IUE Search Output Columns

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

Data ID
IUE image identifier

The camera name plus a sequential number (e.g., swp16877) used to uniquely identify each IUE observation. The numbering began at 1000, but a handful of images with duplicated image numbers were reassigned with numbers in the 500's. Some image numbers were accidentally skipped as well.

Note that the value of this field is always 8 characters long. For sequence numbers less than 10000, the sequence number is padded with 0 e.g. SWP03456 or LWP00501.

If you enter an image sequence number for a target that has been classified as an "engineering" observation (Wavelength calibration, null, flat field, etc) with an object class of 98 or 99, you will need to select the object class 98 or 99 to see the entry, as these images are not included in the default search.

You may search on this field using a wild card (e.g. SWP1234* )

Clicking on the Image ID entries will display the IUE browse file page which includes:

• a plot of the calibrated fluxes versus wavelength,
• a list of selected keywords from the FITS file primary header,
• the program ID, proposal title and PI name, (the program ID is a link to a program page which includes link to the abstract for GSFC proposals).
• a list of published papers referencing the specific IUE observation,
• and links to:
  - a downloadable ASCII file of fluxes and wavelengths,
  - the IUE observing scripts,
  - the SI image browse file page, and
  - an abbreviated version of the FITS primary header
  (i.e., minus the vicar label and processing history).

Camera Number
Camera Number

The camera used in the observation. Approximate wavelength ranges:

Camera Number	Camera Name	Wavelength Range, Å
3	SWP	1150 - 1975
1	LWP	1850 - 3350
2	LWR	1850 - 3350

Camera 4 or the SWR camera was rarely used due to malfunction.

Image No
Image number

Sequential image number assigned to uniquely identify each image obtained. The numbering began at 1000, but a handful of images with duplicated image numbers were reassigned with numbers in the 500's. Some image numbers were accidentally skipped as well.

This is a numeric field. You may search on ranges of sequence numbers (e.g. 501..520 )

Target Name
Target Name

The Target Name name was assigned using the "preferred" NED or SIMBAD name where available. Otherwise the Name is a version of the "homogeneous" ID assigned by CDS for the IUE project.

GO Object Name
Object name

Object name as given by Guest Observer. Observers were encouraged to use the Henry Draper catalog designation for stars where appropriate, but a variety of names were used for many objects.

All alphebetic characters in this field are capitals, and if you select this field to search on you will need to use all caps. You may use a wild card search for this field e.g. *JUP*

Clicking on the entries in the Object name column of the search results page will display a plot of absolutely-calibrated flux versus wavelength (as originally produced by the staff of the Astrophysics Data Facility (ADF) at the Space Science Data Operations Office at Goddard Space Flight Center). Links to the SI browse image, a gzipped ASCII file of fluxes and wavelengths, and an ASCII file containing an abbreviated version of the FITS primary header, are also included on this page.

Dispersion
Dispersion

Dispersion mode used for the observation. High dispersion mode produces a two-dimensional echelle spectrum containing approximately 60 orders, with a resolution of roughly 0.2 Å. Low dispersion mode produces a single spectrum, or two if both apertures were used, with lower spectral resolution, approximately 6 Å.

The values of this column are HIGH and LOW.

Aperture
Aperture

Aperture used for the exposure. Each spectrograph has a pair of entrance apertures, consisting of a large approximatly 10 x 20 arcsecond oval and a small 3 arcsecond diameter circle. The image size at the focal plane is typically about 3 arcseconds for a point source. Spectra may be trailed along the large aperture. In addition, multiple exposures may be offset within in the large aperture to create a pseudo-trailed spectrum or series of time resolved spectra. The throughput of the small aperture varied significantly depending on the object centering and tracking, with a maximum throughput of about 60%. Thus most point-source spectra were taken using the large aperture. The aperture field is left blank only when the dispersion is not applicable (e.g. flat field images).

