STS-67 Day 6 Highlights

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On Wednesday, March 8, 1995 at 8 a.m. CST, STS-67 MCC Status Report # 12 reports: Astro-2 observations continue, including ultraviolet views of spiral galaxies, the interstellar medium and a very luminous and hot Wolf Rayet star. A successful alignment of the inertial measurement units was performed earlier this morning. Excess water will be dumped through the flash evaporator system today. All consumables are at the appropriate levels at this time in the record-setting mission.

On Wednesday, March 8, 1995 at 4 p.m. CST, STS-67 MCC Status Report # 13 reports: Mission Specialist Wendy Lawrence beamed down a video postcard, narrating a tour of the Space Shuttle Endeavour and showing what life aboard is like. The tour included views of the aft flight deck, where astronomical observations are being conducted; the forward flight deck, where shuttle maneuvers are orchestrated; and the middeck, where experiments are studying biotechnology and flexible space structures and the day-to-day activities such as food preparation and personal hygiene are taken care of.

Oswald worked again with the Middeck Active Control Experiment as Gregory took care of orienting the shuttle for its Astro-2 observations and performed housekeeping duties. Grunsfeld and Parise directed the trio of Astro-2 telescopes toward its targets. Gregory and Grunsfeld also conducted an interview with KFWB Radio in Los Angeles.

On Wednesday, March 8, 1995 at 6 a.m. CST, STS-67 Payload Status Report # 13 reports: (6/5:22 MET) Although payload controllers at Marshall Space Flight Center in Huntsville, Ala., were briefly evacuated to a safe area during severe weather conditions last night, voice communications with the Shuttle continued from Marshall, allowing Mission Specialist John Grunsfeld to coordinate his activities with science teams on the ground .

Grunsfeld pointed the Astro-2 telescopes at a quasi-stellar object, a prime target for the Hopkins Ultraviolet Telescope (HUT), known as HS1700+64. Principal Investigator Dr. Arthur Davidsen and the HUT science team are searching for the helium left over from the primordial fireball that many scientists believe marked the birth of the universe some 10 to 20 billion years ago. To find the ash remnants of the explosive genesis of the universe, astronomers must use the faint glow of extremely distant objects, such as this quasar, located behind the intergalactic gas similar to using a distant flashlight shining through a hazy mist. HUT was aimed at this Astro-2 target, located many billions of light years away, to help scientists search the gas for evidence that helium is absorbing the quasar's ultraviolet light.

Jernigan and Durrance aligned the Wisconsin Ultraviolet Photo- Polarimeter Experiment (WUPPE) telescope to look at two other stars serving as background lights in the study of interstellar polarization the orientation of ultraviolet light waves that travel through the gas and dust between stars. Interstellar polarization studies enable scientists to make allowances for obscuring matter when they study other objects in the universe as well as learn about the obscuring matter itself.

The Ultraviolet Imaging Telescope (UIT), WUPPE and HUT observed the dying remains of a star a white dwarf. This small object, which has burned all its nuclear fuel, allowed WUPPE Principal Investigator Dr. Arthur Code to observe the orientation of the ultraviolet light traveling from the white dwarf to determine its geometry and density. UIT imaged the white dwarf and the surrounding night sky to help scientists search for more of these faint, hot stars.

Gregory maneuvered Endeavour into position during two separate orbits to allow all three Astro-2 ultraviolet telescopes to observe spiral galaxies. One of these spiral galaxies, known as NGC 2841, contains remnants from Supernovae 1912 and 1957A. The second spiral galaxy, called NGC 2403, is a galaxy containing an old yellow star population in its center region that merges into a disc with widely scattered blue star-formation knots in its spiraling "arms." Guest Investigator Dr. Wendy Freedman will use UIT images of these two galaxies in a digital atlas of spiral galaxies.

Two other galaxies were observed by the ultraviolet telescopes nestled in Endeavour's payload bay last night. Guest Investigator Dr. Claus Leitherer used HUT to observe a starburst galaxy and UIT Principal Investigator Theodore Stecher conducted ultraviolet studies of the structure of galaxies during an observation of elliptical galaxy NGC 205.

During four separate orbits, Jernigan and Durrance pointed the three ultraviolet telescopes toward a rare type of star known as a Wolf-Rayet star. This type of star is thought to represent one of the last phases in the life cycle of a massive star. Wolf-Rayet stars have powerful, eroding stellar winds. These strong stellar winds have hastened the evolution of the Wolf-Rayet stars, causing what may once have been massive, luminous stars to become less and less massive throughout their life. "We are looking at the way energy coming out of the star interacts with the atmosphere surrounding the star," explained WUPPE Co-Investigator Dr. Chris Anderson.

