Astro-2 Public Affairs Status Report #24 6:00 p.m. CST (11/17:22 MET), March 13, 1995 Spacelab Mission Operations Control Marshall Space Flight Center Huntsville, Ala. Astro-2 observations today ranged from exotic star formations with odd- sounding names to our familiar celestial neighbor, the Planet Venus. Astronomers collected additional information for a variety of investigations which have been in progress throughout the mission. The Hopkins Ultraviolet Telescope (HUT) team began their block of observations with HH 2H, an object that could be a young star just emerging from the "cocoon" of dust around it. Called Herbig-Haro objects, after the astronomers who discovered them in 1946, these small bright concentrations of dust and gas are believed to be gas jets thrown off during the final evolutionary stages of a protostar, an object that has not collapsed sufficiently to begin the nuclear reactions of a mature star. The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) led an observation of another infant star, AB Aurigae. Called a pre-main sequence star, AB Aurigae is part of a class of young stars that are still surrounded by the dust and gas clouds from which they are formed. These envelopes of matter around the objects are highly active, as evidenced by variations of polarization seen in the optical and infrared wavelengths. WUPPE's ultraviolet observations should help astronomers understand how dust is processed during star formation and how material around young stars is distributed. All three telescopes viewed HUT's choice of Markarian 421, a quasar- like active galaxy nucleus known as a BL Lacertae object. When the first object of this type was identified, in the constellation Lacerta, it was erroneously thought to be a variable star. In the 1960s, astronomers discovered that BL Lac objects are not stars in our Milky Way, but the incredibly more powerful active cores of distant galaxies. Massive black holes are expected to be the power sources for objects in this class. While BL Lac objects produce strong radiation in all observation wavelengths, their radiation is primarily non-thermal -- created not by heat but by the glow of electrons moving at almost the speed of light as they pass through a magnetic field. NASA's Extreme Ultraviolet Explorer satellite discovered strong ultraviolet emission lines in Markarian 421, suggesting it is an excellent subject for HUT's far-ultraviolet studies. Ground-based observations show a high level of polarization in visible light, so WUPPE ultraviolet polarization measurements should provide revealing insights into phenomena in the centers of such galaxies. The observation of Venus this morning followed up on last night's look at Earth's "twin" planet. HUT studied the planet's forbidding atmosphere -- 100 times denser than Earth's and as hot as 900 degrees Fahrenheit (480 degrees Celsius) -- looking at upper atmosphere gases that are excited by ultraviolet solar radiation. Scientists will compare Astro-2 observations of Venus and Mars to see how the two planetary atmospheres, both primarily carbon dioxide but with radically different densities, respond to ultraviolet radiation from the sun. Two HUT observations today, NGC 6090 and 0833+652, were for Guest Investigator Dr. Claus Leitherer's study of starburst galaxies. Leitherer hopes to determine whether ionized hydrogen is being released from the galaxies, which put out a great deal of ultraviolet energy due to the rapid star formation taking place within them. "This is another attempt to view the interstellar medium," explained HUT Principal Investigator Dr. Arthur Davidsen. "We feel certain there must be material left over from the formation of the universe, just like there would be flour left on a cutting board after a loaf of bread is kneaded. But we have never been very successful in observing this material." Davidsen said the material might be highly ionized, possibly by quasars or by starburst galaxies, making it difficult to observe. "If we can find out how much ionized hydrogen starburst galaxies are putting out, we can get a good idea how much they emit into interstellar space," Davidsen said. "We may find that these galaxies are an important source of ionized interstellar hydrogen, or it may not be there at all. Either way, we've helped answer an intriguing question." HUT also led the Astro telescopes in an examination of the planetary nebula nucleus K1-16. Astronomers hope to better understand the chemistry of the nebula and the evolutionary state of its central star. The nebula is unstable, going through periodic pulsations in magnitude and color. While the star's evolutionary status is not clear, astronomers believe it could be on its way to becoming a white dwarf. The Ultraviolet Imaging Telescope (UIT) team made more images of star groupings to study the life cycles of stars. They photographed Abell 1795 and the Hercules Cluster, both clusters of galaxies where star formation is taking place. The Hercules Cluster is made up primarily of spiral galaxies, whose pinwheel arms are stellar nurseries. Abell 1795 is a galaxy cluster which emits large quantities of X-rays. Gas in the cluster is cooling rapidly and could be producing stars at the rate of 300 solar masses per year. UIT's observation of globular star cluster NGC 6752 focused on the opposite end of stellar evolution. The cluster is tight grouping of relatively old stars whose low metal content indicates formation early in the life of the Milky Way galaxy. UIT also imaged elliptical galaxy M32. Late this afternoon, the WUPPE team devoted two observations to planned calibrations of their instrument's sensitivity, with HD 161056 serving as a polarized standard and Beta Ursa Majoris as an unpolarized standard. Tonight's Astro observations again will span the universe, from another distant quasar to the mission's second observation of Earth's moon. Other scheduled observations include individual stars, galaxies, a planetary nebula and a galaxy cluster. 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"