standard input [records] output
input
List of input standard star spectra or root names if using the record number
extension format. All spectra of the same aperture must be of the same
standard star. In beam switch mode or when the same star parameter is set
all spectra must be of the same standard star regardless of aperture number.
records (imred.irs and imred.iids only)
List of records or ranges of records to be appended to the input spectra
names when using record number extension format. The
syntax of this list is comma separated record numbers or ranges of record
numbers. A range consists of two numbers separated by a hyphen.
A null list may be used if no record number extensions are
desired. This is a positional query parameter only if the record
format is specified.
output
The name of a text file which will contain the output from standard.
Each execution of standard appends to this file information about the
standard stars, the calibration bandpasses, and observed counts (see the
DESCRIPTION section for more details). The output must be explicitly
deleted by the user if the filename is to be reused.
samestar = yes
Is the same star in all apertures? If set to no then each aperture may
contain a different standard star the the standard star name is queried
each time a new aperture is encountered. Note that this occurs only
once per aperture and multiple spectra with the same aperture number
must be of the same star. If set to yes the standard star name is only
queried once. When in beam switch mode this parameter is ignored since
all apertures must contain the same star.
beam_switch = no
Beam switch the spectra? If yes then a beam switch mode is used for the spectra
in which successive pairs of object and sky observations from the same aperture
are sky subtracted. This requires that the object type flag OFLAG be present
and that the spectra are appropriately ordered. All object observations must be
of the same standard star and the samestar parameter is ignored.
apertures =
List of apertures to be selected from the input list of spectra. If no list
is specified then all apertures are selected. The syntax is the same as the
record number extensions.
bandwidth = INDEF, bandsep = INDEF
Bandpass widths and separations in wavelength units. If INDEF then the
default bandpasses are those given in the standard star calibration
file. If values for these parameters are specified then a default set
of bandpasses of equal width and separation are defined over the range
of the input spectrum. In both cases the default bandpasses can be
changed interactively if desired.
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 default value is that used in earlier versions of this task which did not allow the user to change this calibration.
extinction =
Extinction file used to make second order extinction corrections across
the bandpasses. The default value is redirected to the package
parameter of the same name. See lcalib for a list of standard
extinction files.
caldir = )_.caldir
Calibration directory containing standard star data. The default is
redirected to the package parameter of the same name. A list of
standard calibration directories may be obtained by listing the file
"onedstds$README"; for example:
cl> page onedstds$README
The user may copy or create their own calibration files and specify the directory. The directory "" refers to the current working directory.
observatory = )_.observatory
Observatory at which the spectra were obtained if not specified in the
image header by the keyword OBSERVAT. The default is a redirection to look
in the parameters for the parent package for a value. The observatory may
be one of the observatories in the observatory database, "observatory" to
select the observatory defined by the environment variable "observatory" or
the parameter observatory.observatory, or "obspars" to select the
current parameters set in the observatory task. See help for
observatory for additional information.
interact = no
If set to no, then the default wavelength set (either that from the star
calibration file or the set given by the bandwidth and bandsep
parameters) is used to select wavelength points along the spectrum where the
sensitivity is measured. If set to yes, the spectra may be plotted
and the bandpasses adjusted.
graphics = stdgraph
Graphics output device for use with the interactive mode. Normally this is
the user's graphics terminal.
cursor =
Graphics cursor input for use with the interactive mode. When null the
standard graphics cursor is used otherwise the specified file is used.
star_name
The name of the star observed in the current series of spectra. Calibration
data for the star must be in the specified calibration directory "caldir".
This is normally a interactive query parameter and should not be specified on
the command line unless all spectra are of the same standard star.
answer
Interactive query parameter.
