Astro-2 Public Affairs Status Report #18 6:00 p.m. CST (8/17:22 MET), March 10, 1995 Spacelab Mission Operations Control Marshall Space Flight Center Huntsville, Ala. The Astro-2 science team in orbit and at Spacelab Control continue to stack up observations of the ultraviolet universe, with spiral galaxies taking center stage for much of the day. The arms of spiral galaxies are sites of new star formation, so the observations should add insight into how stars evolve. The Ultraviolet Imaging Telescope (UIT) team selected the spiral galaxy M 31, better known as the Andromeda galaxy, for observation. The team is mapping groups of hot, bright young stars, called OB associations, to learn more about star formation within the galaxy. Today's observation concentrated on the northern portion of Andromeda, where its brightest OB associations are located. "We mapped the OB associations in the southern portion of M 31 during Astro 1, and our goal on Astro 2 is to complete the picture," said UIT observing team member Barbara Pfarr. At twice the apparent size of our full moon, Andromeda is too big to be photographed in one frame even with UIT's wide field of view. M 31 is roughly the same size as the Milky Way, and it is the nearest galaxy of comparable size to our own. Astro scientists also observed NGC 4631, a large spiral galaxy viewed edge-on. The galaxy is forming stars out of material it is pulling from the disk of a nearby, less massive elliptical galaxy, NGC 4656. The bridge of material it is pulling from its smaller neighbor forms a "tail" on NGC 4631. NGC 4631 is of special interest to UIT and Hopkins Ultraviolet Telescope team members because huge loops and filaments of gas have been thrown above and below the galaxy's central region. Astronomers believe this may be a bubble of gas produced by supernova explosions, with very strong stellar winds blowing material out of the galaxy. HUT will use its far-ultraviolet spectrometer to see if there is hotter gas present -- about 200,000 degrees Fahrenheit (100,000 degrees Celsius) or more -- than has been detected in observations by other telescopes. UIT's ultraviolet images of NGC 4631 will be used to determine how stellar populations are distributed in the galaxy. In addition, they will compare photographs made in different wavelengths with various camera filters to help determine the location of the hot gas, its temperature profile, and its distance from the galactic disk. "We will try to deduce processes by which the gas is heated and cooled, then drops back into the disk," said UIT team member Dr. Andrew M. Smith, "It is theorized that there is a circulation pattern in the gas which is quite large and quite turbulent." The Hercules Cluster of galaxies, also viewed by the Astro telescopes today, furnishes another laboratory for the study of star formation. Galaxy clusters are the largest gravitationally bound groupings in the universe. Such clusters generally contain both elliptical galaxies, which contain few new stars, and spiral galaxies, which contain many young, ultraviolet-bright stars. The Hercules cluster has a greater than average number of spirals, which makes it a good "hunting ground" for new star formation. UIT also led observations of two objects near the end of the stellar life cycle, globular clusters NGC 6752 and M 13. Stars within these tightly bound clusters appear to be about five billion years older than recent evidence suggests the universe itself may be -- something like the children being older than the parents. Ultraviolet studies of old stars within the clusters, near the very end of their lives, could provide better tests for the ages and life cycles of stars. This morning's study of dwarf nova WX Hydri is the second observation of this system, whose decline from outburst is being studied. Though these periodic increases in brightness in WX Hydri are not as bright as they are in some cataclysmic variable systems, they occur fairly frequently -- about once every ten days. WX Hydri sometimes becomes over eight times brighter during an outburst, increasing from a magnitude of about 14.8 during quiet periods to around 11 at its brightest. Information about this dwarf nova and about 10 others is being provided to Astro scientists by amateur astronomers around the world. The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) team finished up one period as prime instrument early this morning, then began another after this afternoon's orbiter water dump. This morning, WUPPE looked at reflection nebula NGC 7023. The first prime observation for WUPPE this afternoon was HD 207198, an interstellar polarization probe. Both were studies clouds of gas and material from which astronomers can learn about the interstellar medium -- the material from which stars and other objects are created. Other celestial objects viewed by the Astro telescopes today included the brightest known Seyfert galaxy, NGC 4151; the Carina dwarf galaxy; spiral galaxy NGC 4258; and NGC 752, an open star cluster in the constellation Andromeda. The crew snatched a few free moments to answer questions left by computer users of all ages on the Astro-2 "home page." Several thousand questions have been received on the Internet World Wide Web page since launch. In addition to the questions they forward to the crew, members of the Astro-2 control team in Huntsville are answering selected questions on-line. Thus far in the mission, the Astro page has been accessed from more than 90,000 different computers in 56 countries. Tonight's menu of celestial observations includes two cataclysmic variables, a white dwarf star, a supernova remnant, a variety of galaxies and a so-called "BL Lacertae Object," the quasar-like nucleus of an elliptical galaxy. 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"