simcado.spectral module

Classes for spectral curves

class simcado.spectral.TransmissionCurve(filename=None, lam=None, val=None, **kwargs)

Bases: object

Very basic class to either read in a text file for a transmission curve or take two vectors to make a transmission curve

Parameters

filenamestr, optional

The path to the file containing wavelength and transmission data where the first column is wavelength in [um] and the second is the transmission coefficient between [0,1].

Alternatively this data can be passed directly. If filename is not provided, lam= and val= must be passed

lamarray, optional

[um] Wavelength bins in a 1D numpy array of length n

valarray, optional

[0 .. 1] The transmission coefficients

Returns

TransmissionCurve object

filter_info(self)

Returns the filter properties as a dictionary

filter_table(self)

Returns the filter properties as a astropy.table

Notes

ONLY works if filter files have the SimCADO header format

The following keywords should be in the header:

author
source
date_created
date_modified
status 
type
center
width
blue_cutoff
red_cutoff

normalize(self, val=1.0, mode='integral')

Normalize the spectral curve

Parameters

valfloat, optional

The value to normalise to. Default is 1.

modestr, optional

• “integral” normalizes the integral over the defined

  wavelength range to val (default: 1.)

• “maximum” normalizes the maximum over the defined

  wavelength range to val (default: 1.)

plot(self, **kwargs)

Plot the transmission curve on the current axis

The method accepts matplotlib.pyplot keywords.

resample(self, bins, action='average', use_edges=False, min_step=None, use_default_lam=False)

Resamples both the wavelength and value vectors to an even grid. In order to avoid losing spectral information, the TransmissionCurve resamples down to a resolution of ‘min_step’ (default: 0.01nm) before resampling again up to the given sampling vector defined by ‘bins’.

Parameters

binsfloat or array of floats

[um]: float - taken to mean the width of bins on an even grid

array - the centres of the spectral bins

• the edges of the spectral bins if use_edges = True

actionstr, optional

[‘average’,’sum’] How to rebin the spectral curve. If ‘sum’, then the curve is normalised against the integrated value of the original curve. If ‘average’, the average value per bin becomes the value for each bin.

use_edgesbool, optional

[False, True] True if the array passed in ‘bins’ describes the edges of the wavelength bins. Default is False

min_stepfloat, optional

[um] default=1E-4, the step size for the down-sample

use_default_lambool, optional

Default is False. If True, bins is ignored and the default wavelength range is used as the resampling grid.

class simcado.spectral.EmissionCurve(filename=None, **kwargs)

Bases: simcado.spectral.TransmissionCurve

Class for emission curves

Create an emission curve from a file or from wavelength and flux vectors. In the latter case, the keywords lam and val have to be specified.

Parameters

- filename: string with the path to the transmission curve file where

the first column is wavelength in [um] and the second is the transmission coefficient between [0,1]

- lam: [um] 1D numpy array of length n

- val: 1D numpy array of length n

- res: [um] float with the desired spectral resolution

- pix_res: [arcsec] float of int for the field of view for each pixel

- area: [m2] float or int for the collecting area of M1

- units: string or astropy.unit for calculating the number of photons

per voxel

Return values are in [ph/s/voxel]

Examples

>>> from simcado.spectral import EmissionCurve
>>>
>>> ec_1 = EmissionCurve("emission_curve.dat")
>>> lam = np.arange(0.7, 1.5, 0.05)
>>> flux = 1. - 0.2 * wave**2   # power-law spectrum
>>> ec_2 = EmissionCurve(lam=lam, val=flux)

convert_to_photons(self)

Do the conversion to photons/s/voxel by using the val_unit, lam, area and exptime keywords. If not given, make some assumptions.

photons_in_range(self, lam_min=None, lam_max=None)

Sum up the photons in the wavelength range [lam_min, lam_max]

Parameters

- lam_min, lam_max: the wavelength limits

Return values are in [ph/s/pixel]

resample(self, bins, action='average', use_edges=False, min_step=None, use_default_lam=False)

Rebin an emission curve

class simcado.spectral.BlackbodyCurve(lam, temp, **kwargs)

Bases: simcado.spectral.EmissionCurve

Blackbody emission curve

Parameters

lam1D np.ndarray

[um] the centres of the wavelength bins

tempfloat

[deg C] float for the average temperature of the blackbody

pix_resfloat, optional

[arcsec] Default is 0.004. Field of view for each pixel

areafloat, optional

[m2] Default is 978m2. Area of the emitting surface

Returns

EmissionCurve object with units of [ph/s/voxel], i.e. photons per second

per wavelength bin per full area per pixel field of view

class simcado.spectral.UnityCurve(lam=array([0.3, 3. ]), val=1, **kwargs)

Bases: simcado.spectral.TransmissionCurve

Constant transmission curve

Parameters

- lam [um]: wavelength array

- val: constant value of transmission (default: 1)

simcado.spectral.get_sky_spectrum(fname, airmass, return_type=None, **kwargs)

Return a spectral curve for the sky for a certain airmass

Parameters

fnamestr

the file containing the spectral curves

airmassfloat, optinal

Default is 1.0. Acceptable values are between 1.0 and 3.0

return_typestr, optional

[“transmission”, “emission”, None] Default is None. A TransmissionCurve or EmissionCurve object will be returned if desired. If None two arrays are returned: (lam, val)

**kwargsoptional

kwargs are passed directly onto the TransmissionCurve or EmissionCurve classes

Returns

TransmissionCurve or EmissionCurve or (lam, val)

By default lam is in [um] and val [ph/s/m2/um/arcsec2] if val is an emission spectrum

Notes

This function is designed to work with a table of values produced by SkyCalc The column names must begin with lambda and then columns must be named according to the airmass following this pattern: “X1.5” for an airmass of 1.5