%matplotlib inline
import warnings
warnings.filterwarnings('ignore')
    

from IPython.display import Image

from IPython.display import HTML

Steve Crawford

(one small member of the much larger astropy community)

Philosopy of Astropy

Contributors of Astropy

Astropy v0.4 and affiliate packages

How to Contribute

History and Motivation

Philosophy of Astropy

The Astropy Project is a community effort to develop a core package for Astronomy in Python and foster interoperability between Python astronomy packages.

Minimize duplication

Create a well-documented and tested core astronomy library

Create frameworks for producing astronomy related code

Build and Support Python Astronomy Community

Contributors to Astropy

Astropy has organically grown from the astropy@scipy.org mailing list

Astropy has over 90 contributors from around the world

Project Coordinators

• Perry Greenfield

• Thomas Robitaille

• Erik Tollerud

Astropy on Github

Astropy Core

v0.4.2

Only has Numpy as a required dependency (easy to install)

Well tested, documented, and stable code

Works on Linux, MacOS X, and Windows

Python 2 and 3 compatible

Latest stable release v0.4.2 on Sept 23

Core data structures and transformations Constants Units and Quantities N-dimensional datasets Data Tables Time and Dates Astronomical Coordinate Systems World Coordinate System Models and Fitting

Connecting up: Files and I/O Unified file read/write interface FITS File handling ASCII Tables VOTable XML handling Miscellaneous Input/Output

Astronomy computations and utilities Convolution and filtering Cosmological Calculations Astrostatistics Tools Virtual Observatory Access

Analysis with Units

from astropy import constants as c
c.G

$6.67384\times 10^{-11} \; \mathrm{\frac{m^{3}}{kg\,s^{2}}}$

M = c.M_earth
M

$5.9742\times 10^{+24} \; \mathrm{kg}$

from astropy import units as u
r = c.R_earth
v_esc = (2 * c.G * M / r)**0.5
v_esc.to(u.km/u.s)

$11.1814 \; \mathrm{\frac{km}{s}}$

v_esc = ((2 * c.G * M / (r+559*u.km))**0.5)
v_esc.to(u.km/u.s)

$10.7214 \; \mathrm{\frac{km}{s}}$

v_esc = ((2 * c.G * 3 * u.m / (r+559*u.km))**0.5)
v_esc.to(u.km/u.s)

---------------------------------------------------------------------------
UnitsError                                Traceback (most recent call last)
<ipython-input-9-871ca449b6fa> in <module>()
      1 v_esc = ((2 * c.G * 3 * u.m / (r+559*u.km))**0.5)
----> 2 v_esc.to(u.km/u.s)

/Users/crawford/programs/astropy/astropy/units/quantity.pyc in to(self, unit, equivalencies)
    586         unit = Unit(unit)
    587         new_val = np.asarray(
--> 588             self.unit.to(unit, self.value, equivalencies=equivalencies))
    589         return self._new_view(new_val, unit)
    590 

/Users/crawford/programs/astropy/astropy/units/core.pyc in to(self, other, value, equivalencies)
    924             If units are inconsistent
    925         """
--> 926         return self.get_converter(other, equivalencies=equivalencies)(value)
    927 
    928     def in_units(self, other, value=1.0, equivalencies=[]):

/Users/crawford/programs/astropy/astropy/units/core.pyc in get_converter(self, other, equivalencies)
    860         except UnitsError:
    861             return self._apply_equivalences(
--> 862                 self, other, self._normalize_equivalencies(equivalencies))
    863         return lambda val: scale * _condition_arg(val)
    864 

/Users/crawford/programs/astropy/astropy/units/core.pyc in _apply_equivalences(self, unit, other, equivalencies)
    823         raise UnitsError(
    824             "{0} and {1} are not convertible".format(
--> 825                 unit_str, other_str))
    826 
    827     def get_converter(self, other, equivalencies=[]):

UnitsError: 'm(3/2) / (kg(1/2) s)' and 'km / s' (speed) are not convertible

Using Coordinates

from astropy import units as u
from astropy.coordinates import SkyCoord
c1 = SkyCoord('00h42m00s', '+41d12m00s', 'icrs')

print("{0} {1}".format( c1.ra,c1.dec))

print c1.to_string('hmsdms')

c2 = SkyCoord(ra=11*u.degree, dec=10*u.degree, distance=11.5*u.pc, frame='icrs')
c1.separation(c2)  

Also available are coordinate transformation between different systems (e.g. ICRS, FK5, galactic) and matching catalags of coordinates.

Modeling

Astropy also has a modelling fitting package. Let's see how it works. Let's create a Gaussian shape and add some noise to it.

import numpy as np
x = np.linspace(-5., 5., 200)
y = 3 * np.exp(-0.5 * (x - 1.3)**2 / 0.8**2)
y += np.random.normal(0., 0.2, x.shape)

Now let's fit the model using the astropy modeling class

from astropy.modeling import models, fitting
g_init = models.Gaussian1D(amplitude=1., mean=0, stddev=1.)
fit_g = fitting.LevMarLSQFitter()
g = fit_g(g_init, x, y)
print(g)

import pylab as plt
plt.figure(figsize=(8,5))
plt.plot(x, y, 'ko')
plt.plot(x, g(x), 'r-', lw=2, label='Gaussian')
plt.xlabel('Position')
plt.ylabel('Flux')
plt.legend(loc=2)
plt.show()

A range of different models already exist for 1-D and 2-D fitting. The API for the modeling class is still being refined but it should be stable in the next major release.

