STS-67 Day 7 Highlights

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On Thursday, March 9, 1995 at 6 a.m. CST, STS-67 Payload Status Report # 15 reports: (7/5:22 MET) Mission Specialist Wendy Lawrence maneuvered the Space Shuttle Endeavour into a position where Payload Commander Tammy Jernigan could align the Ultraviolet Imaging Telescope (UIT) with M33, a nearby spiral galaxy in the constellation Triangulum. This galaxy, also called the Pinwheel galaxy, is approximately 2.4 million light years away, but is bright enough to be seen with binoculars at night. "We are looking at this neighboring spiral galaxy during Astro-2 to learn more about what goes on in that galaxy and compare this information to what we already know about the Milky Way," said Mission Scientist Dr. John Horack.

Payload Specialist Ron Parise aligned the three onboard telescopes, allowing UIT to make deep, wide-field images of a globular cluster of stars known as NGC 362. Globular clusters, massive spherical concentrations of extremely old stars, are generally located outside the plane of the galaxy and form a halo around the center. These old stars (possibly 10 billion years old) provide astronomers with knowledge about the latter part of stellar evolution.

Another type of star cluster, an open cluster, was imaged by UIT last night. An open star cluster is moderate in size, containing from only a few dozen to a few hundred stars. The age of the stars in an open cluster can range from very young stars to older stars. UIT scientists are particularly interested in searching the heavens for white dwarfs and other faint, hot stars to be used as backlighting to study interstellar medium Ð the gas and dust between stars. These data will also provide highly accurate distance measurements and add to astronomers' understanding of the chemical evolution of galaxies.

The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) telescope examined a supergiant, one of the largest, most radiant stars in the sky. The largest of these massive stars may measure 1,000 times the radius of the sun, but their enormous size is coupled with their voracious consumption of nuclear fuel, leading supergiant stars through speedy evolutions and spectacular deaths in the form of stellar explosions called supernovae.

The three Astro-2 ultraviolet telescopes were pointed at Jupiter's moon Io, the most volcanically active body in our solar system. A recent volcanic eruption on that moon, just before the Astro-2 mission began, ejected material onto Io's surface and into Io's atmosphere. Dr. Paul Feldman, co-investigator for the Hopkins Ultraviolet Telescope (HUT) observed Io last night to detect possible changes in the number of sulfur and oxygen ions in Io's atmosphere. As Io orbits Jupiter once every 42 hours, some of this material is left behind, forming a donut-shaped torus of sulfur and oxygen plasma around Io's orbit. This plasma torus will be observed in a separate Jupiter pointing during Astro-2.

Parise next pointed HUT at a starburst galaxy. While most galaxies appear to have developed their stars billions of years ago, some are forming new stars at an enormous rate in a process known as a starburst. The massive, hot young stars emit strong ultraviolet light, detectable by the telescopes onboard the Space Shuttle Endeavour.

Parise also aligned HUT to observe WX Hydri, a dwarf nova in a binary star system. The dwarf nova for this observation, WX Hydri, undergoes irregularly spaced outbursts, approximately once every 10 days. Scientists for HUT and WUPPE are interested in a process associated with binary stars called accretion, where matter is transferred from the smaller star to the larger star, causing the interstellar gas to heat up and create bright ultraviolet emissions.

HUT observed a very hot, massive blue star for Guest Investigator Dr. Nolan Walborn. The star known as NGC 346 #3 is located in a cluster of stars in the Small Magellanic Cloud. This star is being studied because of its strong stellar winds. Data from this Astro-2 observation will be combined with observations made by the Hubble Space Telescope and the European Southern Observatory's CASPEC satellite, giving scientists a better understanding of this star, which has a relatively brief life from 3 to 6 million years. Several other stars in the NG 346 cluster will also be observed during Astro-2.

On Thursday, March 9, 1995 at 8 a.m. CST, STS-67 MCC Status Report # 14 reports: Looking out of the Shuttle's window, Wendy Lawrence recorded volcanic activity on an island south of Burma and replayed the brief video at about 5:45 a.m. CST. An alignment of the inertial measurement units and a water dump through the flash evaporator system were successfully performed this morning. Earlier this morning Commander Stephen Oswald downlinked video of the Middeck Active Control Experiment showing the effects of vibrations on spacecraft. Through this experiment, researchers want to learn how to actively control flexible structures in space. Lawrence continued maneuvering the orbiter while Jernigan and Sam Durrance continued the Astro-2 observations of the ultraviolet universe.

On Thursday, March 9, 1995 at 5 p.m. CST, STS-67 MCC Status Report # 15 reports: Oswald worked with the Middeck Active Control Experiment as Gregory pointed the shuttle so that the payload bay telescopes could acquire their targets. Gregory also flew another simulation on the PILOT landing trainer. Grunsfeld and Parise directed the trio of Astro-2 telescopes toward its targets. Oswald, Grunsfeld and Gregory were interviewed by Glen Farley of KING-TV in Seattle at 4:30 p.m.

