Displaying MAST Spectra

This tool displays selected spectra or light curves from missions archived within MAST. It uses the HTML5 Canvas API for drawing graphics. Canvas is supported by the latest versions of all popular browsers including IE 9, but it is NOT directly supported by IE 6,7 or 8. We are looking into adding support for these earlier IE versions using ExplorerCanvas . Let us know if this would be useful.

With Canvas and javascript, most of the plotting options can be run locally on the users computer and therefore can be executed fairly quickly. Reloading the page or clicking the "Start again" button will retrieve the data from the MAST web server, which takes a little longer, but allows you to return to the original display.

• Zoom - To zoom in on a particular region, click the mouse button and drag it across the desired region. You can drag the mouse right to left or vice versa. As you drag the mouse, a box will be drawn showing the region to be displayed. Releasing the mouse button will display the selected region and the min and max values shown above the plot will be updated. The zoomed-in region will be displayed in histogram mode to more accurately described the digitized data whereas the inital plot is drawn by just connecting points with straight lines. Note zooming with the cursor may not work properly if any part of the box region is outside the plot window. Also, if no points appear, click "Start again" to redraw the original plot.

• Changing plot limits - Besides zooming, the min and max X and Y axes limits can be specified manually by entering new values in the boxes provided. Unlike zooming using the mouse, one can zoom in or out by specifying new limits. To make a change, type in a new value and click return. The new plot range will appear without the page refreshing.

• Reading Cursor Positions - Moving the mouse across the plot window will display the X any Y positions of the cursor (in data units) just below the plot window.

• Scaling one plot to another - If more than one observation is plotted, a set of scale factors will appear just above the plot window. Changing the default value of 1.00 to another value and clicking return will scale the flux (y-axis) values for one plot with respect to the other(s). Typically small scale factors should be used so the modified values do not go beyond the plotted flux limits.

• Multiple Plots - Up to 30 observations can be coplotted however the more data points requested, the more memory is required and the longer it takes to download data from the server to your browser. Tests have shown plotting up to 900,000 data points is possible, but over 1,000,000 points may cause problems.

• Label Display - By default, the dataset name(s) are displayed in the upper right corner of the plot in the same color as the corresponding spectrum or light curve. The labels can be removed or re-added by clicking the On/Off buttons displayed on the plot page. Note that for Kepler plots where 2 light curves are displayed for each observation, the dataset name will appear in two different colors. Labels have not been added to the Kepler preview page though.

• Changing Selected Files - If you know the file names of observations from the same mission, and the plotted names appear on the plot page, it's possible to add or remove them from the plot without returning to the search form. Just change the name or names displayed in the "Selected File(s)" box and click "start again". More than one file can be specified using commas as delimiters. (Note however that this option may not be available for all plots.)

Tips

• Clicking "Start again" will replot the data and reset all parameters to their default values except for Kepler light curves for which the data type remains unchanged. Write down scale factors if you want to save them.
• For Kepler previews, clicking "Back to previous quarter" will display the previous page displayed in the same browser window.
• For spectra dominated by a few bright emission lines, it may be hard to zoom in on the continuum if it lies close to the minimum flux value. To make it easier to zoom in, first decrease the "Min Flux" value.
• When plotting multiple spectra, you can use the scale factor to help identify individual spectra. For example, changing a particular scale factor from the default 1.0 to 1.1 will cause that particular spectrum to stand out.
• To quickly remove a spectrum from a multi-spectrum plot, set its scale factor to 0.0. Resetting it to 1.0 or clicking "start again" will restore it. For more permanent removal, delete the file name from the "Selected File(s)" window. This will remove it until a new plot is drawn from the search results page.
• To save a plot, either click the "Create png image" button, or do a screen capture of the original page. Note the png image appears to have a black background but it will appear gray when you save it to disk. When printing, the background color will not appear. Note however that any displayed dataset names do not currently appear in the plot image.
• When plotting multiple spectra/light curves, widening the browser window slightly may help organize the scale factor list.

Source of Data

The data available for plotting comes from various sources. The files used for the various MAST missions are as follows:

• Kepler - Data is extracted from the online (public) FITS light curve files produced by the Kepler project. Bothe the PDCsap and the Sap Flux vectors are plotted by default.
• HST - FITS preview files created at CADC
• IUE - ASCII preview files created by NSSDC
  Note that small aperture observations will only be displayed when there is no corresponding large aperture observation. If both double aperture exposures are submitted for plottng, the large aperture spectrum is displayed twice.
• FUSE - ASCII preview files created by MAST(?)
• TUES - ASCII preview files created by MAST(?)
• BEFS - ASCII preview files created by MAST(?)
• EUVE - ASCII preview files created by MAST(?)
• WUPPE - ASCII preview files created by MAST(?)
• HPOL - ASCII preview files created by MAST(?)
• HUT - FITS "spectral container" files created by MAST
  Note: only the first HUT spectrum is plotted for those cases where two are stored in the same file.