We have implemented in Astro-WISE two Galactic extinction maps:
In the case of SFD map we used an original IDL program rewritten in python
http://astro.berkeley.edu/ marc/dust/data/data.htmlhttp://astro.berkeley.edu/ marc/dust/data/data.html
To find the Galactic extinction towards an extragalactic object one can use the SFD map for which you have to provide galactic coordinates:
awe> longvec=45.0 awe> latvec=45.0 awe> from astro.util.extinction import extinction awe> ret=extinction(longvec,latvec) awe> print(ret) [0.0439861752093]
The returned value is an excess ratio (EB-V
The Galactic extinction can be calculated with an interpolation between pixels
closest to the desired direction:
Note: The number precision used in the IDL code is lower than in the python
implementation. This can cause differences in derived EB-V
Arenou extinction model based on Hipparcos data and provides an extinction
inside the Galaxy, i.e., for a selected distance. The user can provide a
distance (in kpc), if the distance is omitted, an extinction for 15 kpc will be
returned (according to the model).
or, for 100 pc distance,
A number of functions for coordinate transformations are available in Astro-WISE (which are based on the IDL astro library).
Input parameters:
Example:
Convert coordinates (0.0,0.0) to galactic coordinates
Convert galactic coordinates (0.0,0.0) to FK4 coordinates for epoch 2008.0, in degrees
Input parameters:
Example:
awe> longvec=[0.0,45.0,90.0]
awe> latvec=[0.0,45.0,90.0]
awe> from astro.util.extinction import extinction
awe> ret=extinction(longvec,latvec)
awe> print(ret)
[101.313850403, 0.0439861752093, 0.012209450826]
awe> longvec=[0.0,45.0,90.0]
awe> latvec=[0.0,45.0,90.0]
awe> from astro.util.extinction import extinction
awe> ret=extinction(longvec,latvec,interp=True)
awe> print(ret)
[99.697704474, 0.0443909994508, 0.0119094799738]
Absolute difference
sky area fraction
< 0.1%
99.8 %
< 1%
99.8 %
> 5%
00.02 %
> 10%
00.004 %
> 50%
00.0004 %
1.1.2 Arenou extinction map: inside the Galaxy
awe> longvec=[0.0,45.0,90.0]
awe> latvec=[0.0,45.0,90.0]
awe> from astro.util.extinction import extinction
awe> ret=extinction(longvec,latvec,source='Arenou')
awe> print(ret)
[0.51390040827009664, 0.017030418212218647, 0.032073867112540198]
awe> longvec=[0.0,45.0,90.0]
awe> latvec=[0.0,45.0,90.0]
awe> d=[0.1,0.1,0.1]
awe> from astro.util.extinction import extinction
awe> ret=extinction(longvec,latvec,source='Arenou',dist=d)
awe> print(ret)
[0.08085090032154342, 0.017030418212218647, 0.0032773954983922873]
1.1.3 Coordinate transformation
awe> from astro.util.idllib import glactc
awe> glactc(0.0,0.0,2008.0)
(96.112413056666824, -60.188305254568284)
awe> from astro.util.idllib import glactc
awe> glactc(0.0,0.0,2008.0,degree=True,fk4=True,eqtogal=False)
(266.53170097124888, -28.938911978654406)
awe> from astro.util.idllib import precess
awe> ra=329.887720833
awe> dec=-56.9925147222
awe> precess(ra, dec, 1950.0,1975.0,fk4=True)
(330.3144305415542, -56.871861264857067)