1. Ingesting spectrograms into Specview

 

1.1 How to ingest spectrograms stored in files

The Read from file entry in the File menu should be used to ingest spectrograms stored in files, into Specview.

 

input_menu

The Read from file menu entry gives access to a file selector that enables the user to navigate the file system and select a file for input. The user can also type the file name (complete with path). The file is read, validated and if required, an instrument/format-dependent selector will pop up on screen to allow further selection on the file contents.

By default, the file selector will show directories, FITS files, IUE NEWSIPS files, text files, and display save files. FITS files are recognized by the suffix ".fits" in the file name. IUE NEWSIPS files are FITS format but have special suffixes such as ".mxhi" and ".mxlo". Text files are recognized by the suffix ".txt". GHRS/FOS file names are subject to special handling (see Sec. 1.6.5).

Bug: occasionally you may get an error message that looks like this:

[Fatal Error] XXXXXXXXXX: Content is not allowed in prolog.

This is harmless and apparently comes from some of the XML libraries, which refuses to turn off error reporting even when told to do so.

1.1.1 Display save files

Spectrograms can also be read via a display save file. See Sec. 2.16 for details

1.1.2 Web Services

The Read from Web Service entry gives access to a list of supported web services that provide spectral data. So far, only the Web Service at http://voservices.net/spectrum/ is accessible on an experimental basis. Only access via spectrogram ID is supported at this time. One types in the spectrogram ID number (e.g. 200000) and the data is retrieved and displayed.

 

This feature is disabled for now due to incompatibilities between the web service and Java 1.5-6.

1.1.3 File lists

The input file can be a text file which lists, one per row, actual file names, complete with full path, which store the spectrograms to be read. In this case, Specview will proceed in ingesting, but not displaying, all the files in the list that it can locate and understand. A progress window will show the file names as they are ingested. Upon finishing the list, Specview will stop and wait for a user command. Usually the user will then ask to plot from memory buffer (See Sec. 1.3).

Lists may be stored in both local files and remote locations pointed to by URLs. Also, files listed in the list can reside in both the local file system or in remote locations pointed to by URLs.

An input list must have its name necessarily ended by a ".txt" suffix. List names ended with other suffixes won't work because they cannot be validated throughout a URL connection.

Files that support multiple spectrograms per file must be entered in the list with all necessary information to locate the desired spectrograms within the file. The format to enter this information is instrument dependent, and is described under each one of the supported file formats below (see Sec. 1.6).

1.1.4 Virtual Observatory

Spectrograms from the Virtual Observatory can be read by Specview via the Read from VO entry in the file menu. See Sec 13.

 

 

1.2 Data Quality filtering at input time

Selecting Mask bad data on input in the Input menu (Sec. 1.1) will set the Data Quality filtering mechanism in Specview , from that point on, to automatically filter out all data points that have one or more flagged anomalies. “Bad” data points are ingested anyhow; they just won’t show up on display operations and won’t be used in data analysis operations.

 

At any time, flagged out data points can be brought back to life again by using the interactive Data Quality selector described in Sec 2.10.  With this selector it is possible to fine-tune Data Quality filtering to filter out selected, instrument dependent anomalies.

This functionality can also be selected from the command line (Sec. 8) and can be initialized from a preferences file (Sec 9).

Some specific file / instrument types may override these selections, in the sense that data read from these files will always have certain anomalies filtered out.

 

1.3 Accessing already read spectrograms

Once a spectrogram is read and displayed, it is kept in a memory buffer. Spectrograms can be recalled from that buffer for redisplay and / or processing.

 

The Display menu lists the available spectrograms in memory and allows one to display any one of them either in the main window or in a secondary window (Sec 2.3): 

 

 

window_menu

 

 

Bug: If the spectrogram name is too long, it won’t display. Use the Co plot/combine entry instead.

 

Either the Co plot/combine entry in the Display menu, or the Co plot menu in the main Specview menu bar, give access to an independent view of the memory buffer, displaying a spectrogram selector like this:

 

 

memory_buffer

 

Strings used to identify single spectrograms are composed of the file name plus additional information used to locate the spectrogram within the file. The specific format is instrument and file dependent.

Composite spectrograms (spectrograms composed of multiple internal spectrograms, such as echelle format) are represented by tree nodes that can be opened and closed. Opening a tree node causes the names of the internal members of the composite to be displayed. Again, the detailed format will depend on the spectrogram.

