An instance of the BroadBand class represents either a built-in standard broadband filter (including transmission curve data), a uniform filter over a specified wavelength range (with a constant transmission curve in that range), or a custom filter based on a given wavelength grid and transmission curve. More...

Public Member Functions
def	__init__ (self, bandspec)
	The constructor creates a BroadBand instance in one of the following three ways, depending on the type of the bandspec argument: More...

def	builtinBandNames (cls)
	This function returns an iterable over all built-in band names, in arbitrary order. More...

def	convolve (self, wavelengths, fluxes, *numWavelengths=None, flavor=None)
	This function calculates and returns the band-averaged value \(\left<F_\lambda\right>\) for a given spectral energy distribution \(F_\lambda(\lambda)\). More...

def	effectiveWidth (self)
	This function returns the effective band width (a wavelength interval) as defined in the class header as an astropy quantity in micron. More...

def	maxWavelength (self)
	This function returns the maximum wavelength for the band, as an astropy quantity in micron. More...

def	minWavelength (self)
	This function returns the minimum wavelength for the band, as an astropy quantity in micron. More...

def	name (self)
	This function returns the band's name, i.e. More...

def	pivotWavelength (self)
	This function returns the pivot wavelength as defined in the class header, as an astropy quantity in micron. More...

def	transmissionCurve (self)
	This function returns a tuple containing a copy of the wavelength and transmission arrays representing the transmission curve for this band. More...

def	wavelengthRange (self)
	This function returns a tuple of astropy quantities specifying the wavelength range for this band in micron. More...

Private Member Functions
def	_bandNameFromSpec (self, bandspec)
	This function matches the given band specification with all built-in band names, i.e. More...

def	_loadALMA (self)
	This function loads the transmission curve for the ALMA format. More...

def	_loadEUCLID (self)
	This function loads the transmission curve for the EUCLID format. More...

def	_loadJCMT (self)
	This function loads the transmission curve for the JCMT format. More...

def	_loadPLANCK (self)
	This function loads the transmission curve for the PLANCK format. More...

def	_loadSVO (self)
	This function loads the transmission curve for the SVO format. More...

def	_normalize (self)
	This function normalizes the transmission curve after it has been loaded during construction, and attaches the appropriate astropy units (micron and 1/micron, respectively) It expects _bandname, _wavelengths, _transmissions, and _photoncounter to be set. More...

Private Attributes
	_bandname

	_photoncounter

	_transmissions

	_wavelengths

Static Private Attributes
dictionary	_bandinfo
	The band information dictionary described in the class header. More...

Detailed Description

An instance of the BroadBand class represents either a built-in standard broadband filter (including transmission curve data), a uniform filter over a specified wavelength range (with a constant transmission curve in that range), or a custom filter based on a given wavelength grid and transmission curve.

Refer to the constructor of this class for information on how to construct one of these two types of BroadBand objects.

Band properties and operations

This class offers operations such as determining the band's pivot wavelength and convolving an SED or a frame data cube with the band's transmission curve.

Refer to the appendix in Camps et al. 2016 (MNRAS 462, 1057-1075) for a brief introduction of the relevant concepts and a derivation of the corresponding formulas. For the purposes of this class, a band is defined through its arbitrarily scaled transmission curve \(T(\lambda)\). The relative transmission at a given wavelength can then be written as

\[ T_\text{rel}(\lambda) = \frac{ T(\lambda) } { \max[ T(\lambda) ] }. \]

Given a spectral energy distribution \(L_\lambda(\lambda)\), the mean specific luminosity over the band \(\left<L_\lambda\right>\) can then be obtained through

\[ \left<L_\lambda\right> = \frac{ \int L_\lambda(\lambda)T(\lambda) \,\mathrm{d}\lambda } { \int T(\lambda) \,\mathrm{d}\lambda }. \]

The pivot wavelength of the band is defined as the wavelength at which the mean specific luminosity can be properly converted between wavelength and frequency representations. It is given by

\[ \lambda_\mathrm{pivot} = \sqrt{ \frac{ \int T(\lambda) \,\mathrm{d}\lambda } { \int T(\lambda) \,\mathrm{d}\lambda/\lambda^2 } }. \]

The effective width of the band is defined as the horizontal size of a rectangle with height equal to the maximum transmission and with the same area as the one covered by the band's transmission curve. It is given by

\[ W_\mathrm{eff} = \frac{ \int T(\lambda) \,\mathrm{d}\lambda } { \max[ T(\lambda) ] }. \]

As set forth by Camps et al. 2016, for energy measuring devices (bolometers) the total system transmission \(T(\lambda)\) is usually given by the instrument designers, and it can be used directly for this class. For photon counters (including all instruments in the UV, optical and near infrared), the total system response \(R(\lambda)\) is usually given instead. The transmission curve needed for this class can be derived from the response curve through

\[ T(\lambda) = \lambda\,R(\lambda). \]

When applicable, this operation is performed by the constructor just after loading the response curve data from file.

