extinction_coefficient is a astronomy Python package to provide temperature- and extinction-dependent empirical dust extinction or reddening coefficients from far-ultraviolet (UV) to the mid-infrared (IR). See our paper for more infomation (Zhang & Yuan, 2022).
For a given band a, the extinction coefficient is defined as E(a)/E(B-V), i.e. the ratio of the extinction in a band to the color excess of B−V;
Similarly, for a given color a-b, the reddening coefficient is defined as E(a-b)/E(B-V).
Note that the E(B-V) in this package is taken directly from the SFD whole-sky 2D dust-reddening map of Schlegel et al. (1998).
Our coefficients are mostly valid in the E(B-V) range of 0-0.5 mag and the temperature range of 4000-10000 K. But note that the temperature range varies depending on the band (see Table 4 of Zhang & Yuan (2022)). No extrapolation for out-of-range input values, but rather assignment of boundary values.
Note: The band names used in the code need to be consistent with the table. there are ' in the passbands of SDSS.
| Surveys | Passbands |
|---|---|
| GALEX | FUV, NUV |
| Pan-STARRS 1 | g, r, i, z, y |
| SDSS | u', g', r', i', z' |
| Gaia | BP, G, RP |
| 2MASS | J, H, Ks |
| WISE | W1, W2, W3, W4 |
# from PyPI (recommmand)
pip install extinction_coefficient
# from the master trunk on the repository, considered developmental code
pip install git+https://github.com/vnohhf/extinction_coeffcient.git
extinction_coefficient can be installed from the source code after downloading it from the git repo (https://github.com/vnohhf/extinction_coeffcient/):
python setup.py install
To get a single value extinction or reddening coefficients obtained when temperature and extinction are not considered, just put mode = 'simple':
from extinction_coefficient import extinction_coefficient
extinction_coefficient('g', mode='simple')
extinction_coefficient('BP-RP', mode='simple')
extinction_coefficient(["BP-RP","FUV-g"], mode='simple')To obtain extinction or reddening coefficients for (a group of) specific Teff and E(B-V):
Band = 'BP'
EBV = 0.3
Teff = [5000, 6000]
extinction_coefficient(Band,EBV=EBV,Teff=Teff)Band = np.array(["BP-RP","FUV-g","y-H","u'-W2"])
EBV = [0.1, 0.1, 0.3, 0.5]
Teff = 5500
extinction_coefficient(Band,EBV=EBV,Teff=Teff)If Teff is unknown in advance, the observed BP-RP color can be entered as a substitute. This program first makes a rough reddening correction to the observed BP-RP and then converts them to Teff using an empirical polynomial relationship between intrinsic color (BP-RP)0 and Teff. After a iterate, the exact reddening coefficients is calculated using Teff.
Band = ["BP-RP","FUV-g","i'-z'"]
EBV = [0.1, 0.3, 0.5]
BP_RP = np.array([0.3, 0.6, 1.2])
extinction_coefficient(Band,EBV=EBV,BP_RP=BP_RP)extinction_coefficient(Band,EBV=None,BP_RP=None,Teff=None,mode='func')
Args:
Band: str or array-like, shape (n, )
The passband or color index. If color index are entered, '-' need to be used to connect
the two passband name strings (e.g. "BP-RP"). There support GALEX passbands: "FUV", "NUV";
Pan-STARRS 1 passbands: "g", "r", "i", "z", "y";
SDSS passbands: "u'", "g'", "r'", "i'", "z'";
Gaia DR3 passbands: "BP", "G", "RP";
2MASS passbands: "J", "H", "Ks";
WISE passbands: "W1", "W2", "W3", "W4";
EBV: float or array-like, shape (n, ), optional
The E(B-V), in magnitude.
BP_RP: float or array-like, shape (n, ), optional
The observed (BP-RP) color index.
Teff: float or array-like, shape (n, ), optional
The effective temperature, in Kelvins.
mode: {'func', 'simple'} (default: 'func')
The calculate mode of extinction or reddening coefficients. Possible values:
'func': interpolation results on functions of Teff and E(B-V).
'simple': single value coefficients obtained when temperature and extinction are not considered.
Returns: float or array-like, shape (n, )
Empirical extinction or reddening coefficients. Has the largest shape as the input obj:`Band`, obj:`EBV`,
obj:`BP_RP`, or obj:`Teff`.