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MAST Image Access via Aladin

This page describes how to use Aladin to access images stored in the Multimission Archive at the Space Telescope Science Institute (MAST).

More Information on Available MAST Images

The data that are accessible are listed below by Mission/Instrument. Under each instrument is a description of the filters and associated wavelengths (bandpass).

Note that the HST images available via Aladin are preview images prepared by our colleagues at CADC. Generally these images (stored in FITS format) are resampled to a smaller size, but provide a good representation of the full data.

Click on the insturment name link to find out more information about the instrument and associated filters. The data available through this interface currently include HST imaging instruments (ACS, NICMOS, WFPC2, STIS, FOC, WF/PC). The Galaxy Explorer (GALEX) data, the ASTRO/UIT data, VLA-FIRST images, and High-Level Science Products are also included in this tool.


High-Level Science Products (HLSP) HLSP are fully processed (reduced, co-added, cosmic-ray cleaned etc.) images that are ready for scientific analysis. At this writing all the HLSP available through this service are from ACS, WFPC2, and FOC. See the instrument section for more information about those instruments.

Galaxy Explorer (GALEX)

GALEX has a microchannel plate detector and images between 1,350 - 2,800 Å GALEX has a 1.2 sq. degree field of view and 5"/pixel resolution. GALEX began operations in 2003. GALEX obtains direct images in the near_UV (NUV) and the far-UV (FUV).

Name Effective
FUV 268 269
NUV 616 732

This information was taken from the GALEX FAQ. Please consult this FAQ and other documentation found on the GALEX webpages for additional information about the GALEX instrument.

ASTRO Ultraviolet Imaging Telescope (UIT)

UIT consisted of an f/9 Ritchey-Chretien telescope with an aperture of 38 cm. Two detectors covered the near-ultraviolet and far-ultraviolet wavelength ranges from 1200 to 3300 A. The far-ultravilet (FUV) camera's intensifier had a CsI photocathode, while the near-UV (NUV) camera had a Cs2Te photocathode. Six filters were available for each camera. Magnetically focussed two-stage image intensifiers produced images that were recorded on 70 mm film (Kodak IIa-O). The resulting images cover a 40 arcmin field of view, with a resolution of 3 arcsec. For comparison, the Wide Field Camera #2 on HST has much smaller field of view, 2.5 arcmin x 2.5 arcmin, with a higher resolution of about 0.1 arcsec. UIT acquired data for 259 targets during 2 shuttle missions (12/90 & 3/95).

UIT filters. The "A" filters were sensitive in the near-UV while the "B" filters were sensitive in the Far-UV. The near-UV camera was only operational for the ASTRO-1 flight.
Name Effective wavelength FWHM
A1 2488 Å 1147 Å
A2 1892 Å 412 Å
A3 1964 Å 173 Å
A4 2205 Å 244 Å
A5 2558 Å 456 Å
A6 Grating  
B1 1521 Å 354 Å
B2 1359 Å 160 Å
B3 1445 Å 256 Å
B4 1585 Å 129 Å
B5 1615 Å 255 Å
B6 1497 Å 404 Å


    The final images from FIRST, produced by coadding the twelve (or sometimes more) single-field pointings adjacent to each pointing center, have 1.8" pixels, a typical rms of 0.15 mJy, and a resolution of 5". At the 1 mJy source detection threshold, there are ~90 sources per square degree, ~35% of which have resolved structure on scales from 2-30".

    Note that the images are fairly large, typically 1150x1550 pixels = 7.1 Mbytes to cover a 34.5 arcmin x 46.5 arcmin = 0.45 square degree area of the sky. A 10 pixel strip at the top of each image contains a copyright notice.

    Help using Aladin

    Available Image Manipulation Tools

    Aladin offers a variety of image manipulation tools including histogram calculation, color mapping, contour plotting blinking, zooming, etc. Click on the HELP button on the main Aladin window to find out more about these features.

    Using Aladin with MAST

    Aladin is accessed in 2 different ways within the MAST web site:
    • from the HST and UIT preview pages Aladin displays a particular image,
    • from the "Searches-tools" pulldown menu Aladin is called without any input image and the user must search and select the image for download.
    In either mode, clicking the "LOAD" button will display the Aladin Server Selector window and allow other images to be displayed. On this page, click on "MAST" in the left column under image servers and follow the directions below in
    Using the MAST Search Form.

    One limitation of using applets is the limited memory they are allowed. Since the applet actually runs on the users computer, the memory allowed is determined by the users browser. Users may find larger images (e.g. GALEX images) are cropped when displayed for this reason. See the specview page on java plugin memory size for information on increasing available memory.

    Users may also want to consider installing a stand-alone version of Aladin which would run as a java application on their own computer. MAST data can be retrieved in the same way as described here. See the CDS page on downloading Aladin for more information.

    Using the MAST Search Form

    Clicking on "MAST" in the Aladin Server Selector window, displays the MAST Search form. This is actually an interface to the MAST SIAP service and allows searches on all MAST missions and High level Science Products containing images in FITS format. The 3 search options currently available include:

    1. Target - Either an RA, Dec set of numbers, or a target name to be resolved by SIMBAD.
    2. Radius - Search radius (actually half the width of a square region) in arcminutes. By default, arcminutes are assumed, but values can also be specified as, for example, 1.0 deg or 5". Rectangular search regions can also be specified as "w x l". The default search area is a square with a half width of 14' (i.e., a square 0.28' x 0.28'). Note that for most Aladin image servers, a cone search is performed with a default radius of 14'. Setting the search parameters for one server, sets the same values for all. For rectangular searches, a circle inscribing the rectangle is calculated for cone searches.
    3. Mission/Instrument - Specifies which MAST mission or instrument should be searched. The default is to search "all" which includes all HST instruments, all High Level Science Prodcuts, GALEX, VLA-FIRST and UIT. Selecting individual missions or instruments may result in faster searches. Note many of the High Level Science Products only cover small portions of the sky.

    Clicking "SUBMIT" will begin the request and results will be displayed within the gray window. Results are sorted by filter names and show the data set name and image size. Clicking on an entry brings up another window showing information about the data set. The image can be displayed either by clicking the "LOAD" button in this window, or double clicking the entry in the search results window.