The values of this column are LARGE and SMALL.

Reference
Literature References

The ref column specifies the number of published papers referencing the listed IUE observation. A dash (i.e., "-") indicates that there are no known papers referencing the listed observation. Note that. the database is not complete (see details below). Clicking on an entry in this column (i.e., an entry other than a "-"), will display the list of referenced papers including title, primary author, and journal citation. The journal references use the ADS Bibliography code, and are links to the ADS Abstract Service.

The papers cited in the IUE reference database were primarily compiled by IUE staff member Pat Pitts, from 26 journals (see list below) published between 1978-1985, and 1990-1994. Publications from other years were completed by MAST staff members. In some papers, the specific observations that were used could not be determined.

• Astronomical Journal
• Astronomy and Astrophysics Supplement
• Astronomy and Astrophysics
• Astrophysical Journal
• Astrophysical Journal Supplement
• Icarus
• Bulletins of the Astronomical Institute of Czechoslovakia
• Canadian Journal of Physics
• Geophysical Research Letters
• Monthly Notices of the Royal Astronomical Society
• Irish Astronomical Journal
• Journal Of Geophysical Research
• Nature
• Moon & Planets
• Science
• Observatory
• Physica Scripta
• Proceedings of the Astronomical Society of Australia
• Proceedings of the National Academy of Sciences
• Publications of the Astronomical Society of Japan
• Publications of the Astronomical Society of the Pacific
• Review of Geophysics & Space Physics
• Revista Mexicana Astronomia y Astrofisica
• Royal Society Philosophical Transactions
• Advances in Space Research
• Astrophysics and Space Science

HLSP
High Level Science Products

The HLSP column specifies the number of high level or science ready data products are available that used this spectra. If the IUE observation was a double aperture exposure, the number will appear in the entry for both apertures. The information provided does not always specfy if both apertures were used or if only one of the apertures was used. Click on the number in the column to see a list of the projects using this spectra. The number indicates the number of products, not the number of projects, so if a project produced more than one product using the observation, all are counted.

Category or IUE Object Class
IUE object class

An IUE classification system used for categorizing IUE observations. The object class was specified by the Guest Observer; thus, one object may be archived under more than one object class. Note: by default, object classes 98 and 99 are excluded from queries. This can be over-ridden by specifying object class as one of the search criteria.

If you do not use the category selection on the main page, but choose to search on the category field using one of the "user-specified" fields, you will need to use the numeric number. (See the link above for the translation).

RA (B1950)
Object Right Ascension (B1950)

The right ascension, in the B1950 equinox, as specified by the Guest Observer. These values may not represent the precise pointing, since acquisition was performed in real time.

Dec (B1950)
Object Declination (B1950)

The declination, in the B1950 equinox, as specified by the Guest Observer. These values may not represent the precise pointing, since acquisition was performed in real time.

RA (J2000)
Object Right Ascension (J2000)

The right ascension, in the J2000 equinox, as specified by the Guest Observer. These values may not represent the precise pointing, since acquisition was performed in real time.

Dec (J2000)
Object Declination (J2000)

The declination, in the J2000 equinox, as specified by the Guest Observer. These values may not represent the precise pointing, since acquisition was performed in real time.

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.

Ecliptic Latitude

Ecliptic Latitude for the observation.

Ecliptic Longitude

Ecliptic Longitude for the observation

Galactic Latitude

Galactic Latitude for the observation.

Galactic Longitude

Galactic Longitude for the observation.

Obs Start Time
Observation date and time

The starting date and time of the exposure. Greenwich Mean Time (GMT) is used.

Program ID
IUE program identification code

Alphanumeric code identifying the observing program under which the observation was made. The program IDs were assigned for each episode of observing proposals. NASA, ESA, and SERC followed different naming conventions.

Clicking on a Program ID entry will return a page with information about the proposal, access to the abstract, a list of journal articles using data acquired for this program and a list of all IUE observations associated with the given program ID.