In addition to what has been shown so far, a number of core data structures and transformations have been included here to help build and coordinate other packages. These include:

• Quantity: An object with a value and unit
• Table: functionality for storing and manipulating heterogeneous tables of data
• NDData: A general astronomical data object including data, meta, uncertainty, wcs
• Time: functionality for manipulating astronomical relevant times and dates
• WCS: World Coordinate Systems

Accessing Data

Tools for accessing the virtual observatory

from astropy.vo.client import conesearch

Tools for reading/writing FITS files (formerly pyfits)

from astropy.io import fits

Tools for reading in ascii tables including CDS, IPAC, HTML, Latex, Sextractor

from astropy.io import ascii
table = ascii.read("ftp://cdsarc.u-strasbg.fr/pub/cats/VII/253/snrs.dat", 
                   readme="ftp://cdsarc.u-strasbg.fr/pub/cats/VII/253/ReadMe")

print table

Cosmology in Astropy

from astropy.cosmology import WMAP9 as cosmo
cosmo.H(0)

cosmo

A number of cosmological models are already available and the user can define their own cosmological models including dark energy and neutrino properties

from astropy.cosmology import WMAP7 
from astropy.cosmology import WMAP9 as cosmo
from astropy.cosmology import Planck13 

z = np.linspace(0,10,200)

plt.figure(figsize=(8,5))
plt.plot(z, WMAP7.luminosity_distance(z)-cosmo.luminosity_distance(z), 'b-', label='WMAP7')
plt.plot(z, cosmo.luminosity_distance(z)-cosmo.luminosity_distance(z), '-', color='black', label='WMAP9')
plt.plot(z, Planck13.luminosity_distance(z)-cosmo.luminosity_distance(z), 'g-', label='Planck13')
plt.xlabel('z')
plt.ylabel('$\Delta D_L [%s]$' % cosmo.luminosity_distance(0).unit)
plt.legend(loc=2)
plt.show()

Useful statistics for Astronomy

from astropy import stats
for x in stats.funcs.__all__: print x

Astropy Framework

Development of testing, documentation, and installation infrastructre to make it easier to build and deploy your own code

Package Template

Astropy Affiliated Packages

Astropy Affiliated Packages

• APLpy
• astroML
• astropysics
  
• astroquery
• ccdproc
• gammapy
• ginga
• montage-wrapper
  
• photutils
• pydl
  
• pyvo
• sncosmo
  
• specutils

These packages are at different stages of development and there are a number of other packages in early development which are not mentioned here. Some of the packages will be integrated into the core astropy package.

APLPY

import aplpy
gc = aplpy.FITSFigure('2MASS_k.fits')
gc.show_rgb('2MASS_arcsinh_color.png')

astroquery

from astroquery.simbad import Simbad
result_table = Simbad.query_object("m1")
result_table.pprint(show_unit=True)

Services available to query include Vizier, Simbad, NED, SDSS, GAMA, archives, catalogs, and many more online resources

ccdproc

import ccdproc
ccd = ccdproc.CCDData.read('a8280418.fits', unit=u.adu)
ccd.header

ccd = ccdproc.subtract_overscan(ccd, fits_section=ccd.header['biassec'], 
                                median=True, model=models.Polynomial1D(5))
ccd = ccdproc.trim_image(ccd, fits_section=ccd.header['trimsec'])
ccd = ccdproc.create_deviation(ccd, readnoise=ccd.header['rdnoise']*u.electron, 
                              gain=ccd.header['gain']*u.electron/u.adu)
ccd.write('out.fits', clobber=True)

from astropy import log
log.setLevel('ERROR')

fc = aplpy.FITSFigure(ccd.data)
fc.show_grayscale()

How to get involved

Download and install astropy

Join astropy@scipy.org

Provide feedback (submit issues, ask questions)

Use the astropy template and astropy classes for your packages

Look for 'easy' issues and submit a pull request

Contribute code either to astropy or an affiliated package

Astropy Resources

Websites
Homepage: http://www.astropy.org/
Documentation: http://docs.astropy.org/
Tutorials: http://www.astropy.org/astropy-tutorials/

Github
https://github.com/astropy

Contacts
Twitter: @astropy
General Mailing List: astropy@scipy.org
Mailing list for developers: astropy-dev@googlegroups.com

Reference
'Astropy: A community Python package for astronomy', Astropy Collaboration et al. 2013, Astronomy and Astrophysics, 558, AA33

Acknowledgement
This talk made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration, 2013).

Special thank you to Thomas Robitaille, Adrian Price-Whelan, Mathew Craig, and the Astropy Community for material for this talk.