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Ouput Field Help

This page describes the fields that may be returned by one of the HST Archive Search forms.

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.)

  1. 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.

  2. 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).

  3. 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.

  4. One numerical column can be plotted versus another using VOPlot although see the Help page regarding issues with the latest version of Java.

  5. For some missions, thumbnail images of the returned entries can be displayed by clicking the link listed just below the VOPlot link.

  6. The mark column, as described below, can be used to plot spectra and download files. Plots are now interactive with added features.

Column Information

You can press this checkbox to either mark a dataset for retrieval or to coplot selected spectra. Both functions are described below.

  • Retrieve Data - After you have marked for retrieval all the datasets that you're interested in, hit the Retrieve Marked Datasets for Retrieval button to initiate the retrieval.

    Proprietary datasets will have a @ character next to their mark buttons (and in some browsers will show up with a yellow background). Proprietary datasets can be marked and retrieved by appropriately authorized users. If you are a principal investigator and would like to retrieve your data (or would like to authorize one of your co-investigators to retrieve your data), contact us at

  • Plot Spectra - If you want to coplot multiple spectra from the seach results page (i.e., up to 15), click the checkboxes next to the datasets you are interested in, then hit the Plot marked spectra button to initiate the plotting process. The requested spectra will be displayed on a page with options to rescale the plot or rescale individual spectra. Note however that the listed datasets on the search results page may be a mixture of images, spectra without preview data, and spectra for which preview data is available. Only datasets in the last category can be plotted and all other selections will be ignored. One indication that preview data exists is to see if the entry in the "target name" field is linked. If the entry is not linked, no preview data exists. Also, NICMOS, FOC, and some STIS spectral data are not in a form that can be plotted, so these files will be ignored as well.

Users running Javascript-enabled browsers will see some buttons at the top and bottom of the search results labelled Mark all, Unmark all, etc. These buttons may be used to mark or unmark all of the datasets in the search results; mark or unmark only the proprietary datasets; or mark or unmark only the public datasets.

The name of the target of the observation, as given by the proposer. If the target name is hyperlinked, then a preview image or spectrum is available for that observation. Clicking on the target name in that case will bring up the preview form (which lets you select the format of the preview).

Occasionally, you will see target names like PAR, UNKNOWN-TARGET, and so on; these are (most likely) parallel observations, which are observations done by one instrument while another is making the primary observing of the telescope's visit.

The equatorial right ascension of the instrument aperture, in equinox J2000. (The output equinox selector on the search form doesn't work yet.)

(For the WFPC2, the aperture right ascension coincides with the V1 right ascension, which is the middle of the field of view.)

The equatorial declination of the instrument aperture, in equinox J2000. (The output equinox selector on the search form doesn't work yet.)

(For the WFPC2, the aperture declination coincides with the V1 declination, which is the middle of the field of view.)

V3 Position Angle
The V3 position angle (PA_V3) is the direction in degrees east from north that the tip of the L shape formed by the 3 WF chips would point, if the L shape is imagined to form the tip of an arrow. (see WFPC2 Position & Orientation). The V3 position angle is 180 degrees different (exactly opposite in direction) from the U3 position angle, which is specified by the observer during the Phase 2 proposal process as the "ORIENT".

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.

The HST instrument that performed the observation.

Operating Mode
The operating mode of the instrument that performed the observation.

Cent Wave
The central wavelength, in Ångstroms, of the observation. For images, this is the central wavelength of the filter used, while for spectra, it is midpoint of the wavelength range of the spectrum.

Exp Time
The exposure time of the observation, in seconds.

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. Note that because the literature references are based on proposal id, the specific data set(s) listed may not be cited in the references. Please also note that matching HST proposal ID's to published papers is an ongoing project and never completely up to date.

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

The ID number of the observing program. Clicking on an entry in this field will display the HST proposal search page containing the proposal title, PI's name, abstract, ads links to published papers, and a table of all known observations.

Start Time
The starting time of the observation (GMT).

Release date
The release date for the dataset, in GMT. HST data has a nominal proprietary period of one year (though in special cases, this may be shortened or extended). The Release Date field gives the end of the dataset's proprietary period. After this date, no special priveleges are required to retrieve the data.

Dataset Name
The unique identifier for an HST observation.

This value is hyperlinked. By clicking on it, you can bring up detailed information about the observation.)

Archive Class
Classes of data files in the HST Archive.

Program ID
THe SOGS Program ID for the proposal that requested the data.

Observation Set
The observation set within the program. This is usually the same as the visit number, though in a small number of cases it will be different. The obset ID is used as the fourth and fifth letters of a dataset name. You can enter a comma separated list here. If necessary, obset IDs will be padded with leading zeroes to two characters.

The Observation number from the SOGS header.

Obs Type
Type of observation: IMAGE or SPECTRUM.

Unique identifier assigned to association.

Target Description
A short description of the target, supplied by the observer. Like target names, these may not always be reliable- one observer's CLUSTER OF GALAXIES may be another's ELLIPTICAL- but they are generally better than nothing (especially where solar system objects are concerned; planet, asteroid, and comet names are more likely to be spelled out in the target description than in the target name).

Broad Category
The broad category to which the target for a given observation belongs, e.g. Star, Galaxy, Quasar, Planet

RA V1 (J2000)
Right Ascension at the V1 position.

Dec V1 (J2000)
Declination at the V1 position

Exp Flag
The exposure interruption indicator.

Stop Time
Time the observation stopped.

Instrument Configuration
Configuration of the Instrument

Name of the instrument configuration for this optical configuration, e.g.: - FOC/288 (F/288 FOC configuration) - FOS/RD (Red-range FOS detector).

Aperture - Concatenated identifier for the 1-4 aperture elements used in the given optical configuration.

Filters or Gratings used for the observation.

Concatenated identifier for the 1-4 spectral elements used in the given optical configuration.

Sepctral Res
Spectral resolution for this optical configuration (for spectra)

Spectrum End
Maximum wavelength for this HST spectrum

Spectrum Start
Minimum wavelength for this HST spectrum

Bandwidth of the data (STIS) or RMS bandwidth of the photmode (NICMOS and ACS).

The dispersion for an HST spectrographic observation.

Pixesl Res
Plate scale (arcsec/pixel)

FGS Lock
The commanded FGS lock (FINE, COARSE, GYRONS, UNKNOWN)

MT Flag
The moving target flag; T if it is a moving target.

PI Last Name
Last Name for the Primary Investigator.

Ecliptic Latitude
Ecliptic Latitude for the observation in decimal degrees

Ecliptic Longitude
Ecliptic Longitude for the observation in decimal degrees.

Galactic Latitude
Galactic Latitude for the observation.

Galactic Longitude
Galactic Longitude for the observation.

Sun Alt
Altitude of the sun above the Earth's limb (deg).

PA Aper
Position angle of aperture used with target.


Was COSTAR deployed at the tiem the dataset was obtained (T/F).

Indicator of observation type ( S=Science, C=Calibration ))

FOV Config/ra
Field of view configuration.

Generation Date
Date data came from OPUS.

Archive Date
Date data written to hard media in the archive.

Preview Name
Name of preview - usually the same as the data set name

Exposure Start Time
Exposure start time or start time of the 1st exposure in file (STIS)

Exposure Stop Time
Expsoure stop time or stop time of the 1st exposure in file (STIS)

Scan Type
observation mode, either staring (nominal) or spatial scan (target is trailed through the field of view). Values include \null - not a scan i.e. observation was taken in nominal staring mode, C - observation taken in continuous scan mode, D - observation taken in scan mode with a dwell.