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Three petrologic constraints, heating and cooling timescales and the frequency of compound chondrules, are applied to the shock wave and lightning models of chondrule formation. Shocks fit the constraints well; lightning requires high gas densities.
My group, in close collaboration with Dr. Zhang's group at University of Alabama-Huntsville, have been systematically analyzing and re-analyzing a substantial amount of archival data from previous and ongoing X-ray missions, in order to study possible relativistic effects around stellar-mass black holes and neutron stars. Our effort has been focused primarily on the data from the Rossi X-ray Timing Explorer. We carefully studied interesting quasi-periodic X-ray variability in newly discovered black hole candidates (XTE J1859+226 and XTE J1550-564), which, as we had proposed earlier, could be caused by general relativistic process (e.g., frame dragging) around the central black hole. We also discovered an intriguing temporal correlation between X-ray photons at different energies that is associated with the quasi-periodic signals of interest. The results provided new insights into the physical origin of the phenomena. Furthermore, we studied the spectral lines of black hole candidates which provide another avenue for studying general relativistic processes around black holes. The lines-may originate in the relativistic jets (which could be powered by the spin of the black hole) or in the disk around the black hole, as in the cases of 4U 1630-47 and GX 339-4 (two well-known black hole candidates), and may thus be distorted or shifted due to relativistic effects. Of course, neutron star systems were not forgotten either. After examining the properties of newly discovered fast quasi-periodic variability (at kiloHertz) associated with such systems, we proposed a relativistic model to explain the origin of the signals. We have also started to use new great observatories in orbit (such as Chandra and XMM-Newton) to observe the sources that are of interest to us. Finally, interesting results were also been obtained from our collaborations with other groups who are interested in some of the same objects. Such collaborative efforts have greatly enhanced the project and will likely continue in the future.
This grant primarily covered the development of the thermal X-ray emission model code called APEC, which is meant to replace the Raymond and Smith (1977) code. The new code contains far more spectral lines and a great deal of updated atomic data. The code is now available (http://hea-www.harvard.edu/APEC), though new atomic data is still being added, particularly at longer wavelengths. While initial development of the code was funded by this grant, current work is carried on by N. Brickhouse, R. Smith and D. Liedahl under separate funding. Over the last five years, the grant has provided salary support for N. Brickhouse, R. Smith, a summer student (L. McAllister), an SAO predoctoral fellow (A. Vasquez), and visits by T. Kallman, D. Liedahl, P. Ghavamian, J.M. Laming, J. Li, P. Okeke, and M. Martos. In addition to the code development, the grant supported investigations into X-ray and UV spectral diagnostics as applied to shock waves in the ISM, accreting black holes and white dwarfs, and stellar coronae. Many of these efforts are continuing. Closely related work on the shock waves and coronal mass ejections in the solar corona has grown out of the efforts supported by the grant.
Amateur astronomers are, in general, an enthusiastic and dynamic group of individuals who can help greatly in astronomy public outreach and education programs. In the U.S., they outnumber professional astronomers by over a factor of ten. Over eighty amateur astronomers from all over the U.S. and abroad attended a unique workshop in Huntsville, Alabama in April of this year. Most attendees were provided with travel grants under the condition that they disseminate knowledge gained at the workshop to civic groups, astronomy clubs and science teacher groups in their home communities. Twelve lecturers were given over two days, primarily by active high-energy researchers from NASA-MSFC and NASA-GSFC. Funding for the workshop was provided by a variety of NASA-sponsored projects, offices within OSS and private funding sources. The workshop attendees were selected by the AAVSO, which also administered the funding for the workshop. This high-leverage educational and public outreach program was deemed to be highly successful and bodes well for similar, future workshops. Many of the participants have already begun to give public talks on HEA and GRBs.
