Astro-2 Public Affairs Status Report #12 6:00 p.m. CST (5/17:22 MET), March 7, 1995 Spacelab Mission Operations Control Marshall Space Flight Center Huntsville, Ala. Ultraviolet astronomy continued like clockwork on this sixth day of the Astro-2 Spacelab mission. Mission Specialist John Grunsfeld and Payload Specialist Ron Parise took turns getting well-earned breaks this afternoon, with the crew member on duty acquiring targets and science teams at Spacelab Mission Operations Control handling observation procedures from the ground. The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) and Hopkins Ultraviolet Telescope (HUT) viewed Wolf-Rayet star HD 191765 twice this morning, completing a set of observations begun last night. "This is a fairly faint star, so we are observing it four times to get all the information we need," explained Guest Investigator Dr. Regina Schulte-Ladbeck of the University of Pittsburgh. "We know this star's polarization varies over time, so we put all the observations within a 12-hour period in order to make them as nearly the same as possible." Schulte-Ladbeck noted that the first observation showed very high ultraviolet polarization, and she feels confident that all four data sets will yield the same result. Wolf-Rayet stars are thought to be a final life stage of very hot, massive and luminous stars. Powerful stellar winds cause matter to be lost from them, making them less and less massive over time. Schulte-Ladbeck is studying the mechanism of mass loss from the stars, as mass is returned to the interstellar medium and new stars are formed. "Wolf-Rayets are depositing chemically processed matter containing elements like carbon, nitrogen and oxygen for the next generation of stars, so the new stars will be different," she explained. This afternoon, WUPPE and HUT viewed EZ Canis Majoris, a much brighter Wolf-Rayet which was observed for a briefer time during Astro-1. Ultraviolet polarization studies can help astronomers determine the shape of the material being thrown out from the star, so they can formulate a three- dimensional "map" of its structure. The WUPPE instrument also focused on the bright ultraviolet star HD 25090 to illuminate the interstellar medium for their polarization study of the dust between stars. Determining characteristics of interstellar dust will help astronomers make allowances for the existence of this obstructing matter when studying other objects and to study its function as the source of new stars. All three telescope teams joined today's observations of two active galaxies, thought to have supermassive black holes at their centers. NGC 4151 is a Seyfert-1 type galaxy, which emits very bright ultraviolet radiation. NGC 1068 is a Seyfert-2, with ultraviolet emissions that are not as strong. "Astro-1 and Hubble Space Telescope observations suggest there are opaque disks of cold gas around the cores of these galaxies," said HUT team member Dr. Gerard Kriss. "It could be that there is no difference in the two Seyfert types, except that we're viewing Seyfert-2's from the side with the gas disk obscuring the hot core, and we see Seyfert-1's from the top with our view of the hot gas unobstructed. It's something like not being able to see the hole in a donut when you look at the donut from the side." Actually, Kriss said, NGC 4151 is in the "twilight zone" of Seyferts, exhibiting unusual characteristics that suggest it might be tilted at an intermediate angle to Earth. "NGC 4151 was five times as bright today as it was during Astro-1 observations in 1990, and there was a 10 percent increase in brightness today over what we saw when we first observed it two days ago," said Kriss. The galaxy is known to be extremely variable, so Astro-2 scientists hope to view it several more times to capture it at various levels. The multiple pointings should help Hopkins astronomers learn more about the location, composition, density and temperature of the gas. Astro-1 observations of NGC 1068 revealed unanticipated evidence that gas clouds were heated by shock waves speeding from the galaxy's core. Speaking on air-to-ground communication loops from Spacelab Control, Kriss guided Payload Specialist Sam Durrance in placing the telescope's view just outside the core of NGC 1068, to look for the location of the shock-heated gas. Ultraviolet Imaging Telescope (UIT) team members will search today's photographs of irregular galaxy NGC 4449 for young stars. Active star formation is on-going in these arms, but not in the symmetrical distribution more common in spiral galaxies. The Hopkins telescope focused on a supernova remnant near the galaxy's nucleus, which has a rich store of atomic oxygen buried in a region of ionized hydrogen. While the images should reveal details of star formation regions, spectral measurements of the supernova remnant should show the composition and temperature of the ionized gas. UIT also photographed an open cluster of hot stars, called N4. These diffuse clusters of stars are thought to be young systems, less than 10 million years old. UIT's wide field of view allows the camera to make ultraviolet images of many stars at a time, so the images will be used to identify hot binary stars pulling matter from one another, planetary nebulae, X-ray sources, white dwarfs and other faint, hot stars. Other observations today included two white dwarf stars, RE 0512 and GD153; the rapid-star formation galaxy NGC 2903; and another portion of the Cygnus Loop supernova remnant . Galaxy observations for tonight include several spirals, an elliptical and a starburst galaxy. A number of individual stars will be studied, including repeated observations of another Wolf-Rayet star. HUT will take continue their search for intergalactic helium, and WUPPE will make more interstellar polarization studies. 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"