STS-67 Day 8 Highlights

Back to STS-67 Flight Day 07 Highlights:

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.

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.

Go to STS-67 Flight Day 9 Highlights: