EUVE Search Output Columns

This document defines the catalog entries describing the EUVE DS/S Science Archive as delivered to STScI and other archive sites by the EUVE project. Most of the documentation below was provided by Mark Abbott from the EUVE GO Center.

Archive Background:

Each EUVE observation has a nighttime part and some also have a daytime part. For each part, the observational data consists of two FITS files, one containing events and one containing images. Both FITS file contains multiple image and binary table extensions.

There is a limit to the size of a single observation that we could process. This was due both the processing limitations and to limits on how big the resulting FITS file or a given event list could be and still be practical to work with. Observations which exceeded that size were split in two pieces, normally at the mid-point between the start and end times of the observation. The two pieces were then processed as if they were separate observations. They are recognizable as back-to-back observations of the same target in the catalog, with no gap between them. Users will typically always want both pieces in such a situation.

Certain observations, usually pointed surveys or maps of diffuse objects, were carried out as a large number of individual pointings along a grid or line on the sky. The complete set of pointings were too large to fit into a single field-of-view of the EUVE Deep Survey telescope. Also, overlaying the pointings would make exposure determination very difficult without access to event lists and therefore reduce the usefulness of the image part of the archive. Therefore those observations were split into one piece for each pointing and the pieces were treated as separate observations. They will appear in the catalog as many consecutive, short observations of the same target. Users will typically want all the pieces.

General Results Options

Most mission search results pages have the following general features/options. (Note that the sorting, paging and VOPlot options all require JAVASCRIPT to be supported and turned on, and the interactive plotting option uses HTML5 which is not supported in Internet Explorer before version 9.)

Clicking on the column headings at the TOP of the results table will sort the returned results based on the selected field. Clicking the column heading a second time will sort the results in descending order. As of August, 2014 sorting is now possible with RA and Dec coordinates in sexigesimal notation, and the previous bugs whereby exponents are ignored in numbers using exponential notation (e.g., 6.3E-3 is sorted as if it were 6.3), and signs were ignored in floating point numbers have both been corrected. Note however that the sort functions (like many interactive features) are written in javascript which is not always supported in older browsers. Alternatively, selecting the sort options in the initial query does not depend on javascript, and will sort the entire search result, not just the displayed rows.
Clicking one of the column headings at the END of the results table (or clicking the "columns help" link at the top of the page) will display help information about the search results page and the displayed columns (i.e., this page).
By default, results are shown with 500 entries per page, with links to additional pages if more than 500 entries were returned. The number of rows per page can be modified using the "Records per Page" form element on the search form. The total number of entries returned is set by the "Maximum Records" value from the search page.
One numerical column can be plotted versus another using VOPlot although see the Help page regarding issues with the latest version of Java.
For some missions, thumbnail images of the returned entries can be displayed by clicking the link listed just below the VOPlot link.
The mark column, as described below, can be used to plot spectra and download files. Plots are now interactive with added features.

Column Information

Mark

Mark this image to use the coplotting utility.

To Coplot:
After selecting up to 15 observations to be plotted, click on the "Plot marked spectra" button to coplot the selected observations.

The spectra that you selected will be automatically scaled to the full range of wavelengths and nearly the full range of fluxes (i.e., y axis plot scale runs from 0 (or .25 * the minimum flux for spectra with negative fluxes) to the 10th highest flux). Each spectrum is automatically assigned a color, up to a maximum of 15. The spectra are labelled by their dataset names, with a summary of the datasets plotted given below the plot. After inspecting the plot, you may wish to change the selection of datasets which are displayed. Use your browser "Back" button to do this.

Plot range
Adjust the minimum and maximum wavelengths (in \305ngstroms) and minimum and maximum fluxes (in erg/cm2/sec/\3 05) to select the spectral region of interest and to exclude noisy data.

Plot dimensions
Adjust the X size and Y size in pixels to create the size of plot desired. The maximum dimensions are 850 by 64 0 pixels.

Redraw plot
Use this button to replot the spectra when you have changed the plot range or plot dimensions.

Data ID

The unique identifier for an EUVE observation. EUVE data ids contain the target name, observation date and a character indicating if the target was taken in the night (N) or day (D) part of the orbit. Examples of data ids are: am_her__9808040924N and comet_hale-bopp__9411201903N.

Target Name

The name of the astronomical object. This is the official name under which targets were processed for the EUVE Archive. It is not necessarily the name under which the target was originally proposed or observed. A single name was consistently used thoughout the archive for targets which were observed more than once.

Observation Start Time

This is the GMT time, to the nearest second, of the start of the observation. The target name and observation date together serve to uniquely identify each EUVE observation. (Note the first EUVE observation was obtained in June, 1992.)

Day/Night

Entries will contain either the word "night" or "day" indicating which part of the observation is being cataloged. Some observations will have both parts, others will only have a night part.

RA (J2000)

Object's Right Ascension in J2000 coordinates specified in hours, minutes, and seconds. These values were used as the Right Ascension of the source when processing the data. These are not necessarily the same as the coordinates used to point the spacecraft during the observation. They are typically either taken from SIMBAD (with proper motions applied) or were supplied by the Guest Observer. The same coordinates were used throughout the archive for multiple observations of the same source except in certain special cases. Note for moving targets, these are the mean of the ephemeris coordinates during the observation.

Dec (J2000)

Object's declination in J2000 coordinates specified in degrees, minutes, and seconds. These values were used when processing the data, and are not necessarily the same as the coordinates used to point the spacecraft during the observation. They are typically either taken from SIMBAD (with proper motions applied) or were supplied by the Guest Observer. The same coordinates were used throughout the archive for multiple observations of the same source except in certain special cases. Note for moving targets, these are the mean of the ephemeris coordinates during the observation.

