NVAS Queries (astroquery.nvas)¶
Getting started¶
This module may be used to retrieve the NVAS VLA archive images. All images are
returned as a list of HDUList objects. Images may be
fetched by specifying directly an object name around which to search - in this
case the name will be resolved to coordinates by astropy name resolving methods
that use online services like SESAME. The search centre may also be entered as
a coordinate using any coordinate system from astropy.coordinates. ICRS
coordinates can also be entered directly as a string that conforms to the
format specified by astropy.coordinates. Some other parameters you may
optionally specify are the radius and the frequency band for which the image
must be fetched. You can also specify the maximum allowable noise level in mJy
via the max_rms keyword parameter. By default this is set to 10000 mJy
>>> from astroquery.nvas import Nvas
>>> import astropy.units as u
>>> images = Nvas.get_images("3c 273", radius=2*u.arcsec, band="K", max_rms=500)
1 images found.
Downloading http://www.vla.nvas.edu/astro/archive/pipeline/position/J122906.7+020308/22.4I0.37_TEST_1995NOV15_1_352.U55.6S.imfits
|===========================================| 10M/ 10M (100.00%) 19m37s
>>> images
[[<astropy.io.fits.hdu.image.PrimaryHDU at 0x3376150>]]
The radius may be specified in any appropriate unit using a Quantity
object. Apart from that it may also be entered as a string in a format
parsable by Angle. The frequency bands are specified
using the band keyword parameter. This defaults to a value of all - i.e all
the bands. Here’s a list of the valid values that this parameter can take.
"all", "L", "C", "X", "U", "K", "Q"
Let’s look at an example that uses coordinates for specifying the search centre.
>>> from astroquery.nvas import Nvas
>>> import astropy.coordinates as coord
>>> import astropy.units as u
>>> images = Nvas.get_images(coord.SkyCoord(49.489, -0.37,
... unit=(u.deg, u.deg), frame='galactic'),
... band="K")
You may also fetch UVfits files rather than the IMfits files which is the
default. To do this simply set the get_uvfits to True, in any of the query
methods. You can also fetch the URLs to the downloadable images rather than the
actual images themselves. To do this use the
get_image_list() which takes in all the same
arguments as get_images() above except for the
verbose argument which isn’t relevant in this case.
>>> from astroquery.nvas import Nvas
>>> import astropy.coordinates as coord
>>> import astropy.units as u
>>> image_urls = Nvas.get_image_list("05h34m31.94s 22d00m52.2s",
... radius='0d0m0.6s', max_rms=500)
WARNING: Coordinate string is being interpreted as an ICRS
coordinate. [astroquery.utils.commons]
>>> image_urls
['http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.5+220114/1.51I4.12_T75_1986AUG12_1_118.U3.06M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.5+220114/1.51I3.92_T75_1986AUG20_1_373.U2.85M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.5+220114/4.89I1.22_T75_1986AUG12_1_84.8U2.73M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.9+220052/1.44I1.26_AH0336_1989FEB03_1_197.U8.29M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.9+220052/1.44I1.32_AH0336_1989FEB03_1_263.U3.84M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.9+220052/4.91I0.96_AH595_1996OCT14_1_41.3U2.45M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.9+220052/4.91I0.89_AH595_1996OCT11_1_43.2U2.45M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.9+220052/4.91I0.99_AH0595_1996OCT16_1_66.4U2.55M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.9+220052/8.46I2.18_AM503_1996FEB23_1_243.U2.59M.imfits',
'http://www.vla.nrao.edu/astro/archive/pipeline/position/J053431.9+220052/8.46I1.60_AM503_1996FEB01_1_483.U2.59M.imfits']
Reference/API¶
astroquery.nvas Package¶
Revision History
Refactored using common API as a part of Google Summer of Code 2013.
- Originally contributed by
Adam Ginsburg (adam.g.ginsburg@gmail.com)
Classes¶
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Configuration parameters for |