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calcphot stsdas.hst_calib.synphot


NAME · USAGE · DESCRIPTION · PARAMETERS · EXAMPLES · REFERENCES
SEE_ALSO

NAME

calcphot -- Calculate photometric quantities for synthetic spectra and passbands.

USAGE

calcphot obsmode spectrum form

DESCRIPTION

This task will calculate predicted count rates or fluxes in a given passband for a specified object. Other information such as average wavelength, full width at half-maximum, and rms wavelength can also be calculated. The output may be saved to an STSDAS table if desired.

PARAMETERS

obsmode [string]
This is a sequence of commands that create the synthetic passband. The commands can be placed in a file, whose name is passed to this parameter, preceded by a "@" character, e.g., @filename. Each line in this command file is treated as a separate set of commands.

Each command may either be a simple bandpass, which is represented by a comma separated string of keywords uniquely specifying an observing mode of the telescope, or a more complex command, described in the help file for calcband. The keywords which make up the observing mode are explained further in the obsmode task.

spectrum [string]
This is a sequence of commands that create the synthetic spectrum. The commands can be placed in a file, whose name is passed to this parameter, preceded by a "@" character, e.g., @filename. Each line in this command file is treated as a separate set of commands.

The commands that can be passed to this parameter are described in detail in the help file for the calcspec task.

form = photlam [string]
Desired output form for the calculation. The following forms are recognized:

	FNU		ergs / s / cm^2 / Hz
	FLAM		ergs / s / cm^2 / A
	PHOTNU		photons / s / cm^2 / Hz
	PHOTLAM		photons / s / cm^2 / A
	COUNTS		photons / s 
	ABMAG		-2.5 log_10 (FNU)  - 48.60
	STMAG		-2.5 log_10 (FLAM) - 21.10
	OBMAG		-2.5 log_10 (COUNTS)
	VEGAMAG		-2.5 log_10 (F/F_vega)
	JY		10^-23 ergs / s / cm^2 / Hz
 	MJY		10^-26 ergs / s / cm^2 / Hz

Note that if form = counts or obmag, the result will be integrated over the passband and normalized to the collecting area of the HST. If any of the photometric forms is specified the result of the calculation is the flux of the spectrum in spectrum observed in the mode obsmode in the units given by form. The task always calculates and displays the values of PIVLAM and FWHMLAM in addition to the quantity chosen by form.

A standard magnitude system is VEGAMAG, for which Vega by definition has magnitude 0 at all wavelengths. The AB and ST magnitude systems are based on constant flux per unit frequency and per unit wavelength, respectively. The zero points for these two systems are set for convenience so that Vega has magnitude 0 in both systems for the Johnson V passband.

(func = "effstim") [string]
The desired output function. The default value (effstim) calculates the predicted count rate or flux. This is the function most users of calcphot will wish to use.

The other function compute various functions of the product of the passband throughput and the spectrum. The spectrum is first converted into the units specified by the parameter form before computing the function, so results will be dependent on whether the form has frequency or wavelength units. The sole exception is the effective wavelength (efflerg), which is always calculated with the flux in units of "flam".

The "efflphot" function is deprecated. It is provided solely to facilitate comparisons with "efflam" results calculated by earlier versions of calcphot, which incorrectly implemented the Koornneef et al definition of effective wavelength.

	NAME		PARAMETER
	=======		=========
	EFFSTIM		effective stimulus   	(form)
	AVGLAM		average wavelength   	(Angstroms)
	BARLAM		mean log wavelength  	(Angstroms)
	FWHMLAM		FWHM bandwidth       	(Angstroms)
	RMSLAM		rms bandwidth        	(Angstroms)
	EFFLERG		effective wavelength 	(Angstroms)
	EFFLPHOT	(deprecated - see above)(Angstroms)
(vzero = " ") [string]
A list of values to substitute for variable zero. Each value in the list is substituted in turn for the string $0 wherever it occurs in the input spectrum. The values must be real numbers. Using vzero is the equivalent of placing the input spectrum several times in a file, with each spectrum containing one of the values in the list. The list may contain single values or ranges. The endpoints of the ranges are separated by a dash. An optional step size follows the range, preceded by the letter x. If the step size is not present, the step size defaults to 1 or -1, depending on the order of the endpoints. The following table gives several examples of valid lists
	.1,.2,.3,.4	A list of single values
	.1-.4x.1	The same list expressed as a range
	-1 - -4 	A range with an implicit step size of -1
	1-9,10-20x2	A list of more than one range
(output = "none") [file name]
Name of the table file in which to store results.

The name of the first column is COUNTRATE if the effective stimulus is computed. Otherwise, it is the name of the functional form. The names of the remaining columns are FORM, OBSMODE and TARGETID. There is one table row for each calculation performed. This table can be used as input to the plspec task and other tasks using the pfile (photometry file) parameter.

(wavetab = " ") [file name]
Name of an optional wavelength table or file. An appropriate table can be generated by using the genwave task. If a table is used, the wavelength column name must be "WAVELENGTH". If an ASCII file is used the first column is taken to be the wavelength column. The subdirectory 'synphot$data has ASCII wavelength tables useful for specific HST passbands.

If no wavelength table is specified, a default wavelength set is used. The default wavelength table covers the wavelength range where the obsmode and spectrum are non-zero. Wavelengths are spaced logarithmically over this range. If there is more than one obsmode and spectrum, the range is computed based on the first pair. If the wavelength range of the obsmodes and spectra differ significantly, a wavelength table should be specified explicitly.

(result) [real]
The result of the synthetic photometry calculation. This can be the observed flux of the spectrum in the observation mode or it can be an average wavelength. See the form parameter for valid forms to be calculated.

This parameter contains the result of the last calculation performed, so if several spectra or modes are given in a file, or a list of values for vzero is specified, then only the last calculation will be saved.

(refdata = "") [pset name]
Parameter set for reference data used in calculations. This pset contains the following parameters:

area = 45238.93416:  HST telescope area in cm**2.

grtbl = "mtab$*.tmg":  HST graph table.  By default, this
        uses the most recent version available. 

cmptbl = "mtab$*.tmc":  Instrument component table.  By 
        default, this uses the most recent version available.

EXAMPLES

1. Calculate the pivot wavelength, full width at half-maximum (FWHM), and the total flux (in counts per second) of a 5000 K blackbody in the WFPC F555W passband. The blackbody spectrum is renormalized to have a V magnitude of 18.6.

sy> calcphot "band(wfpc,f555w)" "rn(bb(5000),band(v),18.6,vegamag)" counts

2. Perform the same calculation, only use the abbreviated notation for the bandpass.

sy> calcphot wfpc,f555w "rn(bb(5000),band(v),18.6,vegamag)" counts

3. Calculate the pivot wavelength and FWHM of a 5000 K blackbody in both the WFPC F555W and F785LP passbands. Find the color difference (in instrumental magnitudes) of the blackbody in the two passbands for values of E(B-V) of 0.0, 0.25, and 0.5.

sy> calcphot "band(wfpc,f555w) - band(wfpc,f785lp)" "bb(5000)*ebmv($0)" \
>>> obmag vzero="0.0,0.25,0.5"

REFERENCES

Written by B.Simon based on XCAL code written by Keith Horne. Modified by V.Laidler. (effective wavelength modifications)

Koornneef et al, 1986, "Synthetic Photometry and the Calibration of the Hubble Space Telescope", Highlights of Astronomy vol 7

SEE ALSO

calcband, calcspec, countrate


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