STS-67 Day 8 Highlights
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- On Friday, March 10, 1995 at 6 a.m. CST, STS-67 Payload Status Report # 17
reports: (8/5:22 MET) Payload Specialist Ronald Parise pointed the
Hopkins Ultraviolet Telescope (HUT) at a binary star system called AM
Herculis. This star system has a white dwarf and a normal low-mass
companion star, locked in a tight orbit around each other. As these
two stars move around each other, material from the low-mass star is
transferred to the white dwarf. During this transfer, matter from the
companion star is heated as it spirals down onto the white dwarf,
generating a great deal of ultraviolet emission. Because of these
outbursts (which may occur every couple of weeks to months or years),
binary star systems such as these are called cataclysmic variables.
- Several Astro-2 observations have been made of the AM Herculis
binary star system because of its unique characteristics. In this
star system, the white dwarf star has a strong magnetic field. As
material from the companion star is being transferred, the magnetic
field of the white dwarf causes the matter to assemble around its
magnetic poles. HUT astronomers are using observations of cataclysmic
variables during this mission to learn more about how the magnetic
transfer of matter differs from the normal transfer of matter between
binary stars. In another study of cataclysmic variables, HUT observed
EM Cygni, a dwarf nova which has no magnetic field.
- During the night portion of two separate orbits, Pilot William
Gregory maneuvered Endeavour into the proper orbital position for
Parise to align HUT for observations of quasar 1700+64. HUT
scientists are using this quasar, located in the constellation Draco,
to search the vast region of space between distant galaxies for
evidence of helium left over from the primordial fireball that many
scientists believe marked the birth of the universe. HUT Principal
Investigator Dr. Arthur Davidsen is using the light from this
extremely distant quasar as back lighting to shine through the
intergalactic medium. Astronomers will use data from these Astro-2
observations to verify recent findings from the Hubble Space Telescope
as well as measure the density and ionization state of the
intergalactic helium.
- Parise also aligned HUT with two white dwarf stars for a study by
HUT Guest Investigator Dr. David Finley. White dwarfs are one of the
extremely dense remnants of normal stars like the sun. Those being
studied with HUT are young and extremely hot stars. Finley is using
these HUT observations to get very accurate measurements of the
temperatures and surface gravity of white dwarf stars and determine
the properties of hydrogen under conditions of extreme temperature and
pressure.
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- Another HUT investigation looked at a portion of a supernova
remnant called the Cygnus Loop. Guest Investigator Dr. John Raymond
observed this "middle-aged" supernova remnant to study the physics of
collisionless shocks, the destruction of grains in shocked gas,
instabilities behind radiative shocks, and shock wave parameters.
- Parise aimed HUT at Jupiter's moon Io again last night. A recent
volcanic eruption on Io ejected material into Io's atmosphere and onto
its surface. HUT scientists are observing Io to detect changes in the
number of sulfur and oxygen ions in its atmosphere as a result of the
volcanic eruption.
- The Ultraviolet Imaging Telescope (UIT) imaged two globular
clusters last night a metal-poor cluster and a metal-rich
cluster. The metal-poor globular cluster, known as NGC 2808, is made
up of relatively old stars. The low metal content of these stars
indicates they were formed early in the life of the Milky Way galaxy.
Astronomers theorize that the metal-rich globular cluster, called 47
Tucanae, once belonged to a small metal-rich galaxy that was swallowed
up by the Milky Way in the remote past. The UIT science team will use
images from these two types of globular clusters to search for hot
binaries that are transferring matter from the massive star to its
low-mass companion (accretion), hot white dwarfs, planetary nebulae,
and objects associated with X-ray sources in globular clusters.
- Payload Specialist Sam Durrance pointed the Wisconsin Ultraviolet
Photo-Polarimeter Experiment (WUPPE) telescope at a young stellar
object, still forming out of interstellar dust. WUPPE astronomers
will analyze data about the polarization of the ultraviolet light in
this object to learn more about the star- formation processes taking
place there.
- WUPPE scientists also gathered data about hot stars with bright
emission lines last night. Principal Investigator Dr. Arthur Code
will use information about the orientation of light waves traveling
through the circumstellar disk of this star, called 48 Persei, to
understand more about the material around it. Although this type of
star was first noted because of bright emission lines, over 100 years
of study have shown stars like these to be unusual in many other
respects. Each spectral region studied provides astronomers with
information about a different part of the material around the star.