The tool tip displays information about the file contents. Right-click the mouse over the spectrogram identification string to get a more detailed view of the spectrogram contents.

Plot: Select the spectrogram you want to display and click the Plot/Coplot button.

Delete: Spectrograms can also be deleted from the buffer; just select their identifications and click the Delete button. Multiple selection is allowed with the Shift and Ctrl keys.

Note: internal members of a composite spectrogram cannot be individually selected for plotting or deletion.

 

1.3.1 Tiled plotting

Selecting multiple spectrograms in the memory buffer window and clicking the Tile button generates a tiled plot in a separate window. See Sec. 1.3.2 for a detailed description of the tiled plot mode.

 

Multiple selection is accomplished with the help of the Shift and Control keys, and can be system dependent.
 

 

 

1.4 Co plotting spectrograms

In the memory buffer selector window (Sec. 1.3), if you select more than one entry and click the Plot/Coplot button,, the selected spectrograms will be combined into a single composite spectrogram, and the result will be displayed and stored in the buffer as well.

 

The identification of such composite spectrograms will be usually comprised of the word “Coplot”, plus the contents of the TARGNAME keyword from the first file in the composite. Again, the exact form may depend on a number of factors.

 

Before being combined, the selected spectrograms will be checked for compatibility in their contents and physical units, and only the contents that are common to all selected entries will end up in the result.

Note that the end result of this operation is the same as you would have with a simple "over plot" function. That is, the spectral data in memory is not combined in any way, as it would be, say, by a spectrogram splicing algorithm. The raw data from the multiple input spectrograms is completely preserved in the resulting combination. It is just packaged "as is" within a single object so it can be plotted and eventually submitted to ulterior analysis as a single entity. The rationale behind this approach is that ideally one wants to perform measurements and fit spectral models to the original, raw data, not to a spliced or otherwise processed version of it.

Read in Sec. 1.5 how to apply a "true" combination algorithm to the selected spectrograms.

Input spectrograms can be expressed in different physical units and still be co-plotted. The only requirement is that their physical units be supported by Specview's internal units conversion mechanism (Sec. 1.7 and 7).

A drawback of the current implementation is that spectrogram data are not being weighted to account for differences in resolution and / or dispersion. Thus attempts to fit models to combined data that span a large range in dispersion or resolution will not give optimal results (in the sense of minimum chi-squared).

Multiple selection is accomplished with the help of the Shift and Control keys, and can be system dependent.
 

 1.5 Combining spectrograms

In the memory buffer selector window (Sec 1.3), if one selects one or more entries and clicks the Process button, a Processor Manager will be invoked. The processor applies a sequence of operations on the selected spectrogram(s), resulting eventually in a single spliced or co-added, and eventually low-pass filtered spectrogram.

 

The identification associated with such a spectrogram will be usually comprised of the word “Processed”, plus the contents of the TARGNAME keyword from the first file in the list submitted to the Processor Manager. Again, the exact form may depend on a number of factors.

 

Read more about it in Section 5.
 
 
   

1.6 Supported instruments and file formats

At this time, Specview supports all FITS files with 1-D spectroscopic data from HST instruments, as delivered by the Space Telescope Science Institute Archive. FITS files with 1-D data from a few other instruments / missions are also supported. Virtual Observatory SED-compliant files can be read, although at this time only limited support exists for this format. Specview also has the capability of ingesting spectrograms from plain FITS tables and from simple text based files. These options should allow users to input almost anything into it, including SED data and spectrograms from other sources and wavelength ranges.

 

FITS files can be gzipped as well. These are recognized by the file name suffix “.fits.gz”.

 

 


 

1.6.1 STIS 1-D extracted spectrograms

These are the files created by the CALSTIS pipeline (or alternatively by the stsdas.hst_calib.stis.x1d task) and which get the suffix _x1d.fits when delivered from the STScI Archive. They are multi-extension FITS files that store at each extension a binary table. Each table row stores a spectral order, and each spectral order contains several entries for wavelength, flux density, gross, net, background counts, data quality, errors, etc.

When the file is selected as described in Sec. 1.1, it is scanned and, depending on its contents, an interactive window is displayed to enable further interaction with the user.

STIS_1D_selector

The window contains an extension selector (that only shows up if the file has more than one extension – not the case in the above example) and a list with all spectral orders found in the table at the selected extension.  If the extension contains only one spectral order, no list is displayed. By selecting rows (with the help of the Shift and Control keys) and clicking the Go button, the spectrograms at each row are read and displayed. By clicking the All button, all rows in the table are read at once.

