Astro-2 Public Affairs Status Report #22
6:00 p.m. CST (10/17:22 MET), March 12, 1995
Spacelab Mission Operations Control
Marshall Space Flight Center 
Huntsville, Ala. 

   With the Astro-2 mission in its eleventh day, astronomers continue
to stack up new clues about what makes the universe "tick" -- how it
got started, how it evolved and where it is going.
 
   The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) team
selected Nova Circinus 1995 for observation this morning.  This is the
third "new" nova -- a binary star system whose first outburst was
observed very recently -- to be studied by the Astro-2 telescopes.
"Though all three novae went into outburst since the first of the
year, each is at a different stage in its history," said WUPPE
Principal Investigator Dr. Arthur Code.  "By comparing their
polarization, we hope to determine whether gas from novae outbursts is
expelled in a spherical shape and then becomes more asymmetrical, and
if so, how quickly the asymmetry develops."  Light is polarized when
it encounters an asymmetrically shaped object, such as a flattened gas
disk, which causes the light to vibrate in preferred directions.

   "Every day brings new surprises," said HUT Co-investigator Dr. Bill
Blair, describing the success today of two supernova remnant
observations he admits were long-shots.  HUT led a study of the
supernova remnant Puppis A, the third supernova remnant Astro-2 has
observed in our Milky Way galaxy.  HUT and WUPPE examined a filament
of gas in the remnant's eastern region, apparently an interaction
between an interstellar cloud and the blast wave speeding from the
supernova explosion. "The International Ultraviolet Explorer barely
detected this remnant, so we didn't know what to expect," said Blair.
"We thought dust in the interstellar medium might block its
ultraviolet radiation, but we got a very nice spectrum which showed
strong nitrogen emissions."  Blair said it is possible the nitrogen
could have been thrown out by the massive star thousands of years
before it exploded as a supernova, and now the shock wave from the
blast is catching up with nitrogen expelled from the star.

   Supernova 1006, whose explosion in A.D. 1006 makes it a relatively
recent supernova, provided another first.  "The shock wave from this
supernova is moving very fast, plowing through interstellar space at
about 2,000 kilometers (1,250 miles) per second, as opposed to 150 to
200 kilometers per second in remnants like Puppis A," said Blair.  "We
thought its emissions might be too faint for us to observe, but we
felt it was important enough to attempt.  This gives us a new range of
velocity that has never been observed before in the ultraviolet."
Blair said the HUT spectrum may show the primary passage of the
supernova blast wave as it first encounters interstellar gas.
Comparison with optical observations could help astronomers understand
the basic physics of supernova shock fronts.

   The Ultraviolet Imaging Telescope team led eight highly successful
observations in a row.  UIT captured the mission's first images of the
Whirlpool Galaxy (M 51) for Dr. Wendy Freedman's atlas of spiral
galaxies.  The Whirlpool Galaxy is the larger of two interacting
galaxies close enough together to disturb each other through
gravitational force.  M 51 is a large spiral galaxy with a mass 100
billion times that of our sun.  It is interacting with NGC 5195, a
much less massive galaxy.  Astronomers will study UIT photographs to
learn more about the formation of stars in that system, especially in
the bridge of matter that joins the two interacting galaxies.

   UIT also imaged CB_4, a cold cloud of interstellar gas and dust
which is sufficiently dense to obscure starlight from objects behind
it, while it reflects light from objects in front of it.  Though this
so-called dark cloud is relatively faint, Astro scientists were able
to obtain measurements to test models of dust in the interstellar
medium during a daylight observation.

   The imaging telescope also photographed a cluster of galaxies known
as the Coma Cluster.  UIT is examining the dense cluster, made up
primarily of elliptical galaxies, to obtain simultaneous information
on large samples of galaxies.  Astronomers will study the integrated
ultraviolet properties of these large samples to determine constraints
on the physics of cooling flows, as hot gas may condense into stars as
it rains down on a galaxy from the intra-cluster medium.  Scientists
also will look for the presence of dark matter, which does not emit
appreciable radiation.

   HUT and WUPPE observed NGC 4874, the central elliptical galaxy in
the Coma Cluster, to determine the ages of its stars.  Though
elliptical galaxies have comparatively few young stars, they emit more
ultraviolet radiation than would be expected from a population of old
stars.  Astro-1 observations of ellipticals suggest this radiation may
come from aging stars in a previously unknown stage of evolution.
Astro-2 is following up on the mystery.

   UIT photographed the open star cluster NGC 7789, and investigations
into new star formation included observations of elliptical galaxy NGC
185, irregular galaxy NGC 1313 and rapid star formation galaxy NGC
4631.  WUPPE led the mission's first observation of the Planet Mars,
and it observed interstellar polarization probe HD 217490 to add to
its ongoing study of the dust scattered throughout our Milky Way.
Dr. Brian Espey got excellent HUT and WUPPE data on the symbiotic star
system RR Telescopii for his study of closely orbiting stars with
radically different temperatures.
	
   In addition to observing a variety of stars and galaxies tonight,
the Astro-2 telescopes will view the Planet Venus and study
interstellar polarization and extinction in the Large Magellanic
Cloud.

To follow the mission in progress, visit Astro-2's home page on the
Internet World Wide Web: URL "http://astro-2.msfc.nasa.gov"