Also, to further simplify the above formulas, the constructor normalizes the transmission curve to unity, i.e.

\[ \int T(\lambda) \,\mathrm{d}\lambda = 1. \]

Built-in bands

The table below lists the built-in bands available at the time of writing. The first column lists the complete band name; the second column indicates the corresponding pivot wavelength.

Band name	Pivot wavelength (micron)
2MASS_2MASS_J	1.2393
2MASS_2MASS_H	1.6495
2MASS_2MASS_KS	2.1639
ALMA_ALMA_10	349.89
ALMA_ALMA_9	456.2
ALMA_ALMA_8	689.59
ALMA_ALMA_7	937.98
ALMA_ALMA_6	1244.4
ALMA_ALMA_5	1616
ALMA_ALMA_4	2100.2
ALMA_ALMA_3	3043.4
EUCLID_VIS_VIS	0.71032
EUCLID_NISP_Y	1.0808
EUCLID_NISP_J	1.3644
EUCLID_NISP_H	1.7696
GALEX_GALEX_FUV	0.15351
GALEX_GALEX_NUV	0.23008
GENERIC_JOHNSON_U	0.35247
GENERIC_JOHNSON_B	0.44169
GENERIC_JOHNSON_V	0.55251
GENERIC_JOHNSON_R	0.6899
GENERIC_JOHNSON_I	0.8739
GENERIC_JOHNSON_J	1.2431
GENERIC_JOHNSON_M	5.0122
HERSCHEL_PACS_70	70.77
HERSCHEL_PACS_100	100.8
HERSCHEL_PACS_160	161.89
HERSCHEL_SPIRE_250	252.55
HERSCHEL_SPIRE_350	354.27
HERSCHEL_SPIRE_500	515.35
IRAS_IRAS_12	11.41
IRAS_IRAS_25	23.609
IRAS_IRAS_60	60.409
IRAS_IRAS_100	101.14
JCMT_SCUBA2_450	449.3
JCMT_SCUBA2_850	853.81
PLANCK_HFI_857	352.42
PLANCK_HFI_545	545.55
PLANCK_HFI_353	839.3
PLANCK_HFI_217	1367.6
PLANCK_HFI_143	2130.7
PLANCK_HFI_100	3001.1
PLANCK_LFI_70	4303
PLANCK_LFI_44	6845.9
PLANCK_LFI_30	10674
RUBIN_LSST_U	0.368
RUBIN_LSST_G	0.47823
RUBIN_LSST_R	0.62178
RUBIN_LSST_I	0.75323
RUBIN_LSST_Z	0.86851
RUBIN_LSST_Y	0.97301
SLOAN_SDSS_U	0.35565
SLOAN_SDSS_G	0.47025
SLOAN_SDSS_R	0.61756
SLOAN_SDSS_I	0.749
SLOAN_SDSS_Z	0.89467
SPITZER_IRAC_I1	3.5508
SPITZER_IRAC_I2	4.496
SPITZER_IRAC_I3	5.7245
SPITZER_IRAC_I4	7.8842
SPITZER_MIPS_24	23.759
SPITZER_MIPS_70	71.985
SPITZER_MIPS_160	156.43
SWIFT_UVOT_UVW2	0.20552
SWIFT_UVOT_UVM2	0.22462
SWIFT_UVOT_UVW1	0.25804
SWIFT_UVOT_U	0.34628
SWIFT_UVOT_B	0.43496
SWIFT_UVOT_V	0.54254
TNG_OIG_U	0.37333
TNG_OIG_B	0.43978
TNG_OIG_V	0.53729
TNG_OIG_R	0.63902
TNG_NICS_J	1.2758
TNG_NICS_H	1.6265
TNG_NICS_K	2.2016
UKIRT_UKIDSS_Z	0.88264
UKIRT_UKIDSS_Y	1.0314
UKIRT_UKIDSS_J	1.2501
UKIRT_UKIDSS_H	1.6354
UKIRT_UKIDSS_K	2.2058
WISE_WISE_W1	3.3897
WISE_WISE_W2	4.6406
WISE_WISE_W3	12.568
WISE_WISE_W4	22.314

Built-in band implementation

The hard-coded class dictionary _bandinfo maps the band name for all built-in bands to the information needed to load the corresponding transmission curve. The value tuple includes the following items:

the directory name (relative to this package's data directory), which also indicates the file format.
the name of the file from which to load the data, located in the specified directory.
additional information, depending on the format, or None if the format does not need extra information.

