# 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.
|===========================================|  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",

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

 Conf Configuration parameters for astroquery.nvas.