VLA FIRST
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:
Target - Either an RA, Dec set of numbers, or a target name
to be resolved by SIMBAD.
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.
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.
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