If the Coadd box is checked, the selected spectral orders are spliced together into a single entity before being displayed. Spectral orders are resampled to a common wavelength scale, and overlapping flux values at the end of each are coadded with matching flux values in neighboring orders. Error values taken from the error array are used as weights in the coadd operation. Note that in this mode the only array from the original file that is preserved in the ingested spectrogram is the flux array.

If, upon scanning the file,  Specview finds that it contains a single FITS extension, and the table in this extension harbors a single row (most likely from a first order grating or prism), the interactive window is skipped entirely and the spectrogram is ingested and displayed without further ado.

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL, suffixed with a string that includes a FITS extension selector, and a row selector. The FITS extension selector is just a one indexed value enclosed in square brackets. The row selector is a comma-separated list of numbers, zero indexed, also enclosed in square brackets. No co addition is supported. An example would be:
 

http://specview.stsci.edu/o47s01k9q_x1d.fits[1][0,1,2,17,18]

 

 Bug: Co added echelle spectrograms won’t save correctly to a display file (Sec. 2.10). Reading such files will cause an exception to be thrown.

 

 

1.6.2 STIS 2-D rectified spectrograms

These are the files created by the CALSTIS pipeline (or alternatively by the stsdas.hst_calib.stis.x2d task) and which get the suffix _x2d.fits when delivered from the STScI Archive. They are multi-extension FITS files that are organized into IMSETs. An IMSET is a set of three FITS image extensions that store flux, error and data quality information associated with a single spectral order.

When the file is selected as described in Sec. 1.1, it is scanned and a interactive window is displayed to enable further interaction with the user.

STIS_2D_selector

The user must select a single IMSET (multiple selection is disabled) and hit one of the Go buttons to read the spectrogram.  Spectrograms stored in these files are still in two-dimensional format, and some kind of collapse into a 1-D format must be performed at this point to allow ingestion into Specview.  The user has the option to read all  image lines present in the IMSET to add them together into a single 1-D array. Or alternatively, read a given number of lines about the center line and collapse them. Or, read from a specific bottom line up to a specific top line. The Top and Bottom windows show initially the range available in the selected IMSET.

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL, suffixed with a string that includes an IMSET selector and an image section. The IMSET selector is a square bracket enclosed set of two values, the IMSET name (always "SCI") and the IMSET position in the file. The image section follows the IRAF syntax for image sections (but without the stride argument. An example would be:
 

http://specview.stsci.edu/o47st01060_x2d.fits[SCI,1][*,*]

 

 

1.6.3 ACS

Specview provides support for files generated by the aXe 1-D extraction tool developed at the HST ECF ( http://www.stecf.org/software/axe/).  Support for these files in Specview is still under development; expect possible changes in future versions.

These are FITS files with multiple extensions. Each extension stores the extracted information at a particular location in the grism image. When the file is selected as described in Sec. 1.1, it is scanned and an interactive window is displayed to enable further interaction with the user. If the file stores a single spectrogram in a single FITS extension, this step is not executed and Specview proceeds directly to read and display the spectrogram data.
 

ACS_selector
 

Multiple selections are allowed, and are displayed simultaneously in a single plot window.

The command-line and list entry syntax for a file of this type requires a file name with full path and preceded by an eventual URL, suffixed with a one indexed FITS extension selector. An example would be:
 

http://specview.stsci.edu/acs_grism.fits[1]

 

1.6.4 COS

Albeit being structured as a table with two or three rows (one row per detector segment), these files store a single spectrogram, thus they are ingested as soon as selected by the file selector (Sec 1.1). The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

/data/obi-wan3/busko/data//l61hm1a30_x1d.fits

 

1.6.5 GHRS / FOS

Spectrograms from both GHRS and FOS instruments are delivered by the STScI Archive in a very similar format. Each spectrogram is spread out into up to four FITS files. The files have standard suffixes that identify their contents:

The wavelength and flux files are mandatory; both the error and data quality files are optional and are ingested if found. The file selector (Sec. 1.1) will not show the wavelength, error and data quality files. The user selects the desired flux file and Specview automatically handles the suffixes and looks for the other files. If at least the wavelength file is found in the same directory where the flux file is, the files are scanned and the user is presented with a interactive window that allows selection of one or more exposures. These exposures correspond to the groups in the GEIS format these spectrograms where originally stored in.
 

GHRSFOS_selector

Only one exposure can be selected.

