.units sub-package defines a Unit class to represent base units, which can be manipulated without attaching them to values, for example to determine the conversion factor from one set of units to another. Any other arbitrary cosmology can be represented by sub-classing one of the basic cosmology classes. The astropy.wcs sub-package also serves as a useful FITS WCS validation tool, as it is able to report on many common mistakes or deviations from the standard in a given FITS file. Using two 64-bit floating-point values allows users to represent times with a dynamic range of 30 orders of magnitude, providing for example times accurate to better than a nanosecond over timescales of tens of Gyr. We thank the GitHub (http://www.github.com) team for providing us with an excellent free development platform. These distances can be given in physical units or as redshifts. We have illustrated each section with simple and concise code examples, but for more details and examples, we refer the reader to the online documentation3. 2.1.1 or Fig. 2.6), and cosmological utilities (Sect. It is possible to convert any one of the tables in a VOTable file to a Table object (Sect.
At the time of writing, astropy includes several thousand tests, which are small units of code that check that functions, methods, and classes in astropy are behaving as expected, both in terms of scientific correctness and from a programming interface perspective. The astropy.io.ascii sub-package (formerly the standalone project asciitable8) provides the ability to read and write tabular data for a wide variety of ASCII-based formats. For n-dimensional data the NumPy ndarray is the most popular. 22 SAAO, PO Box 9, Observatory 7935, 7925 Cape Town, South Africa
Astronomical coordinates may be expressed in a myriad of ways: the classes support string, numeric, and tuple value specification through a sophisticated input parser. The astropy.cosmology sub-package contains classes for representing widely used cosmologies, and functions for calculating quantities that depend on a cosmological model. Editor-in-Chief: T. Forveille 19 Center for Cosmology and Particle Physics, New York University, New York, NY 10003, USA Coordinate objects are created using standard Python object instantiation via a Python class named after the coordinate system (e.g., ICRSCoordinates).
2.7) for conversion to physical distances. In fact, the astropy package will likely remain a continuously-evolving package, and will thus never be considered complete in the traditional sense. 4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 4 illustrates the most basic use of this functionality to convert a position on the sky from ICRS to Galactic coordinates. To achieve this, it combines API and implementation ideas from existing Python coordinates packages. 1. Some examples are the angular diameter distance, comoving distance, critical density, distance modulus, lookback time, luminosity distance, and Hubble parameter as a function of redshift. We invite members of the community to join the effort by adopting the Astropy package for their own projects, reporting any issues, and whenever possible, developing new functionality. Currently parameters from the WMAP 5-year (Komatsu et al. We note that the Time class includes support for leap seconds in the UTC time scale. 11 S.V.National Institute of Technology, 395007 Surat., India JD, MJD, ISO 8601) that are used in astronomy (Guinot & Seidelmann 1988; Kovalevsky 2001; Wallace 2011). 15 Laboratoire dAstrophysique de Marseille, OAMP, Universit Aix-Marseille et CNRS, 13388 Marseille, France As a convenience, it is also possible to query the online SIMBAD5 database to resolve the name of a source (see Fig. Support for reading and writing FITS files is provided by the astropy.io.fits sub-package, which at the time of writing is a direct port of the PyFITS7 project (Barrett & Bridgman 1999). In cases when these calculators are not precise enough to enable a meaningful comparison, the code is tested against calculations performed with Mathematica. Quantity conversion using the astropy.units sub-package. Greenfield 2011, for a recent review). Published by: EDP Sciences, The European Southern Observatory (ESO), 5. 25 Gemini Observatory, 670 N. Aohk Place, Hilo, HI 96720, USA The Python programming language1 has become one of the fastest-growing programming languages in the astronomy community in the last decade (see e.g.