You may search on this field using wild cards (e.g. CS*AD) This can be useful as some US observers had multiyear programs with similar Program IDs

Trail Flag
Trail flag.

The trail mode indicates if the target was trailed along either the FES X-axis, the FES Y-axis, or not trailed.
Values for trailed exposures are:
Values for trailed are X (trailed along FES X-axis),
Y (trailed along FES Y-axis)
and N (not trailed).

Multiple Flag
Multiple flag.

This flag indicates the acquisition of multiple spectra in the large aperture. Multiple exposures result in 2 or more individual spectra spatially displaced from one another. The flag is set to indicate that these spectra were
displaced along the FES X-axis (flag set to X),
the FES Y-axis (flag set to Y),
the major axis of the large aperture (flag set to A)
or another configuration (flag set to O).
If the image does not contain multiple spectra, the flag is set to N.

Multiple spectra in the large aperture can be of the same object or of different objects. Multiple spectra may have been acquired by deliberately re-pointing the spacecraft for each separate spectrum or serendipitously, with a nearby object yielding an additional spectrum.

Segmented Flag
Segmented flag.

This value flags superimposed segmented spectra obtained by more than one commanded exposure. This situation may occur if no guide star is available for FES tracking during a long exposure and the target must be re-centered in the aperture or if the length of the exposure is greater than the maximum commandable exposure time (447 minutes). Segmented exposures result in a single spectrum, as opposed to multiple exposures flaged under the multiple flag.

Values for segmented are N (no) and Y (yes).

Primary Investigator Name
PI Name

Name of the Primary Investigator of the program for which the data were acquired.

Exposure Time
Commanded exposure length

The commanded integration time in seconds. The effective exposure time (which is the actual time used to derive the absolute fluxes) will differ somewhat depending on how the observation was obtained.

Trailed exposure times are not based on a commanded exposure time, but on the effective trail rate, the aperture size, and the number of passes through the aperture. The effective trail rate is derived from the commanded trail rate by applying an OBC quantitization correction.

EBV
Color excess

The color excess, E(B-V), of the observed object as given by the Guest Observer. Color Excess value not assigned for most VILSPA observations.

BV
Color index

The color index, B-V, of the observed object as given by the Guest Observer. Color index not assigned for most VILSPA observations.

Spectral Type
Spectral type

The MK spectral type of the observed object, as given by the Guest Observer. Not assigned for most VILSPA observations.

Luminosity
Luminosity

The luminosity of the observed object, as given by the Guest Observer. Not assigned for most VILSPA observations.

FES Mode
FES mode

The FES mode used during acquisition of the object. The two characters denote either fast or slow (F, S) track, and underlap or overlap (U, O) mode; e.g. FO means fast track, overlap.

FES Counts
FES counts

The FES counts recorded for the object during acquisition. The mode and counts can be used to compute an apparent FES magnitude, which may be converted to a visual magnitude.

FA Status flag
FA Status at MAST

The Final Archive status flag. If Final Archive data exists for the observation, the flag is set to F. Otherwise the field is null.

Raw Status Flag
Raw Status at MAST

This flag indicates if the GO format Raw data are archived at MAST. If available the flag is set to R otherwise it is null. Some data were lost at read or later lost or corrumpted in the archiving process at NSSDC.

SIPS Status Flag
IUESIPS Status at MAST

This flag indicates if the GO format IUESIPS extracted data are archived at MAST. If available the flag is set to S otherwise it is null.

Volume Number
Script Volume Number

The binder number the original observing script for GSFC observations was stored in. The GSFC Observing Scripts have been scanned and are now stored in directories by the original volume number.

Page Number
Script page number

The estimated "page number" for the original observing script. Used to help find and display the scanned GSFC observing scripts. The scripts are most easily found by clicking on the appropriate link of the IUE preview pages.