The command-line and list entry  syntax for a file of this type includes the file name with full path and preceded by an eventual URL, suffixed with a one indexed FITS extension selector. An example would be:
 

http://specview.stsci.edu/y31r01037_c1f.fits[2]


Notice that the suffix must correspond to the flux file ("_c1f" in this example). FITS extensions replace the concept of "groups" used earlier with GEIS files.
 
 

1.6.6 IUE MXHI

These files share a very similar format with the STIS 1-D extracted echelle spectrograms (Sec. 1.6.1). The main difference is that there is always only one FITS extension, thus the FITS extension selection does not show up on the interactive window. The operation is identical with the STIS case, including the co add option. The command-line and list entry syntax for a file of this type is also almost identical with the STIS 1-D case, except that a FITS extension selector is not required.. An example would be:
 

http://specview.stsci.edu/swp37399.mxhi[0,1,3,4,8,23]


A notable point is that the file name suffix is not ".fits", despite the file being in FITS format.

Note that the generic table reader discussed in Sec. 1.6.16 can read old format IUESIPS files.

 Bug: Co added echelle spectrograms wouldn’t save correctly to a display file (Sec. 2.16). Reading such files will cause an exception to be thrown.

 

1.6.7 IUE MXLO

These files store a single spectrogram, thus they are ingested as soon as selected by the file selector (Sec. 1.1). The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

http://specview.stsci.edu/lwp02019.mxlo


A notable point is that the file name suffix is not ".fits", despite the file being in FITS format.

Note that the generic table reader discussed in Sec. 1.6.16 can read old format IUESIPS files.

 
 

1.6.8 FUSE

These files store a single spectrogram, thus they are ingested as soon as selected by the file selector (Sec. 1.1). The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

http://specview.stsci.edu/p211010200100all2ttagfcal.fit

 

Both old and new (3.0) files are supported. BUT NOT YET CALFUSE 3.14.

 

1.6.9 SDSS

These files store a single spectrogram, thus they are ingested as soon as selected by the file selector (Sec. 1.1). The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

http://specview.stsci.edu/spSpec-52282-0328-001.fits

 

SDSS files contain information about the radial velocity of the source. Thus they can be displayed in either observed or rest wavelengths. The selection is performed with the X axis control in the display window (Sec. 2.2).

 

1.6.10 ISO - LWS

Spectrograms from the ISO LWS instrument obtained in single-scan high resolution mode (LSAM  LWS01 files only) can be ingested by Specview. When a file of this type is selected by the file selector (Sec. 1.1), the file is scanned and an interactive window is displayed to enable further interaction with the user.  

ISOLWS_selector

The window contains a list with segments. These are spans of data that belong to a unique combination of detector, scan direction, and scan count (respectively columns LSANDET; LSANSDIR and LSANSCNT in the LSAM file). Each segment spans a wavelength range whose end points are listed in microns. By selecting segments (with the help of the Shift and Control keys) and clicking the Go button, the data from each segment are read and displayed. By clicking the All button, all segments in the table are read at once.

By default, data points that have any of the status flags set, are removed from the initial plot. They can be displayed with the use of the interactive Data Quality selector (Sec. 2.10). In some circumstances, an entire segment may be masked out; this will show as INDEF entries in the MINW and MAXW columns.

If the Coadd box is checked, the selected segments are co added together into a single entity before being displayed. Segments are resampled to a common wavelength scale, and overlapping flux values are coadded with matching flux values in other segments. Error values taken from the error array are used as weights in the coadd operation. Note that in this mode the only array from the original file that is preserved in the ingested spectrogram is the flux array.

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL, suffixed with a segment selector. This segment selector is a comma-separated list of segment indices, zero indexed, enclosed in square brackets. No coaddition operation is supported. An example would be:

http://specview.stsci.edu/ISO/lsam72400204.fits[0,1,2,24,38]

 

If no segment selector is provided, the entire file is read at once. Note that the segment indices are  not stored in the table itself, they are built on the fly by Specview when working in interactive mode.

Bug: ISO spectrograms won’t save correctly to a display file (Sec. 2.16). Reading such files can cause an exception to be thrown.

 

1.6.11 ISO - SWS

Quick look spectrograms from the ISO SWS instrument  (SSP files) can be ingested by Specview. When a file of this type is selected by the file selector (Sec. 1.1),  the file is scanned and, depending on the file contents, either an interactive window is displayed to enable further interaction with the user, or the file contents are displayed at once.