Four papers have been written. One reports on the major study funded by this grant: a pan-chromatic study of the quasar continuum at redshift 3. Two others make use of the quasar continuum shapes to find the minimum total accretion luminosity of the Universe, and hence the efficiency and spin of supermassive black holes; the second shows that the reemission of absorbed quasar radiation alleviates a major problem with galaxy formation and the FIR background. The last paper recognizes the role quasars may play in the initial formation of dust in the early Universe. The major study of a sample of z=3 and its comparison with a sample of z=0.l quasars across the whole X-ray to radio spectrum was completed and accepted for publication in ApJ Supplements. This study comprises the thesis work of Olga Kuhn. The two samples are matched in evolved luminosity, and so should be sampling the same black hole population at different z, and in different accretion states. Despite this no strong differences were found between the samples, except in the 'small bump' region of the optical/UV. This region is dominated by FeII emission, and may indicate abundance evolution in quasars. The lack of overall spectral changes argues strongly against a single population of quasars fading over cosmic time, and for a multiple generation, or multiple outburst model for quasars. A study of the total luminosity absorbed from quasars and re-emitted in the infrared produced two results (reported in two papers): The minimum intrinsic luminosity/Gpc(3) from AGN compared with the measured mass density in supermassive black holes [Gpc(-3)] requires a conversion efficiency of accreted mass into luminosity of greater than 15%. Non-rotating black holes cannot exceed 5% efficiency, while rapidly rotating black holes can reach 47%. Hence our result requires that most supermassive black holes must be rapidly rotating. The second result comes from considering the contribution that the re-radiated quasar radiation makes to the far infrared background (FIRB). The effective temperature of the re radiation is tightly constrained, but the detailed shape (e.g. line emission, range of temperature) is only of second order importance. At least 15perhaps 20-25% of the FIR background must come from AGN. This contribution significantly relieves problems in galaxy evolution that come from trying to use only starlight to make the FIRB. The third paper addresses the origin of the dust obscuration that is so widespread in AGN. The standard assumption is that the dust comes from the normal star-formation processes in galaxies and is drawn close to the nucleus along with the gas that powers the accretion. In complete contrast, using a wind outflow model for the broad emission line (BEL) region (Elvis 2000) as a basis, we show that BEL clouds will expand, cool and form dust as they flow outward, in strict analogy to the stellar winds of red supergiants.
Polycyclic aromatic hydrocarbons (PAHs) are now considered to be an important and ubiquitous component of the organic material in space. PAHs are found in a large variety of extraterrestrial materials such as interplanetary dust particles (IDPs) and meteoritic materials. PAHs are also good candidates to account for the infrared emission bands (UIRs) and the diffuse interstellar optical absorption bands (DIBs) detected in various regions of the interstellar medium. The recent observations made with the Infrared Space Observatory (ISO) have confirmed the ubiquitous nature of the UIR bands and their carriers. PAHs are thought to form through chemical reactions in the outflow from carbon-rich stars in a process similar to soot formation. Once injected in the interstellar medium, PAHs are further processed by the interstellar radiation field, interstellar shocks and energetic particles. A long-term laboratory effort has been undertaken to measure the physical and chemical characteristics of these carbon molecules and their ions under experimental conditions that mimic the interstellar conditions. These measurements require collision-free conditions where the molecules and ions are cold and chemically isolated. The spectroscopy of PAHs under controlled conditions represents an essential diagnostic tool to study the evolution of extraterrestrial PAHs. The laboratory results will be discussed as well as the implications for astronomy and for molecular spectroscopy. A review of the data generated through laboratory simulations of space environments and the role these data have played in our current understanding of the properties of interstellar PAHs will be presented. We will also present the new generation of laboratory experiments that are currently being developed in order to provide a closer simulation of space environments and a better support to space missions.
The goal of the project is to obtain, derive, and develop statistical and data analysis tools that would be of use in the analyses of high-resolution, high-sensitivity data that are becoming available with new instruments. This is envisioned as a cross-disciplinary effort with a number of collaborators.
We have combined Selected Area Electron Diffraction (SAED) and cryogenic techniques in an instrumental configuration that allows observing the structure of vapor deposited ice as it evolves during warmup. The ice is deposited in-situ inside an Hitachi H-500 H transmission electron microscope at a base pressure of 1-5 x 10(exp -7) torr on a thin amorphous carbon substrate at 15K or 86K and warmed up at a rate of 1-2 K/min. We find a progression of amorphous forms and well defined amorphous to amorphous transitions. Apart from the well known low-density form of ice, we confirm the presence of a high-density form and find a third amorphous form that coexists with cubic ice. We will report too on the amorphous to crystalline transition and the implications of these results for radical diffusion and gas retention observed in laboratory analog studies of interstellar and cometary ices.