On Thursday, March 9, 1995 at 6 p.m. CST, STS-67 Payload Status Report # 16 reports: (7/17:22 MET) The Astro-2 observatory teamed up with NASA's Hubble Space Telescope today for a close examination of the planet Jupiter's "northern lights." Though Jupiter is always in daylight from Earth's perspective, ultraviolet photographs reveal a glowing circle of charged particles in its upper atmosphere, comparable to the beautiful aurora borealis visible in our far northern latitudes. Payload Specialist Sam Durrance, whose astronomical specialty is Jupiter, carefully centered the Hopkins Ultraviolet Telescope's (HUT) view on the northern region of the planet. The Astro telescopes made high-quality spectral and polarimetric measurements, as well as wide-field, far- ultraviolet images. At the same time, Hubble's Wide Field/Planetary Camera 2 obtained high resolution, far-ultraviolet images of the auroral region. Dr. Paul Feldman, professor of physics at The Johns Hopkins University, is the lead scientist for both the HUT and Hubble observations.

"We're very interested in whether the recent volcanic eruption on Jupiter's moon Io produced more ions in the planet's magnetosphere and led to a brighter aurora. There is some debate as to whether atmospheric ionization in the Jovian system is created primarily by sunlight, as it is in Earth's atmosphere, or by volcanic activity on Io," said Feldman. "We obtained a very nice spectrum of molecular hydrogen, the dominant component of Jupiter's upper atmosphere, which we will analyze in correlation with the Hubble images. By combining the two, we will get a scientific product that is greater than the sum of the two individual observations."

Several of today's observations were for scientific programs designed by Astro-2 guest investigators. As mission planning began, NASA invited astronomers to suggest experiments and observations that could be conducted using one or more of the ultraviolet telescopes. A committee of astronomers reviewed the proposals and selected ten to be included in the observation schedule.

Dr. John Raymond, of the Smithsonian Institution Astrophysical Observatory, used the Hopkins telescope to view two supernova remnants, the Cygnus Loop and Vela F. Both are relatively nearby, with little foreground matter to block a clear view. Raymond is studying the products of supernova explosions -- outwardly moving shock waves containing more energy than most galaxies radiate in a year. As the shock wave and debris from the explosion moves outward, it heats the interstellar medium in its path and may trigger the formation of new stars rich with the elements ejected in the explosion. Scattered long ago by these immense blasts, some of the iron and other heavy elements helped form the world in which we live.

Dr. Claus Leitherer, from the Space Telescope Science Institute, took spectral measurements of the starburst galaxy 1050+40, one where rapid star formation is taking place. Leitherer's colleague, Dr. Nolan Walborn, viewed O-type star SK-61837 in the Large Magellanic Cloud, the nearest galaxy to our own Milky Way. Walborn is studying O stars, the hottest and most massive of the "normal" stars, in a far-ultraviolet portion of the spectrum where they had not been studies previously. Both Leitherer and Walborn used the Hopkins telescope for their investigations.

Guest Investigator Dr. Gregory Bothun, of the University of Oregon, used the Ultraviolet Imaging Telescope (UIT) to observe galaxy VCC 530, one of a recently recognized class of astronomical objects. "They are called "low- surface-brightness" galaxies because they are fainter than the dark night sky. It has only been in recent years, with improvements in telescopes, that we have been able to detect them," said Dr. Barry Madore, another UIT guest investigator. "The most fascinating thing about this class of galaxies is that ground-based observations show some of them are blue. This could be due to an absence of dust, or because they are made up of very metal-poor stars, or maybe they are a new type we're not been aware of before. By viewing them in ultraviolet light, we can get a better understanding of where they came from and what their properties are."

UIT Principal Investigator Ted Stecher, of the Goddard Space Flight Center, chose a cluster of galaxies known as Abell 1367 for observation. The galaxies in this cluster are primarily spirals, like our own Milky Way. Examining photographs of spiral-rich clusters gives astronomers a better understanding of the spatial structure and development of spiral galaxies. UIT made images of Abell 1367 during Astro 1 as well. Stecher also selected NGC 6946, a rapid- star-formation galaxy. Ultraviolet radiation emphasizes the hot stars and dust features associated with spiral arms and suppresses the cool star background of the galactic bulge and underlying disc.

Other observations today spanned the life cycle of stars, from studies of the elderly Schweizer-Middleditch white dwarf star to another search for intergalactic helium left over from the birth of the universe. The Astro telescopes are currently in the midst of a nearly four-hour-long observation series to study the magnetic cataclysmic variable binary star, AM Herculis.

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