NAME

magband -- Compute the average magnitude for a list of bandpasses

USAGE

magband spectra table output

PARAMETERS

spectra

The list of one-dimensional spectra to process. Any image template may be used.

table

The name of the file containing the table with the list of wavelength bandpasses. This is a text file with two columns. The first one is the bandpass wavelength, and the second the bandpass width. Both should be in Angstroms.

output

The output file name. If more than one input image is specified the output from the task is appended to this file.

format = "wide"

There are two possible output formats for the output file. If format=wide a multicolumn output is generated, where each column is one wavelength bandpass, and each line one image. if format=long a three column output is generated, where each column is the wavelength, magnitude and width of the bandpass, respectively. Each line is a different bandpass. The image name is specified in a separate line with a "#" sign in the first column, at the beginning of the bandpass list.

fnu = no

Is flux in units of f-nu ?. If this parameter is yes the spectrum are converted to f-lambda before computing the magnitudes.

convert = yes

Convert wavelengths in the image headers to Angstroms when they are in meters ? (i.e. when they are less than one).

flux = no

Output flux instead of magnitudes ?.

fnuzero = 3.68E-20

The absolute flux per unit frequency at a magnitude of zero. This is used to convert the calibration magnitudes to absolute flux by the formula

Flux = fnuzero * 10. ** (-0.4 * magnitude)

The flux units are also determined by this parameter. However, the frequency to wavelength interval conversion assumes frequency in hertz. The default value is based on a calibration of Vega at 5556 Angstroms of 3.52e-20 ergs/cm2/s/hz for a magnitude of 0.048. This is the same default value used in onedspec.standard .

interpolation = "standard"

Interpolation type. The interpolation types are linear for linear, poly3 for cubic polynomial, poly5 for quintic polynomial, spline3 for cubic spline, and standard for the same algorithm used by the task onedspec.standard (this is a linear interpolation).

start = "W0"

The name of the starting wavelengt keyword in the image header. Wavelengths are converted to Angstroms if they are in meters.

delte = "WPC"

The name of the wavelength increment keyword in the image header. Wavelengths are converted to Angstroms if they are in meters.

DESCRIPTION

First the task reads in the bandpasses table and stores it into memory. Then, for each image in the input list it computes the average magnitude, or flux, for each bandpass centered in the bandpass wavelength. Pixel values are interpolated if the boundaries of the bandpass are at fractional pixel values, according to the interpolation type selected. It is required that the input spectra are one-dimensional, and dispersion corrected. Otherwise they are skipped with a warning message. If a bandpass is totally or partially outside of a spectrum wavelength range, an INDEF value is printed as the magnitude for that bandpass. The output of the task is a text file with a multicolumn or multiline format. The second one is compatible with the input expected by the task onedspec.standard .

EXAMPLES

Compute the average magnitude for a list of five bandpasses, and output the results in two different formats. There is only one input spectrum in f-nu.

lo> type table
3509. 45.
4566. 45.
5840. 45.
6440. 45.
7782. 45.
8092. 45.

lo> magband fnu5501.imh table outw form="wide" fnu=yes
lo> type outw
Wavelen.   3509   4566   5840   6440   7782   8092 
Width        45     45     45     45     45     45 

fnu5501.  6.665  5.503  5.759  5.859  6.090  6.110 

lo> magband fnu5501.imh table outl form="long" fnu=yes
lo> type outl

# fnu5501. 
  3509  6.665     45 
  4566  5.503     45 
  5840  5.759     45 
  6440  5.859     45 
  7782  6.090     45 
  8092  6.110     45 

SEE ALSO

onedspec.standard