This massive reference work (hereafter EAA) summarizes a great deal of what we knew in the astronomical sciences at the most recent Millennium. An associated website may keep much of it up-to-date for years to come. The contents are extensive indeed: the index alone consists of 76 pages, each with three columns of fine-type listings, and there are 'nearly 700 main articles'. The main articles are what make EAA worthwhile. They are generally by experts, who took much care in their preparation. The degree to which the articles are illustrated and referenced, however, seems to depend on the inclination of the individual author. On the other hand, articles on Saturn's rings and on its satellites are heavily illustrated, but with just two or three citations in each. The coverage of solar physics is especially thorough in EAA. There are numerous articles on major topics, notably in the physics and phenomena of the corona and the chromosphere, and some on more specialized areas, such as 'Polar Plumes' and 'Coronal Cavities.'
This period included many scientific observations made with the Chandra Observatory. The results, as is well known, are spectacular. Fortunately, the HRMA performance continues to be essentially identical to that predicted from ground calibration data. The Telescope Scientist Team has improved the mirror model to provide a more accurate description to the Chandra observers and enable them to reduce the systematic errors and uncertainties in their data reduction. There also has been progress in the scientific program. At this time 47 distant clusters of galaxies have been observed. We are performing a systematic analysis of this rather large data set for the purpose of determining absolute distances utilizing the Sunyaev Zel'dovich effect.
In collaboration with G Micela, S. Sciortino, and others at the Osservatorio Astronomico di Palermo G. S. Valens, we conducted studies of X-ray emission from normal stars, primarily via observations of several open star clusters and star forming regions (viz. the Pleiades, NBC 2516, NBC 2264, and the Orion Nebula Cluster). Our work was based on combined data from several X-ray observatories, Einstein, ROSAT, XMM-Newton and Chandra, as well as ground-based optical and radio data. Preliminary results were presented at several meetings: HEAD/AAS, November, 1997 a 195th AAS Meeting, January 2000 a Three Islands Conference, April 2000 a X-ray Astronomy 2000, September 2000 a 197th AAS Meeting, January 2001 Two Years of Science with Chandra, September 2001
Four papers have been written. One reports on the major study funded by this grant: a pan-chromatic study of the quasar continuum at redshift 3. Two others make use of the quasar continuum shapes to find the minimum total accretion luminosity of the Universe, and hence the efficiency and spin of supermassive black holes; the second shows that the reemission of absorbed quasar radiation alleviates a major problem with galaxy formation and the FIR background. The last paper recognizes the role quasars may play in the initial formation of dust in the early Universe.
The ADS was represented at the AAS meeting in San Diego with an oral talk and a demonstration. The demonstration was hugely successful, especially in light of the fact that the meeting was attended by about 1,200 Physics teachers. This was a group that we had no contact with before. They were very interested in the ADS. Having made contact with this group should help to further propagate knowledge about the ADS in the Physics community and bring it to the attention of young scientists. Two new mirror sites were established, one in India and in Russia. The site in India is fully operational, the site in Russia is waiting for the data tapes to be loaded. The preprint database is already functional. The mirror site in India is expected to become a full article mirror site soon. The mirror site in Russia is expected to become a partial article mirror site in the near future. The mirror site in China now has a full article mirror. This is the second full article mirror site after the one in Japan. The mirror site at the CDS in France is working on configuring disks for another full article mirror.
This period included many scientific observations made with the Chandra Observatory. The results, as is well known, are spectacular. Fortunately, the High Resolution Mirror Assembly (HRMA) performance continues to be essentially identical to that predicted from ground calibration data. The Telescope Scientist Team has improved the mirror model to provide a more accurate description to the Chandra observers and enable them to reduce the systematic errors and uncertainties in their data reduction. We also have made considerable progress in improving the scattering model. There also has been progress in the scientific program. At this time 58 distant clusters of galaxies have been observed. We are performing a systematic analysis of this rather large data set for the purpose of determining absolute distances utilizing the Sunyaev Zel'dovich effect. These observations also have been used to study the evolution of the cluster baryon mass function and the cosmological constraints which result from this evolution.