The interactive window is similar to the one depicted above for the ISO-LWS files, and is built in a similar way. The coadd option is also supported. The interactive window will be displayed for AOT types S02, S06, and S07. Files with AOT type S01 will be displayed as a single spectrogram.

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes and co add option are supported. An example would be:
 

file:C:/data/ISO/SWS/ssp35400352.fits

 

Bug: ISO spectrograms won’t save correctly to a display file (Sec. 2.16).

 

1.6.12 ISO - PHT

Quick look spectrograms from the ISO PHT instrument  (PSP files) can be ingested by Specview. When a file of this type is selected by the file selector (Sec. 1.1),  the file is scanned and displayed at once.

For now, only files with AOT names P03 (multi-filter photometry) and P40 (spectrophotometry) are supported.

 

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

file:C:/data/ISO/PHT/psp07901912.fits

 

 

Bug: ISO spectrograms won’t save correctly to a display file (Sec. 2.16).

 

 

 

1.6.13 FORS

 

These files store a single spectrogram, thus they are ingested as soon as selected by the file selector (Sec. 1.1). The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

http://specview.stsci.edu/FORS2/ M144_990652_40_370wgc.fits

 

Note that some of these files are not flux calibrated. They can be displayed in raw form but further processing can be quite limited.

 

1.6.14 2dF

These files store a single spectrogram, thus they are ingested as soon as selected by the file selector (Sec. 1.1). The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

http://specview.stsci.edu/2dF/test1.fits

 

Note that these files are not flux calibrated. They can be displayed, but only a limited set of operations can be performed with them.

 

1.6.15 FITS tables generated by STScI's Archive preview

The STScI Archive generates preview spectra for HST instruments in a FITS table format. Specview can directly ingest these files by just selecting the file name on the file selector window (Sec. 1.1).

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. No suffixes are supported. An example would be:
 

http://specview.stsci.edu/preview.fits

 

1.6.16 Generic FITS tables

Spectrograms stored in "generic” FITS tables can also be read by Specview. If Specview detects a FITS table file but cannot recognize it as belonging to any of the formats described above, it will nevertheless scan the file, looking for column and row information. Only "flat" (as opposed to "array") columns will be recognized as valid. Multiple extension files are supported.

 

Once the file scanning is complete, Specview will either read the spectrogram right away, or display a selector window that enables the user to pick the two columns to be interpreted as wavelength and flux, respectively.  The spectrogram is read immediately in case the table has only two columns, and the first colun has associated to it a valid (supported) wavelength units (see Sec. 1.7).

generic_fits_selector

Clicking on the Go button causes the data from the selected columns to be read, and the spectrogram so defined to be displayed.

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. The file name ends with in a ".fits" suffix, plus a FITS extension number (1-indexed) enclosed in square brackets. After that, a square bracket enclosed set of two blank-separated strings represents the column names of respectively the wavelength and flux arrays. An example would be:
 

http://specview.stsci.edu/myfile.fits[1][WAVE FLUX]

 

 

Bug: under Windows, the widget above may display empty. If that happens, just resize it a little bit to force a redraw.

 

1.6.17 Text based format

This format is mostly appropriate for reading SED data, or other spectral data that does not come from any of the supported instruments above, but nevertheless can be cast into a simple text table..

A text based spectrogram consists of an ASCII file whose name ends with the suffix ".txt".

The first line in the file must store the object's name.

The second and third lines store the physical units of the wavelength and flux density, respectively. They must be spelled as described in Sec. 1.7.

From the 4th line on, each line stores a spectral datum in free format, comprised of two or three floating point values separated by blank spaces. The first value is the wavelength/frequency/energy, the second is the monochromatic flux density, and the optional third is the error associated with the flux density. Both fixed point and scientific notation (with E, e, D, d) are recognized.

The error value can be entered either as an absolute value or as a percentage of the flux value. In this case, the numeric value must be posfixed with a ‘%’ character. The two alternate error forms cannot be mixed in a single file.

Comments can be added anywhere by preceding the comment with the character '#'. Text will be ignored from that point up to the end of the line.

Here is a simple example, where a single data point was commented out:

# Photometry and radio measurements taken from Veron & Veron AGN catalog.
#
NGC3516
nm
Jy
# 60000000  0.004 0.0
550       0.04  0.0
440       0.03  0.0
360       0.01  0.0

The number of data points that can be input with this format is limited to 200,000. Data points must be ordered in either ascending or descending wavelength/frequency/energy order.

