Astro-2 Public Affairs Status Report #14 6:00 p.m. CST (6/17:22 MET), March 8, 1995 Spacelab Mission Operations Control Marshall Space Flight Center Huntsville, Ala. The three Astro-2 telescopes continued to probe the ultraviolet universe today, taking complementary measurements on celestial objects chosen in turn by each instrument team. 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. An observation of the planet Jupiter and its moon Io is next on the experiment schedule. The steady pace of astronomical observations will continue throughout the night, with subjects of study running the gamut from compact white dwarfs to huge starburst galaxies to the vast reaches of intergalactic space. 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"