to write the plot to the graphics buffer.
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Each group of an FOS or GHRS GEIS file contains the results of a separate subintegration. FOS readouts taken in ACCUM mode are cumulative, so the last group contains the results of the entire integration. In contrast, GHRS readouts and FOS readouts in RAPID mode are independent. If you want to see the results of an entire GHRS FP-SPLIT integration, you will need to align and coadd the spectra in the groups of the GHRS file as described in Volume 2 of this handbook. You can also combine all the groups in an FOS or GHRS data file, without wavelength alignment, using the rcombine task in the hst_calib.ctools package. See online help for details.
st> sgraph y3bl0104t.c1h[19]Given an input flux image (.c1h), the task fwplot (in the hst_calib.ctools package) will look for the corresponding wavelength (.c0h) file and plot flux versus wavelength. If requested, it will also look for the error (.c2h) file and plot the error bars. To see a plot of the same spectrum as above, but with a wavelength scale and error bars, type
st> fwplot y3bl0104t.c1h[19] plterr+If you ever need to plot the contents of multiple groups offset from one another on the same graph, you can use the grspec task in the graphics.stplot package. For example, to plot groups 1, 10, and 19 of a given flux file, you can type
st> grspec y3bl0104t.c1h 1,10,19Note that grspec expects group numbers to be listed as a separate parameter, rather than enclosed in the standard square brackets.
st> sgraph o43ba1bnm_x2d.fits[1][*,100:1000]Displaying the long-slit spectral image using the display task (see page 3-4) will allow you to see the range of your spectrum in x and y pixel space, so you can choose a suitable image section for plotting.
To plot STIS spectra in BINTABLE extensions, you first need to understand how STIS spectra are stored as binary arrays in FITS table cells. Chapter 2 (page 2-9) discusses this format and describes the selectors syntax used to specify these data arrays. Each row of a STIS echelle table contains a separate spectral order, and each column contains data of a certain type, such as WAVELENGTH data or FLUX data. To specify a particular array, you must first type the file name, then the extension containing the BINTABLE, then the column selector, then the row selector. For example, to select the WAVELENGTH array corresponding to spectral order 80 of the echelle spectrum in extension 4 of stis.fits, you would specify the file as:
stis.fits[4][c:WAVELENGTH][r:sporder=80]The sgraph task and the igi plotting package to be discussed below both understand the selectors syntax. In particular, if you wanted to plot the flux versus wavelength in STIS echelle order 80, you could type:
st> sgraph "stis.fits[4][r:sporder=80] WAVELENGTH FLUX"Remember to include the quotation marks. Otherwise, sgraph will complain about too many positional arguments. Note also that sgraph understands only row selector syntax; columns are chosen by name.
The STIS-specific echplot task is particularly useful for browsing STIS echelle spectra. It can plot single spectral orders, overplot multiple orders on a single plot, or plot up to four orders in separate panels on the same page. For example, to overplot the orders contained in rows two through four and row six on a single page:
cl> echplot "stis_x1d.fits[1][r:row=(2:4,6)]" output.igi \Note that the plot_style parameter governs how the spectral orders are plotted. The plot_style values s, m, and p plot one order per page, several orders on a single plot, and one order per panel, respectively. The default brightness unit is calibrated FLUX, although you can specify other quantities (e.g., NET counts) using the flux_col parameter. See the online help for details.
>>> plot_style=m
to write the plot to the graphics buffer.
Plots will be printed on the printer defined by the IRAF environment variable -stdplot. Type show stdplot to see the current default printer; use set stdplot = printer_name to set the default printer.
st> fwplot y3bl0104t.c1h[19] device=psi_landThe above commands would write a plot of flux vs. wavelength in landscape-mode into a temporary PostScript file, named /tmp/pskxxxx by a UNIX system. See the online help for more about psikern, including plotting in color and incorporating PostScript fonts into your plots.
st> gflush
/tmp/pskxxxx
.