Astro-2 Public Affairs Status Report #22 6:00 p.m. CST (10/17:22 MET), March 12, 1995 Spacelab Mission Operations Control Marshall Space Flight Center Huntsville, Ala. With the Astro-2 mission in its eleventh day, astronomers continue to stack up new clues about what makes the universe "tick" -- how it got started, how it evolved and where it is going. The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) team selected Nova Circinus 1995 for observation this morning. This is the third "new" nova -- a binary star system whose first outburst was observed very recently -- to be studied by the Astro-2 telescopes. "Though all three novae went into outburst since the first of the year, each is at a different stage in its history," said WUPPE Principal Investigator Dr. Arthur Code. "By comparing their polarization, we hope to determine whether gas from novae outbursts is expelled in a spherical shape and then becomes more asymmetrical, and if so, how quickly the asymmetry develops." Light is polarized when it encounters an asymmetrically shaped object, such as a flattened gas disk, which causes the light to vibrate in preferred directions. "Every day brings new surprises," said HUT Co-investigator Dr. Bill Blair, describing the success today of two supernova remnant observations he admits were long-shots. HUT led a study of the supernova remnant Puppis A, the third supernova remnant Astro-2 has observed in our Milky Way galaxy. HUT and WUPPE examined a filament of gas in the remnant's eastern region, apparently an interaction between an interstellar cloud and the blast wave speeding from the supernova explosion. "The International Ultraviolet Explorer barely detected this remnant, so we didn't know what to expect," said Blair. "We thought dust in the interstellar medium might block its ultraviolet radiation, but we got a very nice spectrum which showed strong nitrogen emissions." Blair said it is possible the nitrogen could have been thrown out by the massive star thousands of years before it exploded as a supernova, and now the shock wave from the blast is catching up with nitrogen expelled from the star. Supernova 1006, whose explosion in A.D. 1006 makes it a relatively recent supernova, provided another first. "The shock wave from this supernova is moving very fast, plowing through interstellar space at about 2,000 kilometers (1,250 miles) per second, as opposed to 150 to 200 kilometers per second in remnants like Puppis A," said Blair. "We thought its emissions might be too faint for us to observe, but we felt it was important enough to attempt. This gives us a new range of velocity that has never been observed before in the ultraviolet." Blair said the HUT spectrum may show the primary passage of the supernova blast wave as it first encounters interstellar gas. Comparison with optical observations could help astronomers understand the basic physics of supernova shock fronts. The Ultraviolet Imaging Telescope team led eight highly successful observations in a row. UIT captured the mission's first images of the Whirlpool Galaxy (M 51) for Dr. Wendy Freedman's atlas of spiral galaxies. The Whirlpool Galaxy is the larger of two interacting galaxies close enough together to disturb each other through gravitational force. M 51 is a large spiral galaxy with a mass 100 billion times that of our sun. It is interacting with NGC 5195, a much less massive galaxy. Astronomers will study UIT photographs to learn more about the formation of stars in that system, especially in the bridge of matter that joins the two interacting galaxies. UIT also imaged CB_4, a cold cloud of interstellar gas and dust which is sufficiently dense to obscure starlight from objects behind it, while it reflects light from objects in front of it. Though this so-called dark cloud is relatively faint, Astro scientists were able to obtain measurements to test models of dust in the interstellar medium during a daylight observation. The imaging telescope also photographed a cluster of galaxies known as the Coma Cluster. UIT is examining the dense cluster, made up primarily of elliptical galaxies, to obtain simultaneous information on large samples of galaxies. Astronomers will study the integrated ultraviolet properties of these large samples to determine constraints on the physics of cooling flows, as hot gas may condense into stars as it rains down on a galaxy from the intra-cluster medium. Scientists also will look for the presence of dark matter, which does not emit appreciable radiation. HUT and WUPPE observed NGC 4874, the central elliptical galaxy in the Coma Cluster, to determine the ages of its stars. Though elliptical galaxies have comparatively few young stars, they emit more ultraviolet radiation than would be expected from a population of old stars. Astro-1 observations of ellipticals suggest this radiation may come from aging stars in a previously unknown stage of evolution. Astro-2 is following up on the mystery. UIT photographed the open star cluster NGC 7789, and investigations into new star formation included observations of elliptical galaxy NGC 185, irregular galaxy NGC 1313 and rapid star formation galaxy NGC 4631. WUPPE led the mission's first observation of the Planet Mars, and it observed interstellar polarization probe HD 217490 to add to its ongoing study of the dust scattered throughout our Milky Way. Dr. Brian Espey got excellent HUT and WUPPE data on the symbiotic star system RR Telescopii for his study of closely orbiting stars with radically different temperatures. In addition to observing a variety of stars and galaxies tonight, the Astro-2 telescopes will view the Planet Venus and study interstellar polarization and extinction in the Large Magellanic Cloud. To follow the mission in progress, visit Astro-2's home page on the Internet World Wide Web: URL "http://astro-2.msfc.nasa.gov"