? Display help page a Add a new band by marking the endpoints d Delete band nearest the cursor in wavelength r Redraw current plot q Quit with current bandpass definitions w Window plot (follow with '?' for help) I Interrupt task immediately :show Show current bandpass data
DESCRIPTION Observations of standard stars are integrated over calibration bandpasses and written to an output file along with the associated calibration fluxes from tabulated calibration data. The output data is used by the task sensfunc to determine the detector sensitivity function and possibly the extinction. The spectra are required to be dispersion corrected. The input spectra may be in either "onedspec" or "echelle" format and may have many different observation apertures. The spectra may also be beam switched and use the a record number extension format.
The input spectra are specified by a list of names or root names if using the record number extension format. In the latter case each name in the list has each of the specified record numbers appended. A subset of the input spectra may be selected by their aperture numbers using the parameter apertures. The spectrum name, aperture number, and title are printed to the standard output. The airmass is required but if absent from the image header it may be computed from the observation header parameters and the latitude task parameter (normally obtained from the observatory task).
The name of the standard star is obtained by querying the user. If the parameter samestar is yes or beam switch mode is selected then all spectra are assumed to be of the same standard star and the query is made once. If the parameter is no then a query is made for each aperture. This allows each aperture to contain a different standard star. Note however that multiple observations with the same aperture number must be of the same standard star.
If the standard star name is not recognized a menu of the available standard stars in the calibration directory, the file "standards.men", is printed and then the query is repeated. Thus, to get a list you can type ? or help.
The standard star names must map to a file containing tabulated calibration data. The calibration filename is formed from the star name with blanks, "+",and "-" removed and converted to lower case and the extension ".dat" added. This name is appended to a calibration directory, so the directory name must have an appropriate directory delimiter such as "$" or "/". Generally one of the system calibration directories is used but one may copy and modify or create new calibration files in a personal directory. For the current working directory the calibration directory is either null or "./".
The calibration files consist of lines with wavelengths in Angstroms, calibration magnitudes, and bandpass widths in Angstroms. The magnitudes are converted to absolute flux per unit frequency using the parameter fnuzero defined by
Fnu = fnuzero * 10. ** (-0.4 * magnitude)
Thus, fnuzero is the flux at magnitude zero. The flux units are determined by this number. The default value was chosen such that Vega at 5556 Angstroms has a magnitude of 0.048 and a flux of 3.52e-20 ergs/cm2/s/hz. This is the same value that was used by all previous versions of this task.
The beam switch mode is selected with the beam_switch parameter. This mode requires that all apertures are of the same star, the header keyword OFLAG be present to identify object and sky spectra, and that the sequence of spectra specified are paired such that if an object spectrum is encountered first the next spectrum for that aperture (spectra from other apertures may appear in between) is a sky spectrum or the reverse. These restrictions are not fundamental but are made so that this mode behaves the same as with the previous version of this task. The sky spectrum is subtracted from the object spectrum and the result is then used in generating the observed intensities in the calibration bandpasses.
If the spectra have been extinction corrected (EX-FLAG = 0) the extinction correction is removed. The specified extinction file is used for this operation and so must be the same as that used when the extinction correction was made. The airmass is also required in this step and, if needed to compute the airmass, the observatory specified in the image or observatory parameter is used. The treatment of extinction in this task is subtle. The aim of this task is to produce observed integrated instrumental intensities without extinction correction. Thus, the extinction correction is removed from extinctionn corrected spectra. However, a correction is made for an extinction gradient across the bandpasses. This is done by applying an extinction correction, integrating across the bandpass, and then correcting the integrated intensity for the extinction at the center of the bandpass. An alternative way to look at this is that the integral is weighted by the ratio of the extinction correction at each pixel to the extinction correction at the center of the bandpass. This correction or weighting is why the extinction file and latitude are parameters in this task even though for nonextinction corrected spectra they appear not to be needed.