- On Friday, March 10, 1995 at 5 p.m. CST, STS-67 MCC Status Report # 17
reports: Commander Steve Oswald conducted more work with the Middeck
Active Control Experiment, the MACE device, which is collecting
engineering data about the effect of vibrations on free-floating
structures. Pilot Bill Gregory spent some time answering questions
sent by computer users on the Internet regarding Endeavour's astronomy
mission. Hundreds of thousands of questions have been placed on the
Internet since the start of the mission, prompting the astronauts to
respond when time permits.
- On Friday, March 10, 1995 at 6 p.m. CST, STS-67 Payload Status Report # 18
reports: (8/17:22 MET) The Ultraviolet Imaging Telescope (UIT)
team selected the spiral galaxy M 31, better known as the Andromeda
galaxy, for observation. The team is mapping groups of hot, bright
young stars, called OB associations, to learn more about star
formation within the galaxy. Today's observation concentrated on the
northern portion of Andromeda, where its brightest OB associations are
located. "We mapped the OB associations in the southern portion of M
31 during Astro 1, and our goal on Astro 2 is to complete the
picture," said UIT observing team member Barbara Pfarr. At twice the
apparent size of our full moon, Andromeda is too big to be
photographed in one frame even with UIT's wide field of view. M 31 is
roughly the same size as the Milky Way, and it is the nearest galaxy
of comparable size to our own.
- Astro scientists also observed NGC 4631, a large spiral galaxy
viewed edge-on. The galaxy is forming stars out of material it is
pulling from the disk of a nearby, less massive elliptical galaxy, NGC
4656. The bridge of material it is pulling from its smaller neighbor
forms a "tail" on NGC 4631. NGC 4631 is of special interest to UIT
and Hopkins Ultraviolet Telescope team members because huge loops and
filaments of gas have been thrown above and below the galaxy's central
region. Astronomers believe this may be a bubble of gas produced by
supernova explosions, with very strong stellar winds blowing material
out of the galaxy. HUT will use its far-ultraviolet spectrometer to
see if there is hotter gas present -- about 200,000 degrees Fahrenheit
(100,000 degrees Celsius) or more -- than has been detected in
observations by other telescopes.
- UIT's ultraviolet images of NGC 4631 will be used to determine how
stellar populations are distributed in the galaxy. In addition, they
will compare photographs made in different wavelengths with various
camera filters to help determine the location of the hot gas, its
temperature profile, and its distance from the galactic disk. "We
will try to deduce processes by which the gas is heated and cooled,
then drops back into the disk," said UIT team member Dr. Andrew
M. Smith, "It is theorized that there is a circulation pattern in the
gas which is quite large and quite turbulent."
- The Hercules Cluster of galaxies, also viewed by the Astro
telescopes today, furnishes another laboratory for the study of star
formation. Galaxy clusters are the largest gravitationally bound
groupings in the universe. Such clusters generally contain both
elliptical galaxies, which contain few new stars, and spiral galaxies,
which contain many young, ultraviolet-bright stars. The Hercules
cluster has a greater than average number of spirals, which makes it a
good "hunting ground" for new star formation.
- UIT also led observations of two objects near the end of the
stellar life cycle, globular clusters NGC 6752 and M 13. Stars within
these tightly bound clusters appear to be about five billion years
older than recent evidence suggests the universe itself may be --
something like the children being older than the parents. Ultraviolet
studies of old stars within the clusters, near the very end of their
lives, could provide better tests for the ages and life cycles of
stars.
- This morning's study of dwarf nova WX Hydri is the second
observation of this system, whose decline from outburst is being
studied. Though these periodic increases in brightness in WX Hydri
are not as bright as they are in some cataclysmic variable systems,
they occur fairly frequently -- about once every ten days. WX Hydri
sometimes becomes over eight times brighter during an outburst,
increasing from a magnitude of about 14.8 during quiet periods to
around 11 at its brightest. Information about this dwarf nova and
about 10 others is being provided to Astro scientists by amateur
astronomers around the world.
- The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) team
finished up one period as prime instrument early this morning, then
began another after this afternoon's orbiter water dump. This
morning, WUPPE looked at reflection nebula NGC 7023. The first prime
observation for WUPPE this afternoon was HD 207198, an interstellar
polarization probe. Both were studies clouds of gas and material from
which astronomers can learn about the interstellar medium -- the
material from which stars and other objects are created.
- Other celestial objects viewed by the Astro telescopes today
included the brightest known Seyfert galaxy, NGC 4151; the Carina
dwarf galaxy; spiral galaxy NGC 4258; and NGC 752, an open star
cluster in the constellation Andromeda.
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