This graphic shows an example of how the Hubble Source Catalog was
constructed for a small part of the Hubble Deep Field. The catalog
includes data from 76 separate images for the same region. Only three
of these original images are shown on the left: one taken in orange
light by the Wide Field Planetary Camera 2 (top); one taken in blue
light by the Advanced Camera for Surveys (middle); and one taken in
infrared light with the Wide Field Camera 3 (bottom). Note that the
"sources," or objects, in each original image are not perfectly aligned
with the final position from the Hubble Source Catalog (the pink
circles). Specially developed software had to shift all the images
slightly to align the sources before making the final version of the
catalog. Credit: NASA, B. Whitmore (STScI), and the Hubble Source Catalog Development Team
Astronomers at the Space Telescope Science Institute and the Johns
Hopkins University, both in Baltimore, Maryland, have created a new
master catalog of astronomical objects called the Hubble Source
Catalog. The catalog provides one-stop shopping for measurements of
objects observed with NASA's Hubble Space Telescope.
Hubble has amassed a rich legacy of images and other scientific data
over its 25 years of exploring the universe. All of the images are
stored in the computer-based Barbara A. Mikulski Archive for Space
Telescopes (MAST), which astronomers use for their research. The
archive is bursting with more than a million images, which contain
roughly 100 million small sources ranging from distant galaxies to
compact star clusters to individual stars. For astronomers, however, a
major challenge is the difficulty involved with sifting through the
archival gold mine to collect the data they want to analyze. The Hubble
Source Catalog now allows astronomers to readily perform a computer
search for characteristics of these sources.
The Hubble Source Catalog is a database from which astronomers can
obtain the Hubble measurements of specific astronomical objects they
want to investigate. A query to this database can take just seconds or
minutes, while previously it might have required a few months of hard
work by searching separate files throughout the archive. This
capability promises to open the door to exciting new areas of research
with Hubble that otherwise might have been too cumbersome to tackle.
"The Hubble Source Catalog is arguably the Hubble Space Telescope's
ultimate legacy," said astronomer Tamás Budavári of the Johns Hopkins
University, a member of the Hubble Source Catalog development team.
"Not only is it a one-stop shop, but it's the first place to go. It's
the table of contents for and the summary of most Hubble observations.
If a zillion investigators pointed Hubble in the same direction at their
region of interest in different wavelengths, now we have taken all of
those observations and put them together into a compilation of the
measurements for all objects within that region."
Building the catalog, however, was a challenging task. "To make this
possible, we had to develop new methods to align overlapping images and
to determine which sources in different images are actually the same
astronomical object," said development team member Steve Lubow of the
Space Telescope Science Institute.
Hubble's archive is a diverse collection of data from different
instruments, exposure times, and orientations on the sky. This
diversity greatly complicates the construction of the catalog.
"Now we can have an even more holistic view of the Hubble universe
because you can conduct multi-wavelength and time-domain analyses,"
Budavári said. "Additionally, due to the improved accuracy of positions
in the catalog, we can compare Hubble's observations to those by other
observatories, such as the Sloan Digital Sky Survey or the Galaxy
Evolution Explorer."
Brad Whitmore, who leads the development team at the Space Telescope
Science Institute, cautions, however, that, "In many cases, astronomers
will find that they need to go back to the original images and make
the measurements that are unique to their science project, such as
measuring the very faintest objects in the image."
The catalog brings together observations from the three primary
cameras that have served Hubble since 1993: the Wide Field Planetary
Camera 2, Advanced Camera for Surveys, and Wide Field Camera 3. The
three cameras combined make observations spanning a wide swath of the
spectrum, from ultraviolet to visible and near-infrared light. The
catalog lists all of the sources, and includes both a summary and
compilation of the measurements for each object. The measurements
include information about the brightness of sources, as well as a
source's color and shape. Astronomers released the first version of the
catalog on Feb. 25.
The new catalog allows astronomers to produce more research using
Hubble archival data. "The number of science papers based on Hubble
archival data has been larger than the number of papers written by the
original investigators for over a decade," Whitmore said. "With this
catalog, we hope to accelerate that trend by making it easier to obtain
and work with the data, and to allow researchers to address questions
that they wouldn't even try to do before because it would be too
time-consuming and costly."
Patterned after the Sloan Digital Sky Survey's online catalog, the
Hubble Source Catalog is a unique addition to the growing number of
online astronomical archives that allow astronomers, amateurs, and the
public to explore and study the universe from the comfort of their
office, sofa, or favorite coffee shop.
The Hubble Source Catalog, however, wasn't designed only for today's
astronomers. It will be a valuable resource for future researchers
using the next generation of telescopes, such as NASA's James Webb
Space Telescope, an infrared observatory scheduled to launch in 2018.
"We didn't build this catalog for the next year, or two, or three,"
Whitmore said. "We built this catalog for the next several decades. It
will be a great resource long after Hubble has been decommissioned."
The project started with grant funding from NASA's Advanced
Information Systems Research Program and is currently being supported
by the Space Telescope Science Institute. The Hubble Space Telescope
project and MAST have provided monetary support for the catalog's
development.
Users can access the Hubble Source Catalog primarily through the MAST Discovery Portal (http://mast.stsci.edu), which has been enhanced to support the Hubble Source Catalog project. More details are available at https://archive.stsci.edu/hst/hsc/.
In addition to Whitmore, Budavári, and Lubow, the catalog development
team consists of Sahar Allam of Fermi National Accelerator Laboratory
in Batavia, Illinois, and Stefano Casertano, Thomas Donaldson, Ronald
Downes, Lee Quick, Louis-Gregory Strolger, Geoff Wallace, and Rick
White of the Space Telescope Science Institute.
Join Hubble scientists during a live Hubble Hangout discussion about the
Hubble Source Catalog at 3pm (EDT) on Thurs., March 19 to learn more.
Visit: http://hbbl.us/Fne .
Contact
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Brad Whitmore
Space Telescope Science Institute, Baltimore, Md.
410-338-4474
whitmore@stsci.ed
Source: HubbleSite