Comments
Comments

Comments about the raw image quality, recorded just after the data were read down. For Goddard images, the DN values for emission lines, continuum spectrum, and background level are recorded in the form E=nnn, C=nnn, B=nnn. VILSPA used a numerical code.

Img Type
Image type

The image type, used for data processing. S = single spectrum, D = double (large and small aperture) spectra, M = multiple (psuedo- trailed) spectra in the large aperture, L = multiple spectra in the large aperture plus a small aperture spectrum, B = single image with both dispersions used, each using a single aperture, and Y = single image with both dispersions with both apertures used for at least one of those dispersions.

UVC Voltage
UVC voltage

The voltage on the camera's Ultraviolet Converter during the observation. The LWR camera was operated at a reduced voltage of -4.5 kV after October 1983, reducing its sensitivity. The SWP and LWP were operated only at -5.0 kV, as well as the LWR before October 1983.

Lamp
Lamp

Lamp used during the observation. For most observations, no lamp was used. The possible entries are N (none), T (tungsten flood lamp), and U (UV-flood lamp).

Roll Angle
Spacecraft roll angle

The roll angle of the spacecraft during the observation. This may be used to compute the orientation of the apertures as projected on the sky.

Pos Angle
Position angle

The position angle of the large apertures during the observation.

Missing Minor Frames
Missing minor frames

Number of missing minor frames. Data lost during transmission to the ground occur in packets of 96 pixels (a minor frame of telemetry).

Microphonics
Microphonics

Microphonics affecting the image. This flag may be either N (no) or Y (yes). This was typically seen in the LWR camera as several lines of periodically corrupted data (a "ping"). Weak pings were seen on rare occasions on the SWP camera but are not flagged. In addition, early SWP images were contaminated with low-level microphonics due to intereference from the Panoramic Area Sensor, which was subsequently turned off.

Non-standard Image
Non-standard image

Non-standard image flag. Values are N (no) or Y (yes). If the image is flagged as non-standard, it was obtained using unusual camera parameters and may not be a useful image.

Bad Scan
Bad scan

Bad scan flag. Values are N (no) or Y (yes). The LWP camera experienced scan difficulties, primarily early in the mission. The command software was revised to detect the scan failure and recommanded the scan, possibly having some small effects on the data quality. The anomaly largely disappeared after the camera became the default long-wavelength camera in late 1983.

Heater Warmup
Heater warm-up time

Values range from 0 to 5 minutes. This technique to avoid microphonic noise on the LWR camera was used often after 1981, typically with a heater warm-up time of 4 minutes. By turning on the read beam, the camera warmed up and the "ping" typically occured before the image read began or high in the image where it did not affect the spectrum.

Read Mode
Read flag

Values are F (full) and P (partial). The technique of reading down just the portion of the image containing the low dispersion spectrum, i.e. the partial image, was used on rare occasions. The image was then embedded into a 768 by 768 pixel array before processing.

Lost Flag
Image lost flag

Image has been lost and is unrecoverable.

Values are:
N - RAW GO format data unreadable
R - RAW GO format data lost
U -
Y -

Only Raw Image Archived
"Copy Raw Image" flag

Values are N (no) and Y (yes). Some images were deemed to be not useful, and only the raw data were archived (in IUESIPS format). When possible, these data were later processed with the Final Archive Processing System (NEWSIPS).

Other
Other abnormal condition flag

Values are N (no), Y (yes), D (DMU corruption), and B (both DMU corruption and some other abnormality). DMU corruption of the camera data occurred very late in the mission on a sporadic basis.

FES-X
FES-X

Location of the guide star in the FES during the observation, given in FES units.

FES-Y
FES-Y

Location of the guide star in the FES during the observation, given in FES units.

Prep
Camera prep

Camera preparation sequence. Values are S (standard), XS (overexposed), X (XPREP only), N (N prep), F (fast prep), T (TPREP), and BAD (none or bad prep). Only images obtained with the S and XS preps are considered fully calibrated.

