demonstrated by measurements made with the Goddard 

 High Resolution Spectrograph aboard the Hubble Space Tele- 

 scope. These data are critical in analyzing spectral features of 

 atomic and molecular species in the interstellar medium. 



Calculations of the radiative association rates for a variety 

 of atoms have been carried out by Division theonsts to ex- 

 plore molecule formation in the Early Universe. Radiative as- 

 sociation is a process in which atoms come together and emit 

 a photon, thereby forming a stable molecule. Although this 

 process is slow, it can be important under conditions such as 

 those existing in the Early Universe. Indeed, primordial mole- 

 cules may have played an important role in cooling and en- 

 abling gravitational collapse to occur, thus forming the first 

 generation of stars. 



SAO scientists have compiled a molecular line data-base 

 covering the far-infrared region of the spectrum that has be- 

 come the standard, definitive database used by scientists 

 world-wide for analyzing atmospheric measurements in this 

 waveband. 



A technique for obraining spin-polarized xenon atoms in a 

 dual noble gas maser experiment is being explored for medi- 

 cal application in magnetic resonance imaging (MRI). SAO 

 scientists are working with doctors at the Brigham and 

 Women's Hospital in Boston to develop xenon-enhanced MRI 

 to improve diagnoses of diseases in soft-tissue structures. 



built in-house at SAO. SAO was also selected by NASA to op- 

 erate the AXAF Science Center (ASC), which will receive, ana- 

 lyze, and archive AXAF data and function as a central 

 clearinghouse of informanon and support for astronomers 

 using the facility. During the construction of AXAF, the ASC 

 will provide support for testing and verification of the ground 

 system, for mirror and instrument calibration, and for plan- 

 ning orbital operations which relate to science data. SAO's ini- 

 tial ASC contract is for 10 years — with the potential for at 

 least another 10 years beyond that. 



Highlights of 1994 included: 



Using observations of two supernova remnants made by the 

 Japanese ASCA x-tay satellite, a binational team led by an 

 SAO scientist identified significant amounts of iron, calcium, 

 and other newly synthesized elements in the spectra of the 

 two objects. The strong signal of iron, combined with a 

 weaker emission from oxygen, suggest that these two rem- 

 nants belong to a small class of supernovas that produced the 

 bulk of iron in the Universe, a result that could help refine 

 current models of such stellar explosions. 



Two SAO scientists, using data gathered by the ROSAT sat- 

 ellite, discovered a huge, hot, gaseous halo surrounding a dis- 

 tant galaxy, thus providing evidence for the presence of both 

 so-called cooling flows and dark matter, with the latter find- 

 ing having implications for cosmology. 



High Energy Astrophysics Division 



Stephen Murray, Associate Director 



Research in high-energy asrrophysics concentrates on some of 

 the most energetic objects and processes in the Universe. 

 Studying their x-ray emission is essential for understanding 

 their formation, evolution, and ultimate fate. Because x-rays 

 are absorbed by the Earth's atmosphere, observations must be 

 made from balloons, rockets, and satellites. 



The Einstein (HEAO-2) Observatory operated in space 

 from 1978 to 1981 and, more than a decade later, the Einstein 

 data still represent a unique view of the sky in the x-ray band. 

 At SAO, the original satellite data have been transferred onto 

 compact disks (CD-ROMs) for long-term archiving and, in co- 

 operation with NASA, for distribution at no cost to the world 

 astrophysics community. To date, some 4000 sets have been 

 distributed. 



The ROSAT satellite, launched June I, 1990, carries a high- 

 resolution x-ray imager (HRI) built by SAO. The satellite con- 

 ducted the first-ever, all-sky imaging survey and is still 

 engaged in detailed observations of selected objects. As part 

 of its role in the U.S. ROSAT Science Data Center, SAO has 

 developed and distributed to the astronomical community 

 software for the analysis and interpretation of ROSAT data. 



The Advanced X-ray Astrophysics Facility (AXAF) will be 

 the highest resolution, most sensitive x-ray telescope ever 

 flown; and, in preparation for launch in 1998, SAO has been 

 involved in the fabrication and testing of ics special optics. In- 

 deed, the High Resolution Camera is being designed and 



Optical and Infrared Astronomy 

 John Huchra, Director 



Optical and infrared data are fundamental to astronomy, and 

 research in this division includes observational cosmology, 

 searches for extrasolar planets, infrared observations of star- 

 forming regions of the galaxy, atmospheric chemistry, optical 

 interferometry, and gamma-ray astronomy. The Division is 

 also charged with the operation of — and the development of 

 instrumentation for — the ground-based facilities operated by 

 CfA: the Fred L. Whipple Observatory (FLWO), the Multiple 

 Mirror Telescope (MMT), and the Oak Ridge Observatory 

 (ORO). 



Significant research and development activities in 1994 

 include: 



Research by Division members using different, but com- 

 plementary methods, suggests that the Universe may be 

 significantly younger than previously estimated. Based on 

 ground-based measurements of the expanding photo- 

 spheres of selected supernovas, the fitst group established a 

 new value for the Hubble Constant, or expansion rate of 

 the Universe, a rate that translates into a maximum age of 

 14 billion years. A second team, including an SAO scien- 

 tist, used Space Telescope observations of variable stars in 

 the Virgo Cluster of galaxies to determine an age of 8 to 

 12 billion years. The new possible "ages" for the Universe 

 pose difficult theoretical quescions, since a universe only 8 

 ot 9 billion years old would be younger than many stars 

 within it. 



47 



