STS-67 Day 4 Highlights
Back to STS-67 Flight Day 03 Highlights:
- On Sunday, March 5, 1995 at 6 a.m. CST, STS-67 Payload Status Report # 07
reports: (3/5:22 MET) 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 in the 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.
- On Sunday, March 5, 1995 at 1 p.m. CST, STS-67 MCC Status Report # 07
stated that there has been some indications that the crew's stationary
bicycle exercise is imparting some vibration to the shuttle that is
interfering with the Instrument Pointing System's ability to precisely
direct the Astro-2 telescopes at their targets. The crew is being
asked to schedule exercise a little earlier so that the vibration has
stopped by the time Endeavour moves into darkness and celestial
observations must resume.
- On Sunday, March 5, 1995 at 6 p.m. CST, STS-67 Payload Status Report # 08
reports: (3/17:22 MET) Both the Hopkins telescope and the
Wisconsin Ultraviolet Photo- Polarimeter Experiment (WUPPE) examined
two Seyfert galaxies, Markarian 279 and Fairall 9, in a study that
could provide insights into some of the most powerful events in the
universe. Named for Vanderbilt University astronomer Carl Seyfert,
who identified this type of galaxy in 1943, Seyferts have extremely
bright, compact cores containing clouds of gas moving at thousands of
miles per second. Astronomers theorize that supermassive black holes
would be the only source capable of generating the immense power given
off by these objects.
- The HUT team also practiced acquiring quasar Q 1542+54 to
refine procedures for locating it efficiently in future observations.
Their success gives them an additional illumination source to use in
their search for intergalactic helium. Yesterday, they successfully
locked onto the quasar 1700+64, which will likely remain their primary
target for the study.
- Several observations today examined the dust and gas from which
stars form. HUT selected a reflection nebula and the star which
illuminates it. The star, AE-Aurigae, is a very hot, massive blue
star with surface temperatures from 50,000 to 70,000 degrees
Fahrenheit (28,000 to 40,000 Kelvin). Light from the star illuminates
a cloud of dust surrounding it, creating a bright, colorful nebula.
Observation by the Astro telescopes may help determine the composition
of the dust and the sizes and shapes of the grains.
- The first observation of the day with WUPPE as the lead instrument
was HD 50138, viewed after Mission Specialist John Grunsfeld and
Payload Specialist Ron Parise took over science crew duties. This
pre-main-sequence star is thought to be a young object, several times
more massive than our sun, that has just formed out of the
interstellar gas and dust. Polarization measurements should help show
the shape of the nebula which surrounds the star and indicate where it
is coming from. The study should help astronomers learn more about
the ways in which young stars form and how their birth clouds
- The WUPPE team also observed the star HD 197770, an interstellar
polarization probe. The star serves much like a flashlight,
illuminating the vast and normally invisible clouds of dust and gas in
the space between stars. The materials in these swirling clouds are,
in essence, the stuff of past and future stars. Over eons, as stars
grow old, they kick out vast amounts of very hot material -- mostly
gas and dust -- into space. These materials form into clouds, and
over many thousands of years the clouds collapse and form new stars.
By determining how much the ultraviolet light passing through the
clouds is polarized, or vibrating in a preferred direction rather than
randomly, WUPPE can provide further clues as to the nature of this
- Phi Persei, a hot, rapidly spinning star, was another subject of
study for WUPPE. The star exhibits an unusual ultraviolet spectrum
that may be caused by a shell of gas around the star, possibly the
remains of a layer that has been spun off the star by its rapid
rotation. This shell is thought to be in the form of a disk around
the equator of the star, and the scattering of starlight by the disk
polarizes the light.
- Celestial objects chosen for observation by the Ultraviolet
Imaging Telescope (UIT) included M31, the famous Andromeda galaxy in
our "local group," the cluster of galaxies which includes our own
Milky Way. UIT researchers are conducting ultraviolet studies of the
structure of local group galaxies. They will also examine the
photographs to study the physics of star formation contained in these
- The UIT team also selected various kinds of open and globular
star clusters, groups of stars formed from the same basic material at
the same time. By comparing clusters of different ages and by looking
at different types of stars of the same age, astronomers can learn a
great deal about how each type of star changes in its lifetime.
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