standard input [records] output
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.
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.
? 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!
observatory, lcalib, sensfunc,