Astro-2 Public Affairs Status Report #24
6:00 p.m. CST (11/17:22 MET), March 13, 1995
Spacelab Mission Operations Control
Marshall Space Flight Center
Huntsville, Ala.

   Astro-2 observations today ranged from exotic star formations with
odd- sounding names to our familiar celestial neighbor, the Planet
Venus.  Astronomers collected additional information for a variety of
investigations which have been in progress throughout the mission.

   The Hopkins Ultraviolet Telescope (HUT) team began their block of
observations with HH 2H, an object that could be a young star just
emerging from the "cocoon" of dust around it.  Called Herbig-Haro
objects, after the astronomers who discovered them in 1946, these
small bright concentrations of dust and gas are believed to be gas
jets thrown off during the final evolutionary stages of a protostar,
an object that has not collapsed sufficiently to begin the nuclear
reactions of a mature star.

   The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) led
an observation of another infant star, AB Aurigae.  Called a pre-main
sequence star, AB Aurigae is part of a class of young stars that are
still surrounded by the dust and gas clouds from which they are
formed.  These envelopes of matter around the objects are highly
active, as evidenced by variations of polarization seen in the optical
and infrared wavelengths.  WUPPE's ultraviolet observations should
help astronomers understand how dust is processed during star
formation and how material around young stars is distributed.

   All three telescopes viewed HUT's choice of Markarian 421, a
quasar- like active galaxy nucleus known as a BL Lacertae object.
When the first object of this type was identified, in the
constellation Lacerta, it was erroneously thought to be a variable
star.  In the 1960s, astronomers discovered that BL Lac objects are
not stars in our Milky Way, but the incredibly more powerful active
cores of distant galaxies.  Massive black holes are expected to be the
power sources for objects in this class.  While BL Lac objects produce
strong radiation in all observation wavelengths, their radiation is
primarily non-thermal -- created not by heat but by the glow of
electrons moving at almost the speed of light as they pass through a
magnetic field.  NASA's Extreme Ultraviolet Explorer satellite
discovered strong ultraviolet emission lines in Markarian 421,
suggesting it is an excellent subject for HUT's far-ultraviolet
studies.  Ground-based observations show a high level of polarization
in visible light, so WUPPE ultraviolet polarization measurements
should provide revealing insights into phenomena in the centers of
such galaxies.

   The observation of Venus this morning followed up on last night's
look at Earth's "twin" planet.  HUT studied the planet's forbidding
atmosphere -- 100 times denser than Earth's and as hot as 900 degrees
Fahrenheit (480 degrees Celsius) -- looking at upper atmosphere gases
that are excited by ultraviolet solar radiation.  Scientists will
compare Astro-2 observations of Venus and Mars to see how the two
planetary atmospheres, both primarily carbon dioxide but with
radically different densities, respond to ultraviolet radiation from
the sun.

   Two HUT observations today, NGC 6090 and 0833+652, were for Guest
Investigator Dr. Claus Leitherer's study of starburst galaxies.
Leitherer hopes to determine whether ionized hydrogen is being
released from the galaxies, which put out a great deal of ultraviolet
energy due to the rapid star formation taking place within them.
"This is another attempt to view the interstellar medium," explained
HUT Principal Investigator Dr. Arthur Davidsen.  "We feel certain
there must be material left over from the formation of the universe,
just like there would be flour left on a cutting board after a loaf of
bread is kneaded.  But we have never been very successful in observing
this material."  Davidsen said the material might be highly ionized,
possibly by quasars or by starburst galaxies, making it difficult to
observe.  "If we can find out how much ionized hydrogen starburst
galaxies are putting out, we can get a good idea how much they emit
into interstellar space," Davidsen said.  "We may find that these
galaxies are an important source of ionized interstellar hydrogen, or
it may not be there at all.  Either way, we've helped answer an
intriguing question."

   HUT also led the Astro telescopes in an examination of the
planetary nebula nucleus K1-16.  Astronomers hope to better understand
the chemistry of the nebula and the evolutionary state of its central
star.  The nebula is unstable, going through periodic pulsations in
magnitude and color.  While the star's evolutionary status is not
clear, astronomers believe it could be on its way to becoming a white
dwarf.

   The Ultraviolet Imaging Telescope (UIT) team made more images of
star groupings to study the life cycles of stars.  They photographed
Abell 1795 and the Hercules Cluster, both clusters of galaxies where
star formation is taking place.  The Hercules Cluster is made up
primarily of spiral galaxies, whose pinwheel arms are stellar
nurseries.  Abell 1795 is a galaxy cluster which emits large
quantities of X-rays.  Gas in the cluster is cooling rapidly and could
be producing stars at the rate of 300 solar masses per year.  UIT's
observation of globular star cluster NGC 6752 focused on the opposite
end of stellar evolution.  The cluster is tight grouping of relatively
old stars whose low metal content indicates formation early in the
life of the Milky Way galaxy.  UIT also imaged elliptical galaxy M32.

   Late this afternoon, the WUPPE team devoted two observations to
planned calibrations of their instrument's sensitivity, with HD 161056
serving as a polarized standard and Beta Ursa Majoris as an
unpolarized standard.  Tonight's Astro observations again will span
the universe, from another distant quasar to the mission's second
observation of Earth's moon.  Other scheduled observations include
individual stars, galaxies, a planetary nebula and a galaxy cluster.

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"