Jernigan and Durrance also brought the Astro-2 telescopes into alignment with two very hot, massive blue stars that emit large amounts of ultraviolet radiation. There is evidence that the outer layers of these two rapidly spinning stars have been peeled off by their stellar winds. From the data gathered during Astro-2, HUT scientists will strive to determine accurate temperatures of these stars to learn more about their surrounding atmosphere, search for stellar winds, and study absorption in the gas and dust between the stars.

On Wednesday, March 8, 1995 at 6 p.m. CST, STS-67 Payload Status Report #14 reports:(6/17:22 MET) The Hopkins Ultraviolet Telescope (HUT) team led the observation of U Geminorum and SS Cygni, two dwarf novas which were also observed during Astro-1. A a dwarf nova, a particular type of cataclysmic variable star, is actually made up of two stars -- a "normal" star like our sun in extremely close orbit with a dense white dwarf. Interaction of the two creates periodic outbursts.

This morning, U Geminorum was at a different phase than it was during Astro-1, when it had just gone through an outburst. "After the outburst, the white dwarf was very hot. Today, the white dwarf was much cooler, since it has been a long time since U Geminorum's last outburst," said HUT Principal Investigator Dr. Arthur Davidsen.

Though SS Cygni was also at quiet stage today, it looked totally different from more typical dwarf novas like U Geminorum. "We could tell SS Cygni is unusual based on our limited Astro-1 observation, but today's much better data reinforces that," said Davidsen. "Normally, the white dwarf is obvious at the center of a cataclysmic variable, but the spectrum from SS Cygni doesn't look like a white dwarf. Instead of seeing light distributed across the spectrum the way we would with a dense star, we see pronounced emission lines that suggest something like a thin, transparent gas disk may surround the dwarf." Davidsen said a disk of gas is created during a hot outburst, but it generally dissipates when a variable is quiet. HUT team members will analyze today's data to help determine what makes SS Cygni apparently unique.

Members of the American Association of Variable Star Observers and amateur astronomers all over the world are monitoring variable stars in both hemispheres 24 hours a day. They furnish regular reports via electronic mail to the Astro-2 experiment teams, so exploding stars can be added to the mission's observation schedule.

HUT also observed V 1329 Cygni, a closely orbiting set of stars with widely different temperatures called a symbiotic star system. Dr. Brian Espey will use far-ultraviolet spectra obtained by the Hopkins instrument to help determine the temperature of the hot star component.

The Ultraviolet Imaging Telescope (UIT) team chose two galaxies for wide-field ultraviolet photography. The first was M 49, the largest elliptical galaxy in the Virgo cluster of galaxies. At twice the size of our Milky Way and ten times more mass, M 49 is one of the biggest galaxies in the nearby universe. "We are interested in trying to trace the source in these galaxies of strong ultraviolet emissions, which were first detected by Dr. Art Code [WUPPE principal investigator] about 20 years ago," said UIT Co-Investigator Dr. Robert O'Connell. "We still don't understand where they are coming from." Astro-1 observations of elliptical galaxies called into question some previously popular theories about the source of the ultraviolet radiation.

UIT also obtained images of M 104, a spiral galaxy viewed edge-on from Earth. M 104 is sometimes called the Sombrero Galaxy because it resembles the shape of a wide-brimmed hat. "The regions where star formation occurs are in the 'brim' of the hat, while the large bulge -- the hat's 'crown' -- is made up of old stars, maybe even a black hole," said UIT Guest Investigator Dr. Barry Madore, who operates what may be the world's largest computerized electronic database of galaxies for NASA at Caltech. "Very old blue stars put out radiation in a glowing halo that surrounds the hat shape," Madore added. These halos had not been imaged in the ultraviolet before Astro-1. Studies of 47 Tucanae, a globular cluster chosen by UIT for study, could shed new light on stellar aging, since some stars within such closely grouped associations seem to age differently than those found elsewhere in our galaxy.

The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) team concentrated on very hot individual stars for their observation choices today. The instrument made spectral and polarimetric measurements of Zeta Tauri and 28 Tauri, two Oe/Be stars in the constellation Taurus which show bright hydrogen emission lines. The WUPPE team also selected supergiant stars P Cygni and AG Carinae. Massive stars like these process helium and hydrogen into heavier elements, and recycle material into the interstellar medium through supernova explosions and stellar winds.

Light from both types of stars is scattered by various processes in their atmospheres, creating pronounced polarization. However, WUPPE observations of both star types during Astro-1 showed ultraviolet polarization that was different from theoretical predictions. Astro 2 observations will provide data against which to test refined theories. The WUPPE team also completed a series of observations of Wolf-Rayet star HD 96548, in another study of how stars deposit matter containing processed elements like oxygen, nitrogen and carbon into the interstellar medium.

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