Effective Exposure Time
Effective exposure time

Effective integration time in seconds, used in deriving the absolute fluxes. The effective time is equal to the commanded exposure time corrected for camera rise time and camera exposure quantization for most exposures, or aperture length and trail rate quantization for trailed exposures. Note for multiple exposures in the large aperture, the absolute fluxes are based on the total of the individual effective exposure times.

V Magnitude
Visual magnitude

The visual magnitude of the observed object, as given by the Guest Observer for GSFC observations. For VILSPA observations, the magnitude was calculated.

Observing Station
Observing station

Values are VILSPA and GSFC (Goddard Space Flight Center). Some images were started at one station and read down at the other. The station that performed the read is considered to be the observing station. Usually NASA programs were observed from Goddard, and ESA and UK programs from VILSPA. However on occasion, usually due to pointing constraints, a NASA program was observed from VILSPA or vice versa.

Observer's Name
Guest Observer's name

The name of the IUE Guest Observer. Note that frequently the Guest Observer was different than the Principal Investigator to whom the observing time was awarded. As needed, names were truncated to 16 characters.

Track Mode
Track Mode

The spacecraft tracking mode. Values may be G (gyros), F (FES only), or B (both FES and gyros, used in the two gyro mode). In general, tracking with gyros was used only for short exposures or for moving targets, since better pointing stability could be maintained with FES tracking.

THDA at Read
THDA Read

Records the temperature of the camera head amplifier during the read of the image. Used in calibrations.

THDA at Start
THDA Start

Records the temperature of the camera head amplifier at the beginning of the exposure. Used in calibrations.

THDA at End
THDA End

Records the temperature of the camera head amplifier at the end of the exposure. Used in calibrations.

Focus
Telescope Focus

Values are on a unitless scale, where values of -1 to -2 are considered optimum out of a possible range of -12 to +8.

FPM
Background Radiation

Reading on the Flux Particle Monitor (FPM) at the beginning of the observation. Values range from 0.08 to 3.5. High radiation or radiation during a long exposure results in a high background level on the image. The flux monitor began to give occasional spurious reading starting May 14, 1991, and steadily became worse. It was useless by late September and was turned off Oct. 4, 1991.

IUESIPS Processing Date
IUESIPS Processing Date

The date that the IUESIPS version of the data were processed.

FA Date
The IUE Final Archive processing Date

The date that the NEWSIPS version of the data was processed.

Data Background
The background level.

The background level in DNs in the raw image, as estimated by the NEWSIPS processing algorithm.

Data Counts
Data Counts

The continuum level in DNs in the raw image, as estimated by the NEWSIPS processing algorithm.

Asym Ext Prof
The asymmetrical profile flag.

Indicates that the NEWSIPS processing software detected asymmetry in the spectrum perpendicular to the dispersion. May indicate a multiple source or extended source.

Num. Spline Nodes
The number of spline nodes.

For low dispersion images, indicates the number of spline nodes used in the SWET extraction algorithm. The maximum value used is 15, the minimum 3.

No. Bad Pixels
The percentage of bad pixels

The percentage of bad pixels as indicated by the nu flags in the SI image.

CC Percentage
Cross Correlation Percentage

The percentage of cross-correlations that were successful. For low dispersion images, typically 95% or more cross-correlations were successful. For high dispersion images, the success rate was often as low as 60% for well-exposed images.

CC Median
The median cross-correlation coefficient.

In general the best signal-to-noise ratio is achieved when this value is 0.7 or greater, i.e. there is a good match between the image and the ITF.

Mean Shift
Mean Shift

The mean shift between the image and the ITF, determined during the cross-correlation step. Mean shifts of 0.5 pixel or less tend to yield the best signal-to-noise ratio.

Max Shift
Max Shift

The maximum shift between the image and the ITF, determined during the cross-correlation step. Values greater than 1 pixel may indicate a large local distortion in the image, where the signal-to-noise ratio may be degraded.

Homogeneous Catalog
The homogeneous catalog ID.

The IUE Guest Observers used various object names and coordinates for the same objects, often making it difficult to find all the observations for a given object. To assist users, all objects observed by IUE have been assigned homogeneous data as provided by the Centre d'Donnee Stellaire (SIMBAD). The data include the catalog, object name, RA, and DEC.

Homogeneous Object ID
The homogeneous object name.

See above.

Homogenous Complimentary ID
The homogeneous complementary ID.

See above.

Homogeneous RA (B1950)
Homgeneous Right Ascension

The homogeneous right ascension of the observed object, in the B1950 equinox. See above. For extended sources, the coordinates are the center of the source.

Homogeneous Dec (B1950)

The homogeneous declination of the observed object, in the B1950 equinox. See above. For extended sources, the coordinates are of the center of the source

Homogeneous RA (B2000)

The homogeneous right ascension of the observed object, in the B2000 equinox. See above. For extended sources, the coordinates are of the center of the source?

Mark

Mark this image for retrieval from MAST or to use the coplotting utility.

To Retrieve:
After selecting the desired files, either click the "Download NEWSIPS files as a tar file" button, or click the "more retrieval options" button for more options.

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 Ångstroms) and minimum and maximum fluxes (in erg/cm2/sec/Å) 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 640 pixels.

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

Image Type
Image Type

Image Type assigned during Core Item Verification. Values include:
S - Single Exposure
D - Double Aperture Exposure (Two exposures - one in Large and one in the small aperture)
B - Double Dispersion Exposure
M - Multiple Exposure (more than one spectrum in large aperture)
L - Double Aperture Multiple Exposure (one exposure in the small aperture, multiple exposures in the Large. Y - Double Aperture, Double Dispersion Exposure

Data Type

Requests can be submitted for either IUESIPS or NEWSIPS files. NEWSIPS data types include:

• MX - extracted spectra (the default file type and most used)
• EXTRACT-FA - the extracted files and the spatially resolved image file from which the spectra are extracted,
• ALL-FA - all the files produced by NEWSIPS,
• SI - the spatially-resolved image files only,
• RI - the raw image files (withoput any corrections),
• LI - the linearized image file.

IUESIPS data types include:

• ME - extracted spectral files,
• EXTRACT - the extracted files plus the low dispersion spatially-resolved image files
• ALL - the entire set of IUESIPS-produced files,
• ELBL - the low dispersion spatially resolved image file only,
• RAW - the uncorrected raw image file.

NEWSIPS files are in FITS format while IUESIPS data is archived in IUE GO format and needs special software to be read. IUESIPS data however is also available in RDAF format (see below). In general, NEWSIPS data is recommended for most users.

Conversion Options

IUESIPS data can be requested in either GO or RDAF formats. The default format is GO. IUE RDAF software uses RDAF format files, however the IDL program GOTORDAF can be used to convert GO format files to RDAF format (see also RDAFTOGO).

File Download Options The current IUE file download options include:

Data Format:

• NEWSIPS - FITS files produced by the IUE New Spectral Image Processing System,
• IUESIPS_GO - IUE GO format files produced by the original IUE Spectral Image Processing System,
• IUESIPS_RDAF - IUESIPS-processed files in RDAF-format.

Data Compression Options:

• .tar - uncompressed files bundled in a tar file. (Note, prior to 10/21/99, the individual files were also gzipped by default.)
• .tar.gz - files are bundled into a tar files which is then compressed using gzip.
• .zip - files are bundled (and compressed) into a zip file,

Download times vary according to the number of CD's needed to be mounted in order to fulfill the data request. Users know when the request is completed when the browsers "Download window" disappears. Requests for a few files are normally completed in a couple of minutes.