The observed instrumental intensities are integrated within a set of bandpasses by summing the pixels using partial pixels at the bandpass edges. Initial bandpasses are defined in one of two ways. A set of evenly spaced bandpasses of constant width covering the range of the input spectrum may be specified using the parameters bandwidth and bandsep in the same units as the spectrum dispersion. If these parameters have the value INDEF then the bandpasses from the calibration file which are entirely within the spectrum are selected. Generally these bandpasses are the actual measured bandpasses though one is free to make calibration files using estimated points. The calibration bandpasses are preferable because they have been directly measured and they have been placed to avoid troubles with spectral lines. However, when the coverage or resolution is such that these bandpasses do not allow a good determination of the instrumental response the evenly spaced bandpasses may be needed. The calibration fluxes are linearly interpolated (or extrapolated) from the calibration data points to the defined bandpasses.
Each spectrum adds a line to the output file containing the spectrum image name, the sky spectrum image name if beam switching, the aperture or beam number, the number of points in the spectrum, the exposure time, airmass, wavelength range, and title. If the airmass is not found in the image header it is computed using the latitude parameter and observation information from the header.
Following the spectrum information, calibration data is added for each bandpass. The bandpass wavelength, absolute flux (per Angstrom), bandpass width, and observed instrumental intensity in the bandpass are added to the output file. As discussed above, the observed intensity does not include an extinction term but does apply a small correction or weighting for the variation of the extinction across the bandpass.
The setting and editing of the bandpasses may be performed interactively if the interact flag is set. In this case the user is queried for each spectrum. The answers to this query may be "no" or "yes" to skip editing or edit the bandpasses for this spectrum, "NO" or "YES" to skip or not skip editing all spectra of the same aperture with no further queries for this aperture, and "NO!" or "YES!" to skip editing or edit all spectra with no further queries.
When editing the bandpasses a graph of the spectrum is made with the bandpasses plotted at the computed intensity per pixel. The cursor and colon commands available are summarized in the section CURSOR KEYS. Basically bandpasses may be added or deleted and the current bandpass data may be examined. Additional keys allow the usual windowing and cursor mode operations. When satisfied with the bandpasses exit with 'q'. The edited bandpasses for that aperture remain in effect until changed again by the user. Thus if there are many spectra from the same aperture one may reply with "NO" to queries for the next spectra to accept the current bandpasses for all other spectra of the same aperture.
1. To compile observations of three standard stars using a beam switched instrument like the IIDS:
cl> standard.recformat=yes cl> standard nite1 1001-1008 std beam_switch+ interact- [nite1.1001][0]: HZ 44 - Night 1 [nite1.1004][0]: HZ 44 - Night 1 [nite1.1005][0]: HZ 44 - Night 1 [nite1.1008][0]: HZ 44 - Night 1 Star name in calibration list: hz 44 cl> standard nite1 1009-1016 std beam_switch+ interact- ... cl> standard nite1 1017-1024 std beam_switch+ interact- ...
This will create a file "std" which will contain sensitivity measurements from the beam-switched observations of the three standard stars given. Note that standard is run separately for each standard star.
The spectra will be from the images: nite1.1001, nite.1002 ... nite1.1024, and the default calibration file, "onedstds$irscal.dat" will be used.
2. For echelle spectra all apertures, the orders, are of the same star and so the samestar parameter is set. Usually the resolution is much higher than the calibration data so in order to get sufficient coverage bandpasses must be interpolated from the calibration data. Therefore the evenly spaced bandpasses are used.
cl> standard.recformat=no cl> standard.samestar=yes cl> standard ech001.ec std bandwidth=10 bandsep=15 [ech001.ec][0]: Feige 110 Star name in calibration list: feige 110 [ech001.ec][0]: Edit bandpasses? (no|yes|NO|YES|NO!|YES!): yes [ech001.ec][1]: Edit bandpasses? (no|yes|NO|YES|NO!|YES!): yes [ech001.ec][2]: Edit bandpasses? (no|yes|NO|YES|NO!|YES!): NO!
STANDARD V2.10
Giving an unrecognized standard star name will page a list of standard
stars available in the calibration directory and then repeat the
query.
observatory, lcalib, sensfunc,