Exposure Time

This is the median exposure for a given observation. There are four EUVE detectors which normally collect data simultaneously during an observation. Each detector will have a different exposure time. In this field are listed the median of the exposures of the individual detectors, (in units of kiloseconds unless seconds were requested, and rounded off to the nearest kilosecond or second). Note that sometimes one detector can be way off from the others and skew this number, or an observation can be very short producing an exposure time of zero. For the true exposure times you need to look in the headers of the images.fit extensions.

Observer

The name of the PI of the proposal which has been associated with this observation in the CEA database. This is not always a very meaningful field, because many times multiple proposals (and PIs) were given simultaneous data rights to the target in the same observing cycle. In that case, only one of the PIs is listed here. The observer is listed as "EUVE" for targets which were scheduled as calibration targets. However, for most calibration targets, there was also a PI to whom the data was proprietary; unfortunately, our archive does not contain these PI names for calibration targets.

Reference

The number of known literature references associated with the listed proposal ID. Clicking on an entry in this field (other than a "-") will display a list of references with links to the online ADS papers.

High-Level Science Products

The number of High-Level Science Products associated with this particular observation.

Program ID

EUVE Program ID The Project did not connect the program IDs with the observations. Using proposals, and proposal target lists provided by the EUVE Project, MAST staff were able to match most of the observations with a proposal. The remaining observations were mostly taken for project purposes.

Total Size

This is the summed size of the events.fit and images.fit files for this part of this observation, in kilobytes. The events normally consume a lot more space than the images.

Object Category

This is a broad category for the target. Values include:

wd - white dwarfs
late - late-type stars
early - early-type stars
cv - cataclysmic variables
ex - extragalactic objects
ss - solar system objects
pulsar - pulsars
pn - planetary nebulae
noid - unidentified
lmxb - low-mass X-ray binaries
snr - supernova remnants
grb - gamma-ray bursters
other - none of the above

Spectral Type

The spectral type and luminosity class of the observed star. Generally the spectral type is a measure of the star's temperature. Spectral type is designated using the Morgan-Keenan spectral classification system, and is specified as one of ten letters (OBAFGKMRNS) followed by a number from 0 to 9 designating subdivisions. The hottest stars observed are generally around type O3. Spectral type is not appropriate for non-stellar objects (e.g., galaxies, planets, etc.), so the field may be left blank. Luminosity class is designated using the Morgan-Keenan luminosity classification system, and is specified by a Roman numeral from I to VI, with finer subdivisions indicated by an appended a or b. Ia represents the most luminous class.

Old Filename

Old EUVE Archive ID number (gonum): this is the old ID number the target was assigned in the now obsolete EUVE spectral browser and archive. Notice that there is not a one-to-one correspondence between the old archive and the new one, so some targets have more than one ID number associated with them and other IDs are used by multiple targets. The old ID might be of use for historical purposes or for users who know the old ID of a target they want. EUVE has stopped assigning ID numbers to publically released targets as of the Feb. 1, 1998 release.

Release (i.e., Public) Date

This is the date on which an observation becomes public. If this field is blank, the target is already public. If there is a date present, the target is still proprietary to its Guest Observer and should not be made public until the indicated date. EUVE releases data on monthly intervals. Targets observed in Cycles 1-4 of the EUVE Guest Observer program have one year proprietary periods. In Cycle 5 (which began in 1997) and later, the period is six months. The period begins when the data is delivered, not when it was observed, and we sometimes make exceptions if there was a problem with the data delivery, etc., so the public dates cannot be inferred from the data itself. Also, some EUVE observations are done in parts over an extended period of time; the proprietary period is determined from the delivery date of the last part.

Angular Separation

The angular separation in arcminutes between the observation and the search center (the coordinates you're searching on). This is calculated during the search, and the search results are sorted in order of increasing angular separation. It has the nice effect of sending parallels to the bottom of the list. (If you're interested in the parallels, you can sort the list in descending order of angular separation.)

It also means that you can give a search radius like, say, 2 .. 8 to find all observations between 2 and 8 arcminutes from some position. This could be used, for example, to exclude observations of the nucleus of a galaxy, or the central star in a planetary nebula.

Data Files

Each EUVE observation has a nighttime part and some also have a daytime part. For each part, the observational data consists of two FITS files, one containing events (EVT) and one containing images (IMG). Both FITS file contains multiple image and binary table extensions. A third file is now available containing the extracted spectral data (SPEC). This file was produced by Damian Christian as follows:
" EUVE spectra were extracted automatically using the the euvextract routine in the IRAF euv.euvred package and the archive 2-D images. These spectra are suitable for most analyze, but investigators should be warned that background subtraction may not be optimal for extended sources or sources requiring the highest signal to noise." These invesigators are encouraged to re-extract their spectra from the 2-D images."
The extracted spectra were merged into a single file and stored in a one-row binary table FITS format following the SSAP standard adopted by the VO community. Clicking on the "SPEC", "IMG" or "EVT" entry will result in downloading the spectral, image or event file, respectively. Warning: some browsers will try to display the file rather than downloading it. In these cases, try holding down the SHIFT KEY while clicking the left mouse button. If this still doesn't work, try clicking the second or third mouse button instead.

Note the EUVE IMG and EVT files can be rather large (i.e., up to 200 MB) and may take several minutes to download.