Note that data delivered from the STScI archive in preview form (ASCII table) for other instruments (IUE, HUT, EUVE etc) can generally be input to Specview with minimal editing of  the supplied table.  Below is an example of a HUT preview file edited for input into Specview. The only changes are the inclusion of the comment character '#' in the header lines (except object name !), and the inclusion of appropriate wavelength and monochromatic flux density units.

#
# File produced by MAST     14-Nov-2000 12:53:07.00
#
# Object =
NGC3516
# Instrument = ASTRO-2 HUT
# Exposure time (sec) = 1819.98
# GMT obs. date (dd/mm/yy) = 13/03/95
# Obs. start time (ddd:hh:mm:ss) = 072:01:37:51
# Door configuration = 5
# Aperture wheel position = 7
# Day/Night = N
# Wavelength scale (A) = 814.020 + 0.518830*n for n=0,2047
#
Angstrom
erg/s/cm^2/Angstrom
#
 814.02001953125  -3.1851100000E-15 3.70038000000E-16
 814.538879394531 -3.1824600000E-15 3.69713000000E-16
 815.057678222656 -3.1798000000E-15 3.69388000000E-16
 815.576538085938 -3.1770900000E-15 3.69117000000E-16
 816.095336914063 -3.1743800000E-15 3.68791000000E-16
 816.614196777344 -3.1717800000E-15 3.68466000000E-16
 817.132995605469 3.98168000000E-15 5.20081000000E-15
  817.65185546875 -3.1664100000E-15 3.67870000000E-16
 818.170654296875 3.97501000000E-15 5.19203000000E-15
 818.689514160156 7.53808000000E-15 6.34827000000E-15
 819.208312988281 4.04950000000E-16 3.67436000000E-15
 819.727172851563 7.52545000000E-15 6.33760000000E-15
 820.245971679688 4.04245000000E-16 3.66818000000E-15
 820.764831542969 7.51282000000E-15 6.32702000000E-15
 821.283630371094 -3.1478700000E-15 3.65701000000E-16
...
...
...

The command-line and list entry syntax for a file of this type includes the file name with full path and preceded by an eventual URL. An example would be:
 

http://specview.stsci.edu/hut.txt



 

1.6.18 Virtual Observatory SED documents

This format is self-descriptive. If the document resides in the local file system, its file name must end with a “.xml” or “.vot” suffix.

 

Support for such documents in Specview ‘s current version is still limited to most (but not all) features described in version 0.92 of the IVOA SED Data Model. 

 

An arbitrary SED document will probably be read correctly and result in some displayable spectrogram. However, some information in the input document may be ignored (e.g. curation and frame metadata).

 

Currently Specview only supports the VOTable serialized form of the SED Data Model. FITS serialization will be available in a future version.

 

 

1.7 Physical units

To take advantage of Specview's internal units conversion mechanisms and spectrogram combining functionality, input spectrograms must be expressed in one of the standard physical units listed below:

Wavelength / frequency / energy / wavenumber:

Monochromatic flux density:


Spectrograms expressed in other units, or with no units at all, will be ingested and displayed, but further operations may not be available.

There is some leeway in the spelling of the units strings. The implementation tends to follow the precepts described in Standards for Astronomical Catalogues: Units, CDS Strasbourg (http://vizier.u-strasbg.fr/doc/catstd-3.2.htx).

Specview also accepts the spelling forms found in all of the supported file formats. For instance, STIS 1-D files have flux density units spelled as erg/s/cm**2/Angstrom using a non-recommended, longer form. Capitalization is also ignored, and in some cases a final ‘s’ (as in Angstroms or Watts) is also ignored. Spelling forms defined in the IVOA SED Data Model document are also supported (mostly).

 

1.7.1 Intensity units

There is in place a prototype mechanism that provides limited support for intensity units (such as used by model or theoretical spectra). In normal use, Specview will not recognize such units as valid. This is legacy behavior caused by the original requirement that mandated Specview to be primarily a visualization tool for Hubble Space Telescope observational data.

 

However, if two conditions are met, Specview will be able to recognize intensity units as valid, and operate with them.

 

The first condition is that the intensity units in the input files are spelled exactly as explained above for flux density units, but with an additional/srsuffix.

 

The second condition is that the user set in her preferences file (see Sec. 9) the optional IntensityUnits property to true.

 

In this mode, Specview will be able to handle only data expressed in intensity units; flux density units will not be recognized as valid.