STS-67 Day 9 Highlights

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On Saturday, March 11, 1995 at 6 a.m. CST, STS-67 Payload Status Report # 19 reports: (9/5:22 MET) Pilot William Gregory maneuvered the Endeavour into a position where Mission Specialist John Grunsfeld and Payload Specialist Ronald Parise could align the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) with Nova Centauri 1995. "The WUPPE instrument has given us some spectacular spectral 'signatures' of the elements (such as carbon, nitrogen or oxygen) that may be present in the atmosphere following this very recent explosion," said Guest Investigator Dr. Joni Johnson of the University of Wisconsin in Madison. "We'll be analyzing these data for quite some time, looking for clues about the atmospheric composition, as well as the structure, of this new nova."

Nova Centauri 1995, which occurred just two weeks before the launch of Astro-2, is the result of a Red Giant, transferring material to a compact white dwarf companion star. After a period of time (perhaps 1,000 years or more) the material which accreted onto this white dwarf reached extremely high temperatures and pressure, causing a thermonuclear explosion. WUPPE scientists were excited to be able to observe this rare new nova so soon after its beginning.

Parise also pointed the WUPPE telescope to a massive star that is known to have bright emission lines. Scientists are studying this type of star to learn more about the composition of material surrounding the star and how it is effected by stellar winds.

WUPPE scientists also got another look at a rare Wolf-Rayet star overnight. Wolf-Rayet stars are thought to represent one of the final phases in the evolution of massive stars. This type of massive star has powerful, eroding stellar winds carrying material outward. The interaction between the star's light and this material causes the radiation to be polarized (oriented in one particular direction) rather than in all different directions. The polarization of light coming from this Wolf-Rayet star can tell astronomers something about the properties of the stellar winds around it.

Mission Specialist Wendy Lawrence maneuvered the orbiter to different positions last night, allowing the WUPPE science team to observe two galaxies in the Local Group. Payload Commander Tammy Jernigan operated the Instrument Pointing System, while Payload Specialist Sam Durrance aimed the Astro-2 telescopes at the galaxies. These two galaxies served as background lights for the study of interstellar polarization, the direction that light travels between stars.

The Ultraviolet Imaging Telescope (UIT) imaged Holmberg 2 (a dwarf galaxy) and a portion of the Andromeda spiral galaxy, M31, to help UIT astronomers learn more about young stellar formations in galaxies. One of the major science goals of the UIT is to map out our "twin sister" galaxy, Andromeda (M31). UIT also imaged a galaxy known as NGC 3310, allowing investigators to study the design of spiral galaxies and related structures, the nature of stellar populations, and learn more about the material between stars associated with bars, irregular, and anemic (poor in structure) galaxies.

The Hopkins Ultraviolet Telescope (HUT) observed two Seyfert 1 galaxies, Markarian 279 and NGC 3516. These targets are active galaxies with bright, compact nuclei, radiating in wavelength ranges from infrared to X- ray. HUT Project Scientist Dr. Gerard Kriss arranged simultaneous X-ray observations of NGC 3516 using the Japanese X-ray satellite ASCA (the Advanced Satellite for Cosmology and Astrophysics). Astro-2 and ASCA will revisit NGC 3516 for another observation in two days. UIT scientists observed these galaxies to better understand how energy is transferred between the nuclei and surrounding regions.

Parise pointed HUT at a dwarf nova called Z Camelopardalis (Z CAM). This stellar system has two stars locked in a tight orbit around each other, with an orbital period of seven hours. The companion star to Z CAM is a low mass star which transfers matter onto Z CAM, causing outbursts of ultraviolet emissions.

Parise aligned HUT with a portion of the supernova remnant Cygnus Loop D. HUT scientists are studying a very bright, radiative filament on the western edge of the Cygnus Loop, to learn more about the shock waves generated during the death of a star. Astronomers will analyze these HUT data to determine temperatures, densities, and chemical compositions of the gaseous filaments in the interstellar medium.

On Saturday, March 11, 1995 at 6 p.m. CST, STS-67 Payload Status Report # 20 reports: ( 9/17:22 MET) On the tenth day of the STS-67 mission, Astro-2 scientists took their first look in the extreme ultraviolet at what may be the most massive star in the known universe. They also focused their observations on spiral galaxies, elliptical galaxies, and star clusters.

HD 269810, a faint O-class star located in the Large Magellanic Cloud, is about 190 times as massive as Earth's sun and qualifies as a candidate for the most massive star ever observed. Hopkins Ultraviolet Telescope Guest Investigator Dr. Nolan R. Walborn, of the Space Telescope Science Institute, used the HUT instrument to study the star's unusually powerful stellar wind, or expanding outer layer, like it has never been seen before. Although this star probably possesses the most mass a star can have, its stellar wind is depleting this mass at an accelerated rate. These observations provide crucial information regarding the ultimate fate of the most massive stars.

Dr. Walborn uses the HUT to study a sample of very hot O class stars that are currently being observed in ultraviolet wavelengths of 1200 angstroms and above by the Hubble Space Telescope. However, only HUT is able to take its unprecedented measurements of these stars in the 900-1200 angstrom wavelength range. Commenting on what he called the "beautiful" real-time data acquired from this observation, Dr. Walborn said, "Now we have new information about a current candidate for the most massive star known. This was the star I wanted to see, and now we have it."

Earlier this morning, Payload Specialist Sam Durrance successfully pointed the Astro telescopes at a somewhat challenging target, the elliptical galaxy M60, to enable the science teams to obtain an overall average spectrum of stars in its core. A roughly sphere-shaped galaxy with no clearly discernible internal structure, M60 contains older, evolved stars and therefore represents a stable stage of development. Due to the faintness of this galaxy and the absence of suitable guide stars for automatic targeting, manual acquisition of this target was necessary.

The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) also observed the center of the M60 giant elliptical for polarized radiation, or radiation preferentially oriented in one direction. M60 is part of rich cluster of galaxies in the Virgo constellation, containing about 2500 galaxies, and has a notable ultraviolet excess.

The Ultraviolet Imaging Telescope (UIT) viewed NGC 6791, an unusual open cluster located 14,000 light years away in the Lyra constellation. Open clusters are diffuse collections of 100 to 1,000 stars and are usually thought to be young systems, less than 10 million years old. As one of the oldest known open clusters, NGC 6791 is three billion years older than our solar system. Because UIT's field of view is well matched to the sizes of these clusters, UIT scientists are able to perform ultraviolet observations of many stars at the same time.

Another target for UIT, M101 in the Ursa Major constellation, was a big spiral galaxy with arms that are wide and not very tightly wound. A perfect example, or prototype, of spiral structure, it is the highest priority spiral galaxy for UIT. This galaxy contains bright regions, such as Searle 2 (named for Dr. Leonard Searle, the astronomer who first discovered that region), of glowing hydrogen ionized by hot blue stars. UIT's ultraviolet imaging offers a powerful new tool for the study of these regions, especially since it emphasizes these hot stars. Ultraviolet imaging also suppresses the cool star background of the galaxy, allowing the young hot stars to become more evident to astronomers studying the evolution of stars.

On Saturday, March 11 1995 at 5 p.m. CST, STS-67 MCC Status Report # 19 reports: Gregory continued work with the Portable In-Flight Landing Operations Trainer, PILOT, a laptop computer and hand controller designed to simulate Shuttle landings. The device helps Shuttle Commanders and Pilots to stay sharp during long duration flights.

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