SVO

The band descriptions in the SVO directory were downloaded from the SVO filter profile service web site http://svo2.cab.inta-csic.es/theory/fps in XML format.

The last item of the value tuple in the _bandinfo dictionary is a Boolean flag indicating the type of instrument (because this information cannot be derived from the SVO file contents): the flag is True for photon counters and False for bolometers.

JCMT

The transmission curves for the SCUBA-2 450 and 850 micron instruments on the JCMT telescope were converted to a simple text column format from 'model450' and 'model850' data downloaded at http://www.eaobservatory.org/jcmt/instrumentation/continuum/scuba-2/filters/

The JCMT instruments are bolometers.

PLANCK

The PLANCK transmission curves are provided as a text column file for each of the following bands:

Band name	Frequency (GHz)	Wavelength (micron)
LFI 030	28	10600
LFI 044	44	6810
LFI 070	70	4260
HFI 100	100	3000
HFI 143	142	2100
HFI 217	222	1380
HFI 353	352	850
HFI 545	545	550
HFI 857	857	350

The PLANCK instruments are bolometers.

ALMA

The ALMA transmission curves are provided as a single text column file for all bands. ALMA sensitivity depends on the amount of water in the atmosphere, quantified by the precipitable water vapour (pwv) in mm. However, because we use only transmission curves normalized in each band, the effect of the pwv is minimal for our purposes. Somewhat arbitrarily, we opted to use the data for pwv = 0.2 mm.

The ALMA instruments are bolometers.

The last item of the value tuple in the _bandinfo dictionary specifies the wavelength range for each ALMA band supported here, so that we can select the appropriate portion of the transmission curve (provdided in a single file).

ALMA BAND	Frequency range (GHz)	Wavelength range (mm)	Wavelength range (micron)
1	31 - 45	unsupported	unsupported
2	67 - 90	unsupported	unsupported
3	84 - 116	3.57 - 2.59	2590 - 3570
4	125 - 163	2.40 - 1.84	1840 - 2400
5	162 - 211	1.84 - 1.42	1420 - 1840
6	211 - 275	1.42 - 1.09	1090 - 1420
7	275 - 373	1.09 - 0.80	800 - 1090
8	385 - 500	0.78 - 0.60	600 - 780
9	602 - 720	0.50 - 0.42	420 - 500
10	787 - 950	0.38 - 0.32	320 - 380

EUCLID and RUBIN

The Euclid and Rubin response curves are provided as simple text column files with wavelength in Angstrom. Some files include a lot of leading and/or trailing wavelength points with zero or very small transmission; our load function removes these points.

All Euclid and Rubin instruments are photon counters.

Constructor & Destructor Documentation

◆ init()

def pts.band.broadband.BroadBand.__init__	(	self,
		bandspec
	)

The constructor creates a BroadBand instance in one of the following three ways, depending on the type of the bandspec argument:

if bandspec is a string, it looks for a built-in standard broadband filter based on the text segments in the string, and then loads the corresponding transmission curve from built-in resources (residing in this package's data directory). To specify a band, it suffices to include just two segments of its name (case insensitive) that uniquely identify the band, seperated by an underscore or a space. For example, to select the HERSCHEL_PACS_100 band, one could enter "Herschel 100", "PACS 100", or "HERSCHEL_PACS_100".
if bandspec is a tuple with two numbers, a bolometer-type band is constructed with a uniform transmission curve in the indicated (min,max) wavelength range (expressed in micron).
if bandspec is a two-dimensional numpy.ndarray, a bolometer-type band is constructed using bandspec[:,0] as wavelength grid and bandspec[:,1] as transmission curve. The wavelengths are assumed to be expressed in micron, while the transmission curves are assumed dimensionless. The array layout used here is identical to what one would obtain when applying numpy.loadtxt() to the input file for a SKIRT FileBand.

If bandspec has a different type, or if its string contents does not unambiguously match a built-in band name, the constructor raises an exception.

Note: During the first part of construction, _wavelengths are initialized in micron but without explicit units, and _transmissions have arbitrary scale. Thus, these are plain numpy arrays, not astropy quantities. At the end of construction, the _normalize() function attaches the appropriate units.

Member Function Documentation

◆ _bandNameFromSpec()

def pts.band.broadband.BroadBand._bandNameFromSpec	(	self,
		bandspec
	)

private

This function matches the given band specification with all built-in band names, i.e.

the keys of the _bandinfo dictionary. If there is a single match, the corresponding key is returned. If there is no match, or if there are multiple matches, an exception is raised. To match a band name, a band specification must include just two segments of the band name (case insensitive). On both sides of the match, segments are separated by whitespace and/or underscores.