Astro-2 Public Affairs Status Report #7
6:00 a.m. CST (3/5:22 MET), March 5, 1995
Spacelab Mission Operations Control
Marshall Space Flight Center
Huntsville, Ala.

	Observations of the distant regions of the universe continued
throughout the third night of the Astro-2 mission, as scientists
focused their attention on some of the least understood objects in
space.

	Commander Steve Oswald maneuvered the Space Shuttle Endeavour
to enable the Hopkins Ultraviolet Telescope (HUT) to lead an
observation of a mysterious star in the constellation Cassiopeia.
This star, known to astronomers as KPD0005, belongs to a class of
planetary nebulae, or clouds of gas with bright centers, that includes
some of the hottest stars known.  So hot are these stars' surfaces, in
fact, that their elements are completely ionized, making their
chemical composition difficult to analyze.  Only ultraviolet
astronomy, such as the Astro-2 instruments employ, can yield answers
to questions about the chemistry and evolution of this type of star.

	Following this, the HUT science team then turned their
attention back to the search for signs of interstellar helium, using
light from a distant quasar, known as 1700+64.  Since it is believed
that helium was formed in the Big Bang at the beginning of the
universe, the actual detection of intergalactic helium would probably
be the most significant scientific result that the HUT observations
might produce.  Because of the enormous distances of these objects,
the targets are necessarily faint, and such observations are the most
difficult that HUT scientists will attempt.  They are also the most
sensitive measurements ever made for interstellar helium.

	Another priority for the HUT scientists involves the study of
Type II Seyfert galaxies.  These galaxies, such as NGC1068 which was
observed last night, have bright centers that emit energy over a broad
range of frequencies.  It is believed that the core of NGC #1068 is
ionized by shock waves of gas moving at hundreds of miles per second,
and the ultraviolet observations by the Astro-2 instruments are
testing this hypothesis.

	The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE)
team has also taken great interest in NGC 1068 and made some very
difficult indirect observations of the galaxy's core using the
electron cloud above the galaxy as a polarization mirror.  "By
observing the diffuse light reflected from the electron cloud, we are
able to take measurements of the otherwise obscure nucleus of the
galaxy," said WUPPE co-investigator Karen Bjorkman.  On Astro-1,
observations by WUPPE helped confirm that a thick torus, or
doughnut-shaped cloud, exists around the nucleus of NGC #1068, while
HUT observations showed unexpectedly high temperatures near the torus.

	Early this morning, WUPPE scientists also took the opportunity
to view a couple of interactive binary star systems, V356 Sagittarii
and Vela X-1.  A binary star system consists of a pair of stars that
orbit each other.  In the case of an interactive binary, the stars
stay so close to each other that they actually exchange gases.

	Astronomers believe that in an X-ray binary such as Vela X-1,
a neutron star (or pulsar) gravitationally strips material off of its
companion star.  A lot of the stripped material settles into orbit to
form an oval disc shape.  Polarization measurements by WUPPE allow
scientists to measure the size and shape of this disc, and it also
provides information about the stars involved.  As WUPPE Principal
Investigator Arthur Code observed, "the unique feature of interactive
binary stars' polarization is that we can use that information to
calculate the mass exchanged between the stars."  Last night's
observations were enhanced by the fact that the Astro-2 instruments
could view both members of each binary side by side as they interact.

	The Ultraviolet Imaging Telescope (UIT) made observations of
an open cluster called NGC #3532.  This is a diffuse cluster of stars
and is believed to be less than ten million years old.  Because UIT's
field of view is well matched to the sizes of most clusters in our
Milky Way Galaxy, UIT scientists are able to perform ultraviolet
observations of many stars at the same time.  UIT observers are
searching for ultraviolet counterparts to X-ray sources as well as for
white dwarfs and other faint, hot stars.  These ultraviolet-bright
objects are of great interest for several reasons: they can be used as
probes of the interstellar medium; they can be used to provide highly
accurate distance measurements to the clusters; and they will enhance
understanding of the chemical evolution of the Milky Way Galaxy.

	UIT also imaged several ancient globular clusters in our Milky
Way galaxy as well as other nearby spiral galaxies.  The latter
observations will be used to further our understanding of
star-formation in the spiral arms of these galaxies.

	During the next twelve hours, the Astro-2 instruments will
begin with further observations of active galactic nuclei and quasars.


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"