SAO TASKS ACCOMPLISHED: Abstract Service: (1) Continued regular updates of abstracts in the databases, both at SAO and at all mirror sites; (2) Established a new naming convention of QB books in preparation for adding physics books from Hollis or Library of Congress; (3) Modified handling of object tag so as not to interfere with XHTML definition; (4) Worked on moving 'what's new' announcements to a majordomo email list so as not to interfere with divisional mail handling; (5) Implemented and tested new first author feature following suggestions from users at the AAS meeting; (6) Added SSRv entries back to volume 1 in preparation for scanning of the journal; (7) Assisted in the re-configuration of the ADS mirror site at the CDS and sent a new set of tapes containing article data to allow re-creation of the ADS article data lost during the move; (8) Created scripts to automatically download Astrobiology.
With the advent of SOFIA and Herschel, new spectral windows will be opened for spectroscopy in the sub-millimeter region. To conduct science in this band, laboratory measurements must be carried out to provide accurate transition frequencies for molecular identification and physical interpretation. We are presently conducting such measurements using gas-phase submm direct absorption techniques. Of particular interest are simple molecules containing iron-peak elements, including carbides, and metal hydride ions (MH+), both which possess favorable transitions at submm wavelengths.
Planetary science deals with a wide variety of natural materials in a wide variety of environments. These materials include metals, minerals, ices, gases, plasmas, and organic chemicals. In addition, the newly defined discipline of astrobiology introduces biological materials to planetary science. The environments range from the interiors of planets with megapascal pressures to planetary magnetospheres, encompassing planetary mantles, surfaces, atmospheres, and ionospheres. The interplanetary environment includes magnetic and electrical fields, plasma, and dust. In order to understand planetary processes over these vast ranges, the properties of materials must be known, and most of the necessary information comes from the laboratory. Observations of the bodies and materials in the Solar System are accomplished over the full range of the electromagnetic spectrum by remote sensing from Earth or spacecraft. Comets exemplify this; molecular and atomic identifications are made from the hard ultraviolet to radio wavelengths, while X-rays are emitted as comets interact with the solar wind. Gamma rays from the surfaces of the Moon and asteroids are diagnostic of the mineral and ice content of those bodies; eventually, gamma rays will also be observed by probes to comets. A number of planetary materials are available in the laboratory for extensive Study: rocks from the Moon, Mars, several asteroids, as well as dust from comets (and perhaps the Kuiper Belt) are closely studied at every level, including atomic (isotopic). Even pre-solar interstellar grains isolated from meteorites are scrutinized for composition and crystalline structure. Beyond the materials themselves, various agents and processes have altered them over the 4.6-Gy age of the Solar System. Solar radiation, solar wind particles, trapped magnetospheric particles, cosmic rays, and micrometeoroid impacts have produced chemical, physical, and morphological changes in the atmospheres and on the surfaces of all planetary bodies. These processes are not well understood, so studies in a laboratory setting are especially needed.
Comparisons of charge sharing and charge loss measurements between two pixelated Cadmium-Zinc-Telluride (CdZnTe) detectors are discussed. These properties along with the detector geometry help to define the limiting energy resolution and spatial resolution of the detector in question. The first detector consists of a 1-mm-thick piece of CdZnTe sputtered with a 4x4 array of pixels with pixel pitch of 750 microns (inter-pixel gap is 100 microns). Signal readout is via discrete ultra-low-noise preamplifiers, one for each of the 16 pixels. The second detector consists of a 2-mm-thick piece of CdZnTe sputtered with a 16x16 array of pixels with a pixel pitch of 300 microns (inter-pixel gap is 50 microns). This crystal is bonded to a custom-built readout chip (ASIC) providing all front-end electronics to each of the 256 independent pixels. These detectors act as precursors to that which will be used at the focal plane of the High Energy Replicated Optics (HERO) telescope currently being developed at Marshall Space Flight Center. With a telescope focal length of 6 meters, the detector needs to have a spatial resolution of around 200 microns in order to take full advantage of the HERO angular resolution. We discuss to what degree charge sharing will degrade energy resolution but will improve our spatial resolution through position interpolation.